saar

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Author name code: saar
ADS astronomy entries on 2022-09-14
author:"Saar, Steven H."

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Title: Unsigned Magnetic Flux as a Proxy for Radial-velocity
Variations in Sun-like Stars
Authors: Haywood, R. D.; Milbourne, T. W.; Saar, S. H.; Mortier, A.;
Phillips, D.; Charbonneau, D.; Cameron, A. Collier; Cegla, H. M.;
Meunier, N.; , M. L. Palumbo, III
2022ApJ...935....6H Altcode: 2020arXiv200513386H
A major obstacle to detecting and characterizing long-period, low-mass
exoplanets is the intrinsic radial-velocity (RV) variability of host
stars. To better understand RV variability, we estimate disk-averaged
RV variations of the Sun over its magnetic cycle, from the Fe I line
observed by SDO/HMI, using a physical model for rotationally modulated
magnetic activity that was previously validated against HARPS-N solar
observations. We estimate the unsigned magnetic flux and show that
a linear fit to it reduces the RMS of RV variations by 62%, i.e., a
factor of 2.6. We additionally apply the FF' method, which predicts
RV variations based on a star's photometric variations. At cycle
maximum, we find that additional processes must be at play beyond
suppression of convective blueshift and velocity imbalances resulting
from brightness inhomogeneities, in agreement with recent studies
of RV variations. By modeling RV variations over the magnetic cycle
using a linear fit to the unsigned magnetic flux, we recover injected
planets at a period of ≍300 days with RV semi-amplitudes down to
0.3 m s-1. To reach 0.1 m s-1, we will need to
identify and model additional phenomena that are not well traced by
$| {\hat{B}}_{\mathrm{obs}}| $ or FF'. This study motivates ongoing
and future efforts to develop observation and analysis techniques
to measure the unsigned magnetic flux at high precision in slowly
rotating, relatively inactive stars like the Sun. We conclude that
the unsigned magnetic flux is an excellent proxy for rotationally
modulated, activity-induced RV variations, and could become key to
confirming and characterizing Earth analogs.

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Title: HD 166620: Portrait of a Star Entering a Grand Magnetic Minimum
Authors: Luhn, Jacob K.; Wright, Jason T.; Henry, Gregory W.; Saar,
Steven H.; Baum, Anna C.
2022arXiv220700612L Altcode:
HD 166620 was recently identified as a Maunder Minimum candidate
based on nearly 50 years of Ca II H &amp; K activity data from Mount
Wilson and Keck-HIRES (Baum et al. 2022). These data showed clear
cyclic behavior on a 17-year timescale during the Mount Wilson survey
that became flat when picked up later with Keck-HIRES planet-search
observations. Unfortunately, the transition between these two data
sets -- and therefore the transition into the candidate Maunder Minimum
phase -- contained little to no data. Here we present additional Mount
Wilson data not present in Baum et al. (2022) along with photometry over
a nearly 30-year baseline that definitively trace the transition from
cyclic activity to a prolonged phase of flat activity. We present this
as conclusive evidence of the star entering a grand magnetic minimum and
therefore the first true Maunder Minimum analog. We further show that
neither the overall brightness nor the chromospheric activity level
(as measured by S$_{\mathrm{HK}}$) is significantly lower during the
grand magnetic minimum than its activity cycle minimum, implying that
anomalously low mean or instantaneous activity levels are not a good
diagnostic or criterion for identifying additional Maunder Minimum
candidates. Intraseasonal variability in S$_{\mathrm{HK}}$, however,
is lower in the star's grand minimum; this may prove a useful symptom
of the phenomenon.

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Title: VizieR Online Data Catalog: K2-79 and K2-222 photometry and
radial velocity (Nava+, 2022)
Authors: Nava, C.; Lopez-Morales, M.; Mortier, A.; Zeng, Li; Giles,
H. A. C.; Bieryla, A.; Vanderburg, A.; Buchhave, L. A.; Poretti, E.;
Saar, S. H.; Dumusque, X.; Latham, D. W.; Charbonneau, D.; Damasso,
M.; Bonomo, A. S.; Lovis, C.; Collier, Cameron A.; Eastman, J. D.;
Sozzetti, A.; Cosentino, R.; Pedani, M.; Pepe, F.; Molinari, E.;
Sasselov, D.; Mayor, M.; Stalport, M.; Malavolta, L.; Rice, K.;
Watson, C. A.; Martinez Fiorenzano, A. F.; di Fabrizio, L.
2022yCat..51630041N Altcode:
We analyzed 3161 and 3424 photometric K2 observations of K2-79
and K2-222, respectively, collected in long-cadence (29.4minutes)
mode. K2-79 was observed between 2015 February 10 and 2015 April 20
and K2-222 between 2016 January 6 and 2016 March 23. We collected
79 spectra of K2-79 over four seasons between 2015 November 4 and 2019
December 29, and 63 spectra of K2-222 over three seasons between 2016
August 14 and 2019 December 23. All spectra were collected with HARPS-N,
the high-precision spectrograph mounted on the Telescopio Nationale de
Galileo at the Observatorio del Roque de los Muchachos in La Palma,
Spain. The spectrograph covers wavelengths in the range 383-690nm,
with average resolving power R=115000 (4 data files).

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Title: X-Ray Stellar Cycles at Low Rossby Numbers
Authors: Irving, Zackery; Wargelin, Bradford; Do Nascimento,
José-Dias; Saar, Steven
2022HEAD...1910102I Altcode:
Stellar cycles, like that of our Sun, can be explained by dynamo theory,
whereby kinetic energy is converted into magnetic energy via inductive
effects of motions in an electrically conducting fluid. Unlike the
Sun, however, Proxima Centauri (M5.5) is a fully convective star,
and as such is not expected to be able to support a solar-like
dynamo. Nonetheless, there is strong evidence in the optical, UV, and
X-ray wavebands suggesting that Prox Cen possesses an 8-yr activity
cycle. Analysis of this star could therefore provide key insights
into the underlying mechanisms responsible for stellar cycles. We use
Gaussian process regression (GPR) to model the rotational and cyclical
variability of Prox Cen — and three other stars spanning a range of
stellar type, rotation rate, and activity — and examine correlations
(or their lack) among the different wavebands. GPR is preferred over
traditional time-series analysis methods (e.g. fast Fourier transforms,
Lomb-Scargle periodograms) as we are analysing quasi-periodic, unevenly
sampled light curves, and GPR fits are better at following the data
and interpolating over gaps.

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Title: VizieR Online Data Catalog: Ruprecht 147 members &amp;
rot. data for 5 other cl. (Curtis+, 2020)
Authors: Curtis, J. L.; Agueros, M. A.; Matt, S. P.; Covey, K. R.;
Douglas, S. T.; Angus, R.; Saar, S. H.; Cody, A. M.; Vanderburg, A.;
Law, N. M.; Kraus, A. L.; Latham, D. W.; Baranec, C.; Riddle, R.;
Ziegler, C.; Lund, M. N.; Torres, G.; Meibom, S.; Aguirre, V. S.;
Wright, J. T.
2022yCat..19040140C Altcode:
We have observed 130 cluster stars with Robo-AO in 2013 while it was
on the Palomar 60-inch telescope (see Curtis 2016PhDT.......246C),
of which 50 are dwarfs less massive than the 1.4Mȯ cutoff
for this study. See Section 2.3.3. Our team petitioned to adjust
the pointing for K2's Campaign 7 so that it covered Ruprecht 147,
which we then proposed to monitor (GO proposal 7035). Our GO program
was allocated 1086 individual apertures for candidate members. A
series of contiguous apertures, a "superstamp", was created to tile
the inner cluster core in response to a different proposal and covered
96 additional candidates from our preliminary membership list (Cody+
2018RNAAS...2Q..25C). See Section 3.1. We monitored Ruprecht 147
from 2012 April 29 to 2012 October 7 as part of the PTF Open Cluster
Survey. This survey used the robotic 48-inch Oschin (P48) telescope
at Palomar Observatory, CA. See Section 3.2. (2 data files).

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Title: K2-79b and K2-222b: Mass Measurements of Two Small Exoplanets
with Periods beyond 10 days that Overlap with Periodic Magnetic
Activity Signals
Authors: Nava, Chantanelle; López-Morales, Mercedes; Mortier,
Annelies; Zeng, Li; Giles, Helen A. C.; Bieryla, Allyson; Vanderburg,
Andrew; Buchhave, Lars A.; Poretti, Ennio; Saar, Steven H.; Dumusque,
Xavier; Latham, David W.; Charbonneau, David; Damasso, Mario;
Bonomo, Aldo S.; Lovis, Christophe; Collier Cameron, Andrew; Eastman,
Jason D.; Sozzetti, Alessandro; Cosentino, Rosario; Pedani, Marco;
Pepe, Francesco; Molinari, Emilio; Sasselov, Dimitar; Mayor, Michel;
Stalport, Manu; Malavolta, Luca; Rice, Ken; Watson, Christopher A.;
Martinez Fiorenzano, A. F.; Di Fabrizio, Luca
2022AJ....163...41N Altcode: 2021arXiv211102608N
We present mass and radius measurements of K2-79b and K2-222b, two
transiting exoplanets orbiting active G-type stars observed with HARPS-N
and K2. Their respective 10.99 day and 15.39 day orbital periods fall
near periods of signals induced by stellar magnetic activity. The two
signals might therefore interfere and lead to an inaccurate estimate
of exoplanet mass. We present a method to mitigate these effects when
radial velocity (RV) and activity-indicator observations are available
over multiple observing seasons and the orbital period of the exoplanet
is known. We perform correlation and periodogram analyses on subsets
composed of each target's two observing seasons, in addition to the
full data sets. For both targets, these analyses reveal an optimal
season with little to no interference at the orbital period of the
known exoplanet. We make a confident mass detection of each exoplanet
by confirming agreement between fits to the full RV set and the optimal
season. For K2-79b, we measure a mass of 11.8 ± 3.6 M ⊕
and a radius of 4.09 ± 0.17 R ⊕. For K2-222b, we measure
a mass of 8.0 ± 1.8 M ⊕ and a radius of 2.35 ± 0.08
R ⊕. According to model predictions, K2-79b is a highly
irradiated Uranus analog and K2-222b hosts significant amounts of water
ice. We also present a RV solution for a candidate second companion
orbiting K2-222 at 147.5 days.

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Title: VizieR Online Data Catalog: Solar analog rotations from Kepler
&amp; Gaia (Do Nascimento+, 2020)
Authors: Do Nascimento, J. -D., Jr.; de Almeida, L.; Velloso, E. N.;
Anthony, F.; Barnes, S. A.; Saar, S. H.; Meibom, S.; da Costa, J. S.;
Castro, M.; Yana Galarza, J.; Lorenzo-Oliveira, D.; Beck, P. G.;
Melendez, J.
2021yCat..18980173D Altcode:
A major obstacle to interpreting the rotation period distribution
for main-sequence stars from Kepler mission data has been the lack
of a precise evolutionary status for these objects. We address this
by investigating the evolutionary status based on Gaia Data Release
2 parallaxes and photometry for more than 30000 Kepler stars with
rotation period measurements. Many of these are subgiants and should
be excluded in future work on dwarfs. We particularly investigate a
193-star sample of solar analogs and report newly determined rotation
periods for 125 of these. These include 54 stars from a prior sample,
of which we can confirm the periods for 50. The remainder are new, and
10 of them longer than a solar rotation period, suggesting that Sun-like
stars continue to spin down on the main sequence past solar age. Our
sample of solar analogs could potentially serve as a benchmark for
future missions, such as PLAnetary Transits and Oscillations of stars,
and emphasizes the need for additional astrometric, photometric, and
spectroscopic information before interpreting the stellar populations
and results from time series surveys. (1 data file).

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Title: Magnetic and Rotational Evolution of ρ CrB from
Asteroseismology with TESS
Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani;
Buzasi, Derek; Drake, Jeremy J.; Egeland, Ricky; Huber, Daniel; Saar,
Steven H.; Stassun, Keivan G.; Ball, Warrick H.; Campante, Tiago L.;
Finley, Adam J.; Kochukhov, Oleg; Mathur, Savita; Reinhold, Timo;
See, Victor; Baliunas, Sallie; Soon, Willie
2021ApJ...921..122M Altcode: 2021arXiv210801088M
During the first half of main-sequence lifetimes, the evolution
of rotation and magnetic activity in solar-type stars appears to be
strongly coupled. Recent observations suggest that rotation rates evolve
much more slowly beyond middle age, while stellar activity continues to
decline. We aim to characterize this midlife transition by combining
archival stellar activity data from the Mount Wilson Observatory
with asteroseismology from the Transiting Exoplanet Survey Satellite
(TESS). For two stars on opposite sides of the transition (88 Leo and
ρ CrB), we independently assess the mean activity levels and rotation
periods previously reported in the literature. For the less active star
(ρ CrB), we detect solar-like oscillations from TESS photometry, and
we obtain precise stellar properties from asteroseismic modeling. We
derive updated X-ray luminosities for both stars to estimate their
mass-loss rates, and we use previously published constraints on magnetic
morphology to model the evolutionary change in magnetic braking
torque. We then attempt to match the observations with rotational
evolution models, assuming either standard spin-down or weakened
magnetic braking. We conclude that the asteroseismic age of ρ CrB is
consistent with the expected evolution of its mean activity level and
that weakened braking models can more readily explain its relatively
fast rotation rate. Future spectropolarimetric observations across a
range of spectral types promise to further characterize the shift in
magnetic morphology that apparently drives this midlife transition in
solar-type stars.

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Title: Estimating Magnetic Filling Factors from Simultaneous
Spectroscopy and Photometry: Disentangling Spots, Plage, and Network
Authors: Milbourne, T. W.; Phillips, D. F.; Langellier, N.; Mortier,
A.; Haywood, R. D.; Saar, S. H.; Cegla, H. M.; Collier Cameron, A.;
Dumusque, X.; Latham, D. W.; Malavolta, L.; Maldonado, J.; Thompson,
S.; Vanderburg, A.; Watson, C. A.; Buchhave, L. A.; Cecconi, M.;
Cosentino, R.; Ghedina, A.; Gonzalez, M.; Lodi, M.; López-Morales,
M.; Sozzetti, A.; Walsworth, R. L.
2021ApJ...920...21M Altcode: 2021arXiv210509113M
State-of-the-art radial velocity (RV) exoplanet searches are limited
by the effects of stellar magnetic activity. Magnetically active spots,
plage, and network regions each have different impacts on the observed
spectral lines and therefore on the apparent stellar RV. Differentiating
the relative coverage, or filling factors, of these active regions
is thus necessary to differentiate between activity-driven RV
signatures and Doppler shifts due to planetary orbits. In this
work, we develop a technique to estimate feature-specific magnetic
filling factors on stellar targets using only spectroscopic and
photometric observations. We demonstrate linear and neural network
implementations of our technique using observations from the solar
telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory,
and the Total Irradiance Monitor onboard SORCE. We then compare the
results of each technique to direct observations by the Solar Dynamics
Observatory. Both implementations yield filling factor estimates that
are highly correlated with the observed values. Modeling the solar
RVs using these filling factors reproduces the expected contributions
of the suppression of convective blueshift and rotational imbalance
due to brightness inhomogeneities. Both implementations of this
technique reduce the overall activity-driven rms RVs from 1.64 to 1.02
m s-1, corresponding to a 1.28 m s-1 reduction
in the rms variation. The technique provides an additional 0.41 m
s-1 reduction in the rms variation compared to traditional
activity indicators.

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Title: ALMA small-scale features in the quiet Sun and active regions
Authors: Brajša, R.; Skokić, I.; Sudar, D.; Benz, A. O.; Krucker,
S.; Ludwig, H. -G.; Saar, S. H.; Selhorst, C. L.
2021A&A...651A...6B Altcode: 2021arXiv210503644B
 Aims: The main aim of the present analysis is to decipher (i)
the small-scale bright features in solar images of the quiet Sun and
active regions obtained with the Atacama Large Millimeter/submillimeter
Array (ALMA) and (ii) the ALMA correspondence of various known
chromospheric structures visible in the Hα images of the Sun. Methods: Small-scale ALMA bright features in the quiet Sun region
were analyzed using single-dish ALMA observations (1.21 mm, 248 GHz)
and in an active region using interferometric ALMA measurements (3
mm, 100 GHz). With the single-dish observations, a full-disk solar
image is produced, while interferometric measurements enable the
high-resolution reconstruction of part of the solar disk, including
the active region. The selected quiet Sun and active regions are
compared with the Hα (core and wing sum), EUV, and soft X-ray images
and with the magnetograms. Results: In the quiet Sun region,
enhanced emission seen in the ALMA is almost always associated with a
strong line-of-sight magnetic field. Four coronal bright points were
identified, while other small-scale ALMA bright features are most likely
associated with magnetic network elements and plages. In the active
region, in 14 small-scale ALMA bright features randomly selected and
compared with other images, we found five good candidates for coronal
bright points, two for plages, and five for fibrils. Two unclear cases
remain: a fibril or a jet, and a coronal bright point or a plage. A
comparison of the Hα core image and the 3 mm ALMA image of the analyzed
active region showed that the sunspot appears dark in both images
(with a local ALMA radiation enhancement in sunspot umbra), the four
plage areas are bright in both images and dark small Hα filaments are
clearly recognized as dark structures of the same shape also in ALMA.

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Title: Long-term stellar activity variations and their effect on
radial-velocity measurements
Authors: Costes, Jean C.; Watson, Christopher A.; de Mooij, Ernst;
Saar, Steven H.; Dumusque, Xavier; Cameron, Collier; Phillips, David
F.; Günther, Maximilian N.; Jenkins, James S.; Mortier, Annelies;
Thompson, Andrew P. G.
2021MNRAS.505..830C Altcode: 2021MNRAS.tmp.1143C; 2021arXiv210501915C
Long-term stellar activity variations can affect the detectability
of long-period and Earth-analogue extrasolar planets. We have, for
54 stars, analysed the long-term trend of five activity indicators:
log $R^{\prime }_\mathrm{{HK}}$, the cross-correlation function (CCF)
bisector span, CCF full-width-at-half-maximum, CCF contrast, and the
area of the Gaussian fit to the CCF; and studied their correlation
with the RVs. The sign of the correlations appears to vary as a
function of stellar spectral type, and the transition in sign signals
a noteworthy change in the stellar activity properties where earlier
type stars appear more plage dominated. These transitions become more
clearly defined when considered as a function of the convective zone
depth. Therefore, it is the convective zone depth (which can be altered
by stellar metallicity) that appears to be the underlying fundamental
parameter driving the observed activity correlations. In addition, for
most of the stars, we find that the RVs become increasingly redshifted
as activity levels increase, which can be explained by the increase
in the suppression of convective blueshift. However, we also find
a minority of stars where the RVs become increasingly blueshifted
as activity levels increase. Finally, using the correlation found
between activity indicators and RVs, we removed RV signals generated by
long-term changes in stellar activity. We find that performing simple
cleaning of such long-term signals enables improved planet detection
at longer orbital periods.

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Title: Detection Limits of Low-mass, Long-period Exoplanets Using
Gaussian Processes Applied to HARPS-N Solar Radial Velocities
Authors: Langellier, N.; Milbourne, T. W.; Phillips, D. F.; Haywood,
R. D.; Saar, S. H.; Mortier, A.; Malavolta, L.; Thompson, S.; Collier
Cameron, A.; Dumusque, X.; Cegla, H. M.; Latham, D. W.; Maldonado,
J.; Watson, C. A.; Buchschacher, N.; Cecconi, M.; Charbonneau, D.;
Cosentino, R.; Ghedina, A.; Gonzalez, M.; Li, C. -H.; Lodi, M.;
López-Morales, M.; Micela, G.; Molinari, E.; Pepe, F.; Poretti, E.;
Rice, K.; Sasselov, D.; Sozzetti, A.; Udry, S.; Walsworth, R. L.
2021AJ....161..287L Altcode: 2020arXiv200805970L
Radial velocity (RV) searches for Earth-mass exoplanets in the
habitable zone around Sun-like stars are limited by the effects of
stellar variability on the host star. In particular, suppression of
convective blueshift and brightness inhomogeneities due to photospheric
faculae/plage and starspots are the dominant contribution to the
variability of such stellar RVs. Gaussian process (GP) regression
is a powerful tool for statistically modeling these quasi-periodic
variations. We investigate the limits of this technique using 800
days of RVs from the solar telescope on the High Accuracy Radial
velocity Planet Searcher for the Northern hemisphere (HARPS-N)
spectrograph. These data provide a well-sampled time series of stellar
RV variations. Into this data set, we inject Keplerian signals with
periods between 100 and 500 days and amplitudes between 0.6 and
2.4 m s-1. We use GP regression to fit the resulting RVs
and determine the statistical significance of recovered periods and
amplitudes. We then generate synthetic RVs with the same covariance
properties as the solar data to determine a lower bound on the
observational baseline necessary to detect low-mass planets in
Venus-like orbits around a Sun-like star. Our simulations show that
discovering planets with a larger mass (∼0.5 m s-1) using
current-generation spectrographs and GP regression will require more
than 12 yr of densely sampled RV observations. Furthermore, even with
a perfect model of stellar variability, discovering a true exo-Venus
(∼0.1 m s-1) with current instruments would take over
15 yr. Therefore, next-generation spectrographs and better models of
stellar variability are required for detection of such planets.

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Title: Linear and Neural Network Estimates of Magnetic Filling
Factors on Sun-Like Stars
Authors: Milbourne, T.; Phillips, D.; Langellier, N.; Saar, S.;
Walsworth, R.
2021csss.confE.308M Altcode:
State of the art radial velocity (RV) searches for low-mass exoplanets
are limited by the effects of stellar magnetic activity. Previously,
we have shown that different types of active regions - spots,
plage, and network - have different impacts on the apparent stellar
RV. Differentiating the relative coverage of these active regions is
thus necessary in order to successfully disentangle the RV signatures
of stars from potential planetary signals. However, traditional
activity indicators, such as the calcium S-index and photometry, only
indicate the overall coverage by magnetized regions: more information
is necessary to differentiate the different types of active regions. In
this work, we outline techniques to estimate magnetic filling factors
from spots, plage, and networks features on stellar targets using
only spectroscopic and photometric observations. We demonstrate linear
and neural network implementations of our techniques using real solar
observations taken by the solar telescope at HARPS-N, the HK Project at
the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard
SORCE, and compare the results of each technique to filling factors
derived from full-disk images from the Solar Dynamics Observatory. We
conclude by assessing the possibilities of applying these techniques
to non-solar targets.

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Title: Synthetic Spectra of TiO Bands to Identify Diagnostics of
Starspot Properties
Authors: Cheng, K. P.; Neff, J. E.; Giacinto, A.; Johnson, D.; Saar, S.
2021AAS...23755003C Altcode:
Magnetic activity similar to that of the Sun is observed on a variety
of cool stars. Strong magnetic fields in stellar interiors and produce
many magnetic phenomena, including starspots in the photosphere. These
starspots are a major source limiting the precision of high-precision
radial velocity measurements used to characterize exoplanets. In a
previous series of papers, we demonstrated an empirical approach
to measure starspot properties using observed spectra of active
and inactive stars as proxies for the spotted and non-spotted
photosphere. These empirical methods were successful for heavily
spotted stars, but they are not sensitive enough to unravel the jitter
caused by numerous small spots. To overcome these limitations, we have
evaluated a wide range of model atmospheres and spectrum synthesis
codes, and we have assimilated suitable line lists. By characterizing
composite (spot+nonspot) synthetic spectra from the entire range of
parameter space for G and K stars, we have developed new diagnostic
indicators that can be used to measure starspot properties from observed
high-resolution spectra of spotted stars, including spot temperatures,
areas, and the effective decrease in gravity caused by strong magnetic
fields within the spots.

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Title: A Study of Equatorial Coronal Holes and Active regions during
the Maximum Phase of four Solar Cycles
Authors: Karna, Nishu; DeLuca, Edward; Pesnell, William; Saar, Steven;
Karna, Mahendra
2021cosp...43E.920K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in solar activity indicators such as number of sunspots, coronal
holes, active regions (ARs), as well as the occurrence rate of solar
energetic events such as filament eruptions, flares and coronal mass
ejections (CMEs). In this work we performed a statistical study of the
equatorial coronal holes (ECHs) and ARs during the maximum phase of the
last four solar cycles: SC 21 (1979--1982), SC 22 (1989--1992), SC 23
(1999--2002) and SC 24 (2012--2015). We compared the number of ECHs and
ARs, separations between their centroids, solar wind speed, pressure
and the number of intense geomagnetic storms (IGS) data over these four
cycles. We note a strong anticorrelation between the number of ARs and
ECHs. We found that the number of close ARs and ECHs, solar wind speed,
and the number of IGS increases with average sunspot maximum number
for even cycles and decreases with average sunspot maximum for odd
cycles. These odd-even trends largely (though not entirely) disappear
in the relation between the wind properties and the numbers of close
AR and ECH. This suggests a possible link between ECH-AR interactions
and the solar wind phenomena, though residual odd-even trends point to
the importance of other effects (e.g., Sun-earth magnetic alignment)
as well.

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Title: When Do Stalled Stars Resume Spinning Down? Advancing
Gyrochronology with Ruprecht 147
Authors: Curtis, Jason Lee; Agüeros, Marcel A.; Matt, Sean P.; Covey,
Kevin R.; Douglas, Stephanie T.; Angus, Ruth; Saar, Steven H.; Cody,
Ann Marie; Vanderburg, Andrew; Law, Nicholas M.; Kraus, Adam L.;
Latham, David W.; Baranec, Christoph; Riddle, Reed; Ziegler, Carl;
Lund, Mikkel N.; Torres, Guillermo; Meibom, Søren; Aguirre, Victor
Silva; Wright, Jason T.
2020ApJ...904..140C Altcode: 2020arXiv201002272C
Recent measurements of rotation periods ( ${P}_{\mathrm{rot}}$ ) in the
benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC
752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence
of slowly rotating stars in mass-period space, stars temporarily stop
spinning down. These data also show that the duration of this epoch
of stalled spin-down increases toward lower masses. To determine when
stalled stars resume spinning down, we use data from the K2 mission
and the Palomar Transient Factory to measure ${P}_{\mathrm{rot}}$ for
58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which
satisfy our criteria designed to remove short-period or near-equal-mass
binaries. Combined with the Kepler ${P}_{\mathrm{rot}}$ data for the
approximately coeval cluster NGC 6819 (30 stars with M⋆
&gt; 0.85 ${M}_{\odot }$ ), our new measurements more than double
the number of ≍2.5 Gyr benchmark rotators and extend this sample
down to ≍0.55 ${M}_{\odot }$ . The slowly rotating sequence for
this joint sample appears relatively flat (22 ± 2 days) compared to
sequences for younger clusters. This sequence also intersects the Kepler
intermediate-period gap, demonstrating that this gap was not created by
a lull in star formation. We calculate the time at which stars resume
spinning down and find that 0.55 ${M}_{\odot }$ stars remain stalled
for at least 1.3 Gyr. To accurately age-date low-mass stars in the
field, gyrochronology formulae must be modified to account for this
stalling timescale. Empirically tuning a core-envelope coupling model
with open cluster data can account for most of the apparent stalling
effect. However, alternative explanations, e.g., a temporary reduction
in the magnetic braking torque, cannot yet be ruled out.

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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of Four Solar Cycles
Authors: Karna, Mahendra Lal; Karna, Nishu; Saar, Steven H.; Pesnell,
W. Dean; DeLuca, Edward E.
2020ApJ...901..124K Altcode:
The 11 yr solar cycle (SC) is characterized by periodic changes in
solar activity indicators such as the number of sunspots, coronal
holes, and active regions (ARs), as well as the occurrence rate of
solar energetic events such as filament eruptions, flares, and coronal
mass ejections. In this work we performed a statistical study of the
equatorial coronal holes (ECHs) and ARs during the maximum phase
of the last four SCs: SC 21 (1979-1982), SC 22 (1989-1992), SC 23
(1999-2002), and SC 24 (2012-2015). We compared the number of ECHs and
ARs, separations between their centroids, solar wind speed, pressure,
and the number of intense geomagnetic storm (IGS) data over these four
cycles. We note a strong anticorrelation between the number of ARs and
ECHs. We found that the number of close ARs and ECHs, solar wind speed,
and the number of IGS increases with average sunspot maximum number
for even cycles and decreases with average sunspot maximum for odd
cycles. Also, we find strong odd-even trends in the relation between
the wind properties and the numbers of close AR and ECH. These results
obtained from the annual average data suggest a possible link between
ECH and AR proximity and the solar wind phenomena, though odd-even
trends point to the importance of other effects (e.g., Sun-Earth
magnetic alignment) as well.

---------------------------------------------------------
Title: Long-term Periodicities in Kepler Photometry of Open Cluster
NGC 6811
Authors: Velloso, E. N.; do Nascimento, J. -D., Jr.; Saar, S. H.
2020ApJ...900..173V Altcode:
Long-term photometric variability can sometimes be related to the
emergence of starspots in the photosphere following a quasi-periodic
magnetic activity cycle. In order to investigate the existence
and properties of magnetic cycles in a narrow range of fundamental
parameters, we focused on solar-type stars in the intermediate-age
open cluster NGC 6811 (1 Gyr). The cluster membership was analyzed
both in terms of stellar kinematics and Gaia photometry. Rotation
periods and photometric variability were analyzed for 138 stars
from Kepler light curves and we discuss the existing trends and
relationships. We also searched a sample of 11 solar-type stars for
cycle-like periodicities and in each case classified the variability
as either cyclic, multicyclic, flat, or acyclic. The results suggest
a significant scatter, possibly due to sensitive nonlinearities in
the dynamo process. This raises theoretical questions on whether these
periodicities can be associated to activity cycles and what determines
the stellar cycle presence or its period. Also, the lack of solar-twin
flat activity stars in NGC 6811 combined with other recent results,
suggests that the presence of magnetic grand minima in the Sun is a
relatively recent phenomenon.

---------------------------------------------------------
Title: The Secrets of Stellar Siestas: the Magnetic Grand Minimum
Candidate HD 4915
Authors: Saar, Steven
2020cxo..prop.5810S Altcode:
Magnetic grand minima (MGM) are mysterious episodes when the Sun's
magnetic dynamo cycle "takes a siesta" and goes into temporary
quiescence. The phenomenon has never been observed in modern times;
what was the Sun like then? Recently a star was observed to have a
decaying cycle amplitude (in Ca HK), making it a strong candidate for
an MGM episode. We propose to study the star with Chandra and HST,
to explore magnetic heating throughout its outer atmosphere. Results
will be compared with cycle minima and stars with "flat activity"
(objects which may be in MGM or have "dead" dynamos) to explore
similarities and differences, and reveal what may lie in store for
our own Sun in the near future.

---------------------------------------------------------
Title: The Secrets of Stellar Siestas: the Magnetic Grand Minimum
Candidate HD 4915
Authors: Saar, Steven H.; Drake, Jeremy J.; Kashyap, Vinay; Wargelin,
Bradford; Wright, Jason T.
2020hst..prop16421S Altcode:
Magnetic grand minima (MGM) are mysterious episodes when the Sun's
magnetic dynamo cycle "takes a siesta" and goes into temporary
quiescence. The phenomenon has never been observed in modern times;
what was the Sun like then? Recently a star was observed to have a
decaying cycle amplitude (in Ca HK), making it a strong candidate for
an MGM episode. We propose to study the star with Chandra and HST,
to explore magnetic heating throughout its outer atmosphere. Results
will be compared with cycle minima and stars with "flat activity"
(objects which may be in MGM or have "dead" dynamos) to explore
similarities and differences, and reveal what may lie in store for
our own Sun in the near future.

---------------------------------------------------------
Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of four Solar Cycles
Authors: Karna, N.; Karna, M.; Saar, S.; Pesnell, W.; DeLuca, E.
2020SPD....5120903K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in solar activity indicators such as a number of sunspots, coronal
holes, active regions (ARs), as well as the occurrence rate of solar
energetic events such as filament eruptions, flares and coronal mass
ejections (CMEs). In this work we performed a statistical study of
the equatorial coronal holes (ECHs) and ARs during the maximum phase
of the last four solar cycles: SC 21 (1979-1982), SC 22 (1989-1992),
SC 23 (1999-2002) and SC 24 (2012-2015). We compared the number of
ECHs and ARs, separations between their centroids, solar wind speed,
pressure and the number of intense geomagnetic storms (IGS) data
over these four cycles. We note a strong anticorrelation between the
number of ARs and ECHs. We found that the number of close ARs and ECHs
(which are potentially interacting), solar wind speed, and the number
of IGS increases with average sunspot maximum number for even cycles
and decreases with average sunspot maximum for odd cycles. Also,
we find strong odd-even trends in the relation between the wind
properties and the numbers of close AR and ECH. These results suggest a
possible link between ECH-AR interactions and the solar wind phenomena,
though odd-even trends point to the importance of other effects (e.g.,
Sun-earth magnetic alignment) as well.

---------------------------------------------------------
Title: VizieR Online Data Catalog: HARPS-N solar radial velocities
and activity (Milbourne+, 2019)
Authors: Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.;
Saar, S. H.; Cegla, H. M.; Cameron, A. C.; Costes, J.; Dumusque,
X.; Langellier, N.; Latham, D. W.; Maldonado, J.; Malavolta, L.;
Mortier, A. M. L. P., III; Thompson, S.; Watson, C. A.; Bouchy, F.;
Buchschacher, N.; Cecconi, M.; Charbonneau, D.; Cosentino, R.; Ghedina,
A.; Glenday, A. G.; Gonzalez, M.; Li, C. -H.; Lodi, M.; Lopez-Morales,
M.; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Piotto,
G.; Rice, K.; Sasselov, D.; Segransan, D.; Sozzetti, A.; Szentgyorgyi,
A.; Udry, S.; Walsworth, R. L.
2020yCat..18740107M Altcode:
In this work, we analyze 3yr (Jul 2015-Sep 2017) of solar observations
during the decline of Carrington Cycle 24 to test models of
radial-velocity variations of Sun-like stars. We compare solar
telescope/HARPS-N measurements of the solar RVs and logR'HK,
SDO/HMI disk-resolved activity images, and SORCE/TIM measurements of
the TSI. The High Radial-velocity Planet Searcher for the Northern
Hemisphere (HARPS-N) spectrograph at the Telescopio Nazionale Galileo
(TNG) on La Palma is a cross-dispersed echelle spectrograph spanning
the visible range (383-690nm with resolving power R=115000). See
Section 2.1. The Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO) captures full-disk images of the
Sun with near single-granule resolution. We use six images each day,
sampled evenly over the 2.5yr operational period of the solar telescope
at HARPS-N. See Section 2.2. The Total Irradiance Monitor (TIM)
on board the SOlar Radiation and Climate Experiment (SORCE) measures the
Total Solar Irradiance (TSI) using a set of four Electrical Substitution
Radiometers. See Section 2.3. (1 data file).

---------------------------------------------------------
Title: Rotation of Solar Analogs Crossmatching Kepler and Gaia DR2
Authors: do Nascimento, J. -D., Jr.; de Almeida, L.; Velloso, E. N.;
Anthony, F.; Barnes, S. A.; Saar, S. H.; Meibom, S.; da Costa,
J. S.; Castro, M.; Galarza, J. Y.; Lorenzo-Oliveira, D.; Beck, P. G.;
Meléndez, J.
2020ApJ...898..173D Altcode: 2020arXiv200606204D
A major obstacle to interpreting the rotation period distribution
for main-sequence stars from Kepler mission data has been the lack
of a precise evolutionary status for these objects. We address this
by investigating the evolutionary status based on Gaia Data Release
2 parallaxes and photometry for more than 30,000 Kepler stars with
rotation period measurements. Many of these are subgiants and should
be excluded in future work on dwarfs. We particularly investigate a
193-star sample of solar analogs and report newly determined rotation
periods for 125 of these. These include 54 stars from a prior sample,
of which we can confirm the periods for 50. The remainder are new, and
10 of them longer than a solar rotation period, suggesting that Sun-like
stars continue to spin down on the main sequence past solar age. Our
sample of solar analogs could potentially serve as a benchmark for
future missions, such as PLAnetary Transits and Oscillations of stars,
and emphasizes the need for additional astrometric, photometric, and
spectroscopic information before interpreting the stellar populations
and results from time series surveys.

---------------------------------------------------------
Title: Synthetic Spectra of TiO Bands to Identify Diagnostics of
Starspot Properties
Authors: Neff, J. E.; Cheng, K.; Giacinto, A.; Johnson, D.; Saar, S.
2020AAS...23613004N Altcode:
Magnetic activity similar to that of the Sun is observed on a variety
of cool stars. Strong magnetic fields in stellar interiors and produce
many magnetic phenomena, including starspots in the photosphere. These
starspots are a major source limiting the precision of high-precision
radial velocity measurements used to characterize exoplanets. In
a previous series of papers, we demonstrated an empirical approach
to measuring starspot properties using observed spectra of active
and inactive stars as proxies for the spotted and non-spotted
photosphere. These empirical methods were successful for heavily
spotted stars, but they are not sensitive enough to unravel the jitter
caused by numerous small spots. To overcome these limitations, we have
evaluated a wide range of model atmospheres and spectrum synthesis
codes, and we have assimilated suitable line lists. By characterizing
composite (spot+nonspot) synthetic spectra from the entire range of
parameter space for G and K stars, we have developed new diagnostic
indicators that can be used to measure starspot properties from observed
high-resolution spectra of spotted stars, including spot temperatures,
areas, and the effective decrease in gravity caused by strong magnetic
fields within the spots.

---------------------------------------------------------
Title: The spectral impact of magnetic activity on disc-integrated
HARPS-N solar observations: exploring new activity indicators
Authors: Thompson, A. P. G.; Watson, C. A.; Haywood, R. D.; Costes,
J. C.; de Mooij, E.; Collier Cameron, A.; Dumusque, X.; Phillips,
D. F.; Saar, S. H.; Mortier, A.; Milbourne, T. W.; Aigrain, S.; Cegla,
H. M.; Charbonneau, D.; Cosentino, R.; Ghedina, A.; Latham, D. W.;
López-Morales, M.; Micela, G.; Molinari, E.; Poretti, E.; Sozzetti,
A.; Thompson, S.; Walsworth, R.
2020MNRAS.494.4279T Altcode: 2020arXiv200409830T; 2020MNRAS.tmp.1253T
Stellar activity is the major roadblock on the path to finding true
Earth-analogue planets with the Doppler technique. Thus, identifying
new indicators that better trace magnetic activity (i.e. faculae and
spots) is crucial to aid in disentangling these signals from that
of a planet's Doppler wobble. In this work, we investigate activity
related features as seen in disc-integrated spectra from the HARPS-N
solar telescope. We divide high-activity spectral echelle orders by
low-activity master templates (as defined using both log R'HK
and images from the Solar Dynamics Observatory, SDO), creating
'relative spectra'. With resolved images of the surface of the Sun
(via SDO), the faculae and spot filling factors can be calculated,
giving a measure of activity independent of, and in addition to,
log R'HK. We find pseudo-emission (and pseudo-absorption)
features in the relative spectra that are similar to those reported in
our previous work on α Cen B. In α Cen B, the features are shown to
correlate better to changes in faculae filling factor than spot filling
factor. In this work, we more confidently identify changes in faculae
coverage of the visible hemisphere of the Sun as the source of features
produced in the relative spectra. Finally, we produce trailed spectra
to observe the radial velocity component of the features, which show
that the features move in a redward direction as one would expect when
tracking active regions rotating on the surface of a star.

---------------------------------------------------------
Title: Testing the Spectroscopic Extraction of Suppression of
Convective Blueshift
Authors: Miklos, M.; Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.;
Saar, S. H.; Meunier, N.; Cegla, H. M.; Dumusque, X.; Langellier, N.;
Maldonado, J.; Malavolta, L.; Mortier, A.; Thompson, S.; Watson, C. A.;
Cecconi, M.; Cosentino, R.; Ghedina, A.; Li, C. -H.; López-Morales,
M.; Molinari, E.; Poretti, Ennio; Sasselov, D.; Sozzetti, A.;
Walsworth, R. L.
2020ApJ...888..117M Altcode: 2019arXiv191009038M
Efforts to detect low-mass exoplanets using stellar radial
velocities (RVs) are currently limited by magnetic photospheric
activity. Suppression of convective blueshift is the dominant magnetic
contribution to RV variability in low-activity Sun-like stars. Due to
convective plasma motion, the magnitude of RV contributions from the
suppression of convective blueshift is related to the depth of formation
of photospheric spectral lines for a given species used to compute
the RV time series. Meunier et al. used this relation to demonstrate
a method for spectroscopic extraction of the suppression of convective
blueshift in order to isolate RV contributions, including planetary RVs,
that contribute equally to the time series for each spectral line. Here,
we extract disk-integrated solar RVs from observations over a 2.5 yr
time span made with the solar telescope integrated with the HARPS-N
spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary
Islands, Spain). We apply the methods outlined by Meunier et al. We
are not, however, able to isolate physically meaningful contributions
due to the suppression of convective blueshift from this solar data
set, potentially because our data set is taken during solar minimum
when the suppression of convective blueshift may not sufficiently
dominate activity contributions to RVs. This result indicates that,
for low-activity Sun-like stars, one must include additional RV
contributions from activity sources not considered in the Meunier et
al. model at different timescales, as well as instrumental variation,
in order to reach the submeter per second RV sensitivity necessary to
detect low-mass planets in orbit around Sun-like stars.

---------------------------------------------------------
Title: Solar Flare Soft X-Ray Time Series Spectrum Reconstruction
Authors: Goettlicher, C.; Moore, C. S.; Suarez, C.; Saar, S.
2020AAS...23521008G Altcode:
Solar flares are magnetic reconnection events resulting in sudden
bursts of electromagnetic energy, particle acceleration, and hot
plasma heated to over 10 MK. Hot solar flare plasma generates copious
soft X-rays. Hence, spectral soft X-ray measurements provide great
constraints on flare plasma temperature and dynamics. Flare observations
from Low-Earth orbiting satellites like the first Miniature X-ray Solar
Spectrometer (MinXSS-1) CubeSat can be occulted for 30 minutes of the 90
minute orbit, missing vital portions of the temporal evolution of the
spectrum and plasma. In this project, the eclipsed MinXSS-1 spatially
integrated spectra from 0.8 - 15 keV is reconstructed using non-oculted
data by fitting an empirical piecewise temporal-spectral function
consisting of Gaussian, Lorentian, and polynomial components. This
automated procedure fits the original data and adds synthetic data
points to the eclipse period in the temporal profile, which can be
used to reconstruct the spectral profile for energy range specified
in the time series. At both points of egress and ingress there are
larger decreases in the low energy (&lt; 3 keV) soft X-ray flux due to
absorption by nitrogen and oxygen in Earth's atmosphere. Results from
this project could be used in future projects focusing on exoplanet
atmospheres and models of flare plasma evolution.

---------------------------------------------------------
Title: Constructing A Physically Motivated Model of Activity-Driven
Solar and Stellar Radial Velocities
Authors: Iampietro, A.; Saar, S. H.; Haywood, R. D.; Milbourne, T. W.
2019AGUFMSH41F3321I Altcode:
Analysing the periodic radial-velocity variations of a star caused
by an orbiting planet is a highly successful way of inferring the
masses of exoplanets around bright, nearby stars. A major limitation
to this method comes from rotationally modulated stellar activity
signals that hide orbits of small exoplanets by creating variations
in radial-velocity measurements. We look to the Sun as a test of
concept to understand the effects of solar and stellar activity on
radial-velocity variations. We construct a physically grounded model
for the suppression of convective blueshift and rotation of active
regions across the solar/stellar disk. Additionally and for the first
time, we model horizontal velocity flows in and around active regions
(Evershed and moat flows directed radially outward from sun/starspots,
inflows around plage regions). We use SORCE photometry and HARPS-N
Ca II H&amp;K line emission as proxies for these physical effects,
and fit to measured radial-velocity variations of the Sun seen as a
star from the HARPS-N spectrograph. We also model radial-velocity
measurements of the rocky-planet host star CoRoT-7, using CoRoT
photometry and HARPS Ca II H&amp;K emission observations. We apply
our model for stellar activity and compare to previous models that did
not account for horizontal velocity flows. This work is an essential
step towards modelling the physical effects of stellar activity on
radial-velocity variations, which is crucial to uncovering Earth-like
exoplanets orbiting Sun-like stars. This work is supported under
the NSF-REU solar physics program at SAO, grant number AGS-1560313,
performed in part under contract with the California Institute of
Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA
through the Sagan Fellowship Program executed by the NASA Exoplanet
Science Institute (R.D.H.), and supported in part by NASA award number
NNX16AD42G, the Smithsonian Institution, NASA Heliophysics LWS grant
NNX16AB79G (S.H.S.) and the HARPS-N project.

---------------------------------------------------------
Title: A Study of Equatorial Coronal Holes during the Maximum Phase
of Four Solar Cycles
Authors: Karna, N.; Karna, M. L.; Saar, S. H.; Pesnell, W. D.;
DeLuca, E.
2019AGUFMSH44A..03K Altcode:
The 11-year Solar Cycle (SC) is characterized by periodic changes
in the solar activity such as sunspot numbers, coronal holes, active
regions, eruptions such as prominence eruptions, flares and coronal
mass ejections. In this work we performed a statistical study of the
equatorial coronal holes and the active regions during the maximum
phases of four solar cycles (SC 21 (1979, 1980, 1981 and 1982), SC 22
(1989, 1990, 1991 and 1992), SC 23 (1999, 2000, 2001 and 2002) and SC 24
(2012, 2013, 2014 and 2015)). We compared equatorial coronal hole and
active region numbers, separations between equatorial coronal holes and
active regions centroids, solar wind speed and the number of intense
geomagnetic storms data over these four cycles. We found that the
distance between equatorial coronal holes and active regions, the solar
wind speed, and the the number of intense geomagnetic storms increases
with average sunspot maximum number for even cycles and decreases
with average sunspot maximum for odd cycles. We also noticed that the
solar wind speeds, pressures, and the number of intense geomagnetic
storms increase with the numbers of close equatorial coronal holes and
active regions, suggesting a possible link between equatorial coronal
holes--active regions interactions and the wind phenomena.

---------------------------------------------------------
Title: Stars at High Spatial Resolution
Authors: Carpenter, Kenneth G.; van Belle, Gerard; Brown, Alexander;
Cranmer, Steven R.; Drake, Jeremy; Dupree, Andrea K.; Creech-Eakman,
Michelle; Evans, Nancy R.; Grady, Carol A.; Guinan, Edward F.; Harper,
Graham; Karovska, Margarita; Kolenberg, Katrien; Labeyrie, Antoine;
Linsky, Jeffrey; Peters, Geraldine J.; Rau, Gioia; Ridgway, Stephen;
Roettenbacher, Rachael M.; Saar, Steven H.; Walter, Frederick M.;
Wood, Brian
2019arXiv190805665C Altcode:
We summarize some of the compelling new scientific opportunities
for understanding stars and stellar systems that can be enabled by
sub-milliarcsec (sub-mas) angular resolution, UV-Optical spectral
imaging observations, which can reveal the details of the many dynamic
processes (e.g., evolving magnetic fields, accretion, convection,
shocks, pulsations, winds, and jets) that affect stellar formation,
structure, and evolution. These observations can only be provided
by long-baseline interferometers or sparse aperture telescopes in
space, since the aperture diameters required are in excess of 500 m
(a regime in which monolithic or segmented designs are not and will
not be feasible) and since they require observations at wavelengths
(UV) not accessible from the ground. Such observational capabilities
would enable tremendous gains in our understanding of the individual
stars and stellar systems that are the building blocks of our Universe
and which serve as the hosts for life throughout the Cosmos.

---------------------------------------------------------
Title: The Deaths of Stellar Dynamos: Digging in the Magnetic
Graveyard for Old Cold Coronae
Authors: Metcalfe, Travis S.; Drake, Jeremy J.; Saar, Steven H.
2019hst..prop15991M Altcode:
Sun-like stars exhibit three distinct phases of magnetic evolution. In
the saturated regime, the X-ray luminosity is independent of the rapid
rotation. For slightly older stars in the unsaturated regime, the
X-ray luminosity declines in tandem with rotation. Recent observational
evidence suggests that near the middle of their main-sequence lifetimes,
stars may enter a third regime in which rotation remains nearly constant
while magnetic activity continues to decline. We propose to measure
X-ray luminosities for three stars with a range of spectral types
and metallicities, to identify the signature of this third regime
in the old cold coronae of stars that appear to have shut down their
global dynamos. We will use previous observations to help constrain
the coronal temperatures.

---------------------------------------------------------
Title: Temporal evolution and correlations of optical activity
indicators measured in Sun-as-a-star observations
Authors: Maldonado, J.; Phillips, D. F.; Dumusque, X.; Collier Cameron,
A.; Haywood, R. D.; Lanza, A. F.; Micela, G.; Mortier, A.; Saar,
S. H.; Sozzetti, A.; Rice, K.; Milbourne, T.; Cecconi, M.; Cegla,
H. M.; Cosentino, R.; Costes, J.; Ghedina, A.; Gonzalez, M.; Guerra,
J.; Hernández, N.; Li, C. -H.; Lodi, M.; Malavolta, L.; Molinari,
E.; Pepe, F.; Piotto, G.; Poretti, E.; Sasselov, D.; San Juan, J.;
Thompson, S.; Udry, S.; Watson, C.
2019A&A...627A.118M Altcode: 2019arXiv190603002M
Context. Understanding stellar activity in solar-type stars is crucial
for the physics of stellar atmospheres as well as for ongoing exoplanet
programmes. Aims: We aim to test how well we understand stellar
activity using our own star, the Sun, as a test case. Methods:
We performed a detailed study of the main optical activity indicators
(Ca II H &amp; K, Balmer lines, Na I D1 D2, and
He I D3) measured for the Sun using the data provided by the
HARPS-N solar-telescope feed at the Telescopio Nazionale Galileo. We
made use of periodogram analyses to study solar rotation, and we used
the pool variance technique to study the temporal evolution of active
regions. The correlations between the different activity indicators
as well as the correlations between activity indexes and the derived
parameters from the cross-correlation technique are analysed. We
also study the temporal evolution of these correlations and their
possible relationship with indicators of inhomogeneities in the solar
photosphere like sunspot number or radio flux values. Results:
The value of the solar rotation period is found in all the activity
indicators, with the only exception being Hδ. The derived values vary
from 26.29 days (Hγ line) to 31.23 days (He I). From an analysis of
sliding periodograms we find that in most of the activity indicators
the spectral power is split into several "bands" of periods around
26 and 30 days. They might be explained by the migration of active
regions between the equator and a latitude of ∼30°, spot evolution,
or a combination of both effects. A typical lifetime of active regions
of approximately ten rotation periods is inferred from the pooled
variance diagrams, which is in agreement with previous works. We find
that Hα, Hβ, Hγ, Hɛ, and He I show a significant correlation
with the S index. Significant correlations between the contrast,
bisector span, and the heliocentric radial velocity with the activity
indexes are also found. We show that the full width at half maximum,
the bisector, and the disc-integrated magnetic field correlate with
the radial velocity variations. The correlation of the S index and
Hα changes with time, increasing with larger sun spot numbers and
solar irradiance. A similar tendency with the S index and radial
velocity correlation is also present in the data. Conclusions:
Our results are consistent with a scenario in which higher activity
favours the correlation between the S index and the Hα activity
indicators and between the S index and radial velocity variations. Table A.1 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A118">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A118</A>

---------------------------------------------------------
Title: Three years of Sun-as-a-star radial-velocity observations on
the approach to solar minimum
Authors: Collier Cameron, A.; Mortier, A.; Phillips, D.; Dumusque, X.;
Haywood, R. D.; Langellier, N.; Watson, C. A.; Cegla, H. M.; Costes,
J.; Charbonneau, D.; Coffinet, A.; Latham, D. W.; Lopez-Morales, M.;
Malavolta, L.; Maldonado, J.; Micela, G.; Milbourne, T.; Molinari, E.;
Saar, S. H.; Thompson, S.; Buchschacher, N.; Cecconi, M.; Cosentino,
R.; Ghedina, A.; Glenday, A.; Gonzalez, M.; Li, C. -H.; Lodi, M.;
Lovis, C.; Pepe, F.; Poretti, E.; Rice, K.; Sasselov, D.; Sozzetti,
A.; Szentgyorgyi, A.; Udry, S.; Walsworth, R.
2019MNRAS.487.1082C Altcode: 2019MNRAS.tmp.1180C; 2019arXiv190412186C
The time-variable velocity fields of solar-type stars limit the
precision of radial-velocity determinations of their planets' masses,
obstructing detection of Earth twins. Since 2015 July, we have been
monitoring disc-integrated sunlight in daytime using a purpose-built
solar telescope and fibre feed to the HARPS-N stellar radial-velocity
spectrometer. We present and analyse the solar radial-velocity
measurements and cross-correlation function (CCF) parameters obtained
in the first 3 yr of observation, interpreting them in the context
of spatially resolved solar observations. We describe a Bayesian
mixture-model approach to automated data-quality monitoring. We
provide dynamical and daily differential-extinction corrections to
place the radial velocities in the heliocentric reference frame,
and the CCF shape parameters in the sidereal frame. We achieve a
photon-noise-limited radial-velocity precision better than 0.43 m
s-1 per 5-min observation. The day-to-day precision is
limited by zero-point calibration uncertainty with an RMS scatter
of about 0.4 m s-1. We find significant signals from
granulation and solar activity. Within a day, granulation noise
dominates, with an amplitude of about 0.4 m s-1 and an
autocorrelation half-life of 15 min. On longer time-scales, activity
dominates. Sunspot groups broaden the CCF as they cross the solar
disc. Facular regions temporarily reduce the intrinsic asymmetry of
the CCF. The radial-velocity increase that accompanies an active-region
passage has a typical amplitude of 5 m s-1 and is correlated
with the line asymmetry, but leads it by 3 d. Spectral line-shape
variability thus shows promise as a proxy for recovering the true
radial velocity.

---------------------------------------------------------
Title: Stellar Activity of Main Sequence Stars
Authors: Larson, Alex; Miller, Brendan P.; Saar, Steven H.; Gallo,
Elena; Wright, Jason; Hagen, Cedric
2019AAS...23432203L Altcode:
Many main sequence stars have chromospheric activity levels that vary
with time. These can be characterized based on their Ca II H and K line
core emission. Using data obtained from the California Planet Search
we fit a sinusoidal function to a sample of 244 stars to test for
significant cyclic variability. We wrote a python program to analyze
observations taken over timescales of up to 17 years to determine
optimal sinusoidal parameters, with uncertainties estimated through
a bootstrapping technique. We also identify some inactive stars with
virtually no R'HK variability. We find that within our sample the less
active cyclic stars tend to have longer periods. Ongoing work examines
the potential impact of cyclic and flaring stellar activity on known
exoplanets, including those orbiting within the habitable zone.

---------------------------------------------------------
Title: Turbulent Diffusion Derived from the Motions of SDO/AIA
Coronal Bright Points
Authors: Skokić, I.; Brajša, R.; Sudar, D.; Ruždjak, D.; Saar, S. H.
2019ApJ...877..142S Altcode:
Diffusion of magnetic elements on the Sun has an important role
in current solar dynamo models as a part of the mechanism for
redistribution of the magnetic field and as an important part for
maintaining the solar activity cycle. The main goal is to determine the
character of solar magnetic diffusivity and a value of the diffusion
coefficient by analyzing the motions of coronal bright points (CBPs)
within the frame of the random walk model. We tracked positions of
CBPs in Solar Dynamics Observatory/Atmospheric Imaging Assembly images
for a period of 5 months and examined their displacement spectrum. We
calculated spectral index and diffusion coefficient from the spectrum
and investigated their variation with temporal and spatial scale. For
the first time, variations of the spectral index with heliographic
latitude and time were analyzed. Our results indicate subdiffusion with
the spectral index γ = 0.70 ± 0.01 and the corresponding diffusion
coefficient with a value decreasing from 400 to 100 km2
s-1 for temporal scales of 103-105
s and spatial scales of (1.5-7) × 103 km. Seemingly
random variations around the mean value of spectral index were found,
with peak-to-peak amplitudes &lt;0.30 with time and &lt;0.10 with
latitude. The main conclusion is that CBP motions are consistent with
a subdiffusion process.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Optical activity indicators
(Maldonado+, 2019)
Authors: Maldonado, J.; Phillips, D. F.; Dumusque, X.; Collier,
Cameron A.; Haywood, R. D.; Lanza, A. F.; Micela, G.; Mortier, A.;
Saar, S. H.; Sozzetti, A.; Rice, K.; Milbourne, T.; Cecconi, M.; Cegla,
H. M.; Cosentino, R.; Costes, J.; Ghedina, A.; Gonzalez, M.; Guerra,
J.; Hernandez, N.; Li, C. -H.; Lodi, M.; Malavolta, L.; Molinari,
E.; Pepe, F.; Piotto, G.; Poretti, E.; Sasselov, D.; San Juan, J.;
Thompson, S.; Udry, S.; Watson, C.
2019yCat..36270118M Altcode:
File tableA.1.dat lists the daily median activity indexes and their
uncertainties as well as the daily median CCF parameters measured in
the Sun-as-a-star observations. (1 data file).

---------------------------------------------------------
Title: Stars at High Spatial Resolution
Authors: Carpenter, Kenneth; van Belle, Gerard; Brown, Alexander;
Cranmer, Steven R.; Drake, Jeremy; Dupree, Andrea K.; Creech-Eakman,
Michelle; Evans, Nancy R.; Grady, Carol A.; Guinan, Edward F.; Harper,
Graham; Karovska, Margarita; Kolenberg, Katrien; Labeyrie, Antoine;
Linsky, Jeffrey; Peters, Geraldine J.; Rau, Gioia; Ridgway, Stephen;
Roettenbacher, Rachael M.; Saar, Steven H.; Walter, Frederick M.;
Wood, Brian
2019BAAS...51c..56C Altcode: 2019astro2020T..56C
We summarize compelling new scientific opportunities for understanding
stars and stellar systems that can be enabled by sub-milliarcsec angular
resolution, UV/Optical spectral imaging observations. These can reveal
details of many dynamic processes that affect stellar formation,
structure, and evolution.

---------------------------------------------------------
Title: HARPS-N Solar RVs Are Dominated by Large, Bright Magnetic
Regions
Authors: Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.; Saar,
S. H.; Cegla, H. M.; Cameron, A. C.; Costes, J.; Dumusque, X.;
Langellier, N.; Latham, D. W.; Maldonado, J.; Malavolta, L.; Mortier,
A.; Palumbo, M. L., III; Thompson, S.; Watson, C. A.; Bouchy, F.;
Buchschacher, N.; Cecconi, M.; Charbonneau, D.; Cosentino, R.; Ghedina,
A.; Glenday, A. G.; Gonzalez, M.; Li, C. -H.; Lodi, M.; López-Morales,
M.; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Piotto,
G.; Rice, K.; Sasselov, D.; Ségransan, D.; Sozzetti, A.; Szentgyorgyi,
A.; Udry, S.; Walsworth, R. L.
2019ApJ...874..107M Altcode: 2019arXiv190204184M
State-of-the-art radial-velocity (RV) exoplanet searches are
currently limited by RV signals arising from stellar magnetic
activity. We analyze solar observations acquired over a 3 yr period
during the decline of Carrington Cycle 24 to test models of RV
variation of Sun-like stars. A purpose-built solar telescope at
the High Accuracy Radial-velocity Planet Searcher for the Northern
hemisphere (HARPS-N) provides disk-integrated solar spectra, from
which we extract RVs and {log}{R}HK}{\prime
}. The Solar Dynamics Observatory (SDO) provides disk-resolved images
of magnetic activity. The Solar Radiation and Climate Experiment
(SORCE) provides near-continuous solar photometry, analogous to a
Kepler light curve. We verify that the SORCE photometry and HARPS-N
{log}{R}HK}{\prime } correlate strongly with the
SDO-derived magnetic filling factor, while the HARPS-N RV variations
do not. To explain this discrepancy, we test existing models of
RV variations. We estimate the contributions of the suppression of
convective blueshift and the rotational imbalance due to brightness
inhomogeneities to the observed HARPS-N RVs. We investigate the time
variation of these contributions over several rotation periods, and
how these contributions depend on the area of active regions. We find
that magnetic active regions smaller than 60 Mm2 do not
significantly suppress convective blueshift. Our area-dependent model
reduces the amplitude of activity-induced RV variations by a factor of
two. The present study highlights the need to identify a proxy that
correlates specifically with large, bright magnetic regions on the
surfaces of exoplanet-hosting stars.

---------------------------------------------------------
Title: Where's That Flare: A Comprehensive Hard X-Ray Solar Flare
Catalog
Authors: Merhi, Maya; Loftus, Kaitlyn; Saar, Steven
2019AAS...23335901M Altcode:
We have created a hard x-ray solar flare catalog using short channel
wavelength bands of 0.5 to 4 Å from NOAA's Geostationary Operational
Environmental Satellites (GOES) X-Ray Sensor (XRS) data for 2003 to
2018. The Where's That Flare (WTF) catalog was developed using an
automated algorithm designed to use changes in the derivative of the
hard X-ray flux to identify flares. Intended to provide a complete
archive of all hard X-ray solar flare events in GOES XRS data, the WTF
catalog (novelly for the hard X-ray) distinguishes between "simple"
single peak flare events and "complex" multi-peak flare events and is
sensitive to small flares near the background level. To account for the
varying background level of the hard X-ray flux, the detection algorithm
dynamically adapts to the local background to detect flares of all
sizes and complexities. A statistical analysis of flare characteristics
was performed on the WTF catalog investigating correlations between
total energy, flare duration, peak flux, peak time, rise time, decay
time, as well as characteristics of complex events such as number of
peaks per complex event. Frequency distributions of total energy,
flare duration, and number of peaks per complex event were also
investigated and fit with power laws where applicable. Our catalog
is complete to approximately 10-7.5 W/m2 peak flux. In the future,
we will run our algorithm on all available GOES data and use this
catalog in conjunction with NOAA GOES SXI data and NASA Hinode image
data to give spatial locations of solar flares in our catalog. This
work is supported by NSF-REU Solar Physics program at SAO, grant number
AGS-1560313. Keywords: Catalogs, Solar flares, X-ray flares

---------------------------------------------------------
Title: Instrument Calibration of the Interface Region Imaging
Spectrograph (IRIS) Mission
Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell,
T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.;
Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.;
Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M.
2018SoPh..293..149W Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA small
explorer mission that provides high-resolution spectra and images of
the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The
IRIS data are archived in calibrated form and made available to the
public within seven days of observing. The calibrations applied to
the data include dark correction, scattered light and background
correction, flat fielding, geometric distortion correction, and
wavelength calibration. In addition, the IRIS team has calibrated the
IRIS absolute throughput as a function of wavelength and has been
tracking throughput changes over the course of the mission. As a
resource for the IRIS data user, this article describes the details
of these calibrations as they have evolved over the first few years
of the mission. References to online documentation provide access to
additional information and future updates.

---------------------------------------------------------
Title: Stellar Surface Magneto-convection as a Source of Astrophysical
Noise. II. Center-to-limb Parameterization of Absorption Line Profiles
and Comparison to Observations
Authors: Cegla, H. M.; Watson, C. A.; Shelyag, S.; Chaplin, W. J.;
Davies, G. R.; Mathioudakis, M.; Palumbo, M. L., III; Saar, S. H.;
Haywood, R. D.
2018ApJ...866...55C Altcode: 2018arXiv180711423C
Manifestations of stellar activity (such as star-spots, plage/faculae,
and convective flows) are well-known to induce spectroscopic
signals often referred to as astrophysical noise by exoplanet
hunters. For example, setting an ultimate goal of detecting true
Earth analogs demands reaching radial velocity (RV) precisions of
∼9 cm s-1. While this is becoming technically feasible
with the latest generation of highly stabilized spectrographs, it
is astrophysical noise that sets the true fundamental barrier on
attainable RV precisions. In this paper, we parameterize the impact
of solar surface magneto-convection on absorption line profiles, and
extend the analysis from the solar disk center (Paper I) to the solar
limb. Off disk-center, the plasma flows orthogonal to the granule tops
begin to lie along the line of sight, and those parallel to the granule
tops are no longer completely aligned with the observer. Moreover, the
granulation is corrugated and the granules can block other granules, as
well as the intergranular lane components. Overall, the visible plasma
flows and geometry of the corrugated surface significantly impact the
resultant line profiles and induce center-to-limb variations in shape
and net position. We detail these herein, and compare to various solar
observations. We find our granulation parameterization can recreate
realistic line profiles and induced radial velocity shifts, across
the stellar disk, indicative of both those found in computationally
heavy radiative 3D magnetohydrodynamical simulations and empirical
solar observations.

---------------------------------------------------------
Title: How Cool is That? Taking the Temperature of the Coldest
Coronae: the Magnetic Grand Minimum Candidate Tau Ceti
Authors: Saar, Steven
2018cxo..prop.5338S Altcode:
The Sun sporadically has "naps", called magnetic grand minima (MGM),
when its cyclic dynamo sputters into a fitful state with few spots. As
the last of these happened long ago, we know little about this phase of
solar life. There are hints that the Sun will soon enter a new MGM,
raising the question: what happens then? We propose to study the
brightest candidate MGM star, tau Ceti, to explore a proxy for the
solar MGM corona. Previous data show its corona is cold (log T &lt;
6.1) but T is poorly constrained. We will reobserve it using HRC-S
with an enlarged dither pattern, through thick and thin filters. This
yields high T sensitivity at cool T, enabling us to find tau Ceti's
coronal T. We use this to estimate the mix of coronal holes and quiet
areas on the star, and thus the MGM Sun.

---------------------------------------------------------
Title: A First Look at the Effect of Flares on Radial Velocity Jitter
in G Dwarfs: A Punch and a Splash?
Authors: Saar, Steven H.; Palumbo, Michael L., III; Haywood, Raphaelle
D.; Dupree, Andrea K.
2018csss.confE..86S Altcode:
conference poster

---------------------------------------------------------
Title: Magnetic activity cycles in the open cluster NGC 6811?
Authors: Velloso, Eduardo N.; do Nascimento, José-Dias, Jr.; Saar,
Steven H.; Meibom, Søren
2018csss.confE..43V Altcode:
The sun shows a magnetic activity cycle related to the occurrence of
spots on its surface with a strong periodicity of 11 years. With the
advent of space missions like CoRoT and Kepler, astronomers began to
try and find ways to associate the photometric variability of the star
with its intrinsic magnetic activity. Photometric proxies for activity
appear to be correlated with the chromospheric mathcal{S} index and
p-modes from asteroseismology. In order to investigate the existence
and properties of magnetic cycles in a narrow range of fundamental
parameters, we studied solar-type stars in the intermediate-age open
cluster NGC 6811. We searched our sample for cycle-like periodicities
and in each case classified the variability as either cyclic,
multicyclic, flat or acyclic. We checked the usual correlations
between P_cyc, P_rot and Rossby number and we find a high degree of
dispersion among them, which casts doubt on the existence of the Active
branch. We introduce theoretical questions about what determines the
activity cycle period and whether there is some sort of fundamental
difference between cyclic and acyclic stars. The comparison between
stars with the same mass, age and chemistry suggests that neither of
these properties is truly decisive.

---------------------------------------------------------
Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.

---------------------------------------------------------
Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
2018CEAB...42....1B Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.

---------------------------------------------------------
Title: Rotational Modulation and Activity Cycles at Rotational
Extremes: 25 yrs of NURO Photometry for HII 1883
Authors: Milingo, Jackie; Saar, Steven; Marschall, Laurence
2018AAS...23134928M Altcode:
We present a 25 yr compilation of V-band differential photometry
for the Pleiades K dwarf HII 1883 (V660 Tau). HII 1883 has a
rotational period &lt;P_rot&gt; of ~ 0.24 d and displays significant
rotational modulation due to non-uniform surface brightness or
"starspots". Preliminary work yields a cycle period of ~ 9 yrs and
rotational shear (ΔP_rot/&lt;P_rot&gt;) considerably less than
solar. HII 1883 is one of the fastest rotating single stars with a
known cycle. With additional data available we compare newly determined
P_cyc and ΔP_rot/&lt;P_rot&gt; values with those of other stars,
putting HII 1883 into the broader context of dynamo properties in
single cool dwarfs.

---------------------------------------------------------
Title: Radial-Velocity Signatures of Magnetic Features on the Sun
Observed as a Star
Authors: Palumbo, M. L., III; Haywood, R. D.; Saar, S. H.; Dupree,
A. K.; Milbourne, T. W.
2017AGUFM.P53B2651P Altcode:
In recent years, the search for Earth-mass planets using radial-velocity
measurements has become increasingly limited by signals arising
from stellar activity. Individual magnetic features induce localized
changes in intensity and velocity, which combine to change the apparent
radial velocity of the star. Therefore it is critical to identify
an indicator of activity-driven radial-velocity variations on the
timescale of stellar rotation periods. We use 617.3 nm photospheric
filtergrams, magnetograms, and dopplergrams from SDO/HMI and 170.0
nm chromospheric filtergrams from AIA to identify magnetically-driven
solar features and reconstruct the integrated solar radial velocity with
six samples per day over the course of 2014. Breaking the solar image
up into regions of umbrae, penumbrae, quiet Sun, network, and plages,
we find a distinct variation in the center-to-limb intensity-weighted
velocity for each region. In agreement with past studies, we find that
the suppression of convective blueshift is dominated by plages and
network, rather than dark photospheric features. In the future, this
work will be highly useful for identifying indicators which correlate
with rotationally modulated radial-velocity variations. This will allow
us to break the activity barrier that currently precludes the precise
characterization of exoplanet properties at the lowest masses. This
work was supported by the NSF-REU solar physics program at SAO, grant
number AGS-1560313. This work was performed in part under contract
with the California Institute of Technology (Caltech)/Jet Propulsion
Laboratory (JPL) funded by NASA through the Sagan Fellowship Program
executed by the NASA Exoplanet Science Institute.

---------------------------------------------------------
Title: Steps Towards Detecting Coronal Mass Ejections on Stars:
Tests Using Solar Data
Authors: Saar, S.; Cressman, A.
2017AGUFM.P53E2680S Altcode:
One important parameter affecting exoplanet habitability is the
frequency and energy spectrum of coronal mass ejections (CMEs) and
their associated energetic particle fluences. Estimates of CME rates
have been made based on magnetic fluxes, and the frequency of strong
flares, but actual detections have been sparse and debated. We propose
a new way to detect stellar CMEs by watching for their effect on the
He I 1083 nm line with high cadence, high S/N data. Filaments are dark
against the background chromosphere in He I, and a filament eruption
(FE) or CME should lead to a sudden, small step function increase in
total emission, provided the rest of the star was unchanging. He I
disk integrated velocity should show a similar change, depending on
the relative velocity of the newly uncovered underlying material. We
test this idea using CRISP data from the Mauna Loa Solar Observatory
compared to the AIA FE list of MacCauley et al. Though hampered by
the typically short observing window each day, which is not always
well matched to the solar events, we identify several FE with the
distinctive expected He I signatures in integrated light. We compare
our "detections" with the He I signatures of flares (with and without
CMEs), and with randomly selected days of data to better understand
the detection success rate, and the number of false positives. We
note that the signature of flares typically evolves more quickly,
and exhibits more complex intensity and velocity changes (often with
positive and negative excursions). We conclude that He I observations
hold promise for obtaining statistics on stellar CMEs. We plan test
stellar observations in the near future. This work was supported by
NASA Heliophysics grant NNX16AB79G.

---------------------------------------------------------
Title: Automated X-ray Flare Detection with GOES, 2003-2017: The
Where of the Flare Catalog and Early Statistical Analysis
Authors: Loftus, K.; Saar, S. H.
2017AGUFMSH52B..05L Altcode:
NOAA's Space Weather Prediction Center publishes the current definitive
public soft X-ray flare catalog, derived using data from the X-ray
Sensor (XRS) on the Geostationary Operational Environmental Satellites
(GOES) series. However, this flare list has shortcomings for use in
scientific analysis. Its detection algorithm has drawbacks (missing
smaller flux events and poorly characterizing complex ones), and its
event timing is imprecise (peak and end times are frequently marked
incorrectly, and hence peak fluxes are underestimated). It also lacks
explicit and regular spatial location data. We present a new database,
"The Where of the Flare" catalog, which improves upon the precision
of NOAA's current version, with more consistent and accurate spatial
locations, timings, and peak fluxes. Our catalog also offers several
new parameters per flare (e.g. background flux, integrated flux). We
use data from the GOES Solar X-ray Imager (SXI) for spatial flare
locating. Our detection algorithm is more sensitive to smaller
flux events close to the background level and more precisely marks
flare start/peak/end times so that integrated flux can be accurately
calculated. It also decomposes complex events (with multiple overlapping
flares) by constituent peaks. The catalog dates from the operation of
the first SXI instrument in 2003 until the present. We give an overview
of the detection algorithm's design, review the catalog's features,
and discuss preliminary statistical analyses of light curve morphology,
complex event decomposition, and integrated flux distribution. The Where
of the Flare catalog will be useful in studying X-ray flare statistics
and correlating X-ray flare properties with other observations. This
work was supported by Contract #8100002705 from Lockheed-Martin to
SAO in support of the science of NASA's IRIS mission.

---------------------------------------------------------
Title: The Flares of Proxima Cen
Authors: Kashyap, Vinay; Wargelin, Bradford J.; Drake, Jeremy J.;
Saar, Steven H.
2017AAS...23030104K Altcode:
The corona of Proxima Cen has been observed with a variety of
high-energy instruments (ASCA/SIS, XMM/MOS, XMM/pn, Swift/XRT,
Swift/UVOT, Chandra/HRC-I, Chandra/ACIS-S) covering different levels
of activity as the star goes through a stellar cycle. The data exhibit
numerous strong flares as well as lower level flaring activity. In
analogy with the solar case, flare intensities are expected to be
scale-free and distributed as a power-law. We have modeled the flare
distributions separately for each observation in order to explore their
dependence on the energy environment defined by the stellar activity. We
find that the flare distribution indices differ considerably, ranging
from ≈1.4-2, and discuss the causes of such variations, including
dependences on spectral hardness and activity levels.

---------------------------------------------------------
Title: Optical, UV, and X-ray evidence for a 7-yr stellar cycle in
Proxima Centauri
Authors: Wargelin, B. J.; Saar, S. H.; Pojmański, G.; Drake, J. J.;
Kashyap, V. L.
2017MNRAS.464.3281W Altcode: 2016arXiv161003447W
Stars of stellar type later than about M3.5 are believed to be fully
convective and therefore unable to support magnetic dynamos like the
one that produces the 11-yr solar cycle. Because of their intrinsic
faintness, very few late M stars have undergone long-term monitoring
to test this prediction, which is critical to our understanding
of magnetic field generation in such stars. Magnetic activity is
also of interest as the driver of UV and X-ray radiation, as well as
energetic particles and stellar winds, that affects the atmospheres of
close-in planets that lie within habitable zones, such as the recently
discovered Proxima b. We report here on several years of optical,
UV, and X-ray observations of Proxima Centauri (GJ 551; dM5.5e): 15
yr of All Sky Automated Survey photometry in the V band (1085 nights)
and 3 yr in the I band (196 nights), 4 yr of Swift X-Ray Telescope and
UV/Optical Telescope observations (more than 120 exposures), and nine
sets of X-ray observations from other X-ray missions (ASCA, XMM-Newton,
and three Chandra instruments) spanning 22 yr. We confirm previous
reports of an 83-d rotational period and find strong evidence for a
7-yr stellar cycle, along with indications of differential rotation at
about the solar level. X-ray/UV intensity is anticorrelated with optical
V-band brightness for both rotational and cyclical variations. From
comparison with other stars observed to have X-ray cycles, we deduce
a simple empirical relationship between X-ray cyclic modulation and
Rossby number, and we also present Swift UV grism spectra covering
2300-6000 Å.

---------------------------------------------------------
Title: Giant Coronal Loops Dominate the Quiescent X-Ray Emission in
Rapidly Rotating M Stars
Authors: Cohen, O.; Yadav, R.; Garraffo, C.; Saar, S. H.; Wolk, S. J.;
Kashyap, V. L.; Drake, J. J.; Pillitteri, I.
2017ApJ...834...14C Altcode: 2016arXiv161102141C
Observations indicate that magnetic fields in rapidly rotating stars
are very strong, on both small and large scales. What is the nature
of the resulting corona? Here we seek to shed some light on this
question. We use the results of an anelastic dynamo simulation of
a rapidly rotating fully convective M star to drive a physics-based
model for the stellar corona. We find that due to the several kilo
Gauss large-scale magnetic fields at high latitudes, the corona,
and its X-ray emission are dominated by star-size large hot loops,
while the smaller, underlying colder loops are not visible much in
the X-ray. Based on this result, we propose that, in rapidly rotating
stars, emission from such coronal structures dominates the quiescent,
cooler but saturated X-ray emission.

---------------------------------------------------------
Title: Data Mining Solar X-Ray Flares Triggered by Emerging Magnetic
Flux
Authors: Loftus, Kaitlyn; Saar, Steven H.; Schanche, Nicole
2017AAS...22933906L Altcode:
We investigate the association between emerging magnetic flux and solar
X-ray flares to identify, and if possible quantify, distinguishing
physical properties of flares triggered by flux emergence versus
those triggered by other sources. Our study uses as its basis
GOES-classified solar flares from March 2011 through June 2016 that
have been identified by the Space Weather Prediction Center’s flare
detection algorithm. The basic X-ray flare data is then enriched with
data about related EUV-spectrum flares, emerging fluxes, active regions,
eruptions, and sigmoids, which are all characterized by event-specific
keywords, identified via SDO feature finding tools, and archived in the
Heliophysics Events Knowledgebase (HEK). Using appropriate spatial and
temporal parameters for each event type to determine association, we
create a catalogue of solar events associated with each GOES-classified
flare. After accounting for the primitive state of many of these
event detection algorithms, we statistically analyze the compiled
dataset to determine the effects of an emerging flux trigger on flare
properties. A two-sample Kolmogorov-Smirnov test confirms with 99.9%
confidence that flares triggered by emerging flux have a different
peak flux distribution than non-emerging-flux-associated flares. We
observe no linear or logarithmic correlations between flares’ and
their associated emerging fluxes’ individual properties and find
flares triggered by emerging flux are ~ 10% more likely to cause an
eruption inside an active region while outside of an active region,
the flare’s association with emerging flux has no effect on its
likeliness to cause an eruption. We also compare the morphologies of
the flares triggered by emerging flux and flares not via a superposed
epoch analysis of lightcurves. Our results will be of interest for
predicting flare behavior as a function of magnetic activity (where
we can use enhanced rates of emerging flux as a proxy for heightened
stellar magnetic activity).

---------------------------------------------------------
Title: Estimates Of Magnetic Plage Filling Factors Using The Cn Band
Authors: Saar, Steven H.; Judge, Philip
2016csss.confE.151S Altcode:
The 388nm CN band (like the better known "G band" of CH) is used in the
Sun to locate strong magnetic concentrations. Magnetic network and plage
are bright in these molecular bands, since the enhanced chromospheric
heating there destroys the molecule, erasing its absorption and allowing
the continuum to shine through. We take advantage of this to estimate
the filling factor of strong fields in active dwarf stars. CN band
depths in active stars can be compared with those of inactive stars of
very similar temperature and metallicity, and after an adjustment for
line-blanketing, used to estimate a magnetic plage filling factor. We
estimate filling factors for a two stars, and compare them to direct
Stokes I line-broadening measurements. Limitations, caveats, and future
directions are briefly considered.

---------------------------------------------------------
Title: FK Comae Berenices, King of Spin: The COCOA-PUFS Project
Authors: Ayres, Thomas R.; Kashyap, V.; Saar, S.; Huenemoerder,
D.; Korhonen, H.; Drake, J. J.; Testa, P.; Cohen, O.; Garraffo, C.;
Granzer, T.; Strassmeier, K.
2016ApJS..223....5A Altcode: 2016arXiv160103305A
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com:
HD117555; G4 III). This single star is thought to be a recent
binary merger, and is exceptionally active by measure of its
intense ultraviolet (UV) and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with the Hubble Space Telescope
in the UV (1200-3000 Å), using mainly its high-performance Cosmic
Origins Spectrograph, but also high precision Space Telescope Imaging
Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV),
utilizing its High-Energy Transmission Grating Spectrometer; together
with supporting photometry and spectropolarimetry in the visible
from the ground. This is an introductory report on the project. FK Com
displayed variability on a wide range of timescales over all wavelengths
during the week-long main campaign, including a large X-ray flare;
“super-rotational broadening” of the far-ultraviolet “hot
lines” (e.g., Si IV 1393 Å 8 × 104 K) together with
chromospheric Mg II 2800 Å and C II 1335 Å (1-3 × 104
K); large Doppler swings suggestive of bright regions alternately on
advancing and retreating limbs of the star; and substantial redshifts
of the epoch-average emission profiles. These behaviors paint a picture
of a highly extended, dynamic, hot (∼10 MK) coronal magnetosphere
around the star, threaded by cooler structures perhaps analogous to
solar prominences and replenished continually by surface activity
and flares. Suppression of angular momentum loss by the confining
magnetosphere could temporarily postpone the inevitable stellar
spindown, thereby lengthening this highly volatile stage of coronal
evolution. COordinated Campaign of Observations and Analysis,
Photosphere to Upper Atmosphere, of a Fast-rotating Star.

---------------------------------------------------------
Title: Meridional motions and Reynolds stress from SDO/AIA coronal
bright points data
Authors: Sudar, D.; Saar, S. H.; Skokić, I.; Poljančić Beljan,
I.; Brajša, R.
2016A&A...587A..29S Altcode: 2016arXiv160102406S
Context. It is possible to detect and track coronal bright points (CBPs)
in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA)
images. A combination of high resolution and high cadence provides
a wealth of data that can be used to determine velocity flows on the
solar surface with very high accuracy. Aims: We derived a very
accurate solar rotation profile and investigated meridional flows,
torsional oscillations, and horizontal Reynolds stress based on ≈6
months of SDO/AIA data. Methods: We used a segmentation algorithm
to detect CBPs in SDO/AIA images. We also used invariance of the solar
rotation profile with central meridian distance (CMD) to determine
the height of CBPs in the 19.3 nm channel. Results: The best
fit solar rotation profile is given by ω(b) = (14.4060 ± 0.0051 +
(-1.662 ± 0.050)sin2b + (-2.742 ± 0.081)sin4b)°
day-1. The height of CBPs in the SDO/AIA 19.3 nm channel was
found to be ≈6500 km. Meridional motion is predominantly poleward for
all latitudes, while solar velocity residuals show signs of torsional
oscillations. Horizontal Reynolds stress was found to be smaller than in
similar works, but still showed transfer of angular momentum towards the
solar equator. Conclusions: Most of the results are consistent
with Doppler measurements rather than tracer measurements. The fairly
small calculated value of horizontal Reynolds stress might be due to
the particular phase of the solar cycle. Accuracy of the calculated
rotation profile indicates that it is possible to measure changes in
the profile as the solar cycle evolves. Analysis of further SDO/AIA CBP
data will also provide a better understanding of the temporal behaviour
of the rotation velocity residuals, meridional motions, and Reynolds
stress. Table 1 is only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A29">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A29</A>

---------------------------------------------------------
Title: An Application of the Random Walk Model to Proper Motions of
Coronal Bright Points from SDO Data
Authors: Skokić, I.; Sudar, D.; Saar, S. H.; Brajša, R.;
Poljančić-Beljan, I.
2016CEAB...40...23S Altcode:
Atmospheric Imaging Assembly (AIA) images from the Solar Dynamics
Observatory (SDO) were used to follow the motions of coronal bright
points (CBPs) in the period 1 January - 19 May 2011 with a cadence of
10 minutes. This resulted in a data set of 80966 CBPs with measured
lifetimes and mean velocities which were used in a random walk model
to calculate the diffusion coefficient, D. The results show that D has
a value of ≈260 km^2 s^{-1} for CBPs with lifetime below 6 hours,
decreasing to ≈170 km^2 s^{-1} for lifetimes above 12 hours, with
a mean value of ≈230 km^2 s^{-1}.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Granulation model for 508 KIC stars
(Cranmer+, 2014)
Authors: Cranmer, S. R.; Bastien, F. A.; Stassun, K. G.; Saar, S. H.
2016yCat..17810124C Altcode:
A goal of this work is to find self-consistent and accurate ways to
predict the properties of stellar light-curve variability, and to use
this variability to calibrate against other methods of determining
their fundamental parameters. Thus, it may be possible to develop
the analysis of granular flicker measurements in a way that augments
the results of asteroseismology and improves the accuracy of, e.g.,
stellar mass and radius measurements. To assist in this process,
we provide tabulated data for 508 stars with photometric light
curves measured by the Kepler mission, which also includes their
derived masses and predicted values of the turbulent Mach number
(Ma), the root-mean-square (rms) granulation intensity
amplitude σ, and the flicker amplitude F8. These data are
also hosted, with updates as needed, on the first author's Web site
(http://www.cfa.harvard.edu/~scranmer/). With the data is a short code
written in the Interactive Data Language (IDL) that reads the data
and reproduces two of the three panels of Figure4 in the paper. (3 data files).

---------------------------------------------------------
Title: The Hinode/XRT Full-Sun Image Corrections and the Improved
Synoptic Composite Image Archive
Authors: Takeda, Aki; Yoshimura, Keiji; Saar, Steven H.
2016SoPh..291..317T Altcode: 2015SoPh..tmp..176T
The XRT Synoptic Composite Image Archive (SCIA) is a storage and gallery
of X-ray full-Sun images obtained through the synoptic program of
the X-Ray Telescope (XRT) onboard the Hinode satellite. The archived
images provide a quick history of solar activity through the daily
and monthly layout pages and long-term data for morphological and
quantitative studies of the X-ray corona. This article serves as an
introduction to the SCIA, i.e., to the structure of the archive and
specification of the data products included therein. We also describe
a number of techniques used to improve the quality of the archived
images: preparation of composite images to increase intensity dynamic
range, removal of dark spots that are due to contaminants on the CCD,
and correction of the visible stray light contamination that has been
detected on the Ti-poly and C-poly filter images since May 2012.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Time and positions of coronal
bright points (Sudar+, 2016)
Authors: Sudar, D.; Saar, S. H.; Skokic, I.; Poljancic Beljan, I.;
Brajsa, R.
2016yCat..35870029S Altcode:
Positional information about CBPs detected by the segmentation
algorithm are presented. For each CBP time in Julian days (JD) and x
and y coordinates in pixels are given. (1 data file).

---------------------------------------------------------
Title: Simulating Starspot Properties as a Function of Stellar
Properties When Emergence Rates are High
Authors: Hotton, Kate; Saar, Steven H.
2016AAS...22714513H Altcode:
We wish to explore, under various stellar conditions, how aggregate
starspot properties change when spot emergence rates are high. We
use a Sun-based model to simulate the emergence, motion and decay
of starspots on active stars. The spots are generated with a solar
log-normal distribution of areas, and the emergence rate scaled
according to the stellar rotation rate. The initial longitude of each
spot is generated randomly, and initial latitude is generated with
a normal distribution about a changing average, equivalent to the
solar butterfly diagram. The spots are then allowed to decay at a rate
dependent on the stars' surface turbulence, with a motion determined
by the differential rotation and meridional flow. At high emergence
rates spots can erupt into old ones, where we will either experience
a merger or (partial) destruction, depending on their polarity. We
follow this evolution over a magnetic cycle, logging the resulting
distribution of spot sizes, latitudes, decay rates and destruction
(flare) rates, for varying input parameters and stellar conditions. We
compare our results with both stellar observations (including light
curves, apparent spot distributions, measured differential rotation and
flare rates) and theoretical estimates such as magnetic diffusivities.

---------------------------------------------------------
Title: Ultra-luminous X-Ray Sources in HARO II and the Role of X-Ray
Binaries in Feedback in Lyα Emitting Galaxies
Authors: Prestwich, A. H.; Jackson, F.; Kaaret, P.; Brorby, M.;
Roberts, T. P.; Saar, S. H.; Yukita, M.
2015ApJ...812..166P Altcode: 2015arXiv150707900P
Lyman Break Analogs (LBAs) are local proxies of high-redshift Lyman
Break Galaxies. Spatially resolved studies of nearby starbursts have
shown that Lyman continuum and line emission are absorbed by dust and
that the Lyα is resonantly scattered by neutral hydrogen. In order to
observe Lyα emission from star-forming regions, some source of feedback
is required to blow the neutral gas away from the starburst to prevent
scattering and allow the Lyα emission to escape. We show that there
are two X-ray point sources embedded in the diffuse emission of the
LBA galaxy Haro 11. CXOU J003652.4-333316 (abbreviated to Haro 11 X-1)
is an extremely luminous (L{}{{X}}∼ {10}41
erg s-1), spatially compact source with a hard-X-ray
spectrum. We suggest that the X-ray emission from Haro 11 X-1 is
dominated by a single accretion source. This might be an active
galactic nucleus or a source similar to the extreme black hole binary
(BHB) M82 X-1. The hard X-ray spectrum indicates that Haro 11 X-1
may be a BHB in a low accretion state. In this case, the very high
X-ray luminosity suggests an intermediate mass black hole that could
be the seed for formation of a supermassive black hole. Source CXOU
J003652.7-33331619.5 (abbreviated Haro 11 X-2) has an X-ray luminosity
of {L}{{X}}∼ 5× {10}40 erg s-1 and
a soft X-ray spectrum (power-law photon index Γ ∼ 2.2). This strongly
suggests that Haro 11 X-2 is an X-ray binary in the ultra luminous state
(i.e., an Ultra Luminous X-ray source, ULX). Haro 11 X-2 is coincident
with the star-forming knot that is the source of the Lyα emission. The
association of a ULX with Lyα emission raises the possibility that
strong winds from X-ray binaries play an important role in injecting
mechanical power into the interstellar medium, thus blowing away neutral
material from the starburst region and allowing the Lyα to escape. We
suggest that feedback from X-ray binaries may play a significant role
in allowing Lyα emission to escape from galaxies in the early universe.

---------------------------------------------------------
Title: Differential rotation of young solar analogs from NGC 6811
Authors: do Nascimento, José-Dias; Meibom, Soren; Saar, Steven H.
2015IAUGA..2258562D Altcode:
NGC 6811 and is an intermediate-age open cluster in the constellation
of Cygnus and one of the four open clusters observed by Kepler
spacecraft. This fact, make NGC 6811 ideal target for probing the
differential rotation of early-G type main-sequence stars around
1 Gyr. Applying a carefully process we compare results from the
periodogram and wavelet analyses of Kepler light curves for stars with
membership probability estimated from photometric and spectroscopic
campaigns. Here, we present our progress toward the diagnostic and
detection of surface differential rotation (DR) on G-type stars in
the open cluster NGC 6811. We also explore the time dependence by
comparing our results with one solar mass stars from NGC 6819. This
temporal analysis can provide essential observational constraint for
theoretical understanding of DR and dynamo.

---------------------------------------------------------
Title: Rotational Modulation and Activity Cycles at Rotational
Extremes: HII 1883
Authors: Milingo, Jacquelynne; Saar, Steven H.; Marschall, Laurence A.
2015IAUGA..2255707M Altcode:
We present a 23 yr compilation of V-band differential photometry for
the Pleiades K dwarf HII 1883 (V660 Tau). HII 1883 has a rotational
period &lt;Prot&gt; of ~ 0.235 d and displays significant
rotational modulation due to non-uniform surface brightness or
"starspots". Preliminary work with 17 years of data yields a
cycle period (Pcyc) of ~ 8 years and rotational shear
(ΔProt/&lt;Prot&gt;) considerably less than
solar. With additional data available we compare newly determined
Pcyc and ΔProt/&lt;Prot&gt; values
with those of other stars, including HII 1883 in a larger study of
magnetic activity in single cool dwarfs.

---------------------------------------------------------
Title: Linking Stellar Coronal Activity and Rotation at 500 Myr:
A Deep Chandra Observation of M37
Authors: Núñez, Alejandro; Agüeros, Marcel A.; Covey, Kevin
R.; Hartman, Joel D.; Kraus, Adam L.; Bowsher, Emily C.; Douglas,
Stephanie T.; López-Morales, Mercedes; Pooley, David A.; Posselt,
Bettina; Saar, Steven H.; West, Andrew A.
2015ApJ...809..161N Altcode: 2015arXiv150702333N
Empirical calibrations of the stellar age-rotation-activity relation
(ARAR) rely on observations of the co-eval populations of stars
in open clusters. We used the Chandra X-ray Observatory to study
M37, a 500-Myr-old open cluster that has been extensively surveyed
for rotation periods ({P}{rot}). M37 was observed almost
continuously for five days, for a total of 440.5 ks, to measure stellar
X-ray luminosities ({L}{{X}}), a proxy for coronal activity,
across a wide range of masses. The cluster’s membership catalog was
revisited to calculate updated membership probabilities from photometric
data and each star’s distance to the cluster center. The result is a
comprehensive sample of 1699 M37 members: 426 with {P}{rot},
278 with X-ray detections, and 76 with both. We calculate Rossby
numbers, {R}o= {P}{rot}/τ , where τ is the
convective turnover time, and ratios of the X-ray-to-bolometric
luminosity, {L}{{X}}/{L}{bol}, to minimize
mass dependencies in our characterization of the rotation-coronal
activity relation at 500 Myr. We find that fast rotators, for which
{R}o\lt 0.09+/- 0.01, show saturated levels of activity,
with log({L}{{X}}/{L}{bol})=\-3.06+/- 0.04. For
{R}o≥slant 0.09+/- 0.01, activity is unsaturated and
follows a power law of the form {R}oβ , where β
= -{2.03}-0.14+0.17. This is the largest sample
available for analyzing the dependence of coronal emission on rotation
for a single-aged population, covering stellar masses in the range
0.4-1.3 {M}⊙ , {P}{rot} in the range 0.4-12.8
days, and {L}{{X}} in the range {10}28.4-30.5
{erg} {{{s}}}-1. Our results make M37 a new benchmark open
cluster for calibrating the ARAR at ages of ≈ 500 Myr.

---------------------------------------------------------
Title: Differential Rotation as a Function of Mass and Age in
Kepler Clusters
Authors: Saar, Steven; Meibom, Soren; do Nascimento, Jose
2015IAUGA..2258556S Altcode:
We present an update on our ongoing analysis of solar-type stars in
Kepler clusters. We explore the mass, rotation, and age dependence of
surface differential rotation using data from stars in three Kepler
clusters, spanning ages from 0.5 to 2.5 Gyr. We discuss these in the
context of previous measurments.

---------------------------------------------------------
Title: Superflare Rates as a Function of Mass and Age in Kepler
Clusters
Authors: Saar, Steven; Meibom, Soren; Wright, Paul
2015IAUGA..2258518S Altcode:
The rate of very powerful, so-called superflares (log E &gt; 33 ergs)
is of great interest for space weather and planetary habitability. We
identify flares in three Kepler clusters and explore trends in
superflare rates as a function of mass, rotation, and age.

---------------------------------------------------------
Title: How typical is the Sun's magnetic cycle ?
Authors: do Nascimento, José-Dias; Saar, Steven H.; Dumusque, Xavier;
Meibom, Soren
2015IAUGA..2250017D Altcode:
Solar analogs refer to main-sequence stars with 0.8 Msun &lt; mass
&lt; 1.2 Msun. Solar twins are stars with Teff, [Fe/H], mass and
rotation indistinguishable from the Sun. These solar twins shed a
new light on the question of how typical the Sun is within the class
of solar-type stars. From the magnetic activity point of view, some
previous work has suggested that the Sun's magnetic cycle period Pcyc
is unusual compared with similar stars, falling between sequences of
active and inactive stars. Combining a sample from HARPS planet-search
program with high-precision Ca II H &amp; K chromospheric activity
measurements we selected a large number of new reliable Pcyc, and
we revisit the relation between rotation periods Prot
and Pcyc. Our preliminary analysis shows that the Sun does not has
a special position between the active and inactive sequences, but
instead follows a new solar-analog-twin sequence proposed here.

---------------------------------------------------------
Title: Grand Minima in the Sun and Sun-like Stars
Authors: Saar, Steven
2015IAUGA..2258484S Altcode:
The Maunder minimum (about 1645 - 1715), when the numbers of sunspots
dropped precipitously (&lt;2 year-1 during one 30 year
interval), raises the question of the long-term stability of the
solar dynamo. While it now appears that some aspects of the cycle
continued during the minimum, it is also clear that the Sun's dynamo
underwent major short-term changes, and that these grand minima are
not uncommon. I review what is known, and not known, about solar grand
minima. One way to fill in the gaps in our understanding of solar
grand minima is to turn to solar-like stars. I review efforts to find
stars which may be in grand minima, properties of these candidates,
and the light this may shed on the state of the Sun in grand minima.

---------------------------------------------------------
Title: The Radial Velocity Signature and Line Diagnostics Arising
from Realistic, Rotating Stellar Plage Models
Authors: Saar, Steven; Dumusque, Xavier
2015IAUGA..2258500S Altcode:
The radial velocity (RV) signature of starspots has been well-studied
and methods to mitigate for them have been developed. The RV
signature of magnetic plage is smaller, but more complex (since
plage differs from its surroundings more by velocity than intensity)
and less well understood. There are reasons however to expect that
RV jitter from plage may be important, especially in low to moderate
activity stars. We explore the RV effects of stellar plage by taking
spatially resolved solar line bisectors in and out of plage at various
limb angles to construct semi-empirical stellar intensity profiles
profiles of different strengths. These lines are placed on model stars
with various plage configurations, rotated, and disk-integrated. The
resulting spectra are analyzed to yield the RV and various line and
cross-correlation profile diagnostics as a function of rotational
phase. We discuss the results and some ideas for mitigating the inferred
RV signatures.

---------------------------------------------------------
Title: Internetwork Chromospheric Bright Grains Observed With IRIS
and SST
Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson,
Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt,
Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan;
Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean;
Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli,
Sarah; Kankelborg, Charles
2015ApJ...803...44M Altcode: 2015arXiv150203490M
The Interface Region Imaging Spectrograph (IRIS) reveals small-scale
rapid brightenings in the form of bright grains all over coronal holes
and the quiet Sun. These bright grains are seen with the IRIS 1330,
1400, and 2796 Å slit-jaw filters. We combine coordinated observations
with IRIS and from the ground with the Swedish 1 m Solar Telescope
(SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H
3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å,
Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps
in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.}
33), temporal, and spectral resolution. We conclude that the IRIS
slit-jaw grains are the counterpart of so-called acoustic grains,
i.e., resulting from chromospheric acoustic waves in a non-magnetic
environment. We compare slit-jaw images (SJIs) with spectra from the
IRIS spectrograph. We conclude that the grain intensity in the 2796
Å slit-jaw filter comes from both the Mg ii k core and wings. The
signal in the C ii and Si iv lines is too weak to explain the presence
of grains in the 1300 and 1400 Å SJIs and we conclude that the grain
signal in these passbands comes mostly from the continuum. Although
weak, the characteristic shock signatures of acoustic grains can often
be detected in IRIS C ii spectra. For some grains, a spectral signature
can be found in IRIS Si iv. This suggests that upward propagating
acoustic waves sometimes reach all the way up to the transition region.

---------------------------------------------------------
Title: Stellar activity and coronal heating: an overview of recent
results
Authors: Testa, Paola; Saar, Steven H.; Drake, Jeremy J.
2015RSPTA.37340259T Altcode: 2015arXiv150207401T
Observations of the coronae of the Sun and of solar-like stars provide
complementary information to advance our understanding of stellar
magnetic activity, and of the processes leading to the heating of
their outer atmospheres. While solar observations allow us to study
the corona at high spatial and temporal resolution, the study of
stellar coronae allows us to probe stellar activity over a wide range
of ages and stellar parameters. Stellar studies therefore provide us
with additional tools for understanding coronal heating processes,
as well as the long-term evolution of solar X-ray activity. We discuss
how recent studies of stellar magnetic fields and coronae contribute
to our understanding of the phenomenon of activity and coronal heating
in late-type stars.

---------------------------------------------------------
Title: Steps towards a high precision solar rotation profile:
Results from SDO/AIA coronal bright point data
Authors: Sudar, D.; Skokić, I.; Brajša, R.; Saar, S. H.
2015A&A...575A..63S Altcode: 2015arXiv150101285S
Context. Coronal bright points (CBP) are ubiquitous small brightenings
in the solar corona associated with small magnetic bipoles. Aims:
We derive the solar differential rotation profile by tracing the motions
of CBPs detected by the Atmospheric Imaging Assembly (AIA) instrument
aboard the Solar Dynamics Observatory (SDO). We also investigate
problems related to the detection of CBPs resulting from instrument
and detection algorithm limitations. Methods: To determine
the positions and identification of CBPs we used a segmentation
algorithm. A linear fit of their central meridian distance and latitude
vs time was used to derive velocities. Results: We obtained
906 velocity measurements in a time interval of only 2 days. The
differential rotation profile can be expressed as ωrot =
(14.47° ± 0.10° + (0.6° ± 1.0°) sin2(b) = (-4.7° ±
1.7°) sin4(b)) d-1. Our result is in agreement
with other work and it comes with reasonable errors in spite of the
very short time interval used. This was made possible by the higher
sensitivity and resolution of the AIA instrument compared to similar
equipment as well as high cadence. The segmentation algorithm also
played a crucial role by detecting so many CBPs, which reduced the
errors to a reasonable level. Conclusions: Data and methods
presented in this paper show a great potential for obtaining very
accurate velocity profiles, both for rotation and meridional motion and,
consequently, Reynolds stresses. The amount of CBP data that could be
obtained from this instrument should also provide a great opportunity
to study changes of velocity patterns with a temporal resolution of
only a few months. Other possibilities are studies of evolution of
CBPs and proper motions of magnetic elements on the Sun.

---------------------------------------------------------
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
Carlsson, M.; Hansteen, V.
2015ApJ...801...83C Altcode: 2015arXiv150101593C
We report on observations of recurrent jets by instruments on board
the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
(SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
recurrent coronal jets were observed to emanate from NOAA Active Region
11793. Far-ultraviolet spectra probing plasma at transition region
temperatures show evidence of oppositely directed flows with components
reaching Doppler velocities of ±100 km s-1. Raster Doppler
maps using a Si iv transition region line show all four jets to have
helical motion of the same sense. Simultaneous observations of the
region by SDO and Hinode show that the jets emanate from a source
region comprising a pore embedded in the interior of a supergranule. The
parasitic pore has opposite polarity flux compared to the surrounding
network field. This leads to a spine-fan magnetic topology in the
coronal field that is amenable to jet formation. Time-dependent
data-driven simulations are used to investigate the underlying drivers
for the jets. These numerical experiments show that the emergence of
current-carrying magnetic field in the vicinity of the pore supplies
the magnetic twist needed for recurrent helical jet formation.

---------------------------------------------------------
Title: Serendipitous Discovery of a Dwarf Nova in the Kepler Field
Near the G Dwarf KIC 5438845
Authors: Brown, Alexander; Neff, James E.; Ayres, Thomas R.; Kowalski,
Adam; Hawley, Suzanne; Berdyugina, Svetlana; Harper, Graham M.;
Korhonen, Heidi; Piskunov, Nikolai; Saar, Steven; Walkowicz, Lucianne;
Wells, Mark A.
2015AJ....149...67B Altcode:
The Kepler satellite provides a unique window into stellar temporal
variability by observing a wide variety of stars with multi-year,
near-continuous, high precision, optical photometric time series. While
most Kepler targets are faint stars with poorly known physical
properties, many unexpected discoveries should result from a long
photometric survey of such a large area of sky. During our Kepler
Guest Observer programs that monitored late-type stars for starspot and
flaring variability, we discovered a previously unknown dwarf nova that
lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This
dwarf nova underwent nine outbursts over a 4 year time span. The two
largest outbursts lasted ∼17-18 days and show strong modulations with
a 110.8 minute period and a declining amplitude during the outburst
decay phase. These properties are characteristic of an SU UMa-type
cataclysmic variable. By analogy with other dwarf nova light curves,
we associate the 110.8 minute (1.847 hr) period with the superhump
period, close to but slightly longer than the orbital period of the
binary. No precursor outbursts are seen before the super-outbursts
and the overall super-outburst morphology corresponds to Osaki &amp;
Meyer “Case B” outbursts, which are initiated when the outer edge
of the disk reaches the tidal truncation radius. “Case B” outbursts
are rare within the Kepler light curves of dwarf novae. The dwarf nova
is undergoing relatively slow mass transfer, as evidenced by the long
intervals between outbursts, but the mass transfer rate appears to
be steady, because the smaller “normal” outbursts show a strong
correlation between the integrated outburst energy and the elapsed time
since the previous outburst. At super-outburst maximum the system was
at V ∼ 18, but in quiescence it is fainter than V ∼ 22, which will
make any detailed quiescent follow-up of this system difficult.

---------------------------------------------------------
Title: A New Light on the Relation Between Rotation Periods and
Cycle Lengths of Stellar Activity
Authors: do Nascimento, Jose-Dias, Jr.; Saar, Steven H.; Anthony,
Francys
2015csss...18...59D Altcode:
Solar analogs and twins shed a new light on the relation between
rotation period and cycle length of stellar activity . The question of
how typical the Sun is within the class of solar-type stars has been
the subject of active investigation over the past three decades. Some
previous work has suggested that the Sun's magnetic cycle period Pcyc
is unusual compared with similar stars, falling between sequences of
active and inactive stars. The HARPS planet-search has been gathering
high-precision Ca II H&amp;K chromospheric activity measurements for
many years, and has measured a large number of new Pcyc. We collect
the most robust cycles among these for stars which are solar analogs
(main-sequence stars with 0.8M_{⊙} &lt; mass &lt; 1.2M_{⊙}) or solar
twins twins (stars with T_{eff}, [Fe/H] and mass indistinguishable
from the Sun). Combining this new sample with older data, we revisit
the relation between rotation periods Prot and Pcyc. Our preliminary
analysis shows that the Sun does not have a special position between
the active and inactive sequences, but instead follows the a new
solar-analog sequence proposed here.

---------------------------------------------------------
Title: A First Look at Differential Rotation in Kepler Open Clusters
NGC 6811 (1 Gyr) and NGC 6819 (2.5 Gyr)
Authors: Saar, Steven H.; Meibom, Soren; do Nascimento, Jose-Dias, Jr.
2015csss...18..125S Altcode:
Open clusters are ideal targets for controlled studies of stellar
properties, since members are coeval and have the same abundances. We
present the first results of measurements of surface differential
rotation (SDR) in two clusters of different ages in the Kepler field. We
compare results for single stars over a range of masses and rotation
rates, and compare and contrast these with previous results for single
and binary stars. All of these properties are found to have an effect
on the average SDR rate.

---------------------------------------------------------
Title: Solar velocity field determined tracking coronal bright points
Authors: Brajša, R.; Sudar, D.; Skokić, I.; Saar, S. H.; Žic, T.
2015CEAB...39...21B Altcode:
Preliminary data from Atmospheric Imaging Assembly (AIA) instrumenton
board Solar Dynamics Observatory (SDO) satellite were used to determine
solar differential rotation and related phenomena. A segmentation
algorithm, which uses multiple AIA channels in search for intensity
enhancements in EUV and X-ray parts of the spectrum compared to the
background intensity, was applied to obtain positional information of
coronal bright points (CBPs). More than 60000 position measurements
of more than 10000 identified CBPs from the period 1 - 2 January 2011
were analyzed. Rotational and meridional velocities were determined
by tracking identified CBPs and various filters were used to exclude
erroneous results. Also, proper motions of CBPs were calculated from
rotation velocity residuals and meridional velocities. Proper motions
of CBPs were investigated using a random walk model and the diffusion
constant was calculated. These results were compared with the previous
ones obtained by other instruments and methods (especially with the
SOHO-EIT and Hinode data) and a striking agreement of the obtained
diffusion constant with results from other studies was found.

---------------------------------------------------------
Title: Cool Stars and Space Weather
Authors: Vidotto, A. A.; Jardine, M.; Cameron, A. C.; Morin, J.;
Villadsen, J.; Saar, S. H.; Alvarado, J.; Cohen, Ofer; Holzwarth,
V.; Poppenhaeger, K.; Reville, V.
2015csss...18...65V Altcode: 2014arXiv1408.3943V
Stellar flares, winds and coronal mass ejections form the “space
weather”. They are signatures of the magnetic activity of cool stars
and, since activity varies with age, mass and rotation, the space
weather that extra-solar planets experience can be very different
from the one encountered by the solar system planets. How do stellar
activity and magnetism influence the space weather of exoplanets
orbiting main-sequence stars? How do the environments surrounding
exoplanets differ from those around the planets in our own solar
system? How can the detailed knowledge acquired by the solar system
community be applied in exoplanetary systems? How does space weather
affect habitability? These were questions that were addressed in the
splinter session “Cool stars and Space Weather”, that took place
on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we
present a summary of the contributions made to this session.

---------------------------------------------------------
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
2014Sci...346C.315P Altcode: 2014arXiv1410.5842P
The solar atmosphere was traditionally represented with a simple
one-dimensional model. Over the past few decades, this paradigm shifted
for the chromosphere and corona that constitute the outer atmosphere,
which is now considered a dynamic structured envelope. Recent
observations by the Interface Region Imaging Spectrograph (IRIS) reveal
that it is difficult to determine what is up and down, even in the cool
6000-kelvin photosphere just above the solar surface: This region hosts
pockets of hot plasma transiently heated to almost 100,000 kelvin. The
energy to heat and accelerate the plasma requires a considerable
fraction of the energy from flares, the largest solar disruptions. These
IRIS observations not only confirm that the photosphere is more complex
than conventionally thought, but also provide insight into the energy
conversion in the process of magnetic reconnection.

---------------------------------------------------------
Title: The unresolved fine structure resolved: IRIS observations of
the solar transition region
Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title,
A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira,
T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martínez-Sykora, J.
2014Sci...346E.315H Altcode: 2014arXiv1412.3611H
The heating of the outer solar atmospheric layers, i.e., the transition
region and corona, to high temperatures is a long-standing problem
in solar (and stellar) physics. Solutions have been hampered by an
incomplete understanding of the magnetically controlled structure of
these regions. The high spatial and temporal resolution observations
with the Interface Region Imaging Spectrograph (IRIS) at the solar
limb reveal a plethora of short, low-lying loops or loop segments
at transition-region temperatures that vary rapidly, on the time
scales of minutes. We argue that the existence of these loops solves
a long-standing observational mystery. At the same time, based on
comparison with numerical models, this detection sheds light on a
critical piece of the coronal heating puzzle.

---------------------------------------------------------
Title: Evidence of nonthermal particles in coronal loops heated
impulsively by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale,
F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.;
Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kleint, L.; Kankelborg, C.; Jaeggli, S.
2014Sci...346B.315T Altcode: 2014arXiv1410.6130T
The physical processes causing energy exchange between the Sun’s
hot corona and its cool lower atmosphere remain poorly understood. The
chromosphere and transition region (TR) form an interface region between
the surface and the corona that is highly sensitive to the coronal
heating mechanism. High-resolution observations with the Interface
Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to
60 seconds) of intensity and velocity on small spatial scales (≲500
kilometers) at the footpoints of hot and dynamic coronal loops. The
observations are consistent with numerical simulations of heating by
beams of nonthermal electrons, which are generated in small impulsive
(≲30 seconds) heating events called “coronal nanoflares.” The
accelerated electrons deposit a sizable fraction of their energy
(≲1025 erg) in the chromosphere and TR. Our analysis
provides tight constraints on the properties of such electron beams
and new diagnostics for their presence in the nonflaring corona.

---------------------------------------------------------
Title: Prevalence of small-scale jets from the networks of the solar
transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
2014Sci...346A.315T Altcode: 2014arXiv1410.6143T
As the interface between the Sun’s photosphere and corona, the
chromosphere and transition region play a key role in the formation and
acceleration of the solar wind. Observations from the Interface Region
Imaging Spectrograph reveal the prevalence of intermittent small-scale
jets with speeds of 80 to 250 kilometers per second from the narrow
bright network lanes of this interface region. These jets have lifetimes
of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
small-scale bright regions, often preceded by footpoint brightenings
and accompanied by transverse waves with amplitudes of ~20 kilometers
per second. Many jets reach temperatures of at least ~105
kelvin and constitute an important element of the transition region
structures. They are likely an intermittent but persistent source of
mass and energy for the solar wind.

---------------------------------------------------------
Title: On the prevalence of small-scale twist in the solar
chromosphere and transition region
Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.;
Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen,
J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser,
J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martinez-Sykora, J.
2014Sci...346D.315D Altcode: 2014arXiv1410.6862D
The solar chromosphere and transition region (TR) form an interface
between the Sun’s surface and its hot outer atmosphere. There,
most of the nonthermal energy that powers the solar atmosphere
is transformed into heat, although the detailed mechanism remains
elusive. High-resolution (0.33-arc second) observations with NASA’s
Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere
and TR that are replete with twist or torsional motions on sub-arc
second scales, occurring in active regions, quiet Sun regions, and
coronal holes alike. We coordinated observations with the Swedish
1-meter Solar Telescope (SST) to quantify these twisting motions and
their association with rapid heating to at least TR temperatures. This
view of the interface region provides insight into what heats the low
solar atmosphere.

---------------------------------------------------------
Title: An Interface Region Imaging Spectrograph First View on Solar
Spicules
Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen,
V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt,
N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.;
McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli,
S.; Kankelborg, C.
2014ApJ...792L..15P Altcode: 2014arXiv1407.6360P
Solar spicules have eluded modelers and observers for decades. Since
the discovery of the more energetic type II, spicules have become
a heated topic but their contribution to the energy balance of the
low solar atmosphere remains unknown. Here we give a first glimpse of
what quiet-Sun spicules look like when observed with NASA's recently
launched Interface Region Imaging Spectrograph (IRIS). Using IRIS
spectra and filtergrams that sample the chromosphere and transition
region, we compare the properties and evolution of spicules as
observed in a coordinated campaign with Hinode and the Atmospheric
Imaging Assembly. Our IRIS observations allow us to follow the thermal
evolution of type II spicules and finally confirm that the fading
of Ca II H spicules appears to be caused by rapid heating to higher
temperatures. The IRIS spicules do not fade but continue evolving,
reaching higher and falling back down after 500-800 s. Ca II H type
II spicules are thus the initial stages of violent and hotter events
that mostly remain invisible in Ca II H filtergrams. These events
have very different properties from type I spicules, which show lower
velocities and no fading from chromospheric passbands. The IRIS spectra
of spicules show the same signature as their proposed disk counterparts,
reinforcing earlier work. Spectroheliograms from spectral rasters also
confirm that quiet-Sun spicules originate in bushes from the magnetic
network. Our results suggest that type II spicules are indeed the
site of vigorous heating (to at least transition region temperatures)
along extensive parts of the upward moving spicular plasma.

---------------------------------------------------------
Title: Tanagra: Timing Analysis of Grating Data
Authors: Kashyap, Vinay; Posson-Brown, Jennifer; Drake, Jeremy J.;
Saar, Steven H.; Scargle, Jeffrey D; Connors, Alanna
2014HEAD...1411905K Altcode:
We describe the Tanagra dataset, which now contains the complete set
of cool stars observed with the Chandra gratings thus far. We have
analyzed the datasets to produce a catalog of light curves, flare-like
events, measures of spectral variability, evaluations of variability
for strong spectral lines, correlations of intensity between high-
and low-temperature lines, and other useful observational summaries. We
will describe the analysis methods used and the data products obtained,
and highlight some special cases.This work has been supported by the
Chandra archival grant AR0-11001X.

---------------------------------------------------------
Title: Swift Observations of Proxima Cen
Authors: Wargelin, Bradford J.; Saar, Steven H.; Drake, Jeremy J.;
Kashyap, Vinay
2014HEAD...1411901W Altcode:
Swift observed Proxima Cen (dM5.5e) for more than 40 segments (roughly
100 separate exposures) from 2009 to 2012, including several UV grism
observations. We present analyses of variability in the optical, UV,
and X-ray bands on time scales covering individual flares to a possible
multiyear stellar cycle, and show moderate-resolution spectra covering
2300-6000 Angstroms.

---------------------------------------------------------
Title: Calibrating Data from the Hinode/X-Ray Telescope and Associated
Uncertainties
Authors: Kobelski, Adam R.; Saar, Steven H.; Weber, Mark A.; McKenzie,
David E.; Reeves, Katharine K.
2014SoPh..289.2781K Altcode: 2013arXiv1312.4850K; 2014SoPh..tmp...27K
The X-Ray Telescope (XRT) onboard the Hinode satellite, launched 23
September 2006 by the Japan Aerospace Exploration Agency (JAXA), is a
joint mission of Japan, the United States, and the United Kingdom to
study the solar corona. In particular, XRT was designed to study solar
plasmas with temperatures between 1 and 10 MK with ≈ 1″ pixels
(≈ 2″ resolution). Prior to analysis, the data product from this
instrument must be properly calibrated and data values quantified to
accurately assess the information contained within. We present here
the standard methods of calibration for these data. The calibration
was performed on an empirical basis that uses the least complicated
correction that accurately describes the data while suppressing
spurious features. By analyzing the uncertainties remaining in the
data after calibration, we conclude that the procedure is successful,
because the remaining uncertainty after calibration is dominated by
photon noise. This calibration software is available in the SolarSoft
software library.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s−1 velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.

---------------------------------------------------------
Title: Detection of Supersonic Downflows and Associated Heating
Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
Kankelborg, C.
2014ApJ...789L..42K Altcode: 2014arXiv1406.6816K
Interface Region Imaging Spectrograph data allow us to study the solar
transition region (TR) with an unprecedented spatial resolution of
0.”33. On 2013 August 30, we observed bursts of high Doppler shifts
suggesting strong supersonic downflows of up to 200 km s-1
and weaker, slightly slower upflows in the spectral lines Mg II h
and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
with brightenings in the slitjaw images (SJIs). The bursty behavior
lasts throughout the 2 hr observation, with average burst durations
of about 20 s. The locations of these short-lived events appear to
be the umbral and penumbral footpoints of EUV loops. Fast apparent
downflows are observed along these loops in the SJIs and in the
Atmospheric Imaging Assembly, suggesting that the loops are thermally
unstable. We interpret the observations as cool material falling
from coronal heights, and especially coronal rain produced along the
thermally unstable loops, which leads to an increase of intensity
at the loop footpoints, probably indicating an increase of density
and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher
than the free-fall velocity along the loops. On other observing days,
similar bright dots are sometimes aligned into ribbons, resembling
small flare ribbons. These observations provide a first insight into
small-scale heating events in sunspots in the TR.

---------------------------------------------------------
Title: Investigating Molecular Hydrogen in Active Regions with IRIS
Authors: Jaeggli, Sarah A.; Saar, Steven H.; Daw, Adrian N.; Innes,
Davina
2014AAS...22432306J Altcode:
Molecular hydrogen should be the most abundant molecular species in
sunspots, but recent observations with IRIS show that its florescent
signature is absent from above the sunspot umbra, but appears
brightly during flares. In this poster we continue the analysis of
FUV observations of H2 in active regions, examining the correlation
between the intensity of the H2 lines and the lines of C II and
Si IV which are responsible for their excitation. We particularly
focus on differentiating places where H2 is abundant, holes in the
chromospheric opacity where FUV photons can enter more deeply into the
solar atmosphere, and places where the FUV radiation field is intense,
as in flares.

---------------------------------------------------------
Title: Rates of Large Flares in Old Solar-like Stars in Kepler
Clusters NGC 6811 and 6819 With Implications for the Sun
Authors: Saar, Steven H.; Wright, Paul J.; Meibom, Soren; Kashyap,
Vinay; Drake, Jeremy J.
2014AAS...22412343S Altcode:
We hope to better estimate the rate of very strong (Carrington
event-type) flares in the Sun by studying flares of stars in several
open clusters with well determined ages using Kepler data. Here we
derive white light flare distributions for a sample of near-solar-mass
(G0-G5) dwarfs in NGC 6811 (age ~ 1 Gyr) and NGC 6819 2.5 Gyr). We
compare these with solar white light flare rates and, by estimating
X-ray emission from the same flares using a solar-based relationship,
we compare the Kepler results to other solar and stellar X-ray flare
data. We explore implications of our results for the rates of large
solar flares. This research was supported by Kepler grant NNX13AC29G.

---------------------------------------------------------
Title: SOLAR ANALOGS AND TWINS SHED A NEW LIGHT ON THE RELATION
BETWEEN ROTATION PERIODS AND CYCLE LENGTHS OF STELLAR ACTIVITY
Authors: Do Nascimento, José-Dias; Saar, Steven H.; Anthony, Francys
2014AAS...22432208D Altcode:
The question of how typical the Sun is within the class of solar-type
stars has been the subject of active investigation over the past three
decades. Some previous work has suggested that the Sun's magnetic cycle
period Pcyc is unusual compared with similar stars,falling between
sequences of active and inactive stars. The HARPS planet-search has
been gathering high-precision Ca II H&amp;K chromospheric activity
measurements for about 7 years, and has measured a large number of
new Pcyc. We collect the most robust cycles among these for stars
which are solar analogs (main-sequence stars with 0.8 Msun &lt;
mass &lt; 1.2 Msun) or solar twins twins (stars with Teff, [Fe/H]
and mass indistinguishable from the Sun). Combining this new sample
with older data, we revisit the relation between rotationperiods
Prot and Pcyc. Our preliminary analysis shows that the Sun does not
has a special position between the active and inactive sequences,
but instead follows the a new solar-analog sequence proposed here.

---------------------------------------------------------
Title: H2 Emission in the Sun and Stars: A New Window on Spots
and Flares
Authors: Saar, Steven H.; Jaeggli, Sarah A.
2014AAS...22412344S Altcode:
Molecular H2 is likely important for the formation of sun and starspots,
but has been difficult to observe in the past. H2 emission has been
seen in solar FUV spectra of sunspots and flares, where it produced
by fluorescent excitation driven (primarily) by Si IV and O IV. New
observations with IRIS show that the emission is strong in flares,
and in loops connected to pores or the boundaries of umbrae. We find
evidence for H2 emission in the HST spectra of several magnetically
active, flaring, spotted stars. Once the excitation process is better
understood, observations of H2 emission should permit new insight into
spot formation on the Sun and active stars.

---------------------------------------------------------
Title: Coronae at 3 Gyr: First Results from a Chandra Observation
of the Open Cluster Ruprecht 147
Authors: Saar, Steven H.; Curtis, Jason L.; Wright, Jason
2014AAS...22432203S Altcode:
Ruprecht 147 is the oldest nearby star cluster, with an age of 3
Gyr and a distance of 300 pc. This makes it an important benchmark in
exploring activity-age-rotation relationships, bridging the gap between
the Hyades and M67. We present the first results from a deep 250 ksec
ACIS-I observation of the cluster. Analysis of the longest (81 ksec)
pointing detects more than half of the known members in the field,
with spectral types ranging from F6 to K5. The star most like the Sun
in our sample, a G2V, has an X-ray luminosity (0.2-7 keV) of L_X ~
1.1e28 ergs/s, which suggests a scaling with age t of log L_X ~ -b
log t where 1.25 &lt; b &lt; 4, possibly steeper than seen at younger
ages. This research was supported by Chandra grant G02-13022X.

---------------------------------------------------------
Title: High-resolution Observations of the Shock Wave Behavior for
Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
2014ApJ...786..137T Altcode: 2014arXiv1404.6291T
We present the first results of sunspot oscillations from observations
by the Interface Region Imaging Spectrograph. The strongly nonlinear
oscillation is identified in both the slit-jaw images and the
spectra of several emission lines formed in the transition region and
chromosphere. We first apply a single Gaussian fit to the profiles of
the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
sunspot. The intensity change is ~30%. The Doppler shift oscillation
reveals a sawtooth pattern with an amplitude of ~10 km s-1
in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
~12 s, respectively. The line width suddenly increases as the Doppler
shift changes from redshift to blueshift. However, we demonstrate
that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at
a few selected locations on the slit. The temporal evolution of the
line core is dominated by the following behavior: a rapid excursion
to the blue side, accompanied by an intensity increase, followed by a
linear decrease of the velocity to the red side. The maximum intensity
slightly lags the maximum blueshift in Si IV, whereas the intensity
enhancement slightly precedes the maximum blueshift in Mg II. We find
a positive correlation between the maximum velocity and deceleration,
a result that is consistent with numerical simulations of upward
propagating magnetoacoustic shock waves.

---------------------------------------------------------
Title: Stellar Granulation as the Source of High-frequency Flicker
in Kepler Light Curves
Authors: Cranmer, Steven R.; Bastien, Fabienne A.; Stassun, Keivan G.;
Saar, Steven H.
2014ApJ...781..124C Altcode: 2013arXiv1312.5928C
A large fraction of cool, low-mass stars exhibit brightness fluctuations
that arise from a combination of convective granulation, acoustic
oscillations, magnetic activity, and stellar rotation. Much of the
short-timescale variability takes the form of stochastic noise, whose
presence may limit the progress of extrasolar planet detection and
characterization. In order to lay the groundwork for extracting useful
information from these quasi-random signals, we focus on the origin of
the granulation-driven component of the variability. We apply existing
theoretical scaling relations to predict the star-integrated variability
amplitudes for 508 stars with photometric light curves measured by the
Kepler mission. We also derive an empirical correction factor that
aims to account for the suppression of convection in F-dwarf stars
with magnetic activity and shallow convection zones. So that we can
make predictions of specific observational quantities, we performed
Monte Carlo simulations of granulation light curves using a Lorentzian
power spectrum. These simulations allowed us to reproduce the so-called
flicker floor (i.e., a lower bound in the relationship between the
full light-curve range and power in short-timescale fluctuations)
that was found in the Kepler data. The Monte Carlo model also
enabled us to convert the modeled fluctuation variance into a flicker
amplitude directly comparable with observations. When the magnetic
suppression factor described above is applied, the model reproduces
the observed correlation between stellar surface gravity and flicker
amplitude. Observationally validated models like these provide new and
complementary evidence for a possible impact of magnetic activity on
the properties of near-surface convection.

---------------------------------------------------------
Title: Preliminary results on the solar rotation determined tracing
SDO/AIA coronal bright points
Authors: Brajša, R.; Sudar, D.; Skokič, I.; Saar, S. H.
2014CEAB...38..105B Altcode:
In this paper we present preliminary results on the solar differential
rotation measured tracing coronal bright points in SDO/AIA images. An
automatic recognition method was applied to the series of images taken
in the test period, 1-2 January 2011. Coronal bright points are suitable
tracers for the determination of the solar differential rotation,
because they are localized objects which are very well distributed
over solar disc. Results presented in this paper show that the SDO/AIA
data are very useful for that aim, due to the high spatial and temporal
resolution of the images.

---------------------------------------------------------
Title: Strong-Flare Rates of Solar-Like Stars in Kepler Cluster
NGC 6811
Authors: Wright, Paul J.; Saar, S. H.; Meibom, S.; Kashyap, V.; Drake,
J. J.
2014AAS...22315108W Altcode:
Strong flares on the Sun are accompanied by intense ionizing radiation
(X-rays, far UV) and are often associated with coronal mass ejections
(CMEs), which can be hazardous to astronauts, and infrastructure
such as satellites and electrical systems. The rates of the largest
flare events are, however, poorly known. By taking advantage of the
exquisite precision of Kepler photometry, we derive white light flare
distributions for a sample of near-solar-mass (G1-G5) dwarfs in NGC 6811
(age ~ 1 Gyr). Using a solar-based relationship, we estimate the X-ray
emission from these flares in order to compare the results to other
solar and stellar X-ray flare data. We also take a first look at some
stars of different masses, to study the mass dependence of flaring at
fixed age, and explore the implications of our results for the rates
of the largest flaring events on the Sun. This work was supported by
Kepler grants NNX11AC82G and NNX13AC29G and NASA HGI grant NNX10AF29G.

---------------------------------------------------------
Title: The "Horns" of FK Comae and the Complex Structure of its
Outer Atmosphere
Authors: Saar, Steven H.; Ayres, T. R.; Kashyap, V.
2014AAS...22315116S Altcode:
As part of a large multiwavelength campaign (COCOA-PUFS*) to explore
magnetic activity in the unusual, single, rapidly rotating giant FK
Comae, we have taken a time series of moderate resolution FUV spectra
of the star with the COS spectrograph on HST. We find that the star
has unusual, time-variable emission profiles in the chromosphere and
transition region which show horn-like features. We use simple spatially
inhomogeneous models to explain the variable line shapes. Modeling
the lower chromospheric Cl I 1351 Å line, we find evidence for a very
extended, spatial inhomogeneous outer atmosphere, likely composed of
many huge "sling-shot" prominences of cooler material with embedded in
a rotationally distended corona. We compare these results with hotter
hotter transition region lines (Si IV) and optical spectra of the
chromospheric He I D3 line. We also employ the model Cl I profiles,
and data-derived empirical models, to fit the complex spectral region
around the coronal Fe XXI 1354.1 Å line. We place limits on the flux
of this line, and show these limits are consistent with expectations
from the observed X-ray spectrum. *Campaign for Observation of the
Corona and Outer Atmosphere of the Fast-rotating Star, FK Comae This
work was supported by HST grant GO-12376.01-A.

---------------------------------------------------------
Title: X-ray Binaries and Feedback in Lyman-α Galaxies
Authors: Prestwich, Andrea H.; Jackson, F.; Kaaret, P.; Brorby, M.;
Roberts, T. P.; Saar, S. H.
2014AAS...22342807P Altcode:
We describe evidence for a compact, extremely luminous (LX
≈ 1041 ergs s-1) X-ray source in the Lyman
Break Analog (LBA) galaxy Haro 11. The X-ray spectrum is hard with a
power-law photon index γ≈1.2. This source is most likely dominated
by an extreme ULX with LX ≧ 5 × 1040 ergs
s-1, possibly with a contribution of other X-ray binaries
and Inverse Compton emission. If this source is a Black Hole Binary
(BHB) in the low state, as suggested by the hard X-ray spectrum, the
compact object is almost certainly an Intermediate Mass Black Hole
(IMBH). Discovery of an IMBH in a low metallicity star bursting dwarf
would be significant because (1) such objects may be accreted into
larger galaxies to form HLX such as ESO 243-49 HLX-1 and (2) Haro 11
X-1 may be a “seed” black hole which is currently growing rapidly to
form a supermassive black hole. This source is also coincident with the
center of the Lyman-α emission. Outflow from the ULX may occur very
early in the life of the starburst and inject enough mechanical power
into the Interstellar Medium (ISM) to accelerate it and thus reduce
resonant scattering. ULX may be critical to allow Lyman-α photons
to escape. Haro 11 and other LBAs are important for understanding the
role X-ray binaries play in the evolution of young galaxies.

---------------------------------------------------------
Title: Extreme Ultraviolet and X-Ray Observations of Comet Lovejoy
(C/2011 W3) in the Lower Corona
Authors: McCauley, P.; Saar, S.; Raymond, J. C.; Ko, Y.; Saint-Hilaire,
P.
2013AGUFM.P31A1784M Altcode:
On December 16, 2011, Comet Lovejoy (C/2011 W3) came to within
140,000 km of the solar photosphere and survived its perihelion
passage to the surprise of many. We present observations recorded
by two solar observatories, the X-Ray Telescope (XRT) aboard Hinode
and the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics
Observatory. We explore a time series of post-perihelion observations in
eight wavelength bands between 22 and 1600 Å. As material sublimates
from the nucleus and is immersed in coronal plasma, it rapidly ionizes
through charge states that are seldom seen in this environment. O III
through O VII, along with C IV, are observed, and we derive outgassing
rates from these data where applicable. We estimate peak rates of
10^32.5 oxygen atoms per second and a total mass loss of ~10^13 g during
the egress, assuming that all neutral oxygen comes from sublimated water
molecules. From this, we expect that the nucleus was on the order of 600
m in diameter on approach to perihelion. Our data show distinct spikes
in the observed intensity, which we attribute to outbursts triggered by
explosions of interior water ice. AIA is also poised to observe Comet
ISON (C/2012 S1) as it makes its perihelion passage on November 28,
2013. ISON will pass much further from the Sun, but is thought to be
considerably larger, than Lovejoy, so it is uncertain whether or not a
signature will be detected by AIA. We will present these observations,
along with some very preliminary analysis, if they are successful.

---------------------------------------------------------
Title: Fixing the Leak: Empirical Corrections for the Small Light
Leak in Hinode XRT
Authors: Saar, Steven H.; DeLuca, E. E.; McCauley, P.; Kobelski, A.
2013SPD....44...93S Altcode:
On May 9, 2012, the the straylight level of XRT on Hinode suddenly
increased, consistent with the appearance of a pinhole in the entrance
filter (possibly a micrometeorite breach). The effect of this event
is most noticeable in the optical G band data, which shows an average
light excess of ~30%. However, data in several of the X-ray filters is
also affected, due to low sensitivity "tails" of their filter responses
into the visible. Observations taken with the G band filter but with
the visible light shutter (VLS) closed show a weak, slightly shifted,
out-of-focus image, revealing the leaked light. The intensity of
the leak depends on telescope pointing, dropping strongly for images
taken off-disk. By monitoring light levels in the corners of full-Sun
Ti-poly filter images, we determine the approximate time of the event:
~13:30 UT. We use pairs of images taken just-before and after the filter
breach to directly measure the leakage in two affected X-ray filters. We
then develop a model using a scaled, shifted, and smoothed versions
of the VLS closed images to remove the contamination. We estimate
the uncertainties involved in our proposed correction procedure. This
research was supported under NASA contract NNM07AB07C for Hinode XRT.

---------------------------------------------------------
Title: Exploring Low-State Accretion in Polars with a Solar Flux
Rope Model
Authors: Saar, Steven H.; Reeves, K.
2013SPD....44...78S Altcode:
Polars are cataclysmic variables, close binaries consisting
of a strongly magnetic white dwarf (WD) and a cool solar-like
secondary star. They tend to have high and low photometric states,
corresponding to times of high accretion (due to Roche lobe overflow
from the secondary) and low accretion (where the accretion source
is under debate). Since tidal spin-up forces the secondary to
rotate at the orbital period, typically &lt; 1 day, it should be
very magnetically active. We use a solar flux rope/CME model with
field strength Bsec, placed in a strong external field
(BWD), to explore the stability of magnetic loops on the
secondary in the presence of the megagauss WD field. We find that
for low ratios BWD/Bsec, loops confining a
prominence separated by more than a certain distance are stable,
but as the ratio is increased, a second regime of instability for
widely separated loops appears. The two instability regimes grow
with BWD/Bsec, until above a certain value,
no loops are stable. We find that for reasonable masses of loop
confined material, the BWD induced instability may be able
to explain much of the accretion seen in polar low states, as well as
several other observed properties. Implications for polar evolution
are discussed. This research was supported by several NSF grants.

---------------------------------------------------------
Title: Extreme-ultraviolet and X-Ray Observations of Comet Lovejoy
(C/2011 W3) in the Lower Corona
Authors: McCauley, Patrick I.; Saar, Steven H.; Raymond, John C.;
Ko, Yuan-Kuen; Saint-Hilaire, Pascal
2013ApJ...768..161M Altcode: 2013arXiv1304.1544M
We present an analysis of extreme-ultraviolet and soft X-ray emission
detected toward Comet Lovejoy (C/2011 W3) during its post-perihelion
traverse of the solar corona on 2011 December 16. Observations were
recorded by the Atmospheric Imaging Assembly (AIA) aboard the Solar
Dynamics Observatory and the X-Ray Telescope (XRT) aboard Hinode. A
single set of contemporaneous images is explored in detail, along
with prefatory consideration for time evolution using only the 171 Å
data. For each of the eight passbands, we characterize the emission
and derive outgassing rates where applicable. As material sublimates
from the nucleus and is immersed in coronal plasma, it rapidly ionizes
through charge states seldom seen in this environment. The AIA data
show four stages of oxygen ionization (O III-O VI) along with C IV,
while XRT likely captured emission from O VII, a line typical of the
corona. With a nucleus of at least several hundred meters upon approach
to a perihelion that brought the comet to within 0.2 R ⊙
of the photosphere, Lovejoy was the most significant sungrazer in
recent history. Correspondingly high outgassing rates on the order of
1032.5 oxygen atoms per second are estimated. Assuming that
the neutral oxygen comes from water, this translates to a mass-loss
rate of ~9.5 × 109 g s-1, and based only on the
171 Å observations, we find a total mass loss of ~1013
g over the AIA egress. Additional and supporting analyses include a
differential emission measure to characterize the coronal environment,
consideration for the opening angle, and a comparison of the emission's
leading edge with the expected position of the nucleus.

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Title: MMT Hectochelle Spectral Variability of Active Late-type
Stars in the Kepler Field (2013A)
Authors: Brown, Alexander; Walkowicz, Lucianne; Saar, Steven; Hawley,
Suzanne; Kowalski, Adam; Furesz, Gabor; Piskunov, Nikolai
2013noao.prop..286B Altcode:
We have on-going it Kepler photometric monitoring of over 300 active
late-type (mid-A - K) stars as part of our Cycles 1/2/3/4 Guest
Observer (GO) programs with the aim of studying starspot evolution,
differential rotation, activity cycles, and flares. We propose to
use the MMT Hectochelle multiobject spectrograph to observe over
140 of these stars to determine a range of basic physical properties
for the stars, such as radial velocity variations due to binarity,
chromospheric activity levels from Ca II H+K and H(alpha), projected
rotational velocities for comparison to the rotational periods
measured directly by it Kepler, age/youth as indicated by Li I, and
better effective temperature and luminosity estimates. In addition,
to provide a superior sample for statistical studies another 800 GKM
dwarf stars showing either starspot modulation from the it Kepler
Team's data or from our deep XMM X-ray survey will be observed using
the unassigned fibers in each field. These measurements require the
32,000 spectral resolution provided by Hectochelle, which is hard to
obtain efficiently for 13-15th magnitude stars any other way.

---------------------------------------------------------
Title: Deep Imaging of M37, A Better Hyades
Authors: Bowsher, Emily C.; Agueros, M. A.; Covey, K. R.; Hartman,
J. D.; Lopez-Morales, M.; Pooley, D. A.; Saar, S.; West, A. A.
2013AAS...22125207B Altcode:
X-ray emission traces the strength of a star's magnetic dynamo and
is tightly linked to age and stellar rotation. Early studies found
that X-ray luminosity decreases steadily as stars age. However, recent
studies suggest that the picture of X-ray luminosity decaying from 10
Myr to 5 Gyr as a single power-law, and independently of mass, is too
simplistic. Open clusters, with their homogeneous, coeval populations,
provide an ideal environment for calibrating empirically how stellar
activity depends on age and rotation. M37, a Hyades analog, has been
carefully surveyed in the optical, and we have obtained complementary
deep (450 ksec) Chandra ACIS-I imaging of this open cluster. M37's rich
membership, good match to Chandra's field-of-view, and large number
of measured periods 700) make it ideal for examining the evolution
of coronal X-ray emission. Here we report the first results from
our analysis of the combined X-ray and optical data. These data will
enable determinations of X-ray luminosity as a function of rotation
period, tests of whether magnetic effects produce anomalous optical
colors/luminosities for high X-ray luminosity sources, and theta
characterization of M37's interacting binaries.

---------------------------------------------------------
Title: A Large Sample of Magnetically-Active Stars Observed With
Kepler
Authors: Wells, Mark; Neff, J. E.; Brown, A.; Ayres, T. R.; Basri,
G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.;
Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W.; Saar, S. H.;
Walkowicz, L. M.
2013AAS...22135415W Altcode:
We have observed about 325 stars in our Kepler Guest Observer
programs (Cycles 1 through 4). For most of these targets, we are
analyzing extremely high-precision light curves that have been
continuously sampled every 30 minutes for up to 3 years. Our sample
of candidate magnetically-active stars was selected primarily using
GALEX colors. Starspots, pulsations, and variations due to eclipsing
and contact binaries combine to produce a rich variety of light
curves. We have developed semi-automated procedures to characterize
this variability and thus to classify the targets and identify the
physical mechanisms that dominate their Kepler light curves. We will
describe these procedures and discuss the range of physical properties
covered by our final classification scheme. We are using this Kepler
database of variability over timescales of minutes to years to provide
diagnostics of flares, starspot formation, evolution, migration, and
ultimately of stellar cycles in general. This work contains results
obtained using the NASA Kepler satellite and from the Apache Point
Observatory, the MMT (using NOAO community access time), and the
Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants
NNX10AC51G, NNX11AC79G, and NNX12AC85G to the University of Colorado,
by NSF grant AST-1109695 to the College of Charleston, and by a grant
from the South Carolina Space Grant consortium.

---------------------------------------------------------
Title: A Preliminary Study of Active Region Canopies With AIA
Authors: Lucchini, Scott; Saar, S.; Muglach, K.
2013AAS...22115905L Altcode:
Active region canopies are areas frequently accompanying active regions
which have extensive horizontal magnetic fields. The large-scale
canopy fields have a significant effect on the kinds of structures
which can exist beneath them, and how they evolve. Using data
from the Atmospheric Imaging Assembly (AIA), we developed methods
to automatically identify these regions. A Differential Emission
Measure (DEM) analysis is consistent with the idea that the long,
hotter active region loops overlie quite cool, small-scale features
("fibrils"). We suggest that the overlying loops restrict the growth
of underlying structures to mostly very short, cool features. We also
studied evolution of canopy regions over time. In several cases, a
large quiescent filament formed out of the former canopy region over the
course of a few solar rotations, confirming previous suggestions. The
canopy remains visible for several rotations after its active regions
have begun to decay; in this time, the fibril magnetic fields gradually
align in such a way as to form a filament channel. Further analysis
of our large canopy database should uncover more information on the
frequency and characteristics of these canopy-to-filament evolutions,
as well as other canopy properties. This work is supported by the NSF
REU program at SAO (grant ATM-0851866) and contract SP02H1701R from
Lockheed Martin to SAO for SDO research.

---------------------------------------------------------
Title: Fearsome Flashes: A Study Of The Evolution Of Flaring Rates
In Cool Stars Using Kepler Cluster Data
Authors: Saar, Steven
2013adap.prop..242S Altcode:
Strong solar flares can damage power grids, satellites, interrupt
communications and GPS information, and threaten astronauts and high
latitude air travelers. Despite the potential cost, their frequency
is poorly determined. Beyond purely current terrestrial concerns,
how the rate of large flares (and associated coronal mass ejections
[CMEs], high-energy particle fluxes and far UV emission) varies over
the stellar lifetime holds considerable astrophysical interest. These
include: the contributions of flares to coronal energy budgets; the
importance of flares and CMEs to terrestrial and exoplanet atmospheric
and biological evolution; and importance of CME mass loss for angular
momentum evolution. We will explore the rate of strong flares and
its variation with stellar age, mass and rotation by studying Kepler
data of cool stars in two open clusters NGC 6811 (age ~ 1 Gyr) and
NGC 6819 (~2.5 Gyr). We will use two flare analysis methods to build
white-light flare distributions for cluster stars. One subtracts a
low-pass filtered version of the data and analyzes the residue for
positive flux deviations, the other does a statistical analysis of
the flux deviations vs. time lags compared with a model. For near-
solar stars, a known solar relation can then be used to estimate X-ray
production by the white-light flares. For stars much hotter or cooler
or with significantly different chromospheric density, we will use
particle code flare models including bombardment effects to estimate
how the X-ray to white light scaling changes. With the X-ray values,
we can estimate far UV fluxes and CME rates, building a picture of the
flare effects; with the two cluster ages, we can make a first estimate
of the solar rate (by projecting to the Sun's age) and begin to build
up an understanding of flare rate evolution with mass and age. Our
proposal falls squarely in the "Stellar Astrophysics and Exoplanets"
research area, and is relevant to NASA astrophysics goals in promoting
better understanding the evolution of stars and their exoplanets,
and better understanding the environment in which life evolved, and
threats to it, both on Earth and in the wider cosmos.

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Title: Young Star Populations in the Kepler Field
Authors: Brown, Alexander; Neff, J. E.; Wells, M.; Saar, S.; Furesz,
G.; Walkowicz, L. M.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.;
Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.;
Piskunov, N. E.; Ramsey, L. W.
2013AAS...22135414B Altcode:
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that routinely
allow detailed studies of stellar magnetic activity on late-type stars
that were difficult previously. Kepler provides multi-year duration
light-curves that allow investigation of how activity phenomena --
such as the growth, migration, and decay of star-spots, differential
rotation, activity cycles, and flaring -- operate on a wide variety of
single and binary stars. The 105 square degree Kepler Field contains
tens of thousands of late-type stars showing rotational modulation due
to star-spots with periods ranging from one day to a “solar-like”
month. Short rotation periods and high levels of magnetic activity are
strongly correlated. However, there are only two basic reasons why stars
with rotation periods of a few days possess such high angular momentum
--- either they are close binaries or they are young stars. During
Kepler GO Cycles 1 through 4 we have been studying the Long-cadence
(30 minute sampling) photometry of hundreds of active late-type stars
and as an absolutely essential complement we have been obtaining high
resolution optical spectra to understand the physical properties of
these stars. We present results from a spectroscopic survey using the
MMT Hectochelle multi-object echelle of 4 square degrees of the Kepler
Field. We have discovered a significant population of young stars with
Li I absorption indicating ages of ~100 Myr or less at a spatial density
of at least 20 stars per square degree. Our detected young star sample
comprises at least 80 stars and represents a dramatic advance compared
to the previously known sample over the full Kepler Field of three
stars in this age range. Roughly one sixth of the stars observed are
young and a similar number short-period binaries based on 2-4 radial
velocities. We show how the rotational properties of the stars and their
physical properties are related. This work is based on data obtained
with the NASA Kepler satellite and the MMT Hectochelle spectrograph
using NOAO community access time. Support by NASA Kepler grants to the
University of Colorado and by NSF grant to the College of Charleston.

---------------------------------------------------------
Title: Differential Emission Measure Analysis of Multiple Structural
Components of Coronal Mass Ejections in the Inner Corona
Authors: Cheng, X.; Zhang, J.; Saar, S. H.; Ding, M. D.
2012ApJ...761...62C Altcode: 2012arXiv1210.7287C
In this paper, we study the temperature and density properties of
multiple structural components of coronal mass ejections (CMEs)
using differential emission measure (DEM) analysis. The DEM analysis
is based on the six-passband EUV observations of solar corona from the
Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The
structural components studied include the hot channel in the core region
(presumably the magnetic flux rope of the CME), the bright loop-like
leading front (LF), and coronal dimming in the wake of the CME. We find
that the presumed flux rope has the highest average temperature (&gt;8
MK) and density (~1.0 × 109 cm-3), resulting in
an enhanced emission measure over a broad temperature range (3 &lt;=
T(MK) &lt;= 20). On the other hand, the CME LF has a relatively cool
temperature (~2 MK) and a narrow temperature distribution similar to the
pre-eruption coronal temperature (1 &lt;= T(MK) &lt;= 3). The density
in the LF, however, is increased by 2%-32% compared with that of the
pre-eruption corona, depending on the event and location. In coronal
dimmings, the temperature is more broadly distributed (1 &lt;= T(MK)
&lt;= 4), but the density decreases by ~35%-~40%. These observational
results show that: (1) CME core regions are significantly heated,
presumably through magnetic reconnection; (2) CME LFs are a consequence
of compression of ambient plasma caused by the expansion of the CME
core region; and (3) the dimmings are largely caused by the plasma
rarefaction associated with the eruption.

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Title: The thermal and spatial structure of the solar corona over
the cycle and its implication for the coronae of inactive stars
Authors: Testa, P.; Landi, E.; Saar, S.
2012AGUFMSH42A..05T Altcode:
We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT
and SDO/AIA) solar coronal data to systematically measure the thermal
structure of different types of solar features (coronal hole, quiet
Sun, X-ray bright points, active regions...), and how they vary over
the solar cycle. We use a combination of these structures to construct
a model for the quiet corona of the inactive G8V star tau Ceti, which
is a candidate stellar analog of a solar magnetic minimum. Since tau
Ceti is significantly metal-poor relative to the Sun, we reconstruct
the solar results with corresponding lower metallicities to generate
more appropriate coronal structures.

---------------------------------------------------------
Title: Evolution of Coronal Bright Points and Photospheric Magnetic
Fields
Authors: Lamb, D. A.; Saar, S.; DeForest, C.
2012AGUFMSH33A2227L Altcode:
Coronal bright points are excellent probes of the connection between
the photosphere and corona, and occur in sufficiently larger numbers
all over the Sun to make statistical or ensemble studies necessary
and useful. We present initial results on the evolution of coronal
bright points and the state of the associated photospheric magnetic
field. Using an automated bright point detection algorithm that
has found thousands of bright points in multiple SDO/AIA passbands,
combined with an automated magnetic feature tracking algorithm on
SDO/HMI magnetograms, we explore the magnetic conditions necessary
for bright point formation and destruction.

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Title: Secretive Solar Waves Stimulate X-ray Bright Points
Authors: Saar, S. H.; Attrill, G. D.
2012ASPC..454..395S Altcode:
We discuss Hinode XRT observations of temporally-related emission
enhancements in solar X-ray bright points (XBPs) consistent with
excitation by an otherwise unseen wave. In one case, the wave source is
unclear (out of the field of view), in the other which we report here,
the wave seems to be excited by a flaring/erupting XBP. In this latter
case, the wave velocity averaged ∼340 km s-1 in areas
of quiet Sun emission, but was reduced by ∼1/3 in areas of higher
emission and magnetic flux density. Larger loops were mostly unaffected
by the wave's passage, while XBPs could still be excited at distances
of 105 km and more from the apparent origin. Small coronal
dimming regions (displaying characteristic evolution properties in EUV
intensity) are seen next to the flaring XBP, suggesting a small CME
may have been associated with the event. We speculate on the origin
and properties of these mysterious waves, which may prove useful tools
for studying the media through which they travel. These events are
inconspicuous, showing low intensity enhancements of only selected
small regions, and require high cadence, high spatial resolution data
to be detected. Since they are easily overlooked and/or confused
with stochastic variability, these waves may be a fairly common,
but under-recognized component of the flare/CME phenomenon at small
energies and spatial scales. SDO's AIA should be very useful in further
study of these waves.

---------------------------------------------------------
Title: Cooler and Hotter X-ray Bright Points from Hinode/XRT
Observations
Authors: Kariyappa, R.; DeLuca, E. E.; Saar, S. H.; Golub, L.; Damé,
L.; Varghese, B. A.
2012ASPC..454..149K Altcode:
We use a 7-hour (17:00 UT - 24:00 UT) time sequence of soft X-ray images
observed almost simultaneously in two filters (Ti_poly and Al_mesh) on
April 14, 2007 with X-Ray Telescope (XRT) on-board the Hinode mission
to determine the temperature of X-ray bright points (XBPs). A sample
of 14 XBPs and 2 background coronal regions have been identified and
selected on both the images for detailed analysis. The temperature of
XBPs is determined by filter ratio method. We find that the XBPs show
temperature fluctuations and that the average temperature ranges from
1.1 MK to 3.4 MK which may correspond to different X-ray fluxes. These
results suggest the existence of cooler and hotter XBPs and that the
heating rate of XBPs is highly variable on short time scales.

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Title: Spatial and Thermal Study of an Isolated Loop with XRT and EIS
Authors: Saar, S. H.; Schmelz, J. T.; Kashyap, V. L.
2012ASPC..454..241S Altcode:
We use multi-filter contemporaneous XRT and EIS observations of a
small active region to study the spatial and thermal properties of an
isolated quiescent loop. We study the loop as a whole, in segments,
in transverse cuts, and point-by-point, always with some form of
"background" subtraction. We find the loop DEM is not-isothermal, but
is also not extremely broad, with ≍96% of the EM between 6.2 ≤ log
T ≤ 6.7, and an EM-weighted average temperature of log T = 6.48 ±
0.16. There is some evidence for a gradual change in temperature along
the loop, with log T increasing by ≍0.1 from the foot points to the
peak. Including EIS data helps better constrain the EM at low T. Future
work includes combining the analysis with contemporaneous RHESSI data
and to explore XRT-EIS-RHESSI cross-calibration at AR temperatures.

---------------------------------------------------------
Title: Stars in magnetic grand minima: where are they and what are
they like?
Authors: Saar, Steven H.; Testa, Paola
2012IAUS..286..335S Altcode:
We explore various ideas of what a star in a Maunder-like magnetic
minimum would look like, and ways of finding stars in such a state,
and make some estimates of their physical and magnetic activity
properties. We discuss new X-ray observations of a small selection of
candidates for being in magnetic grand minima. These are then compared
with the Sun and other low activity stars.

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Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
W.; Weissman, P.; Comet Lovejoy Collaboration Team
2012AAS...22052507B Altcode:
Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
by space-based instruments, to survive perihelion passage. First
observed by ground-based telescopes several weeks prior to perihelion,
its journey towards the Sun was subsequently recorded by several solar
observatories, before being observed in the weeks after perihelion by
a further array of space- and ground-based instruments. Such a surfeit
of wide-ranging observations provides an unprecedented insight into
both sungrazing comets themselves, and the solar atmosphere through
which they pass. This paper will summarize what we have learnt from the
observations thus far and offer some thoughts on what future sungrazing
comets may reveal about comets, the Sun, and their interaction.

---------------------------------------------------------
Title: Rotational Modulation, Shear, And Cyclic Activity In HII 2927
Authors: Milingo, Jackie; Saar, S. H.; Lehman, S. L.; Marschall,
L. A.; Stauffer, J. R.
2012AAS...22032806M Altcode:
We present a 15 yr compilation of V-band differential photometry for the
Pleiades K4 dwarf HII 2927 (V378 Tau). HII 2927 has a rotational period
(P_rot) of 0.26 d and displays significant rotational modulation due to
non-uniform surface brightness or "starspots". With the long timeline of
data available we can explore many aspects of the star's photometric
variability, with the goal of including them in a larger study of
magnetic activity in single cool dwarfs. Preliminary work yields a cycle
period (P_cyc) of 14.5 +/- 1.9 yrs. We also present preliminary work on
the rotational shear for this star (ΔP_rot/&lt;P_rot&gt;). Measurements
of P_cyc and rotational shear contribute to our understanding of the
magnetic dynamo at the source of stellar activity. We compare our
P_cyc and ΔP_rot/&lt;P_rot&gt; estimates with those of other stars,
including our measurements of fellow Pleaid HII 1883 (V660 Tau).

---------------------------------------------------------
Title: Photometric Uncertainties within Hinode XRT
Authors: Kobelski, Adam; Saar, S. H.; Weber, M. A.; McKenzie, D. E.;
Reeves, K. K.
2012AAS...22020126K Altcode:
We have developed estimates of the systematic uncertainties for
the X-Ray Telescope (XRT) on Hinode. These estimates are included
as optional returns from the standard XRT data reduction software,
xrt_prep.pro. Included in these software estimates are uncertainties
from instrument vignetting, dark current subtraction, split bias
leveling, Fourier filtering and JPEG compression. Sources of uncertainty
that rely heavily on models of plasma radiation or assumptions of
elemental abundances, such as photon noise, are discussed, but not
included in the software. It will be shown that the photon noise
is much larger than the systematic uncertainty. This work is
supported by NASA under contract NNM07AB07C with the Harvard-Smithsonian
Astrophysical Observatory

---------------------------------------------------------
Title: An Exploration of the Emission Properties of X-ray Bright
Points Seen With SDO
Authors: Saar, Steven H.; Elsden, T.; Muglach, K.
2012AAS...22020713S Altcode:
We present preliminary results of a study of X-ray Bright Point (XBP)
EUV emission and its dependence on other properties. The XBPs were
located using a new, automated XBP finder for AIA developed as
part of the Feature Finding Team for SDO Computer Vision. We analyze
XBPs near disk center, comparing AIA EUV fluxes, HMI LOS magnetic
fields, and photospheric flow fields (derived from HMI data) to look
for relationships between XBP emission, magnetic flux, velocity fields,
and XBP local environment. We find some evidence for differences in the
mean XBP temperature with environment. Unsigned magnetic flux is
correlated with XBP emission, though other parameters play a role. The
majority of XBP footpoints are approaching each other, though at
a slight angle from head-on on average. We discuss the results in the
context of XBP heating.

---------------------------------------------------------
Title: Combined XRT and AIA Differential Emission Measure Analysis
of Active Region Loops and Weak Flares
Authors: Saar, S. H.; Schmelz, J. T.
2012ASPC..455..353S Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) provides excellent new tools for exploring the thermal properties
of active regions at high cadence. The thick filters of the Hinode X-ray
Telescope (XRT), however, can add important additional constraints on
high temperature plasma, particularly in flares. We demonstrate the
power of combined AIA and XRT studies by conducting a joint AIA+XRT
differential emission measure analysis of an active region loop and
a weak flare.

---------------------------------------------------------
Title: Differential Emission Measure Analysis for AIA and XRT
Observations of Comet Lovejoy (C/2011 W3)
Authors: McCauley, Patrick; Saar, S. H.; Raymond, J.; Golub, L. E.
2012AAS...22020115M Altcode:
We present observations of Comet Lovejoy (C/2011 W3) recorded by
the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics
Observatory (SDO) and the X-Ray Telescope (XRT) aboard the Hinode
satellite. Lovejoy, a member of the Kreutz family of sungrazing comets,
came to within 1.2 solar radii during its perihelion approach and
escaped, despite expectations to the contrary, on December 6, 2011. The
most significant sungrazer since the launch of SDO, Lovejoy provides an
unprecedented opportunity to examine the effects of a comet traversing
the solar corona. Both the ingress and egress were detected in seven
AIA passbands (131, 171, 193, 211, 304, 335, and 1600 Angstroms),
with XRT successfully imaging the outbound trip using its Al-mesh
filter. We estimate the temperature structure of the emitting plasma
using a differential emission measure analysis and explore interactions
with the solar magnetic field. In several cases, secondary lines in a
given channel appear to be the dominant comet-related emitters. Use of
a radial filter for improved contrast of the faint cometary emission
is also discussed.

---------------------------------------------------------
Title: Measuring Uncertainties in the Hinode X-Ray Telescope
Authors: Kobelski, A.; Saar, S.; McKenzie, D. E.; Weber, M.; Reeves,
K.; DeLuca, E.
2012ASPC..456..241K Altcode:
We have developed estimates of the systematic photometric uncertainties
the X-Ray Telescope (Kano et al. (2008)) on Hinode (Kosugi et
al.(2007)). These estimates are included as optional returns from the
standard XRT data reduction software, xrt_prep.pro. Included in the
software estimates are uncertainties from instrument vignetting, dark
current subtraction, split bias leveling, fourier filtering and JPEG
compression. We show that these uncertainties are generally smaller
than the photon counting uncertainty. However, due to the reliance
on assumptions of plasma radiation models and elemental abundances,
photon counting is not included in the software.

---------------------------------------------------------
Title: Long-term magnetic field monitoring of the Sun-like star ξ
Bootis A
Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin,
J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine,
T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.;
Théado, S.; Van Grootel, V.
2012A&A...540A.138M Altcode: 2011arXiv1109.5066M
 Aims: We aim to investigate the long-term temporal evolution
of the magnetic field of the solar-type star ξ Bootis A, both from
direct magnetic field measurements and from the simultaneous estimate
of indirect activity indicators. Methods: We obtained seven
epochs of high-resolution, circularly-polarized spectra from the
NARVAL spectropolarimeter between 2007 and 2011, for a total of 76
spectra. Using approximately 6100 photospheric spectral lines covering
the visible domain, we employed a cross-correlation procedure to compute
a mean polarized line profile from each spectrum. The large-scale
photospheric magnetic field of the star was then modelled by means
of Zeeman-Doppler Imaging, allowing us to follow the year-to-year
evolution of the reconstructed magnetic topology. Simultaneously, we
monitored the width of several magnetically sensitive spectral lines,
the radial velocity, the line asymmetry of intensity line profiles,
and the chromospheric emission in the cores of the Ca II H and Hα
lines. Results: During the highest observed activity states,
in 2007 and 2011, the large-scale field of ξ Bootis A is almost
completely axisymmetric and is dominated by its toroidal component. The
toroidal component persists with a constant polarity, containing
a significant fraction of the magnetic energy of the large-scale
surface field through all observing epochs. The magnetic topologies
reconstructed for these activity maxima are very similar, suggesting
a form of short cyclicity in the large-scale field distribution. The
mean unsigned large-scale magnetic flux derived from the magnetic
maps varies by a factor of about 2 between the lowest and highest
observed magnetic states. The chromospheric flux is less affected and
varies by a factor of 1.2. Correlated temporal evolution, due to both
rotational modulation and seasonal variability, is observed between
the Ca II emission, the Hα emission and the width of magnetically
sensitive lines. The rotational dependence of polarimetric magnetic
measurements displays a weak correlation with other activity proxies,
presumably due to the different spatial scales and centre-to-limb
darkening associated with polarimetric signatures, as compared to
non-polarized activity indicators. Better agreement is observed on the
longer term. When measurable, the differential rotation reveals a strong
latitudinal shear in excess of 0.2 rad d-1. Based on
observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi,
France) of the Midi-Pyrénées Observatory, which is operated by the
Institut National des Sciences de l'Univers of the Centre National de la
Recherche Scientifique of France.Tables 3-6 are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: MMT Hectochelle Spectral Variability of Active Late-type
Stars in the Kepler Field (2012A)
Authors: Brown, Alexander; Walkowicz, Lucianne; Hawley, Suzanne;
Kowalski, Adam; Saar, Steven; Furesz, Gabor
2012noao.prop..332B Altcode:
We have on-going Kepler photometric monitoring of over 200 active
late-type (mid-A - K) stars as part of our Cycles 1/2/3 Guest Observer
(GO) programs with the aim of studying starspot evolution, differential
rotation, activity cycles, and flares. We propose to use the MMT
Hectochelle multiobject spectrograph to observe over 120 of these stars
to determine a range of basic physical properties for the stars, such
as radial velocity variations due to binarity, chromospheric activity
levels from Ca II H+K and H(alpha), projected rotational velocities
for comparison to the rotational periods measured directly by Kepler,
age/youth as indicated by Li I, and better effective temperature and
luminosity estimates. In addition, to provide a superior sample for
statistical studies another ~1,000 GKM dwarf stars showing either
starspot modulation from the Kepler Team's data or from our on-going
deep XMM X-ray survey will be observed using the unassigned fibers in
each field. These measurements require the 32,000 spectral resolution
provided by Hectochelle, which is hard to obtain efficiently for
13-15th magnitude stars any other way.

---------------------------------------------------------
Title: Computer Vision for the Solar Dynamics Observatory (SDO)
Authors: Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell,
A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.;
Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.;
Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.;
DeForest, C. E.; Angryk, R. A.; De Moortel, I.; Wiegelmann, T.;
Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P.
2012SoPh..275...79M Altcode: 2011SoPh..tmp..144M; 2011SoPh..tmp..213M; 2011SoPh..tmp....8M
In Fall 2008 NASA selected a large international consortium to produce
a comprehensive automated feature-recognition system for the Solar
Dynamics Observatory (SDO). The SDO data that we consider are all of the
Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field
images from the Helioseismic and Magnetic Imager (HMI). We produce
robust, very efficient, professionally coded software modules that
can keep up with the SDO data stream and detect, trace, and analyze
numerous phenomena, including flares, sigmoids, filaments, coronal
dimmings, polarity inversion lines, sunspots, X-ray bright points,
active regions, coronal holes, EIT waves, coronal mass ejections
(CMEs), coronal oscillations, and jets. We also track the emergence and
evolution of magnetic elements down to the smallest detectable features
and will provide at least four full-disk, nonlinear, force-free magnetic
field extrapolations per day. The detection of CMEs and filaments is
accomplished with Solar and Heliospheric Observatory (SOHO)/Large
Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα
data, respectively. A completely new software element is a trainable
feature-detection module based on a generalized image-classification
algorithm. Such a trainable module can be used to find features that
have not yet been discovered (as, for example, sigmoids were in the
pre-Yohkoh era). Our codes will produce entries in the Heliophysics
Events Knowledgebase (HEK) as well as produce complete catalogs for
results that are too numerous for inclusion in the HEK, such as the
X-ray bright-point metadata. This will permit users to locate data on
individual events as well as carry out statistical studies on large
numbers of events, using the interface provided by the Virtual Solar
Observatory. The operations concept for our computer vision system is
that the data will be analyzed in near real time as soon as they arrive
at the SDO Joint Science Operations Center and have undergone basic
processing. This will allow the system to produce timely space-weather
alerts and to guide the selection and production of quicklook images and
movies, in addition to its prime mission of enabling solar science. We
briefly describe the complex and unique data-processing pipeline,
consisting of the hardware and control software required to handle
the SDO data stream and accommodate the computer-vision modules, which
has been set up at the Lockheed-Martin Space Astrophysics Laboratory
(LMSAL), with an identical copy at the Smithsonian Astrophysical
Observatory (SAO).

---------------------------------------------------------
Title: Properties of Candidate Magnetic Grand Minimum Stars
Authors: Saar, S. H.
2011ASPC..448.1239S Altcode: 2011csss...16.1239S
Using a large database of Ca II HK measurements from exoplanet search
candidates, I explore properties of stars with the lowest activity
levels. The minimum R'HK level (using the traditional
calibration) seen in bona-fide dwarfs (as determined spectroscopically)
is a strong function of metallicity: log RHK(min) ≍ -5.1
- 0.2 log M/H. Dwarf stars with a small Δ R'HK above this
boundary uniformly show fractional rms Ca II HK index SHK
variation of σS /&lt;SHK&gt; ≤ 2%. I propose
stars which show this low-variability, low RHK behavior on
timescales of several years (longer than a typical solar minimum) are
candidates for being in magnetic grand minima (MM). These candidate MM
stars span a wide range in M/H and Teff, but show a sharp
cutoff at higher masses. Their v sin i distribution is consistent with
their being drawn from a mostly older (≥ 2 Gyr) stellar population.

---------------------------------------------------------
Title: Long-term Magnetic Field Monitoring of the Sun-like Star ζ
Bootis A
Authors: Morgenthaler, A.; Petit, P.; Aurière, M.; Dintrans, B.;
Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Morin, J.; Ramirez,
J.; Saar, S.; Solanki, S. K.; Théado, S.; Van Grootel V., V.
2011ASPC..448.1203M Altcode: 2011csss...16.1203M
Phase-resolved observations of the solar-type star ζ Bootis A were
obtained using the NARVAL spectropolarimeter at the Telescope Bernard
Lyot (Pic du Midi, France) during years 2007, 2008, 2009 and 2010. The
data sets enable us to study both the rotational modulation and the
long-term evolution of various magnetic and activity tracers. Here,
we focus on the large-scale photospheric magnetic field (reconstructed
by Zeeman-Doppler Imaging), the Zeeman broadening of the FeI 846.84
nm magnetic line, and the chromospheric CaII H and Hα emission.

---------------------------------------------------------
Title: Testing a Predictive Theoretical Model for the Mass Loss
Rates of Cool Stars
Authors: Cranmer, Steven R.; Saar, Steven H.
2011ApJ...741...54C Altcode: 2011arXiv1108.4369C
The basic mechanisms responsible for producing winds from cool,
late-type stars are still largely unknown. We take inspiration from
recent progress in understanding solar wind acceleration to develop a
physically motivated model of the time-steady mass loss rates of cool
main-sequence stars and evolved giants. This model follows the energy
flux of magnetohydrodynamic turbulence from a subsurface convection
zone to its eventual dissipation and escape through open magnetic
flux tubes. We show how Alfvén waves and turbulence can produce
winds in either a hot corona or a cool extended chromosphere, and we
specify the conditions that determine whether or not coronal heating
occurs. These models do not utilize arbitrary normalization factors, but
instead predict the mass loss rate directly from a star's fundamental
properties. We take account of stellar magnetic activity by extending
standard age-activity-rotation indicators to include the evolution of
the filling factor of strong photospheric magnetic fields. We compared
the predicted mass loss rates with observed values for 47 stars and
found significantly better agreement than was obtained from the popular
scaling laws of Reimers, Schröder, and Cuntz. The algorithm used to
compute cool-star mass loss rates is provided as a self-contained and
efficient computer code. We anticipate that the results from this kind
of model can be incorporated straightforwardly into stellar evolution
calculations and population synthesis techniques.

---------------------------------------------------------
Title: Isothermal and Multithermal Analysis of Coronal Loops Observed
with Atmospheric Imaging Assembly. II. 211 Å Selected Loops
Authors: Schmelz, J. T.; Worley, B. T.; Anderson, D. J.; Pathak, S.;
Kimble, J. A.; Jenkins, B. S.; Saar, S. H.
2011ApJ...739...33S Altcode:
An important component of coronal loop analysis involves conflicting
results on the cross-field temperature distribution. Are loops
isothermal or multithermal? The Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory was designed in part to
answer this question. AIA has a series of coronal filters that peak at
different temperatures and cover the entire active region temperature
range. These properties should make AIA ideal for multithermal analysis,
but recent results have shown that the response functions of two of
the filters, AIA 94 and 131 Å, are missing a significant number of
low-temperature emission lines. Here we analyze coronal loops from
several active regions that were chosen in the 211 Å channel of AIA,
which has a peak response temperature of log T = 6.3. The differential
emission measure (DEM) analysis of the 12 loops in our sample reveals
that using data from the 131 Å AIA filter distorts the results, and
we have no choice but to do the analysis without these data. The 94
Å data do not appear to be as important, simply because the chosen
loops are not visible in this channel. If we eliminate the 131 Å data,
however, we find that our DEM analysis is not well constrained on the
cool temperature end of six of our loops. The information revealed
by our 211 selected loops indicates that additional atomic data are
required in order to pin down the cross-field temperature distribution.

---------------------------------------------------------
Title: Warm and Fuzzy: Temperature and Density Analysis of an Fe XV
EUV Imaging Spectrometer Loop
Authors: Schmelz, J. T.; Rightmire, L. A.; Saar, S. H.; Kimble, J. A.;
Worley, B. T.; Pathak, S.
2011ApJ...738..146S Altcode:
The Hinode EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) were
designed in part to work together. They have the same spatial resolution
and cover different but overlapping coronal temperature ranges. These
properties make a combined data set ideal for multithermal analysis,
where EIS provides the best information on the cooler corona (log T
&lt; 6.5) and XRT provides the best information on the hotter corona
(log T &gt; 6.5). Here, we analyze a warm non-flaring loop detected in
images made in a strong EIS Fe XV emission line with a wavelength of
284.16 Å and peak formation temperature of log T = 6.3. We perform
differential emission measure (DEM) analysis in three pixels at
different heights above the footpoint and find multithermal results
with the bulk of the emission measure in the range 6.0 &lt; log T &lt;
6.6. Analysis with the EIS lines alone gave a DEM with huge amounts of
emission measure at very high temperatures (log T &gt;7.2) analysis
with XRT data alone resulted in a DEM that was missing most of the
cooler emission measure required to produce many of the EIS lines. Thus,
both results were misleading and unphysical. It was only by combining
the EIS and XRT data that we were able to produce a reasonable result,
one without ad hoc assumptions on the shape and range of the DEM itself.

---------------------------------------------------------
Title: A Close Look At Middle-Aged Coronae: The Nearby 2.5 Gyr Old
Cluster Ruprecht 147
Authors: Saar, Steven
2011cxo..prop.3327S Altcode:
Just six years ago Kharchenko (2005) used catalog data to identify
Ruprecht 147 (R147) as the 15th closest stellar cluster to the Solar
System. At a distance of only 250 pc, and an age estimated to be 2.5
Gyr, R147 is by far the closest old cluster: the next closest with
an age &gt; 1 Gyr is nearly twice as distant. We request a 240 ksec
observation with ACIS-S near the cluster core to characterize the
coronal emission in cool stars at an unexplored age: ~half solar. The
data will close a large age gap in our understanding of coronal
evolution, improve age-rotation-activity calibration and explore the
coronal consequences of significant magnetic dynamo/activity changes
which appear around this time.

---------------------------------------------------------
Title: A Unified Analysis of Time Variability in Chandra Grating
Observations of Low-Mass Stars
Authors: Posson-Brown, Jennifer; Kashyap, V.; Saar, S.; Drake, J.
2011HEAD...12.1005P Altcode:
We are carrying out a unified study of archival Chandra grating
observations of active low-mass coronal stars and present preliminary
results here. We include ACIS-S/HETG, ACIS-S/LETG, and HRC-S/LETG
observations. Gratings data are optimal for timing analysis since they
are free from pile-up and allow for joint spectro-temporal analysis. We
discuss techniques for timing analysis of gratings data and explore
the distribution of stellar flare energies and the time variability of
individual lines fluxes. This work is supported by CXC NASA contract
NAS8-39073 and Chandra grant AR0-11001X.

---------------------------------------------------------
Title: FK Com Multi-wavelength Campaign
Authors: Kashyap, Vinay; Ayres, T.; Korhonen, H.; Saar, S.; Drake,
J.; Garcia-Alvarez, D.; Huenemoerder, D.
2011HEAD...12.1004K Altcode:
FK Com (G5 III) is an ultrafast-rotating single yellow giant. It is
the eponymous member of its class, and is suspected to have been a
coalesced binary that has spun up. Here we present preliminary results
from a multi-wavelength campaign we have carried out in April-May
2011. We observe the corona with X-rays with the high-resolution
HETG spectrometer on Chandra, the corona and chromosphere FUV with
HST/COS, and obtain surface magnetic information via Zeeman Doppler and
Doppler Imaging with ground-based observations. The X-ray light curve
exhibits significant variability, but unlike previous observations,
is not dominated by large flares. The FUV lines show broad profiles,
and considerable jitter. This study has been supported by Chandra
and HST grants.

---------------------------------------------------------
Title: Starspots, cycles, and magnetic fields
Authors: Saar, Steven H.
2011IAUS..273...61S Altcode:
I make a perhaps slightly foolhardy attempt to synthesize a
semi-coherent scenario relating cycle characteristics, starspots, and
the underlying magnetic fields with stellar properties such as mass
and rotation. Key to this attempt is to first study single dwarfs;
differential rotation plays a surprising role.

---------------------------------------------------------
Title: The dependence of maximum starspot amplitude and the amplitude
distribution on stellar properties
Authors: Saar, Steven H.; Dyke, Michelle; Meibom, Søren; Barnes,
Sydney A.
2011IAUS..273..469S Altcode:
We combine photometric data from field stars, plus over a dozen open
clusters and associations, to explore how the maximum photometric
amplitude (Amax) and the distribution of amplitudes
varies with stellar properties. We find a complex variation of
Amax with inverse Rossby number Ro-1, which
nevertheless can be modeled well with a simple model including an
increase in Amax with rotation for low Ro-1,
and a maximum level. Amax may then be further affected by
differential rotation and a decline at the highest Ro-1. The
distribution of Aspot below Amax varies with
Ro-1 : it peaks at low Aspot with a long
tail towards Amax for low Ro-1, but is more
uniformly distributed at higher Ro-1. We investigate further
dependences of the Aspot distributions on stellar properties,
and speculate on the source of these variations.

---------------------------------------------------------
Title: BOREAS: Mass Loss Rate of a Cool, Late-type Star
Authors: Cranmer, Steven R.; Saar, Steven H.
2011ascl.soft08019C Altcode:
The basic mechanisms responsible for producing winds from cool,
late-type stars are still largely unknown. We take inspiration from
recent progress in understanding solar wind acceleration to develop
a physically motivated model of the time-steady mass loss rates
of cool main-sequence stars and evolved giants. This model follows
the energy flux of magnetohydrodynamic turbulence from a subsurface
convection zone to its eventual dissipation and escape through open
magnetic flux tubes. We show how Alfven waves and turbulence can
produce winds in either a hot corona or a cool extended chromosphere,
and we specify the conditions that determine whether or not coronal
heating occurs. These models do not utilize arbitrary normalization
factors, but instead predict the mass loss rate directly from a star's
fundamental properties. We take account of stellar magnetic activity
by extending standard age-activity-rotation indicators to include
the evolution of the filling factor of strong photospheric magnetic
fields. We compared the predicted mass loss rates with observed values
for 47 stars and found significantly better agreement than was obtained
from the popular scaling laws of Reimers, Schroeder, and Cuntz. The
algorithm used to compute cool-star mass loss rates is provided as a
self-contained and efficient IDL computer code. We anticipate that the
results from this kind of model can be incorporated straightforwardly
into stellar evolution calculations and population synthesis techniques.

---------------------------------------------------------
Title: Rotational modulation, shear, and cyclic activity in HII 1883
Authors: Milingo, J. B.; Saar, S. H.; Marschall, L. A.; Stauffer, J. R.
2011IAUS..273...74M Altcode:
We present a 30 year compilation of V-band differential photometry for
the Pleiades K dwarf HII 1883. HII 1883 has an average rotational period
&lt;Prot&gt; of ~0.235d and displays rotational modulation
due to non-uniform surface brightness as large as 0.2 magnitudes in
V. Preliminary work yields a cycle period of ~9yrs and rotational
shear δProt/&lt;Prot&gt; considerably less than
solar. With such a long baseline of data available we can explore many
aspects of the star's photometric variability. We present studies
of the variation of the rotational modulation amplitude, &lt;V&gt;,
and Prot over the cycle.

---------------------------------------------------------
Title: The Color-period Diagram and Stellar Rotational Evolution—New
Rotation Period Measurements in the Open Cluster M34
Authors: Meibom, Søren; Mathieu, Robert D.; Stassun, Keivan G.;
Liebesny, Paul; Saar, Steven H.
2011ApJ...733..115M Altcode: 2011arXiv1103.5171M
We present the results of a 5 month photometric time-series survey for
stellar rotation periods combined with a 4 year radial-velocity survey
for membership and binarity in the 220 Myr open cluster M34. We report
surface rotation periods for 120 stars, 83 of which are kinematic
and photometric late-type cluster members. A comparison to previous
work serves to illustrate the importance of high-cadence long baseline
photometric observations and membership information. The new M34 periods
are less biased against slow rotation and cleaned for non-members. The
rotation periods of the cluster members span over more than an order
of magnitude from 0.5 days up to 11.5 days, and trace two distinct
rotational sequences—fast (C) and moderate-to-slow (I)—in the
color-period diagram. The sequences represent two different states
(fast and slow) in the rotational evolution of the late-type cluster
members. We use the color-period diagrams for M34 and for younger and
older clusters to estimate the timescale for the transition from the C
to the I sequence and find lsim150 Myr, ~150-300 Myr, and ~300-600 Myr
for G, early-mid K, and late K dwarfs, respectively. The small number
of stars in the gap between C and I suggests a quick transition. We
estimate a lower limit on the maximum spin-down rate (dP/dt) during
this transition to be ~0.06 days Myr-1 and ~0.08 days
Myr-1 for early and late K dwarfs, respectively. We compare
the I sequence rotation periods in M34 and the Hyades for G and K dwarfs
and find that K dwarfs spin down slower than the Skumanich \sqrt{t}
rate. We determine a gyrochronology age of 240 Myr for M34. The gyro-age
has a small formal uncertainty of 2% which reflects the tight I sequence
in the M34 color-period diagram. We measure the effect of cluster age
uncertainties on the gyrochronology age for M34 and find the resulting
error on the gyro-age to be consistent with the ~15% error estimate
for the technique in general. We use the M34 I sequence to redetermine
the coefficients in the expression for rotational dependence on color
used in gyrochronology. Finally, we propose that stability in the phase,
shape, and amplitude of the photometric variability for the 120 rotators
over the ~5 month duration of our survey is due to spot generation at
active stellar longitudes. WIYN Open Cluster Study XLV.

---------------------------------------------------------
Title: Chandra Observations of the Well-Studied 180 Myr Old Open
Cluster M35
Authors: Meibom, Soren; Saar, S. H.; Barnes, S. A.
2011AAS...21813303M Altcode: 2011BAAS..43G13303M
M35 is a relatively close ( 800 pc), rich, young ( 180 Myr) open
cluster which has been the focus of extensive multi-epoch spectroscopic
and photometric study. Some 250 single and 100 binary stars ( 50
with orbits) are confirmed members and 310 have measured rotation
periods. This detailed information about membership, binarity,
and rotation, makes M35 an ideal target for studying not only the
rotation-activity-age relation for cool stars, but also for the effect
of a stellar companion on this relationship. We present preliminary
results of a 130 ksec ACIS-I observation near the core of the M35,
containing 180 cluster members. We explore how the coronal flux and
temperature change across the cluster's color-period diagram, how
binarity affects these results, and compare our findings with other
clusters. This work was funded by Chandra Award No. GO0-11041A.

---------------------------------------------------------
Title: Testing a Predictive Theoretical Model for the Mass Loss
Rates of Cool Stars
Authors: Cranmer, Steven R.; Saar, S. H.
2011AAS...21820503C Altcode: 2011BAAS..43G20503C
All stars are believed to possess expanding outer atmospheres known
as stellar winds. The continual evaporation of gas from stars has a
significant impact on stellar and planetary evolution, and also on
the larger-scale evolution of gas and dust in galaxies. Despite more
than a half-century of study, though, the basic mechanisms responsible
for producing stellar winds are still largely unknown. Fortunately,
there has been a great deal of recent progress toward identifying
and characterizing the processes that produce our own Sun's mass
outflow. Based on this progress, we have developed a new generation
of physically motivated models of stellar wind acceleration for
cool main-sequence stars and evolved giants. These models follow the
production of magnetohydrodynamic turbulent motions from subsurface
convection zones to their eventual dissipation and escape through the
stellar wind. The magnetic activity of these stars is taken into account
by extending standard age/rotation/activity indicators to include the
evolution of the filling factor of strong magnetic fields in stellar
photospheres. We will present tests of these models based on a large
database of observationally determined mass loss rates, in combination
with accurate measurements of the basic properties of these stars
(e.g., masses, radii, luminosities, metallicities, and rotation rates)
on which the mass loss rates must depend. The eventual goal of this
project is to provide a simple stand-alone algorithm for predicting
the mass loss rates of cool stars for use in stellar atmosphere and
population synthesis calculations.

---------------------------------------------------------
Title: Many Flares Make a Corona
Authors: Saar, Steven H.; Kashyap, V.; Drake, J.; Reeves, K.;
Connors, A.
2011AAS...21832202S Altcode: 2011BAAS..43G32202S
It is well known that solar flare energies have a self-similar
distribution. The number of flares, N, of any given energy, E,
follows a power-law distribution, dN/dE E^(-alpha), over many orders
of magnitude, with alpha 1.8. A similar distribution holds for stellar
coronae, but in this case, typically alpha &gt; 2. The value alpha=2
is important because it represents a threshold beyond which it is
possible to ascribe all of the coronal luminosity to increasingly
weaker, but more numerous, flares. Current methods to evaluate the
flare distribution index alpha for stars are limited by two factors:
they either depend on explicit detections of flares, or if the flare
distribution itself is being modeled, then they are highly computation
intensive and are thus slow. We have developed analytical methodology
that substitutes for Monte Carlo simulations over a majority of the
latter calculations. This causes improvements in computational speed
of over 100x. We describe these methods below, and apply it to some
simulated and observed data. This work was supported by CXC NASA
contract NAS8-39073 and Chandra grant AR0-11001X.

---------------------------------------------------------
Title: Kepler Observations of Starspot Evolution, Differential
Rotation, and Flares on Late-Type Stars
Authors: Brown, Alexander; Korhonen, H.; Berdyugina, S.; Walkowicz,
L.; Kowalski, A.; Hawley, S.; Neff, J.; Ramsey, L.; Redman, S.; Saar,
S.; Furesz, G.; Piskunov, N.; Harper, G.; Ayres, T.; Tofany, B.
2011AAS...21820502B Altcode: 2011BAAS..43G20502B
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that
routinely allow detailed studies of stellar magnetic activity on
late-type stars that were difficult, if not impossible, to attempt
previously. Rotational modulation due to starspots is commonly seen
in the Kepler light-curves of late-type stars, allowing detailed
study of the surface distribution of their photospheric magnetic
activity. Kepler is providing multi-year duration light-curves that
allow us to investigate how activity phenomena -- such as the growth,
migration, and decay of starspots, differential rotation, activity
cycles, and flaring -- operate on single and binary stars with a
wide range of mass and convection zone depth. We present the
first results from detailed starspot modeling using newly-developed
light-curve inversion codes for a range of GALEX-selected stars with
typical rotation periods of a few days, that we have observed as part of
our 200 target Kepler Cycle 1/2 Guest Observer programs. The physical
properties of the stars have been measured using high resolution
optical spectroscopy, which allows the Kepler results to be placed
within the existing framework of knowledge regarding stellar magnetic
activity. These results demonstrate the powerful diagnostic capability
provided by tracking starspot evolution essentially continuously for
more than 16 months. The starspots are clearly sampling the stellar
rotation rate at different latitudes, enabling us to measure the
differential rotation and starspot lifetimes. As would be expected,
stars with few day rotation show frequent flaring that is easily seen
as "white-light" flares in Kepler light-curves. We compare the observed
flare rates and occurrence with the starspot properties. This work
contains results obtained using the NASA Kepler satellite and from the
Apache Point Observatory, the MMT (using NOAO community access time),
and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler
grants NNX10AC51G and NNX11AC79G.

---------------------------------------------------------
Title: Kepler Observations of Pulsations In A Sample of
Magnetically-Active Stars
Authors: Neff, James E.; Brown, A.; Hawley, S.; Kowalski, A.;
Walkowicz, L.; Saar, S.
2011AAS...21822704N Altcode: 2011BAAS..43G22704N
We have observed about 200 targets in Kepler Cycle 1/2 Guest Observer
programs. The sample of active star candidates was selected primarily
using GALEX colors, and the Kepler light curves have revealed a rich
variety of variability. Rotational modulation (typical periods a few
days) due to starspots over the multi-year timeline of the Kepler
observations will permit us to measure surface differential rotation
and stellar magnetic cycles. On shorter timescales, the Kepler data
show dramatic evidence of stellar pulsations across much of the HR
diagram. Our selection criteria yielded a sample of magnetically active
G and K dwarfs, which might show solar-like pulsations. It also yielded
subsamples of several well-known pulsators (e.g., Delta Scuti stars)
as well as pulsators that currently defy easy classification. We are
systematically classifying and analyzing the pulsating stars in the our
Kepler GO program. We are particularly interested in using pulsations
to probe the interior properties of active G and K dwarfs, while the
starspots serve as a probe of the convection zone and surface layers. We
will present summary results for several different types of pulsation,
and we will provide a detailed asteroseismic analysis of those stars
in our sample that were observed to have both pulsations and magnetic
activity. This work contains results obtained using the NASA
Kepler satellite and from the Apache Point Observatory, the MMT (using
NOAO community access time), and the Hobby-Eberly Telescope. Funding
is provided by NASA Kepler grants NNX10AC51G and NNX11AC79G.

---------------------------------------------------------
Title: Preliminary Results From An Automated X-ray Bright Point
Detector for AIA
Authors: Saar, Steven H.; Farid, S.
2011SPD....42.2121S Altcode: 2011BAAS..43S.2121S
We present preliminary results of X-ray Bright Point (XBP) properties
derived from a new, automated XBP finder for AIA developed as part
of the Feature Finding Team for SDO Computer Vision. We analyze
several days of data and explore the size, location, intensity,
local environment, and lifetime of the XBPs, and the relationships
between these properties. This work was supported by NASA Grant
NNX09AB03G to the Smithsonian Astrophysical Observatory and contract
SP02H1701R from Lockheed-Martin to SAO.

---------------------------------------------------------
Title: Temperature variability in X-ray bright points observed
with Hinode/XRT
Authors: Kariyappa, R.; Deluca, E. E.; Saar, S. H.; Golub, L.; Damé,
L.; Pevtsov, A. A.; Varghese, B. A.
2011A&A...526A..78K Altcode:
 Aims: We investigate the variability in temperature as
a function of time among a sample of coronal X-ray bright points
(XBPs). Methods: We analysed a 7-h (17:00-24:00 UT) long time
sequence of soft X-ray images observed almost simultaneously in two
filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope
(XRT) onboard the Hinode mission. We identified and selected 14 XBPs
for a detailed analysis. The light curves of XBPs were derived using
the SolarSoft library in IDL. The temperature of XBPs was determined
using the calibrated temperature response curves of the two filters
by means of the intensity ratio method. Results: We find that
the XBPs show a high variability in their temperature and that the
average temperature ranges from 1.1 MK to 3.4 MK. The variations
in temperature are often correlated with changes in average X-ray
emission. It is evident from the results of time series that the XBP
heating rate can be highly variable on short timescales, suggesting
that it has a reconnection origin.

---------------------------------------------------------
Title: Beyond the Limb: A Narrow Band EUV Search for Background
Objects with the AIA
Authors: Schonfeld, Sam; Testa, P.; Saar, S.
2011AAS...21715505S Altcode: 2011BAAS...4315505S
As the star closest to Earth, the Sun provides us with the opportunity
to study up close and test models for X-ray stellar activity. Its close
proximity (and consequent brightness), however, makes it challenging to
observe the Sun and other celestial objects with the same instrument;
thus instrumental cross-calibration difficulties have complicated
comparison of the Sun with other stars. The new Solar Dynamics
Observatory (SDO) launched in February 2010 may at last allow for
direct comparison of the Sun and other stars. The Atmospheric Imaging
Assembly (AIA) onboard the SDO, a series of telescopes taking images of
the full Sun at high spatial and temporal resolution in seven extreme
ultraviolet (EUV) pass bands, can potentially observe background objects
passing within the field of view of the telescopes off the limb of the
Sun. Young stars, active galactic nuclei and other strong X-ray and
EUV emitters may be bright enough to observe after careful background
subtraction. Using technical specifications of the telescopes and
measured X-ray fluxes of various background sources, we determined that
with exposure times of the order of minutes, significantly longer than
the standard 3s exposure, we should be able to observe the brightest
background sources when they pass in the AIA field of view. We also
determined what kinds of instrumental limitations we need to overcome
and how best to make observations of these dim background sources.

---------------------------------------------------------
Title: Atmospheric Imaging Assembly Multithermal Loop Analysis:
First Results
Authors: Schmelz, J. T.; Kimble, J. A.; Jenkins, B. S.; Worley, B. T.;
Anderson, D. J.; Pathak, S.; Saar, S. H.
2010ApJ...725L..34S Altcode:
The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory has state-of-the-art spatial resolution and shows the most
detailed images of coronal loops ever observed. The series of coronal
filters peak at different temperatures, which span the range of active
regions. These features represent a significant improvement over earlier
coronal imagers and make AIA ideal for multithermal analysis. Here,
we targeted a 171 Å coronal loop in AR 11092 observed by AIA on
2010 August 3. Isothermal analysis using the 171-to-193 ratio gave
a temperature of log T ≈ 6.1, similar to the results of Extreme
ultraviolet Imaging Spectrograph (EIT) and TRACE. Differential emission
measure analysis, however, showed that the plasma was multithermal, not
isothermal, with the bulk of the emission measure at log T &gt; 6.1. The
result from the isothermal analysis, which is the average of the true
plasma distribution weighted by the instrument response functions,
appears to be deceptively low. These results have potentially serious
implications: EIT and TRACE results, which use the same isothermal
method, show substantially smaller temperature gradients than predicted
by standard models for loops in hydrodynamic equilibrium and have been
used as strong evidence in support of footpoint heating models. These
implications may have to be re-examined in the wake of new results
from AIA.

---------------------------------------------------------
Title: Multi-stranded and Multi-thermal Solar Coronal Loops: Evidence
from Hinode X-ray Telescope and EUV Imaging Spectrometer Data
Authors: Schmelz, J. T.; Saar, S. H.; Nasraoui, K.; Kashyap, V. L.;
Weber, M. A.; DeLuca, E. E.; Golub, L.
2010ApJ...723.1180S Altcode:
Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer
(EIS) on the Japanese/USA/UK Hinode spacecraft were used to investigate
the spatial and thermal properties of an isolated quiescent coronal
loop. We constructed differential emission measure (DEM) curves
using Monte Carlo based, iterative forward fitting algorithms. We
studied the loop as a whole, in segments, in transverse cuts, and
point-by-point, always with some form of background subtraction, and
find that the loop DEM is neither isothermal nor extremely broad, with
approximately 96% of the EM between 6.2 &lt;=log T&lt;= 6.7, and an
EM-weighted temperature of log T = 6.48 ± 0.16. We find evidence for
a gradual change in temperature along the loop, with log T increasing
only by ≈0.1 from the footpoints to the peak. The combine XRT-EIS
data set does a good job of constraining the temperature distribution
for coronal loop plasma. Our studies show that the strong constraints
at high and low temperatures provided by the combined data set are
crucial for obtaining reasonable solutions. These results confirm
that the observations of at least some loops are not consistent with
isothermal plasma, and therefore cannot be modeled with a single flux
tube and must be multi-stranded.

---------------------------------------------------------
Title: Low-state Magnetic Structures in Polars: Nature or Nurture?
Authors: Kafka, S.; Tappert, C.; Ribeiro, T.; Honeycutt, R. K.; Hoard,
D. W.; Saar, S.
2010ApJ...721.1714K Altcode:
We present an orbit-resolved study of the magnetic cataclysmic
variable (MCV) BL Hyi in its low state, and we explore the origin
of its Hα emission line components, their properties, and their
possible formation mechanism. We tentatively associate one of the
line components with a high-velocity component also seen in the high
state. We propose a scenario in which streaming prominence-like
magnetic loops (super-prominences) are kept in place by magnetic
field interactions between the white dwarf and the donor star and
are responsible for the high-velocity line components in the Balmer
lines. We also discuss how this is in accord with the standard scenario
of the secular evolution for MCVs. Finally, we offer an observational
test of our ideas and present challenges for future theoretical studies.

---------------------------------------------------------
Title: Magnetically Sleepy Stars: An X-ray Survey of Candidate Stars
in Extended Magnetic Minima
Authors: Saar, Steven
2010cxo..prop.3071S Altcode:
The Sun occasionally slips into periods of extended magnetic quiescence
where the normal magnetic cycle largely ceases (e.g., the Maunder
minimum). Understanding these episodes is important for understanding
non-linear magnetic dynamos and the Earth's radiation budget. We
have developed a new method for determining which stars may be in
the stellar analog of these magnetic minima. We propose to study five
such stars with Chandra ACIS-S. Combined with archival spectra of more
stars, we can 1) explore (by proxy) properties of the solar corona in
a Maunder-like minimum, 2) determine what stellar properties affect
this state, and 3) investigate the coronal product of the residual
turbulent dynamo in a solar mass star.

---------------------------------------------------------
Title: Numerical MHD Simulation of Star-Planet Interaction
Authors: Cohen, O.; Kashyap, V. L.; Drake, J. J.; Saar, S. H.; Sokolov,
I. V.
2010epsc.conf..804C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: X-ray coronae and stellar magnetospheres
Authors: Hussain, G. A. J.; Brickhouse, N. S.; Dupree, A. K.; Saar,
S. H.; Jardine, M.
2010AIPC.1248...19H Altcode:
Chandra's spectroscopic resolving power allows us to measure velocity
shifts down to ~30 km/s in line profiles. Observations covering
&gt;2Prot are needed to disentangle flaring and quiescent coronal
emission. The rotational modulation in X-ray lightcurves and spectra
enable us to estimate the size and location of non-flaring X-ray
emitting regions stellar coronae. We probe the coronal structure
in systems covering a range of parameters (e.g., spectral type and
rotation rate), and summarise results from new studies.

---------------------------------------------------------
Title: Steady Heating Model of an Active Region Core
Authors: Winebarger, Amy R.; Schmelz, J. T.; Saar, S. H.; Kashyap,
V. L.; Warren, H. P.
2010AAS...21640711W Altcode: 2010BAAS...41R.861W
If the heating in an active region core is steady, the base pressure of
loop as well as its loop length determines exactly the apex temperature,
density and required heating rate. In this research, we analyze data
of an active region core that is observed with both Hinode XRT and
EIS instruments. We use the density sensitve Fe XII line ratios to
determine the base pressure of the loops and geometrical constraints
to determine the loop lengths. We use the hotter spectral lines coupled
with the XRT filter intensities to determine the differential emission
measure (DEM) of the core plasma. Using the base pressures and loop
lengths, we populate loops in a model active region to determine a
model DEM. We then compare this emission measure distribution to the
observed distribution.

---------------------------------------------------------
Title: Computer Vision for SDO: First Results from the SDO Feature
Finding Algorithms
Authors: Martens, Petrus C.; Attrill, G.; Davey, A.; Engell, A.;
Farid, S.; Grigis, P.; Kasper, J.; Korreck, K.; Saar, S.; Su, Y.;
Testa, P.; Wills-Davey, M.; Bernasconi, P.; Raouafi, N.; Georgoulis,
M.; Deforest, C.; Peterson, J.; Berghoff, T.; Delouille, V.; Hochedez,
J.; Mampaey, B.; Verbeek, C.; Cirtain, J.; Green, S.; Timmons, R.;
Savcheva, A.; Angryk, R.; Wiegelmann, T.; McAteer, R.
2010AAS...21630804M Altcode:
The SDO Feature Finding Team produces robust and very efficient
software modules that can keep up with the relentless SDO data stream,
and detect, trace, and analyze a large number of phenomena including:
flares, sigmoids, filaments, coronal dimmings, polarity inversion
lines, sunspots, X-ray bright points, active regions, coronal holes,
EIT waves, CME's, coronal oscillations, and jets. In addition we track
the emergence and evolution of magnetic elements down to the smallest
features that are detectable, and we will also provide at least four
full disk nonlinear force-free magnetic field extrapolations per day. During SDO commissioning we will install in the near-real time data
pipeline the modules that provide alerts for flares, coronal dimmings,
and emerging flux, as well as those that trace filaments, sigmoids,
polarity inversion lines, and active regions. We will demonstrate
the performance of these modules and illustrate their use for science
investigations.

---------------------------------------------------------
Title: Stellar Coronae at 250 Myr: Chandra Observations of NGC 3532
Authors: Saar, Steven H.; Barnes, S.; Meibom, S.
2010AAS...21642104S Altcode: 2010BAAS...41R.833S
We present preliminary results of a Chandra observation of the 250 Myr
open cluster NGC 3532, one of the best studied clusters for rotation
periods between Pleiades and Hyades ages. We detect over 30 stars
spanning a wide range in rotation period. We discuss the cluster's X-ray
distribution function, rotation-activity relationship, and how X-ray
flux and temperature vary along the cluster's rotational sequences. We
compare the results with other clusters, and draw implications for
the evolution of rotation and activity in young stars.

---------------------------------------------------------
Title: Hinode XRT and EIS Multithermal Analysis of a Coronal Loop
Authors: Schmelz, Joan T.; Saar, S.; Kashyap, V.
2010AAS...21640713S Altcode: 2010BAAS...41..861S
Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer
(EIS) on Hinode were used to investigate the spatial and thermal
properties of an isolated quiescent coronal loop. We constructed
Differential Emission Measure (DEM) curves using Monte Carlo based
reconstruction algorithms. We studied the loop as a whole, in
segments, in transverse cuts, and point-by-point, always with some
form of background subtraction, and find that the loop DEM is neither
isothermal nor extremely broad, with 96% of the EM between 6.2 &lt;
log T &lt; 6.7, and an EM weighted average temperature of log T =
6.48 +/- 0.16. We find evidence for a gradual change in temperature
along the loop, with log T increasing by 0.1 from the footpoints to
the peak. The combined XRT-EIS data can do a good job of constraining
the temperature distribution for coronal loop plasma, but strong high-
and low- temperature constraints are crucial. Solar physics research
at the University of Memphis is supported by a Hinode subcontract from
NASA/SAO as well as NSF ATM-0402729.

---------------------------------------------------------
Title: Cool Star Photometry: Insight Into Temporal and Spatial
Activity Variation
Authors: Saar, Steven H.
2010AAS...21631303S Altcode: 2010BAAS...41R.888S
I briefly review selected significant results from stellar photometry
(broadband and Ca II HK) related to magnetic phenomena in cool stars,
with particular focus on what these results may be telling us about
stellar surface structures, dynamos, and the Sun's place in the broad
scope of stellar activity.

---------------------------------------------------------
Title: Searching for a Stellar Cycle and Spin in Proxima Cen
Authors: Wargelin, Bradford J.; Saar, S. H.; Kashyap, V. L.; Drake,
J. J.
2010HEAD...11.1706W Altcode: 2010BAAS...42R.683W
Although hundreds of stars have been optically monitored to look for
analogs of the solar 11-year activity cycle, almost no M stars have
been examined because of their optical faintness, particularly in the
CaII H and K lines that are the basis of most studies. Proxima Cen
(dM5.5e) has been monitored somewhat regularly in the optical and UV
and there have have been tentative reports of stellar periods ranging
from 1.2 to 7 years. Any cyclicity would be surprising since Prox Cen is
fully convective and should not have an αΩ dynamo. Several rotation
periods have also been suggested, with 83 days currently favored. We
present preliminary results on variability and rotation period after
monitoring Prox Cen for nearly a year using Swift. Support for
this work was provided by NASA through Swift Grant Number NNX09AR09G.

---------------------------------------------------------
Title: Sunspot cycles and Grand Minima
Authors: Sokoloff, Dmitry; Arlt, Rainer; Moss, David; Saar, Steven H.;
Usoskin, Ilya
2010IAUS..264..111S Altcode:
Observational data concerning the long-term history of cyclic solar
activity as recorded in sunspot and isotopic data are discussed in the
context of solar dynamo theory. In particular, a simple dynamo model
based on differential rotation and the mirror asymmetry of convection
with random fluctuations of dynamo governing parameters is shown to
reproduce some basic features of the solar magnetic activity evolution.

---------------------------------------------------------
Title: Solar Mystery Waves Excite X-ray Bright Points
Authors: Saar, Steven H.; Attrill, G. D. R.
2010AAS...21542205S Altcode: 2010BAAS...42..292S
We report on Hinode XRT observations of sequential emission enhancements
in solar X-ray bright points (XBPs) consistent with excitation by an
(otherwise undetected) wave. In one case, the wave appears to have been
excited by a flaring/erupting XBP. The wave velocity averaged about 350
km/s in areas of weak magnetic field and quiet Sun emission, but was
reduced by about 1/3 in areas of higher magnetic flux density. Larger
loops were mostly unaffected by the wave disturbance, which could
still excite XBPs at distances of 4e5 km and more from their apparent
starting point. We speculate on the origin and properties of these
mystery waves, which may be useful as diagnostics of the medium in
which they travel. We suspect these waves may be relatively common,
but heretofore under-recognized due to their low level, enhancement
selectivity, need for high cadence data, and confusion from stochastic
variability. SDO's AIA should aid considerably in further study of this
intriguing phenomenon. This work was supported by NASA contract
NNM07AB07C to SAO.

---------------------------------------------------------
Title: Automated Feature and Event Detection with SDO AIA and HMI Data
Authors: Davey, Alisdair; Martens, P. C. H.; Attrill, G. D. R.;
Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar,
S. H.; Su, Y.; Testa, P.; Wills-Davey, M.; Savcheva, A.; Bernasconi,
P. N.; Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F. .; Cirtain,
J. W.; Deforest, C. E.; Angryk, R. A.; de Moortel, I.; Wiegelmann,
T.; Georgouli, M. K.; McAteer, R. T. J.; Hurlburt, N.; Timmons, R.
2010cosp...38.2878D Altcode: 2010cosp.meet.2878D
The Solar Dynamics Observatory (SDO) represents a new frontier in
quantity and quality of solar data. At about 1.5 TB/day, the data will
not be easily digestible by solar physicists using the same methods
that have been employed for images from previous missions. In order for
solar scientists to use the SDO data effectively they need meta-data
that will allow them to identify and retrieve data sets that address
their particular science questions. We are building a comprehensive
computer vision pipeline for SDO, abstracting complete metadata
on many of the features and events detectable on the Sun without
human intervention. Our project unites more than a dozen individual,
existing codes into a systematic tool that can be used by the entire
solar community. The feature finding codes will run as part of the SDO
Event Detection System (EDS) at the Joint Science Operations Center
(JSOC; joint between Stanford and LMSAL). The metadata produced will
be stored in the Heliophysics Event Knowledgebase (HEK), which will be
accessible on-line for the rest of the world directly or via the Virtual
Solar Observatory (VSO) . Solar scientists will be able to use the
HEK to select event and feature data to download for science studies.

---------------------------------------------------------
Title: Towards accurate cross-calibration of Hinode XRT with other
X-ray observatories: tentative detection of the F star HD199143
with XRT
Authors: Testa, Paola; Saar, Steven
2010cosp...38.2910T Altcode: 2010cosp.meet.2910T
Despite decades of X-ray observations of both solar and stellar
coronae with various instruments, placing solar X-ray emission
levels in a broader astrophysical context is on surprisingly shaky
ground. This is largely due to cross-calibration problems and the
difficulty of observing the same targets with both solar and stellar
instruments. Here we report on a new attempt at direct cross-calibration
between solar and stellar missions: observations by the Hinode X-ray
Telescope (XRT) of a young X-ray active F star, HD199143. This star
has been previously studied by ROSAT and Chandra, and is eclipsed
by the Sun every January. We observed the star for a total of 12.6
hours on ingress and egress, and tentatively detect the source at an
emission level broadly consistent with expectations based on the most
up-to-date calibrations of Hinode, Chandra, and ROSAT count rates for
this star. We discuss further observational and analysis plans.

---------------------------------------------------------
Title: Using Solar Regions as Seen by Hinode XRT to Model the Coronae
of Inactive Stars and Magnetic Minima
Authors: Saar, S.; Testa, P.; Weber, M.; Marsh, J.
2009ASPC..416..543S Altcode:
We use carefully calibrated, multi-filter X-ray data from Hinode XRT to
compute differential emission measures (DEM) for spatially averaged,
less active solar features (coronal holes, quiet Sun, X-ray bright
points). We use linear combinations of these regions to construct model
quiet coronae for comparison with inactive stars, specifically, stars
which may be in Maunder-like magnetic minima. In this way, test how
well a mix of existing solar features can be used to model conditions
in magnetic minima.

---------------------------------------------------------
Title: Examining the Effect of Local Magnetic Field on Coronal Bright
Point Heating and Evolution
Authors: Farid, S.; Saar, S.; Govindan, R.; Deluca, E.
2009ASPC..415...15F Altcode: 2010arXiv1001.3241F
We investigate the effect of the local magnetic field on the
evolution and heating of coronal bright points (BPs) by examining a
BP in a coronal hole and a BP in the nearby quiet sun. We attempt to
discriminate the heating source of BPs by correlating fluctuations in
emission in TRACE 171 Å images, to changes in the unsigned magnetic
flux of the associated bipolar region using GONG magnetograms, and
potential field extrapolations. We confirm that changes in emission of
the larger, quiet-sun bright point can be correlated to fluctuations in
the total unsigned magnetic flux as predicted by previous studies. The
quiet sun BP also appears to have a potential magnetic configuration
over the observation period. However changes in emission in the smaller,
coronal hole bright point appears to be less correlated to changes
in the bipolar region. We also could not reproduce a potential-like
extrapolation at any time during the observation period, possibly
indicating the CH bright point may be non-potential.

---------------------------------------------------------
Title: The Activity Cycles and Surface Differential Rotation of
Single Dwarfs
Authors: Saar, S. H.
2009ASPC..416..375S Altcode:
I present an updated overview of activity cycles in cool
stars. Long-term study of magnetic proxies such as Ca II HK
emission and photometry are the primary tools for investigating
stellar activity cycles. I focus on cycle data from these sources,
specifically for single dwarf stars. These restrictions reduce two
areas of uncertainty: structural changes due to evolution and the
effects of binarity. I explore the relationships between cycle period,
cycle amplitude and various stellar properties, including rotation
and surface differential rotation (SDR). Cycle period relationships
are somewhat ambiguous; similar restrictions on the data set for SDR,
however, reveal interesting trends. Speculations on what the results
might imply for the dynamo are wildly tossed about.

---------------------------------------------------------
Title: Coronal Loop Temperatures Obtained with Hinode XRT: A
Toothpaste-Tube Analogy
Authors: Schmelz, J. T.; Saar, S. H.; Weber, M. A.; Deluca, E. E.;
Golub, L.
2009ASPC..415..299S Altcode:
Multi-filter data observed by the Hinode X-Ray Telescope on 10 and
2007 July 13 were used to investigate the thermal properties of
coronal loops. At several positions along the loops, differential
emission measure analysis revealed a strong peak at log T = 6.1 (which
would predict the presence of a TRACE loop) and a much weaker hot
component (which we speculated might be a nanoflare signature). TRACE
observations, however, did not reveal the predicted loop, so we were
forced to re-examine our assumptions. Good differential emission measure
results require high- and low-temperature constraints, but our data sets
did not contain images from the thinnest and thickest filters, which
would be most likely to provide these constraints. Since differential
emission measure programs aim to match observed intensities and get
low values of χ2, they may place emission measure in high-
and low-temperature bins where it does not belong. We draw an analogy to
squeezing the toothpaste tube in the middle. Our analysis was repeated
for a loop observed on 2007 May 13 when the instrument acquired data
in 11 filters and filter combinations, including both the thinnest and
thickest filters. These results show that the loop is multi-thermal,
with significant emission measure in the range 6.0 &lt; log T &lt; 6.5.

---------------------------------------------------------
Title: Some Like It Hot: Coronal Heating Observations from Hinode
X-ray Telescope and RHESSI
Authors: Schmelz, J. T.; Kashyap, V. L.; Saar, S. H.; Dennis, B. R.;
Grigis, P. C.; Lin, L.; De Luca, E. E.; Holman, G. D.; Golub, L.;
Weber, M. A.
2009ApJ...704..863S Altcode:
We have used Hinode X-Ray Telescope observations and RHESSI upper
limits together to characterize the differential emission measure
(DEM) from a quiescent active region. We find a relatively smooth DEM
curve with the expected active region peak at log T = 6.4. We also
find a high-temperature component with significant emission measure
at log T gsim 7. This curve is consistent with previous observations
of quiescent active regions in that it does not produce observable Fe
XIX lines. It is different from that generated with X-Ray Telescope
(XRT) data alone—RHESSI rules out the possibility of a separate
high-temperature component with a peak of approximately log T = 7.4. The
strength and position of the high-temperature peak in this XRT-only
analysis was, however, poorly determined; adding RHESSI flux upper
limits in the 4-13 keV energy range provide a strong high-temperature
constraint which greatly improves the multi-thermal findings. The
results of the present work as well as those from a growing number
of papers on this subject imply that our previous understanding of
the temperature distribution in active regions has been limited. Hot
plasma (log T ≈ 7) appears to be prevalent, although in relatively
small quantities as predicted by nanoflare models. Other models may
need to be adjusted or updated to account for these new results.

---------------------------------------------------------
Title: Interactions of the Magnetospheres of Stars and Close-In
Giant Planets
Authors: Cohen, O.; Drake, J. J.; Kashyap, V. L.; Saar, S. H.; Sokolov,
I. V.; Manchester, W. B.; Hansen, K. C.; Gombosi, T. I.
2009ApJ...704L..85C Altcode: 2009arXiv0909.3093C
Since the first discovery of an extrasolar planetary system more
than a decade ago, hundreds more have been discovered. Surprisingly,
many of these systems harbor Jupiter-class gas giants located close
to the central star, at distances of 0.1 AU or less. Observations of
chromospheric "hot spots" that rotate in phase with the planetary orbit,
and elevated stellar X-ray luminosities, suggest that these close-in
planets significantly affect the structure of the outer atmosphere of
the star through interactions between the stellar magnetic field and
the planetary magnetosphere. Here, we carry out the first detailed
three-dimensional magnetohydrodynamics simulation containing the two
magnetic bodies and explore the consequences of such interactions on
the steady-state coronal structure. The simulations reproduce the
observable features of (1) increase in the total X-ray luminosity,
(2) appearance of coronal hot spots, and (3) phase shift of these
spots with respect to the direction of the planet. The proximate
cause of these is an increase in the density of coronal plasma in the
direction of the planet, which prevents the corona from expanding and
leaking away this plasma via a stellar wind. The simulations produce
significant low temperature heating. By including dynamical effects,
such as the planetary orbital motion, the simulation should better
reproduce the observed coronal heating.

---------------------------------------------------------
Title: The Activity and Variability of the Sun and Sun-Like
Stars. II. Contemporaneous Photometry and Spectroscopy of Bright
Solar Analogs
Authors: Hall, Jeffrey C.; Henry, Gregory W.; Lockwood, G. Wesley;
Skiff, Brian A.; Saar, Steven H.
2009AJ....138..312H Altcode:
We present 14 years of contemporaneous photometric and spectroscopic
observations of 28 solar analog stars, taken with the Tennessee State
University Automatic Photometric Telescopes at Fairborn Observatory
and the Solar-Stellar Spectrograph at Lowell Observatory. These
are the best observed and most nearly Sun-like of the targets in
our magnitude-limited (V &lt;= 7.5) sample. The correlations between
luminosity and activity reveal the expected inverse activity-brightness
correlations for active stars. Strong direct correlations between
activity and brightness are not prevalent for the less active solar
age stars, but are precision limited. The Sun does not appear to
have unusually low photometric variability when compared with the
most Sun-like inactive solar analogs. We present evidence that
the activity index R'HK is not a good discriminant of
Maunder Minimum candidate stars. On the basis of a star that appears
to have transitioned from a low-variability state to a cycling
state, we investigate the regime in which stars might switch from
faculae-dominated to spot-dominated variations.

---------------------------------------------------------
Title: Computer Vision for The Solar Dynamics Observatory
Authors: Martens, Petrus C.; Angryk, R. A.; Bernasconi, P. N.; Cirtain,
J. W.; Davey, A. R.; DeForest, C. E.; Delouille, V. A.; De Moortel,
I.; Georgoulis, M. K.; Grigis, P. C.; Hochedez, J. E.; Kasper, J.;
Korreck, K. E.; Reeves, K. K.; Saar, S. H.; Savcheva, A.; Su, Y.;
Testa, P.; Wiegelmann, T.; Wills-Davey, M.
2009SPD....40.1711M Altcode:
NASA funded a large international consortium last year to produce
a comprehensive system for automated feature recognition in SDO
images. The data we consider are all AIA and EVE data plus surface
magnetic field images from HMI. Helioseismology is addressed by another
group. We will produce robust and very efficient software modules
that can keep up with the relentless SDO data stream and detect, trace,
and analyze a large number of phenomena, including: flares, sigmoids,
filaments, coronal dimmings, polarity inversion lines, sunspots,
X-ray bright points, active regions, coronal holes, EIT waves, CME's,
coronal oscillations, and jets. In addition we will track the emergence
and evolution of magnetic elements down to the smallest features
that are detectable, and we will also provide at least four full
disk nonlinear force-free magnetic field extrapolations per day. A completely new software element that rounds out this suite is a
trainable feature detection module, which employs a generalized image
classification algorithm to produce the texture features of the images
analyzed. A user can introduce a number of examples of the phenomenon
looked and the software will return images with similar features. We
have tested a proto-type on TRACE data, and were able to "train" the
algorithm to detect sunspots, active regions, and loops. Such a module
can be used to find features that have not even been discovered yet,
as, for example, sigmoids were in the pre-Yohkoh era. Our codes
will produce entries in the Helio Events Knowledge base, and that will
permit users to locate data on individual events as well as carry out
statistical studies on large numbers of events, using the interface
provided by the Virtual Solar Observatory.

---------------------------------------------------------
Title: Hinode X-Ray Telescope Detection of Hot Emission from Quiescent
Active Regions: A Nanoflare Signature?
Authors: Schmelz, J. T.; Saar, S. H.; DeLuca, E. E.; Golub, L.;
Kashyap, V. L.; Weber, M. A.; Klimchuk, J. A.
2009ApJ...693L.131S Altcode: 2009arXiv0901.3122S
The X-Ray Telescope (XRT) on the Japanese/USA/UK Hinode (Solar-B)
spacecraft has detected emission from a quiescent active region
core that is consistent with nanoflare heating. The fluxes from 10
broadband X-ray filters and filter combinations were used to construct
differential emission measure (DEM) curves. In addition to the expected
active region peak at log T = 6.3-6.5, we find a high-temperature
component with significant emission measure at log T &gt; 7.0. This
emission measure is weak compared to the main peak—the DEM is down
by almost three orders of magnitude—which accounts of the fact
that it has not been observed with earlier instruments. It is also
consistent with spectra of quiescent active regions: no Fe XIX lines
are observed in a CHIANTI synthetic spectrum generated using the XRT
DEM distribution. The DEM result is successfully reproduced with a
simple two-component nanoflare model.

---------------------------------------------------------
Title: The Radial Velocity Effects of Stellar Surface Phenomena
Authors: Saar, Steven H.
2009AIPC.1094..152S Altcode: 2009csss...15..152S
Radial velocity (RV) studies have been a very successful tool
for finding and characterizing extrasolar planets. As RV precision
increases, and planet searches press to younger, hotter, and evolved
stars, however, this method will more and more bump against limitations
set by the host stars themselves. Cool stellar surfaces present a range
of troublesome phenomena such as spots, plage, and convective cells,
which can confuse RV measurements. I review how these phenomena affect
precision RV, scaling laws and timescales which characterize their
properties, and some methods to mitigate, circumvent, or correct for
their effects.

---------------------------------------------------------
Title: Thermal And Statistical Properties of X-ray Bright Points
Authors: Saar, S.; Farid, S.; Deluca, E.
2009AIPC.1094..756S Altcode: 2009csss...15..756S
HINODE's X-ray Telescope (XRT) offers a unique combination of
high spatial (~2”) and thermal resolution, full-Sun observations
of the solar corona over a wide range of temperatures (5.8~&lt;log
T~&lt;7.6). We use multi-filter Hinode/XRT data to explore the thermal,
statistical and spatial properties of X-ray bright points (XBPs). We
have developed an automated XBP finder to study BPs over two periods
during November 2007 and May 2008. We detect somewhat fewer XBPs than
SOHO EIT in 195 Å but find comparable values to the 284 Å band. This
is likely due in some part to the somewhat stricter requirements on XBP
shape and enhancement above local background that we have adopted. We
find that most XBPs appear to be relatively cool on average (log T~6.1),
only slightly hotter than the average quiet Sun. There is a trend for
larger XBPs to be hotter, with a sub-class of XBPs which are hotter
still at all sizes. We further investigate the spatial distribution
of XBPs, in particular exploring whether the “overhot” XBPs have
any tendency to appear in or near coronal holes. We find that there
appears to be a notable trend of overhot bright points within the two
data sets and a tendency of those to lie within 40” of coronal holes.

---------------------------------------------------------
Title: The Stars as a Sun: Secular Variations of Cycling and
Non-Cycling Stars
Authors: Hall, Jeffrey C.; Giampapa, Mark S.; Henry, Gregory W.;
Lean, Judith L.; Saar, Steven H.; Soderblom, David R.
2009astro2010S.111H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mass Transport Processes and their Roles in the Formation,
Structure, and Evolution of Stars and Stellar Systems
Authors: Carpenter, Kenneth G.; Karvovska, Margarita; Schrijver,
Carolus J.; Grady, Carol A.; Allen, Ronald J.; Brown, Alexander;
Cranmer, Steven R.; Dupree, Andrea K.; Evans, Nancy R.; Guinan,
Edward F.; Harper, Graham; Labeyrie, Antoine; Linsky, Jeffrey;
Peters, Geraldine J.; Roberge, Aki; Saar, Steven H.; Sonneborn,
George; Walter, Frederick M.
2009astro2010S..40C Altcode: 2009arXiv0903.2433C
We summarize some of the compelling new scientific opportunities
for understanding stars and stellar systems that can be enabled
by sub-mas angular resolution, UV/Optical spectral imaging
observations, which can reveal the details of the many dynamic
processes (e.g., variable magnetic fields, accretion, convection,
shocks, pulsations, winds, and jets) that affect their formation,
structure, and evolution. These observations can only be provided
by long-baseline interferometers or sparse aperture telescopes in
space, since the aperture diameters required are in excess of 500 m -
a regime in which monolithic or segmented designs are not and will
not be feasible - and since they require observations at wavelengths
(UV) not accessible from the ground. Two mission concepts which could
provide these invaluable observations are NASA's Stellar Imager (SI;
http://hires.gsfc.nasa.gov/si/) interferometer and ESA's Luciola
sparse aperture hypertelescope, which each could resolve hundreds
of stars and stellar systems. These observatories will also open an
immense new discovery space for astrophysical research in general and,
in particular, for Active Galactic Nuclei (Kraemer et al. Decadal
Survey Science Whitepaper). The technology developments needed for
these missions are challenging, but eminently feasible (Carpenter et
al. Decadal Survey Technology Whitepaper) with a reasonable investment
over the next decade to enable flight in the 2025+ timeframe. That
investment would enable tremendous gains in our understanding of the
individual stars and stellar systems that are the building blocks of our
Universe and which serve as the hosts for life throughout the Cosmos.

---------------------------------------------------------
Title: Extrasolar Giant Planets and X-Ray Activity
Authors: Kashyap, Vinay L.; Drake, Jeremy J.; Saar, Steven H.
2008ApJ...687.1339K Altcode: 2008arXiv0807.1308K
We have carried out a survey of X-ray emission from stars with giant
planets, combining both archival and targeted surveys. Over 230 stars
have been currently identified as possessing planets, and roughly
one-third of these have been detected in X-rays. We carry out detailed
statistical analysis on a volume-limited sample of main-sequence star
systems with detected planets, comparing subsamples of stars that
have close-in planets with stars that have more distant planets. This
analysis reveals strong evidence that stars with close-in giant
planets are on average more X-ray active by a factor of ≈4 than
those with planets that are more distant. This result persists for
various sample selections. We find that even after accounting for
observational sample bias, a significant residual difference still
remains. This observational result is consistent with the hypothesis
that giant planets in close proximity to the primary stars influence
the stellar magnetic activity.

---------------------------------------------------------
Title: What can we hope to know about the symmetry properties of
stellar magnetic fields?
Authors: Moss, David; Saar, Steven H.; Sokoloff, Dmitry
2008MNRAS.388..416M Altcode:
We summarize evidence that neither dynamo theory nor the observational
data give strong support to the idea that stellar magnetic fields
must have dipolar rather than quadrupolar symmetry with respect to
the stellar equator. We demonstrate that even the most basic model
for magnetic stellar activity, i.e. the Parker migratory dynamo,
provides many possibilities for the excitation of large-scale stellar
magnetic fields of non-dipolar symmetry. We demonstrate the spontaneous
transition of the dynamo-excited magnetic field from one symmetry
type to another. We explore observational tests to distinguish
between the two types of magnetic field symmetry, and thus detect
the presence of quadrupolar magnetic symmetry in stars. Complete
absence of quadrupolar symmetry would present a distinct challenge
for contemporary stellar dynamo theory. We revisit some observations
which, depending on further clarification, may already be revealing
some properties of the quadrupolar component of the magnetic fields
generated by stellar dynamos.

---------------------------------------------------------
Title: First observation of planet-induced X-ray emission: The system
HD 179949
Authors: Saar, S. H.; Cuntz, M.; Kashyap, V. L.; Hall, J. C.
2008IAUS..249...79S Altcode: 2007IAUS..249...79S; 2007arXiv0712.3270S
We present the first observation of planet-induced stellar X-ray
activity, identified for the HD 179949 system, using Chandra /
ACIS-S. The HD 179949 system consists of a close-in giant planet
orbiting an F9 V star. Previous ground-based observations already showed
enhancements in Ca II K in phase with the planetary orbit. We find an
30% increase in the X-ray flux over quiescent levels coincident with the
phase of the Ca II enhancements. There is also a trend for the emission
to be hotter at increased fluxes, confirmed by modeling, showing the
enhancement at 1 keV compared to 0.4 keV for the background star.

---------------------------------------------------------
Title: The Analysis of Hinode/XRT Observations
Authors: Deluca, E. E.; Weber, M.; Savcheva, A.; Saar, S.; Testa,
P.; Cirtain, J. W.; Sakao, T.; Noriyuki, N.; Kano, R.; Shimizu, T.
2008AGUSMSP51B..02D Altcode:
This poster will present the current state of Hinode/XRT analysis
software. We will give an overview of the XRT Analysis Guide. We will
include a detailed discussion of the following topics: Co-alignment
with SOT and EIS Spot removal for dynamics studies Filter calibration
for thermal studies Dark calibrations Sample data sets will be
discussed and links to the data products will be provided.

---------------------------------------------------------
Title: The Fainting of α Centauri A, Resolved
Authors: Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt,
Jürgen H. M. M.
2008ApJ...678L.121A Altcode:
Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD
128620, 128621: G2 V, K1 V) documented a steady fading of the primary's
X-ray corona, which had all but disappeared by early 2005. The steep
decline in LX was at odds with the previous two decades
of high-energy measurements, which showed only modest variability of
the Sun-like star. A Chandra LETGS spectrum in 2007 June, however,
fully resolved the source of the curious X-ray darkening: a depletion
of plasma above ~2 MK had substantially depressed the line spectrum
where the XMM-Newton response peaks (λ lesssim 30 Å), even though the
overall coronal luminosity, dominated by longer wavelength emissions,
had declined only slightly. This is reminiscent of the Sun's magnetic
activity cycle, where the 2-3 MK active regions of sunspot maximum
give way to the spatially pervasive, but cycle-independent, 1 MK
"quiet corona" at minimum. This emphasizes that any discussion of
cyclic coronal variability in low-activity stars will depend crucially
on the energy coverage of the measurements.

---------------------------------------------------------
Title: X-ray Activity and Close-in Giant Planets
Authors: Kashyap, Vinay; Drake, J.; Saar, S.
2008HEAD...10.1704K Altcode:
We have carried out a survey of X-ray emission from stars with close-in
giant planets. Of the greater than 150 stars that have been identified
as possessing planets, a third have been detected in observations
carried out with ROSAT and XMM. We carry out detailed statistical
analyses, comparing subsamples of stars that have close-in planets
with stars that have more distant planets. We establish that X-ray
activity is higher for stars with close-in giant planets. This result
is highly robust and persists for various sample subsets. We attempt
to explain this difference as possibly due to sample biases and find
that a significant residual difference still remains. We interpret
this observational result as being due to the effect of the physical
presence of giant planets in close proximity to the stars. Whether
this is a causal effect or an accidental correlation cannot be decided
with the data at hand. We posit that the interactions between the
planetary and stellar magnetospheres could be the physical cause of
the enhancement. This research was supported by NASA contract
NAS8-39073 (CXC), and NASA grants NNG05GJ63G (XMM/GO) and NAG-10360
(Origins).

---------------------------------------------------------
Title: IC 10 X-1 and NGC 300 X-1 - our nearest ULX
Authors: Prestwich, A. H.; Carpano, S.; Kilgard, R. E.; Saar, S. H.;
Crowther, P. A.; Pollock, A. M. T.; Zezas, A.; Roberts, T. P.; Ward,
M. J.
2008xng..conf...54P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A 21st century view of stellar rotation
Authors: Barnes, Sydney A.; Meibom, Soeren; Saar, Steven
2008noao.prop..476B Altcode:
Cool stars spin down over time. This spindown is simultaneously
impressively regular, surprisingly complex, scientifically intriguing,
and its study even useful to other branches of astronomy. Some of
this beautiful complexity is encapsulated in a new theory of stellar
rotation, called `CgI.' We propose here to explore, develop, and
test this theory using rotation period data in two carefully chosen
Southern open clusters. The proposed data will constitute the definitive
rotational study of the selected clusters for some time to come, because
of the period- and amplitude sensitivity, the large number of periods,
and the multiplexing effects of associated data. Furthermore, the
data have a usefulness that transcends any theory. They will allow the
empirical determination of the (apparently universal) mass dependence of
stellar rotation, several timescales important to rotational spindown,
the full interpretation of extant and allocated X-ray spectroscopy
of the proposed cluster stars, a deep BVI Color-Magnitude Diagram
of the proposed clusters, a make-or-break test of the CgI scenario,
and the exploration of connections with multiplicity (in concert with
separately proposed observations).

---------------------------------------------------------
Title: Instruments: HRC
Authors: Kraft, Ralph; Kenter, Almus; Ayres, Thomas R.; Judge, Philip
G.; Saar, Steven H.; Schmitt, Jurgen H. M. M.; Anderson, Gemma;
Gaensler, Bryan; Chicago Team
2008ChNew..15...13K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Differential Emission Measure and Analysis of X-Ray Bright
Points using Hinode's X-Ray Telescope (XRT)
Authors: Farid, S. I.; Saar, S.; Deluca, E.; Golub, L.; Weber, M.
2007AGUFMSH22A0841F Altcode:
The X-Ray telescope aboard Hinode utilizes up to thirteen filter
combinations with one arc second resolution to provide unprecedented
temperature coverage. In this study, we have used eleven X-Ray filters
to examine the statistical properties of X-ray bright points including
temperature, emission, and size distributions. We have analyzed what
appears to be a population of XRBs that are hotter than the main group
in order to identify any distinguishing properties.We discuss the
results of our analysis and their implications on XBP classification.

---------------------------------------------------------
Title: Response of the Solar Atmosphere to Magnetic Flux Emergence
from Hinode Observations
Authors: Li, Hui; Sakurai, Takashi; Ichimito, Kiyoshi; Suematsu,
Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimizu, Toshifumi; Shine,
Richard A.; Tarbell, Theodore D.; Title, Alan M.; Lites, Bruce; Kubo,
Masahito; Nagata, Shin'ichi; Kotoku, Jun; Shibasaki, Kiyoto; Saar,
Steven H.; Bobra, Monica
2007PASJ...59S.643L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Orbital Period of the Wolf-Rayet Binary IC 10 X-1:
Dynamic Evidence that the Compact Object Is a Black Hole
Authors: Prestwich, A. H.; Kilgard, R.; Crowther, P. A.; Carpano, S.;
Pollock, A. M. T.; Zezas, A.; Saar, S. H.; Roberts, T. P.; Ward, M. J.
2007ApJ...669L..21P Altcode: 2007arXiv0709.2892P
IC 10 X-1 is a bright (LX = 1038 ergs
s-1) variable X-ray source in the Local Group starburst
galaxy IC 10. The most plausible optical counterpart is a luminous
Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet
X-ray binary. In this Letter, we report on the detection of an X-ray
orbital period for IC 10 X-1 of 34.4 hr. This result, combined with a
reexamination of optical spectra, allows us to determine a mass function
for the system of f(M)=7.8 Msolar and a probable mass for
the compact object of 24-33 Msolar. If this analysis is
correct, the compact object is the most massive stellar-mass black
hole known. We further show that the observed period is inconsistent
with Roche lobe overflow, suggesting that the binary is detached and
that the black hole is accreting the wind of the Wolf-Rayet star. The
observed mass-loss rate of [MAC92] 17A is sufficient to power the
X-ray luminosity of IC 10 X-1.

---------------------------------------------------------
Title: A detailed investigation of coronal/magnetic and rotational
changes in cool stars using NGC 3532
Authors: Saar, Steven
2007cxo..prop.2350S Altcode: 2007cxo..prop.2306S
We propose to use Chandra ACIS-I to study the one-to-one correspondence
recently proposed between coronal/dynamo and rotational changes in
cool stars. The goal is insight into the physical basis underlying the
3-part X-ray classification of cool stars (saturated, super-saturated,
and normal rotation-activity), crucial to fully interpreting the
rotational/magnetic/activity evolution of cool stars. We already
have copious optical data on our rich target open cluster NGC 3532,
including 83 rotation periods for the cluster members, making it
uniquely useful for rotation-activity studies. Furthermore, its age,
300Myr, nicely bridges a gap in the age sequence of the best studied
clusters between 100Myr (Pleiades) and 600Myr (Hyades), permitting
detailed study of evolution between these epochs.

---------------------------------------------------------
Title: Exploring the Early FUV History of Cool Stars: Transition
Regions at 30 Myr
Authors: Saar, Steven
2007hst..prop11116S Altcode:
Stellar magnetic activity derives from the so-called "dynamo,"
a hydromagnetic interplay between overturning plasma motions and
differential rotation in stars cool enough to support significant
surface convection zones. The magnetic fields resulting from dynamo
action are in turn are responsible for a wide range of high-energy
emissions, including the spectacular outbursts called flares. Dynamo
powered magnetic activity is not confined solely to stars, but also
must occur, for example, in accretion disks of all descriptions,
and in some planets. A great deal is known about magnetic activity in
middle-aged G dwarfs like our Sun, thanks to its proximity. Less is
known, however, about the much younger stars, newly emerged from the
T-Tauri stage. Yet, it is during this phase that they reach the peak
of their magnetic activity, and subsidiary influences, such as the
impact of ionizing radiation and strong coronal winds on developing
solar systems, also are maximum. One of the key missing ingredients
in our current understanding are measurements of FUV emissions of
such stars, to complement the extensive collections of coronal {1-10
MK} X-ray measurements, particularly from recent ROSAT, Chandra and
XMM-Newton surveys. We propose to conduct sensitive ACS/SBC prism
ultraviolet spectroscopy of selected fields in two young {30 Myr}
Galactic clusters-IC 2391 and IC 2602-to inventory the key C IV emission
index { 0.1 MK} over a much larger and more diverse sample of coeval
objects than has been possible hitherto. A key question is whether the
FUV emissions also suffer the "saturation" and "super-saturation" at
short rotation periods seen in coronal X-rays, or whether they continue
to rise in the fastest rotating stars. The saturation behavior of the
different temperature regimes holds important clues to the organization
of the surface active regions on these very young stars, and should
allow us to distinguish among several competing models.

---------------------------------------------------------
Title: A Flare-induced mass transfer/accretion event in AM Her?
Authors: Saar, Steven H.; Kashyap, Vinay L.; Ringwald, F. A.
2007uasb.conf..249S Altcode:
We report on HST observations of a mass transfer/accretion event in
AM Her which appears to have been induced by a strong flare on the
secondary. UV spectroscopic observations of the magnetic CV, AM Her,
were made with STIS towards the end of a deep photometric minimum in
late 2003. Our goal was to search for evidence of magnetic activity on
the secondary (as seen in the Dopplershifted hot emission lines of C IV
and Si IV), one of the fastest rotating cool stars ever studied in the
UV. There was evidence for quiescent C IV emission at the velocity of
the M star secondary, placing useful limits on its steady transition
region emission. One strong flare was seen in C IV (and near flare
peak, in Si IV and He II as well), with a velocity consistent with
the M dwarf. This was accompanied by a near-simultaneous increase in
continuum emission from the white dwarf; the excess had a temperature
of about 100,000 K. We suggest that this strong flare may have caused
an accretion event on the white dwarf, either by ejecting mass in the
form of a CME, or disrupting a large prominence system.

---------------------------------------------------------
Title: The Outer Solar Atmosphere during the Maunder Minimum:
A Stellar Perspective
Authors: Judge, Philip G.; Saar, Steven H.
2007ApJ...663..643J Altcode:
By comparing solar data with data of “flat activity” stars at UV and
soft X-ray wavelengths, we estimate solar chromospheric, transition
region, and coronal emission as it might have existed during the
Maunder minimum (1645-1715), the most recent of several episodes of
persistently weak sunspot activity. Several flat activity stars from
the Mount Wilson S-index survey have been observed with the Hubble
Space Telescope and ROSAT. Drawing on published data, we reassess
the criteria by which a star may be considered as a Maunder minimum
candidate. Of our targets, HD 10700 and HD 143761 are the most likely
such candidates. Solar UV spectra from the SOHO and UARS spacecraft, and
soft X-ray data from the SNOE spacecraft are compared with the stellar
UV and X-ray data. The comparison suggests that the radiative output
of the Maunder minimum chromosphere, transition region, and corona
were similar to (or at least not much less than) those observed under
conditions close to current solar minima. In turn, this suggests that
the emitting structures (which on the Sun at sunspot minimum are small
scale, &lt;&lt;Rsolar), including the magnetic network,
were also similar. These results have implications for the nature
of the surface magnetic fields and irradiance during the Maunder and
other magnetic minima, and for the solar dynamo.

---------------------------------------------------------
Title: The Sun-as-a-star As Seen By Hinode XRT
Authors: Saar, Steven H.; DeLuca, E. E.
2007AAS...210.9424S Altcode: 2007BAAS...39R.221S
We study full disk images of the Sun taken in multiple filters with
the Hinode XRT during the current low state of the solar cycle (late
2006). Taking advantage of the wide temperature sensitivity of the
XRT, we construct spatially averaged emission measure (EM) curves for
each of several solar region types, including coronal holes, quiet Sun,
bright points, and active regions of various description. These are
used to determine the relative contribution of the various features to
the total solar EM, as a starting point for a program to investigate
their time variation. We also explore use of the average EM curves
for understanding spatially unresolved stellar spectra and their
correlation with underlying magnetic fields. The US XRT team is
supported by a contract from NASA to SAO. Hinode is an international
project supported by JAXA, NASA, PPARC and ESA. We are grateful
to the Hinode team for all their efforts in the design, development
and operation of the mission.

---------------------------------------------------------
Title: Exoplanet-Induced Chromospheric Activity: Realistic Light
Curves from Solar-type Magnetic Fields
Authors: Cranmer, Steven R.; Saar, Steven H.
2007astro.ph..2530C Altcode:
There is growing observational evidence for some kind of interaction
between stars and close-in extrasolar giant planets. Shkolnik et
al. reported variability in the chromospheric Ca H and K lines of
HD 179949 and upsilon And that seemed to be phased with the planet's
orbital period, instead of the stellar rotational period. However, the
observations also indicate that the chromospheric light curves do not
repeat exactly, which may be expected for a planet plowing through a
variable stellar magnetic field. Using the complex solar magnetic field
(modeled with the Potential Field Source Surface technique) as a guide,
we simulate the shapes of light curves that would arise from planet-star
interactions that are channeled along magnetic field lines. We also
study the orbit-to-orbit variability of these light curves and how they
vary from solar minimum (i.e., a more or less axisymmetric stretched
dipole) to solar maximum (a superposition of many higher multipole
moments) fields. Considering more complex magnetic fields introduces
new difficulties in the interpretation of observations, but it may
also lead to valuable new diagnostics of exoplanet magnetospheres.

---------------------------------------------------------
Title: Detection of Orbital Period in the Wolf-Rayet X-ray Binary
IC 10 X-1
Authors: Prestwich, A. H.; Kilgard, R. E.; Carpano, S.; Saar, S.;
Page, K.; Pollock, Andy; Roberts, T.; Ward, M.; Zezas, A.
2006ATel..955....1P Altcode:
We detect periodic flux modulations in the Wolf-Rayet X-ray binary IC 10
X-1 using the SWIFT X-ray Telescope and the Chandra X-ray Observatory,
with period of 34.82h Â± 0.94h.

---------------------------------------------------------
Title: Confirmation of the planet hypothesis for the long-period
radial velocity variations of β Geminorum
Authors: Hatzes, A. P.; Cochran, W. D.; Endl, M.; Guenther, E. W.;
Saar, S. H.; Walker, G. A. H.; Yang, S.; Hartmann, M.; Esposito, M.;
Paulson, D. B.; Döllinger, M. P.
2006A&A...457..335H Altcode: 2006astro.ph..6517H
Aims.Our aim is to confirm the nature of the long period radial velocity
measurements for β Gem first found by Hatzes &amp; Cochran (1993). Methods: .We present precise stellar radial velocity measurements
for the K giant star β Gem spanning over 25 years. An examination of
the Ca II K emission, spectral line shapes from high resolution data
(R = 210 000), and Hipparcos photometry was also made to discern the
true nature of the long period radial velocity variations. 
Results: . The radial velocity data show that the long period, low
amplitude radial velocity variations found by Hatzes &amp; Cochran
(1993) are long-lived and coherent. Furthermore, the Ca II K emission,
spectral line bisectors, and Hipparcos photometry show no significant
variations of these quantities with the radial velocity period. An
orbital solution assuming a stellar mass of 1.7 M_⊙ yields a period,
P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major
axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02). 
Conclusions: .The data presented here confirm the planetary companion
hypothesis suggested by Hatzes &amp; Cochran (1993). β Gem is one of
six intermediate mass stars known to host a sub-stellar companion and
suggests that planet-formation around stars much more massive than
the sun may common.

---------------------------------------------------------
Title: A Flare-induced Mass Transfer/Accretion Event in AM Her?
Authors: Saar, S. H.; Kashyap, V. L.; Ringwald, F. A.
2006IAUJD...4E..30S Altcode:
We report observations of a mass transfer/accretion event in AM
Her which appears to have been induced by a strong flare on the
secondary. UV observations of the magnetic CV, AM Her, were made with
STIS on HST towards the end of a deep photometric minimum in late
2003. Our goal was to search for evidence of magnetic activity on the
secondary (as seen in the Doppler-shifted hot emission lines of C IV
and Si IV), one of the fastest rotating cool stars ever studied in
the UV. There was little evidence for quiescent C IV emission at the
velocity of the M star secondary, placing useful limits on its steady
transition region emission. One strong flare was seen in C IV (and
initially, in Si IV and He II as well), with a velocity consistent with
the M dwarf. This was accompanied by a near-simultaneous increase in
continuum emission from the white dwarf; the excess had a temperature of
about 100,000 K. We argue that this strong flare may have ejected mass
in the form of CME, or disturbed a large prominence system, exciting
an accretion event on the white dwarf. We discuss implications of
the results for low-state CV activity, mass transfer, and cool star
activity at extreme rotation rates.

---------------------------------------------------------
Title: The Many Cycles of Cool Stars
Authors: Saar, S. H.
2006IAUJD...8E..66S Altcode:
Magnetic activity exhibits a rich range time behaviour in cool stars,
from cyclic, to multi-cyclic, anharmonically variable, various
combinations of these, and finally to the virtually non-variable. I
assemble data on cycle periods, amplitudes, and anharmonic degrees,
and compare these various key stellar properties, such as rotation,
differential rotation, binarity, mass, and convective timescales, in
a search for correlations to guide and compare with dynamo theory. The
data come from a broad range of observational sources from the typical
(Ca II HK emission, photometry) to more the exotic (orbital period
variations). The nature of the variation can sometime depend on the
diagnostic used. The trends seen (and sometimes lack thereof) pose
important tests of dynamo models. I also explore stars with very
low activity variability. These seem to be composed of (at least)
two kinds: a group of stars which may be unable to cycle, and a group
whose dynamos may be temporarily quiescent. Both offer further important
clues for how dynamos operate, and the properties which govern them.

---------------------------------------------------------
Title: Maunder Minimum Dwarfs: Defined Out Of Existence?
Authors: Saar, Steven H.
2006SPD....37.1201S Altcode: 2006BAAS...38..240S
It has recently been suggested that there are very few dwarf stars
in the equivalent of a solar Maunder-like magnetic minimum (MM),
implying that the Sun is an unusual star for having such states. I
investigate this issue by comparing Ca II HK fluxes and stellar
properties(Teff, gravity, metallicity M/H) from two large
analyses of exoplanet search spectra. The joint sample includes 731
stars, of which 570 are dwarfs (as defined by gravity).The apparent
lack of MM dwarfs arises from two problems: the definition of what
properties an MM star should have, and issues in the calibration
of Ca II HK fluxes. There are indeed very few dwarf stars with
normalized Ca II HK fluxes log R'HK &lt; -5.1, the
traditional MM level. However, this level was defined using a stellar
sample which included subgiants. The new data show that the minimum
R'HK in subgiants almost always less than that in dwarfs
for all Teff and M/H. Thus, in a sense, MM dwarfs have been
defined out of existence by requiring an R'HK level more
appropriate for evolved stars. Furthermore, the minimum R'HK
observed in dwarfs is a decreasing function of M/H, so that metal-poor
minimum activity dwarfs have unusually high R'HK values
(e.g., log R'HK -4.85 at log M/H -1.0, compared with log
R'HK -4.95 at solar minimum). If MM dwarfs can be metal poor,
these stars may also be candidates. The true scarcity of MM dwarfs,
and by extension, the uniqueness of the solar case, therefore remains an
open question.This work is supported by NASA Origins grant NNG04GL54G.

---------------------------------------------------------
Title: Spot patterns and differential rotation in the eclipsing
pre-cataclysmic variable binary, V471 Tau
Authors: Hussain, G. A. J.; Allende Prieto, C.; Saar, S. H.; Still, M.
2006MNRAS.367.1699H Altcode: 2006astro.ph..2562H; 2006MNRAS.tmp..295H
We present surface spot maps of the K2V primary star in the
pre-cataclysmic variable binary system, V471 Tau. The spot maps show the
presence of large high-latitude spots located at the sub-white dwarf
longitude region. By tracking the relative movement of spot groups
over the course of four nights (eight rotation cycles), we measure
the surface differential rotation rate of the system. Our results
reveal that the star is rotating rigidly with a surface shear rate,
dΩ= 1.6 +/- 6mradd-1. The single active star AB Dor has
a similar spectral type, rotation period and activity level as the K
star in V471 Tau, but displays much stronger surface shear (46 &lt;
dΩ &lt; 58mradd-1). Our results suggest that tidal locking
may inhibit differential rotation; this reduced shear, however, does
not affect the overall magnetic activity levels in active K dwarfs.

---------------------------------------------------------
Title: The Amplitude of Stellar X-ray Cycles
Authors: Martens, P. C. H.; Chattterjee, P.; Saar, S. H.; Acton,
L. W. A.
2005AAS...20710405M Altcode: 2005BAAS...37R1334M
A decade worth of data from the Soft X-ray Telescope onboard the
Japan/US/UK mission Yohkoh shows that the Sun has a variation of
non-flaring disk-integrated soft X-ray emission (0.4 - 2.4 keV) of
about a factor 30 over its sunspot cycle. To date no cyclic variation
of that magnitude has been observed in other late-type stars. We
show that this negative result is partly explained by the inclusion of
EUV emission in stellar observations done with ROSAT: we calculated
what the solar signal would be if observed in the ROSAT passband and
found a cycle amplitude of a factor two to three. That leaves open
the question of the cycle amplitude in soft X-rays for solar-type
stars. To adress this we analysed ROSAT data for the energy band
above the C-K edge, but found no sufficiently frequent observations of
individual stars. The next best approach is to compare the measured soft
X-ray flux for singly observed stars with the average flux predicted
from the star's Rossby number: if cycles with amplitudes as large as
that of the Sun exist, the residual fluxes should be statistically
significant. From a sample of about 15 single and cyclic late-type
stars (as evidenced from Ca-K data) we find that with 99.6% certainty
the residual fluxes are due to X-ray cycles that are similar to or
greater than that of the Sun.

---------------------------------------------------------
Title: Exploring the use of VO to diagnose spot properties on M dwarfs
Authors: O'Neal, D.; Saar, S. H.; Neff, J. E.; Cuntz, M.
2005ESASP.560..853O Altcode: 2005csss...13..853O
No abstract at ADS

---------------------------------------------------------
Title: Testing the Reality of Strong Magnetic Fields on T Tauri Stars:
The Naked T Tauri Star Hubble 4
Authors: Johns-Krull, Christopher M.; Valenti, Jeff A.; Saar, Steven H.
2004ApJ...617.1204J Altcode: 2004astro.ph..9268J
High-resolution optical and infrared (IR) echelle spectra of the
naked (diskless) T Tauri star Hubble 4 are presented. The K-band IR
spectra include four Zeeman-sensitive Ti I lines along with several
magnetically insensitive CO lines. Detailed spectrum synthesis
combined with modern atmospheric models is used to fit the optical
spectra of Hubble 4 in order to determine its key stellar parameters:
Teff=4158+/-56 K; logg=3.61+/-0.50 [M/H]=-0.08+/-0.05
vsini=14.6+/-1.7 km s-1. These stellar parameters are used
to synthesize K-band spectra to compare with the observations. The
magnetically sensitive Ti I lines are all significantly broadened
relative to the lines produced in the nonmagnetic model, while the
magnetically insensitive CO lines are well matched by the basic
nonmagnetic model. Models with magnetic fields are synthesized and
fitted to the Ti I lines. The best-fit models indicate a distribution of
magnetic field strengths on the stellar surface characterized by a mean
magnetic field strength of 2.51+/-0.18 kG. The mean field is a factor
of 2.0 greater than the maximum field strength predicted by pressure
equipartition arguments. To confirm the reality of such strong fields,
we attempt to refit the observed profiles using a two-component magnetic
model in which the field strength is confined to the equipartition
value representing plagelike regions in one component and the field
is allowed to vary in a cooler component representing spots. It is
shown that such a model is inconsistent with the optical spectrum of
the TiO bandhead at 7055 Å.

---------------------------------------------------------
Title: Further Results of TiO-Band Observations of Starspots
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.; Cuntz,
Manfred
2004AJ....128.1802O Altcode:
We present measurements of starspot parameters (temperature and filling
factor) on five highly active stars, using absorption bands of TiO, from
observations made between 1998 March and 2001 December. We determined
starspot parameters by fitting TiO bands using spectra of inactive G and
K stars as proxies for the unspotted photospheres of the active stars
and spectra of M stars as proxies for the spots. For three evolved
RS CVn systems, we find spot filling factors between 0.28 and 0.42
for DM UMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri;
these values are similar to those found by other investigators using
photometry and Doppler imaging. Among active dwarfs, we measured a lower
spot temperature (3350 K) for EQ Vir than found in a previous study of
TiO bands, and for EK Dra a lower spot temperature (~3800 K) than found
through photometry. For all active stars but XX Tri, we achieved good
phase coverage through a stellar rotational period. We also present
our final, extensive grid of spot and nonspot proxy stars. This
paper includes data taken at McDonald Observatory of the University
of Texas at Austin.

---------------------------------------------------------
Title: Planet-Induced Activity Enhancements in the HD 179949 System
Authors: Saar, Steven
2004cxo..prop.1653S Altcode:
Many exoplanets are gas giants extremely close (&lt;0.1 AU)
to their parent stars, suggesting the possibility of exotic
interactions. Recently, weakly enhanced Ca II HK emission was found
in the HD 179949 system, phased to the orbital (~3 d) and not to the
stellar rotation period (~8 d). Theory suggests this enhancement is
due to a magnetic interaction (MI) between the star and planet. Since
the resulting heating should be largest in X-rays, we propose to study
the system with Chandra to further characterize the MI. We will use HST
to study the MI effect on the planet's ablating atmosphere by observing
Doppler shifted H~I around quadrature. These datasets will enable us to
test interaction theories, and estimate exoplanetary magnetic fields,
mass loss and stellar wind properties.

---------------------------------------------------------
Title: A Comparison of the Outer Atmosphere of the “Flat Activity”
Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V)
Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres,
Thomas R.
2004ApJ...609..392J Altcode:
Driven by the desire to understand the roles of acoustic and
magnetic mechanisms in heating the outer atmospheres of Sun-like
stars, we compare solar UV spectra with archival STIS spectra from
the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra
of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The
activity of τ Cet shows occasional rotational modulations but no
long-term cyclic variation. It may be in a phase analogous to the
solar Maunder minimum. Solar disk center intensities from both the
HRTS instrument and the SUMER instrument on SOHO were converted to
Sun-as-a-star fluxes by using center-to-limb data from Dammasch and
colleagues. The derived solar flux spectrum represents conditions
near the minimum of the solar magnetic activity cycle. We find that
the τ Cet line profiles differ systematically from those of the Sun
and α Cen A. While lines formed in the middle chromospheres appear
similar, the entire emission from the upper chromosphere to the middle
transition region of τ Cet has lower flux densities by factors of
~2, the line widths are significantly narrower, and, uniquely, the
transition region lines are not significantly redshifted. The soft
X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is
~9×103 ergs cm-2 s-1, several times
smaller than the median solar value. We also find that the UV spectrum
of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun
is in an intermediate phase of its activity cycle but that its coronal
emission may be somewhat smaller. We discuss the implications of these
results for magnetic fields and heating mechanisms in the stars and
speculate that τ Cet's UV spectrum might represent the solar spectrum
during a grand minimum phase.

---------------------------------------------------------
Title: Applying Zeeman Doppler imaging to solar spectra
Authors: Hussain, G. A. J.; Saar, S. H.; Collier Cameron, A.
2004AN....325..245H Altcode:
A new generation of spectro-polarimeters with high throughput
(e.g. CFHT/ESPADONS and LBT/PEPSI) is becoming available. This
opportunity can be exploited using Zeeman Doppler imaging (ZDI),
a technique that inverts time-series of Stokes V spectra to map
stellar surface magnetic fields (Semel 1989). ZDI is assisted by
“Least squares deconvolution” (LSD), which sums up the signal from
1000's of photospheric lines to produce a mean deconvolved profile
with higher S:N (Donati &amp; Collier Cameron 1997).

---------------------------------------------------------
Title: Searching for Planets in the Hyades. III. The Quest for
Short-Period Planets
Authors: Paulson, Diane B.; Saar, Steven H.; Cochran, William D.;
Henry, Gregory W.
2004AJ....127.1644P Altcode: 2003astro.ph.12122P
We have been using the Keck I High Resolution Spectrograph to search
for planetary companions in the Hyades cluster. We selected four stars
from this sample that showed significant radial velocity variability on
short timescales to search for short-period planetary companions. The
radial velocities of these four stars were monitored regularly with the
Hobby-Eberly Telescope for approximately 2 months, while sparse data
were also taken over ~4 months: we also obtained near-simultaneous
photometric observations with one of the automatic photoelectric
telescopes at Fairborn Observatory. For three of the stars, we detect
photometric variability with the same period present in the radial
velocity (vr) measurements, compatible with the expected
rotation rates for Hyades members. The fourth star continues to show
vr variations and minimal photometric variability but with
no significant periodicity. This study shows that for the three stars
with periodic behavior, a significant portion of the vr
fluctuations are likely due primarily to magnetic activity modulated
by stellar rotation rather than planetary companions. Using simple
models for the vr perturbations arising from spot and plage,
we demonstrate that both are likely to contribute to the observed
vr variations. Thus, simultaneous monitoring of photometric
(photospheric) and spectroscopic (chromospheric) variations is essential
for identifying the cause of Doppler-shifted absorption lines in
more active stars. Some data were obtained with the Hobby-Eberly
Telescope (HET). The HET is operated by McDonald Observatory on behalf
of The University of Texas at Austin, the Pennsylvania State University,
Stanford University, Ludwig-Maximilians-Universität München, and
Georg-August-Universität Göttingen. Additional data presented
herein were obtained at the W.M. Keck Observatory, which is operated as
a scientific partnership among the California Institute of Technology,
the University of California, and the National Aeronautics and Space
Administration (NASA). The Observatory was made possible by the generous
financial support of the W.M. Keck Foundation.

---------------------------------------------------------
Title: Molecular Band Proxies, Model Atmospheres, and Line Depth
Ratios: Comparing Three Methods of Measuring Starspot Parameters on
Highly Active Stars
Authors: O'Neal, D.; Saar, S.; Aufdenberg, J.; Neff, J. E.
2004IAUS..219..957O Altcode: 2003IAUS..219E.135O
In recent years various techniques have been developed to measure the
temperatures and areas of dark cool starspots on magnetically active
stars. We present comparisons among results obtained by applying
three such techniques to the same data sets. The three methods are
(1) fitting TiO-band spectra using spectra of proxy stars (2) fitting
TiO-band spectra using model atmospheres and (3) fitting spectral line
depth ratios. We investigate differences among results obtained by
using each of these methods to compute starspot parameters of several
active spotted stars.

---------------------------------------------------------
Title: Coronal X-Ray Spectroscopy of Solar Analogs
Authors: Telleschi, A.; Güdel, M.; Arzner, K.; Briggs, K.; Audard,
M.; Ness, J. -U.; Mewe, R.; Raassen, A. J.; Skinner, S. L.; Cuntz,
M.; Saar, S.
2004IAUS..219..930T Altcode: 2003IAUS..219E.203T
We present an X-ray study of a series of solar-mass main-sequence stars
with different ages based on data from XMM-Newton and Chandra. This
investigation aims at a closer understanding of the physical mechanisms
of heating and mass transport in magnetically active stars. All targets
are proxies of the Sun that essentially differ only in their rotation
periods and hence in the efficiency of the magnetic dynamo. We present
a spectral analysis that constrains the average elemental composition
and the thermal structure of the coronae at different stages of
their evolution. Further we use the He-like line triplets to derive
characteristic coronal densities and investigate the time variability
in the X-ray light curves. We discuss implications for models related
to heating physics and coronal structure.

---------------------------------------------------------
Title: Stellar Activity Enhancement by Planets: Theory and
Observations
Authors: Saar, S. H.; Cuntz, M.; Shkolnik, E.
2004IAUS..219..355S Altcode: 2003IAUS..219E.119S
Many of the newly discovered exoplanets are apparently gas giants
in close proximity to their parent stars. They therefore raise
tides on their host stars and (if similar to Jupiter) will likely
have substantial magnetospheres which can interact with stellar
fields. Both tidal and magnetospheric interactions can enhance
stellar activity levels. An initial search for such planet-induced
activity using the Ca II IR triplet found no signal but recently
a more sensitive study using the Ca II H and K lines has uncovered
evidence for planet-enhanced emission on HD 179949 and hints of it
in other systems. The phase dependence of the enhanced emission for
HD 179949 suggests a magnetospheric interaction. We discuss a simple
model for this interaction the implications of this possible detection
for diagnosing exoplanetary magnetospheres and future observations.

---------------------------------------------------------
Title: STIS Far UV Studies of Spatial and Temporal Activity Variations
in YY Gem
Authors: Saar, S. H.; Bookbinder, J. A.
2003csss...12.1020S Altcode:
We analyze STIS data of the eclipsing dM0e+dM0e system YY Gem, finding
a spatially variable quiescent level, frequent and sometimes periodic
flaring, and evidence for a spatially extended transition region.

---------------------------------------------------------
Title: Terrestrial planets around M dwarfs via precise radial
velocities. VLT+UVES observations of Barnard's star = GJ 699
Authors: Kürster, Martin; Endl, Michael; Rouesnel, Frederic; Els,
Sebastian; Kaufer, Andreas; Brillant, Stephane; Hatzes, Artie P.;
Saar, Steven H.; Cochran, William D.
2003ESASP.539..485K Altcode: 2003toed.conf..485K
We report on results from a program carried out at the VLT+UVES
in search for terrestrial planets around M dwarf stars with precise
radial velocities (RVs). Because of the small mass of M dwarfs planets
with a few Earth masses and orbital periods of a few days to weeks
can cause RV signals that are detectable with the currently achieved
precision of RV surveys of a few m s-1. As an example we
present our results for Barnard's star (M = 0.16 Msolar)
where we detect the RV secular acceleration as well as variability
related to stellar activity. We determine upper limits to the projected
mass m sin i of hypothetical planetary companions finding that we can
exclude planets with m sin i &gt; 7.5 MEarth in circular
orbits throughout the habitable zone of the star, i.e. at separations
of 0.034 - 0.082 AU. Over the total range of separations accessible
to our data set, i.e. 0.017 - 0.98 AU we exclude planets m sin i
&gt; 0.12 MJupiter. The lowest upper limit is found at
an orbital period of 2.5 d (separation 0.020 AU) with m sin i = 2.9
MEarth. We also find an anti-correlation of the RV data
with an index that measure the filling-in by emission of the core
of the Hα line in the sense that the measured RVs become
bluer when the Hα emission component becomes stronger.

---------------------------------------------------------
Title: Stellar Intrinsic Radial Velocity Noise: Causes and Possible
Cures
Authors: Saar, S. H.; Hatzes, A.; Cochran, W.; Paulson, D.
2003csss...12..694S Altcode:
We explore the causes and test some possible cures for stellar intrinsic
radial velocity noise caused by magnetic activity.

---------------------------------------------------------
Title: Whirling Dervish Dynamos: Magnetic Activity in CV Secondaries
Authors: Saar, Steven
2003hst..prop.9852S Altcode:
The mass-losing secondary stars of cataclysmic variables {CVs}
are the most rapidly rotating cool dwarfs observable. Other rapid
rotators show a maximal, "saturated" level of magnetic activity {e.g.,
X-ray emission}, but there are hints from contact binaries and young
clusters that activity may be suppressed at the highest rotation
rates. CV secondaries are thus important probes of magnetic dynamos at
rotational extremes. Implications for CV evolution {e.g., the “period
gap", accretion variability} may also be profound. Unfortunately,
study of CV secondaries is hampered by pesky accretion-related
phenomena and reflection effects. As a result, little systematic
work has been done. To explore activity in these stars, we therefore
propose to study far-UV spectra of AM Her-type systems {which have no
accretion disks} in deep photometric minima in which accretion is shut
off. Magnetic-related emission from the secondary will be separated
{in velocity} from residual accretion emission by observations near
quadratures. Lower chromospheric irradiation due to the white dwarf
primary will be removed by modeling, yielding the true level of magnetic
activity on the secondary. We will compare the results to other dMe
stars and draw implications for magnetic dynamos and activity at
rotational extremes, and for CV evolution and behavior.

---------------------------------------------------------
Title: The low-level radial velocity variability in Barnard's
star (= GJ 699). Secular acceleration, indications for convective
redshift, and planet mass limits
Authors: Kürster, M.; Endl, M.; Rouesnel, F.; Els, S.; Kaufer, A.;
Brillant, S.; Hatzes, A. P.; Saar, S. H.; Cochran, W. D.
2003A&A...403.1077K Altcode: 2003astro.ph..3528K
We report results from 2 1/2 yr of high precision radial velocity
(RV) monitoring of Barnard's star. The high RV measurement precision
of the VLT-UT2+UVES of 2.65 m s-1 made the following
findings possible. (1) The first detection of the change in the RV of
a star caused by its space motion (RV secular acceleration). (2) An
anti-correlation of the measured RV with the strength of the filling-in
of the H_alpha line by emission. (3) Very stringent mass upper limits
to planetary companions. Using only data from the first 2 years, we
obtain a best-fit value for the RV secular acceleration of 5.15+/-
0.89 m s-1 yr-1. This agrees within 0.95sigma
with the predicted value of 4.50 m s-1 yr-1
based on the Hipparcos proper motion and parallax combined with the
known absolute radial velocity of the star. When the RV data of the
last half-year are added the best-fit slope is strongly reduced to
2.97+/- 0.51 m s-1 yr-1 (3.0sigma away from
the predicted value), clearly suggesting the presence of additional
RV variability in the star. Part of it can be attributed to stellar
activity as we demonstrate by correlating the residual RVs with an
index that describes the filling-in of the H_alpha line by emission. A
correlation coefficient of -0.50 indicates that the appearance of active
regions causes a blueshift of photospheric absorption lines. Assuming
that active regions basically inhibit convection we discuss the
possibility that the fundamental (inactive) convection pattern in this
M4V star produces a convective redshift which would indicate that the
majority of the absorption lines relevant for our RV measurements
is formed in a region of convective overshoot. This interpretation
could possibly extend a trend indicated in the behaviour of earlier
spectral types that exhibit convective blueshift, but with decreasing
line asymmetries and blueshifts as one goes from G to K dwarfs. Based
on this assumption, we estimate that the variation of the visible
plage coverage is about 20%. We also determine upper limits to the
projected mass msin i and to the true mass m of hypothetical planetary
companions in circular orbits. For the separation range 0.017-0.98
AU we exclude any planet with msin i&gt; 0.12 MJupiter and
m&gt; 0.86 MJupiter. Throughout the habitable zone around
Barnard's star, i.e. 0.034-0.082 AU, we exclude planets with msin i&gt;
7.5 MEarth and m&gt; 3.1 MNeptune. Based on
observations collected at the European Southern Observatory, Paranal,
Chile (ESO programmes 65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415,
and 69.C-0722).

---------------------------------------------------------
Title: V471 Tau: mapping magnetic activity in a pre-CV binary system.
Authors: Hussain, G. A. J.; Allende Prieto, C.; Saar, S. H.; Collier
Cameron, A.; Still, M. D.
2003AAS...202.0804H Altcode: 2003BAAS...35..708H; 2003AAS...202..804H
The technique of Doppler imaging enables us to map starspots at the
surfaces of rapidly rotating cool stars. Starspots are probes of
magnetic activity, thus the locations of these spots also indicate
where the strongest magnetic fields tend to emerge. We present surface
spot maps of the K2V component of V471 Tau from 2001-2002. Our spot
maps can be used (a) to show that magnetic activity is confined to
high latitude regions in the K2V component, (b) to measure surface
differential rotation of this component and (c) to evaluate spot
lifetimes in rapid rotators. We conclude that the K2V component of
V471 Tau shows a similar equator-pole lap-time as the Sun and that
its surface spots last on the order of months.

---------------------------------------------------------
Title: XMM-Newton Proposal 02057202
Authors: Saar, Steven
2003xmm..prop..299S Altcode:
We propose to study the weak coronae of "flat activity" stars -
objects with very low, nearly constant chromospheric emission. There
is evidence that in many cases, these coronae are powered by magnetic
fields from the residual turbulent dynamo left while the star's cyclic
dynamo is in a temporary Maunder-like magnetic minimum. These stars
permit us to 1) study the weakest and likely least complex coronae, 2)
investigate the coronal product of a turbulent dynamo in a solar mass
star, and 3) explore (by proxy) the properties of the solar corona in
a Maunder-like minimum.

---------------------------------------------------------
Title: Applying Zeeman Doppler Imaging to Solar Spectra
Authors: Hussain, Gaitee A.; Saar, Steven H.; Collier Cameron, Andrew
2003IAUJD...9E..26H Altcode:
Advances in instrumentation have led to the development of a new
generation of spectro-polarimeters that have a high throughput
(e.g. CFHT/ESPADONS). These spectro-polarimeters will enable us to
analyse magnetic field configurations on a wide variety of stellar
systems. The technique of Zeeman Doppler imaging is an invaluable
tool which inverts a time-series of circularly polarized spectra to
map surface magnetic fields on rapidly rotating stars. Zeeman Doppler
imaging is greatly assisted by least squares deconvolution a technique
that ""sums up"" the signal from thousands of lines in order to boost
the S:N in a mean deconvolved profile. We test these techniques by
applying them to circularly polarized spectra of magnetic features on
the solar surface. The assumptions inherent in standard Zeeman Doppler
imaging: the weak field regime classical Zeeman splitting and that
line profiles are additive are addressed here.

---------------------------------------------------------
Title: Uses of Linear Polarization as a Probe of Extrasolar Planet
Atmospheres
Authors: Saar, S. H.; Seager, S.
2003ASPC..294..529S Altcode: 2003astro.ph..5436S
We point out some advantages of making observations of extrasolar
planets in linearly polarized (LP) light. Older cool stars have quite
low levels (∼ 10-4 to 10-5) of fractional
LP, while extrasolar planets can have relatively high fractional
LP (∼ 0.1). Observations in LP light can therefore significantly
enhance contrast between the planet and its parent star. Data on LP
as a function of planetary orbital phase can be used to diagnose the
properties (e.g., composition, size, and shape) of the scatterers in
the planetary atmosphere. We discuss the feasibility of LP observations
of extrasolar planets.

---------------------------------------------------------
Title: The Effects of Plage on Precision Radial Velocities
Authors: Saar, S. H.
2003ASPC..294...65S Altcode:
I present the first results of semi-empirical modeling of the effects
of magnetic plage on measured radial velocities in G stars. I use solar
line bisectors observed in quiet and active regions at a range of disk
positions as proxies for stellar bisectors. These are then used to
"warp" model line profiles and construct model stars with various
V sin i and plage areas. The models predict the sun should show a
maximum of 10 m/sec short-term RV fluctuations atop approx. 3 m/sec
long-term (cyclic) modulation, while a Hyades age G dwarf with V sin i =
6 km/sec exhibits approx. 90 m/sec (short-term) atop approx. 14 m/sec
(long-term).

---------------------------------------------------------
Title: Stellar Dynamos: Scaling Laws and Coronal Connections
Authors: Saar, S.
2002ASPC..277..311S Altcode: 2002sccx.conf..311S
No abstract at ADS

---------------------------------------------------------
Title: A Lot of Observations of the Coronae of AR Lac
Authors: Pease, D.; Drake, J. J.; Kashyap, V.; Ratzlaff, P. W.; Saar,
S.; Haisch, B.; Dobrzycki, A.; Adams, N. R.; Wolk, S. J.
2002ASPC..277..551P Altcode: 2002sccx.conf..551P
No abstract at ADS

---------------------------------------------------------
Title: Exploring the Role of Acoustic Heating in Cool Dwarfs and
Subgiants
Authors: Saar, Steven
2002hst..prop.9464S Altcode: 2002hst..prop.5811S
Recent observations cast doubt on the importance of acoustic waves
for chromospheric heating in stars. These include low upper limits
to their contribution to upper layers of the solar chromosphere,
and evidence for significant magnetic heating contribution even in
“basal" activity stars. These findings contradict the widely accepted
picture that acoustic heating accounts for a significant fraction, the
“basal component”, of chromospheric heating in inactive stars. To help
resolve this issue, we propose to observe two very inactive stars with
significantly different properties to search for specific signatures of
upward propagating acoustic waves: blue-shifts and enhanced blue wings
in chromospheric lines. Solar data show that the degree of blue-shift
can be used to estimate the acoustic contribution to chromospheric
heating. We will compare the data to HST spectra of similar stars, and
solar spectra from the SUMER instrument on SOHO. Lack of a significant
acoustic signature in our targets would indicate that magnetic heating
generated by a local {turbulent, non-cycling} dynamo is responsible
for the basal component of chromospheric heating in inactive stars. Our
targets may be in a phase analogous to the solar Maunder minimum, and
the HST spectra might serve as a proxy for the solar spectrum in this
state. The spectra will also be used for emission measure analysis
differentially between the Sun and solar-like stars.

---------------------------------------------------------
Title: A new look at dynamo cycle amplitudes
Authors: Saar, S. H.; Brandenburg, A.
2002AN....323..357S Altcode: 2002astro.ph..7392S
We explore the dependence of the amplitude of stellar dynamo cycle
variability (as seen in the Mount Wilson Ca II HK timeseries data) on
other stellar parameters. We find that the fractional cycle amplitude
A_cyc (i.e. the ratio of the peak-to-peak variation to the average)
decreases somewhat with mean activity, increases with decreasing
effective temperature, but is not correlated with inverse Rossby
number Ro-1. We find that A_cyc increases with the ratio
of cycle and rotational frequencies omega_cyc /Omega along two, nearly
parallel branches.

---------------------------------------------------------
Title: Searching for Planets in the Hyades. II. Some Implications
of Stellar Magnetic Activity
Authors: Paulson, Diane B.; Saar, Steven H.; Cochran, William D.;
Hatzes, Artie P.
2002AJ....124..572P Altcode: 2002astro.ph..4216P
The Hyades constitute a homogeneous sample of stars ideal for
investigating the dependence of planet formation on the mass of the
central star. Because of their youth, Hyades members are much more
chromospherically active than stars traditionally surveyed for planets
using high-precision radial velocity techniques. Therefore, we have
conducted a detailed investigation of whether magnetic activity of our
Hyades target stars will interfere with our ability to make precise
radial velocity (vrad) searches for substellar companions. We
measure chromospheric activity (which we take as a proxy for magnetic
activity) by computing the equivalent of the R'HK
activity index (which is corrected for photospheric contributions) from
the Ca II K line. The value of &lt;R'HK&gt; is
not constant in the Hyades: we confirm that it decreases with increasing
temperature in the F stars and also find it decreases for stars cooler
than mid K. We examine correlations between simultaneously measured
R'HK and radial velocities using both a classical
statistical test and a Bayesian odds ratio test. We find that there is
a significant correlation between R'HK and the
radial velocity in only five of the 82 stars in this sample. Thus,
simple R'HK-vrad correlations will
generally not be effective in correcting the measured vrad
values for the effects of magnetic activity in the Hyades. We argue
that this implies long-timescale activity variations (of order a few
years; i.e., magnetic cycles or growth and decay of plage regions)
will not significantly hinder our search for planets in the Hyades
if the stars are closely monitored for chromospheric activity. The
trends in the radial velocity scatter (σ'v)
with &lt;R'HK&gt;, vsini, and Prot
for our stars is generally consistent with those found in field
stars in the Lick planet search data, with the notable exception
of a shallower dependence of σ'v on
&lt;R'HK&gt; for F stars. Data presented herein
were obtained at the W.M. Keck Observatory, which is operated as a
scientific partnership among the California Institute of Technology,
the University of California, and the National Aeronautics and Space
Administration. The Observatory was made possible by the generous
financial support of the W.M. Keck Foundation.

---------------------------------------------------------
Title: Origins of Solar Systems: Removing Activity-Related Radial
Velocity Noise To Improve Extrasolar Planet Searches
Authors: Saar, Steven
2002STIN...0244043S Altcode:
We have continued the super high resolution (R is approximately
200,000), high S/N ((greater than) 300) echelle study of joint line
bisector and radial velocity variations using the McDonald 2-D (two
dimensional) coude. Observing runs in October 2000 and March 2001 were
plagued by poor weather, but runs in June and October 2001 were good. We
have made a preliminary analysis of the limited data in hand, and find
some tantalizing evidence for correlations between median line bisector
displacement and radial velocity v r. The correlation appears
to be specific to the particular star being considered, probably since
it is a function of both spectral type and rotation rate.

---------------------------------------------------------
Title: Hydroxyl 1.563 Micron Absorption from Starspots on Active Stars
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.; Mines,
Jonathan K.
2001AJ....122.1954O Altcode:
We present results from a study of starspots on active stars using a
pair of vibrational-rotational absorption lines of the OH molecule near
1.563 μm. We detect excess OH absorption due to dark, cool starspots
on several active stars of the RS CVn and BY Dra classes. Our results
for the single-lined spectroscopic binaries II Pegasi, V1762 Cygni,
and λ Andromedae augment those from a previous study that used a less
sensitive detector. In this study, we were able for the first time to
use molecular absorption features to measure starspot properties on
double-lined spectroscopic binaries. Measuring the equivalent widths
of these OH lines in inactive giant and dwarf stars of spectral types
G, K, and M, we find that the total equivalent width of the line pair
increases approximately linearly as effective temperature decreases
from 5000 to 3000 K. We measure starspot filling factors by fitting
the spectra of active stars with linear combinations of comparison
star spectra representing the spot and nonspot regions of the star.

---------------------------------------------------------
Title: A search for Ca II emission enhancement in stars resulting
from nearby giant planets
Authors: Saar, S. H.; Cuntz, M.
2001MNRAS.325...55S Altcode:
We present a search for periodicities (Pchr) in the
chromospheric Caii infrared triplet emission of several stars
(τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, 70 Vir and
GL 876) which may be directly attributable to interaction with
close-in giant planets. Activity enhancements could arise from
increased non-radiative heating and dynamo action in planet-induced
tidal bulges (with Pchr~Porb/2), or from
interactions between the stellar and planetary magnetic fields (with
Pchr~Porb). We compare both Pchr
and the phase dependence of the activity with the planetary orbital
period Porb, the orbital phase, and models. No significant
Pchr or phase dependence attributable to planets can be
clearly identified. We place approximate upper limits on the amplitude
of any planet-induced activity. We identify a possible stellar rotation
period for GL 876, and support previous period determinations for
four other stars. We discuss the results and possible directions of
future research.

---------------------------------------------------------
Title: Extensive serendipitous X-ray coverage of a flare star
with ROSAT
Authors: Silverman, J. D.; Eriksen, K. A.; Green, P. J.; Saar, S. H.
2001MNRAS.323..577S Altcode: 2000astro.ph.11027S
We report the serendipitous discovery of a flare star observed
with the ROSAT X-ray observatory. From optical spectra, which show
strong and variable emission lines of the hydrogen Balmer series
and neutral helium, we classify this object as a M3.0Ve star, and
estimate a distance of 52pc from published photometry. Owing to the
close proximity of the star (13.6arcmin) to the calibration source
and RS CVn binary AR Lacertae, long-term X-ray coverage is available
in the ROSAT archive (~50h spanning 6.5yr). Two large flare events
occurred early in the mission (1990 June-July), and the end of a
third flare was detected in 1996 June. One flare, observed with
the Position Sensitive Proportional Counter (PSPC), had a peak
luminosity LX=1.1×1030ergs-1,
an e-folding rise time of 2.2h and a decay time of 7h. This decay
time is one of the longest detected on a dMe star, providing
evidence for the possibility of additional heating during the
decay phase. A large High Resolution Imager (HRI) flare (peak
LX=2.9×1030ergs-1) is also
studied. The `background' X-ray emission is also variable - evidence
for low-level flaring or microflaring. We find that &gt;=59 per cent
of the HRI counts and &gt;=68 per cent of the PSPC counts are caused
by flares. At least 41 per cent of the HRI exposure time and 47 per
cent of the PSPC are affected by detectable flare enhancement.

---------------------------------------------------------
Title: Further Analysis of Stellar Magnetic Cycle Periods
Authors: Saar, S.; Brandenburg, A.
2001ASPC..248..231S Altcode: 2001astro.ph..5070S; 2001mfah.conf..231S
We further investigate relationships between activity cycle periods in
cool stars and rotation to include new cycle data, and explore different
parameterizations of the problem. We find that relations between cycle
and rotational frequencies (omega_cyc vs. Omega) and between their
ratio and the inverse Rossby number (omega_cyc/Omega vs. Ro^{-1})
show many similarities, including three branches and similar rms
scatter. We briefly discuss some implications for dynamo models.

---------------------------------------------------------
Title: Magnetic Fields in Cool Stars (CD-ROM Directory:
contribs/moreno)
Authors: Moreno Insertis, F.; Saar, S. H.; Solanki, S. K.
2001ASPC..223..435M Altcode: 2001csss...11..435M
No abstract at ADS

---------------------------------------------------------
Title: Stellar Dynamos: A Modeling Perspective
Authors: Charbonneau, P.; Saar, S. H.
2001ASPC..248..189C Altcode: 2001mfah.conf..189C
No abstract at ADS

---------------------------------------------------------
Title: Recent Measurements of (and Inferences About) Magnetic Fields
on K and M Stars (CD-ROM Directory: contribs/saar1)
Authors: Saar, S. H.
2001ASPC..223..292S Altcode: 2001csss...11..292S
No abstract at ADS

---------------------------------------------------------
Title: Correcting High Precision Radial Velocities for the Effects
of Stellar Magnetic Activity (CD-ROM Directory: contribs/saar2)
Authors: Saar, S. H.; Fischer, D.; Snyder, N.; Smolec, R.
2001ASPC..223.1051S Altcode: 2001csss...11.1051S
No abstract at ADS

---------------------------------------------------------
Title: New Measurements of Magnetic Fields on T Tauri Stars (CD-ROM
Directory: contribs/krull)
Authors: Johns-Krull, C. M.; Valenti, J. A.; Saar, S. H.; Hatzes, A. P.
2001ASPC..223..521J Altcode: 2001csss...11..521J
No abstract at ADS

---------------------------------------------------------
Title: Self-Consistent Magnetic/Acoustic Chromosphere Models of
Late-Type Stars (CD-ROM Directory: contribs/cuntz1)
Authors: Cuntz, M.; Ulmschneider, P.; Rammacher, W.; Musielak, Z. E.;
Saar, S. H.
2001ASPC..223..913C Altcode: 2001csss...11..913C
No abstract at ADS

---------------------------------------------------------
Title: New Measurements of T Tauri Magnetic Fields: Testing
Magnetospheric Accretion
Authors: Johns-Krull, C. M.; Valenti, J. A.; Piskunov, N. E.; Saar,
S. H.; Hatzes, A. P.
2001ASPC..248..527J Altcode: 2001mfah.conf..527J
No abstract at ADS

---------------------------------------------------------
Title: Starspot Temperature and Filling Factor Measurements for
Active Dwarfs (CD-ROM Directory: contribs/saar3)
Authors: Saar, S. H.; Peterchev, A.; O'Neal, D.; Neff, J. E.
2001ASPC..223.1057S Altcode: 2001csss...11.1057S
No abstract at ADS

---------------------------------------------------------
Title: Analyzing the Effects of Planets and Brown Dwarfs on Stellar
Chromospheric and Coronal Activity (CD-ROM Directory: contribs/cuntz2)
Authors: Cuntz, M.; Musielak, Z. E.; Saar, S. H.
2001ASPC..223.1528C Altcode: 2001csss...11.1528C
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Cycles and Activity in FGK Stars in the Framework
of Babcock-Leighton Dynamos
Authors: Dikpati, M.; Saar, S. H.; Brummell, N.; Charbonneau, P.
2001ASPC..248..235D Altcode: 2001mfah.conf..235D
No abstract at ADS

---------------------------------------------------------
Title: Effects of Stellar Magnetic Activity on High Resolution Line
Profiles and Radial Velocity Measurements.
Authors: Pearson, N. S.; Saar, S. H.; Hatzes, A. P.; Paulsen, D.
2000AAS...197.1107P Altcode: 2000BAAS...32.1417P
We study very high resolution (λ /Δ λ ≈ 200,000), high S/N
(350 - 550) echelle spectra of five G to early K type stars (β Com,
ɛ Eri, 61 UMa, 59 Vir, and ξ Boo A) and construct bisectors for ~30
unblended Fe I absorption lines in each. We collate the bisectors into
subgroups based upon absorption line depth and excitation potential,
calculate many statistical measures of the bisector position and
shape, and average these measurements over the subgroups. We then
search for relationships between the averaged bisector properties
and various stellar properties, such as temperature, activity and v\
sin\ i; several significant trends are found. We investigate how the
bisectors change over time with relation to stellar properties in an
effort to find trends between the bisector properties, stellar magnetic
surface features, and apparent radial velocity (vr). Such
correlations would allow for the correction of some of the scatter
in measurements of the vr, permitting easier detection of
sub-jovian exoplanets. We find changes in certain bisector measures to
be well correlated with vr changes. This work was supported
by National Science Foundation grant AST-9731652.

---------------------------------------------------------
Title: When the Dynamo SPUTTERS:THE Corona of a AN Extremely Inactive
(maunder MINIMUM?) Star
Authors: Saar, Steven
2000cxo..prop..558S Altcode: 2000cxo..prop..427S; 2000chan.prop..427S
The Wilson survey identified a group of stars with very low level,
near-constant Ca II emission. Weak UV and Xray emission in a few of
these stars implies that magnetic heating from a residual (probably
turbulent) dynamo still operates. Many of these stars are likely in the
stellar analog of the Maunder minimum - a period when the normal cyclic
dynamo of the sun was in quiescence. We propose to study the brightest
of these stars with Chandra. The stars present a unique opportunity
to 1) study the properties of the weakest dwarf star coronae, 2) to
investigate the coronal product of a predominantly turbulent dynamo
in a high mass star, exploring its dependence on rotation and mass,
and 3) to potentially study (indirectly) the properties of the solar
corona during magnetic minima.

---------------------------------------------------------
Title: Correcting Radial Velocities for Long-Term Magnetic Activity
Variations
Authors: Saar, Steven H.; Fischer, Debra
2000ApJ...534L.105S Altcode:
We study stars in the Lick planetary survey for correlations
between simultaneous measurements of high-precision radial velocities
vr and magnetic activity (as measured in an SIR
emission index from Ca II λ8662). We find significant correlations in
~30% of the stars. After removing linear trends between SIR
and vr, we find that the dispersion in vr in these
stars is decreased by an average of 17%, or ~45% of the dispersion
above the measurement noise. F stars and less active stars with
variable Ca II H and K lines are the most successfully corrected. The
magnitude of the slope of the SIR versus vr
relations increases proportional to vsini and (excepting M dwarfs)
tends to decrease with decreasing Teff. We argue that the
main cause of these effects is modification of the mean line bisector
shape brought on by long-term, magnetic activity-induced changes in
the surface brightness and convective patterns. The correlations can
be used to partially correct vr data for the effects of
long-term activity variations, potentially permitting study of planets
around some (higher mass) younger stars and planets producing smaller
stellar reflex velocities.

---------------------------------------------------------
Title: Making Sense of Stellar Activity Cycle Periods
Authors: Saar, S. H.
2000SPD....31.1001S Altcode: 2000BAAS...32Q.842S
I explore relationships between the magnetic activity cycle frequency
ωcyc, the rotational frequency Ω , and other stellar
properties in a large sample of dwarfs, evolved stars, active
binaries, and the secondaries of CV systems. The cycles are derived
from various sources, including periodicities in Ca ii, photometry,
and orbital period changes. Dimensional (ωcyc vs. Ω ) and
non-dimensional (ωcyc/Ω vs. Ro-1; where Ro is
the Rossby number) parameterizations give similar results. Stars are
concentrated on three main “branches" with different relationships
between ωcyc and Ω ; the branches may converge at
very short Ω . The oldest, lowest activity stars tend to occupy
the branch with the highest ωcyc. Some stars have
additional secondary ωcyc (perhaps analogous to the Sun's
“Gleissberg" cycle) lying on other branches; the preferred branch
of the primary ωcyc may be mass and Ω dependent. The
density of stars along each branch also depends on Ω and hence age,
indicating ωcyc evolves in time, but in a complex, sometimes
multi-valued fashion. I discuss some possible implications for dynamo
theory and evolution. This work is supported by NSF grant AST-9528563.

---------------------------------------------------------
Title: Observations of Magnetically Active Binary Stars using Phoenix
Authors: O'Neal, D.; Mines, J. K.; Neff, J. E.; Saar, S. H.
2000AAS...196.0514O Altcode: 2000BAAS...32..683O
We present observations of several magnetically-active, post-main
sequence binary systems (all of the RS CVn class) obtained with the
NOAO Phoenix Infrared Spectrograph. Our high-resolution spectra are
centered on the 6397cm-1 (1.563μ m) lines of OH. These
lines are temperature-sensitive and thus are a good diagnostic of the
area coverage of dark, cool starspots on the stars (O'Neal and Neff
1997). Our new observations, using Phoenix, are of higher resolution
and greater signal-to-noise than those we presented previously. By
modeling the active stars as the sum of an inactive comparison star (to
represent the active star's photosphere)and an M star (to represent
the spots), we measure starspot filling factors on II Peg, V1762
Cyg, σ Gem, and λ And. We find filling factors similar to those
we previously measured for the same stars using TiO bands. We also
(for the first time) fit the spectra of double-lined binary stars
with this technique, enabling us to determine the level of starspot
coverage on the active components. Our spectra also contain the highly
Zeeman-sensitive (g=3) Fe I 6388cm-1 line; analysis of
this feature enables us to measure the mean field strength and area
filling factor of the magnetic regions of the active stars. In the
future we will apply Doppler imaging techniques, adapted to our H-band
spectra, to our observations in order to derive images of the starspot
distributions. The authors were guest observers at Kitt Peak National
Observatory, National Optical Astronomy Observatories.

---------------------------------------------------------
Title: On Stellar Activity Enhancement Due to Interactions with
Extrasolar Giant Planets
Authors: Cuntz, Manfred; Saar, Steven H.; Musielak, Zdzislaw E.
2000ApJ...533L.151C Altcode:
We present a first attempt to identify and quantify possible
interactions between recently discovered extrasolar giant planets
(and brown dwarfs) and their host stars, resulting in activity
enhancement in the stellar outer atmospheres. Many extrasolar planets
have masses comparable to or larger than Jupiter and are within a
distance of 0.5 AU, suggesting the possibility of their significant
influence on stellar winds, coronae, and even chromospheres. Beyond
the well-known rotational synchronization, the interactions include
tidal effects (in which enhanced flows and turbulence in the tidal
bulge lead to increased magnetoacoustic heating and dynamo action)
and direct magnetic interaction between the stellar and planetary
magnetic fields. We discuss relevant parameters for selected systems
and give preliminary estimates of the relative interaction strengths.

---------------------------------------------------------
Title: Dynamo mechanisms
Authors: Brandenburg, A.; Saar, S. H.
2000ASPC..198..381B Altcode: 2000scac.conf..381B
No abstract at ADS

---------------------------------------------------------
Title: Time Evolution of the Magnetic Activity Cycle
Period. II. Results for an Expanded Stellar Sample
Authors: Saar, Steven H.; Brandenburg, Axel
1999ApJ...524..295S Altcode:
We further explore nondimensional relationships between the
magnetic dynamo cycle period Pcyc, the rotational period
Prot, the activity level (as observed in Ca II HK), and
other stellar properties by expanding the stellar sample studied in
the first paper in this series. We do this by adding photometric
and other cycles seen in active stars and the secondaries of CV
systems and by selectively adding less certain cycles from the Mount
Wilson HK survey; evolved stars, long-term HK trends and secondary
Pcyc are also considered. We confirm that most stars with
age t&gt;~0.1 Gyr occupy two roughly parallel branches, separated
by a factor of ~6 in Pcyc, with the ratio of cycle and
rotational frequencies ωcyc/Ω~Ro-0.5, where
Ro is the Rossby number. Using the model of the first paper in this
series, this result implies that the α effect increases with mean
magnetic field (contrary to the traditional α-quenching concept)
and that α and ωcyc decrease with t. Stars are not
strictly segregated onto one or the other branch by activity level,
though the high-ωcyc/Ω branch is primarily composed of
inactive stars. The expanded data set suggests that for t&gt;~1 Gyr,
stars can have cycles on one or both branches, though among older
stars, those with higher (lower) mass tend to have their primary
Pcyc on the lower (upper) ωcyc/Ω branch. The
Sun's ~80 yr Gleissberg cycle agrees with this scenario, suggesting that
long-term activity “trends” in many stars may be segments of long
(Pcyc~50-100 yr) cycles not yet resolved by the data. Most
very active stars (Prot&lt;3 days) appear to occupy a new,
third branch with ωcyc/Ω~Ro0.4. Many RS CVn
variables lie in a transition region between the two most active
branches. We compare our results with various models, discuss their
implications for dynamo theory and evolution, and use them to predict
Pcyc for three groups: stars with long-term HK trends,
stars in young open clusters, and stars that may be in Maunder-like
magnetic minima.

---------------------------------------------------------
Title: Line Bisector Variability in Active Dwarfs and its Relationship
to Radial Velocity Variations
Authors: Saar, S. H.; Snyder, N.
1999AAS...19410502S Altcode:
We study absorption line bisectors as diagnostics of the non-uniform
spatial and temporal properties of active, cool dwarf stars. We analyze
high resolution (lambda /Delta lambda ~ 125,000), high signal-to-noise
(200 &lt;= S/N &lt;= 500) line profiles observed with the stellar
echelle spectrograph of the McMath-Pierce Solar telescope. We find that
various measures of the bisector shape can vary on timescales of days,
implying significant spatial non-uniformity of the surface convective
and brightness (starspot) patterns. Observations at fixed rotational
phase show the bisectors can evolve on timescales of a few rotations,
suggesting rapid rearrangement of the stellar surface structures. We
also detect some evidence for correlations between changes in bisector
parameters and changes in high precision radial velocities. The results
are discussed in the context of stellar surfaces and their effect on
radial velocity searches for extrasolar planets.

---------------------------------------------------------
Title: Two-Component Theoretical Chromosphere Models for K Dwarfs
of Different Magnetic Activity: Exploring the Ca II Emission-Stellar
Rotation Relationship
Authors: Cuntz, M.; Rammacher, W.; Ulmschneider, P.; Musielak, Z. E.;
Saar, S. H.
1999ApJ...522.1053C Altcode:
We compute two-component theoretical chromosphere models for K2 V
stars with different levels of magnetic activity. The two components
are a nonmagnetic component heated by acoustic waves and a magnetic
component heated by longitudinal tube waves. The filling factor for the
magnetic component is determined from an observational relationship
between the measured magnetic area coverage and the stellar rotation
period. We consider stellar rotation periods between 10 and 40
days. We investigate two different geometrical distributions of
magnetic flux tubes: uniformly distributed tubes, and tubes arranged
as a chromospheric network embedded in the nonmagnetic region. The
chromosphere models are constructed by performing state-of-the-art
calculations for the generation of acoustic and magnetic energy in
stellar convection zones, the propagation and dissipation of this
energy at the different atmospheric heights, and the formation of
specific chromospheric emission lines that are then compared to the
observational data. In all these steps, the two-component structure of
stellar photospheres and chromospheres is fully taken into account. We
find that heating and chromospheric emission is significantly increased
in the magnetic component and is strongest in flux tubes that spread
the least with height, expected to occur on rapidly rotating stars with
high magnetic filling factors. For stars with very slow rotation, we
are able to reproduce the basal flux limit of chromospheric emission
previously identified with nonmagnetic regions. Most importantly,
however, we find that the relationship between the Ca II H+K emission
and the stellar rotation rate deduced from our models is consistent
with the relationship given by observations.

---------------------------------------------------------
Title: A Search for Acoustic Heating in the Chromospheres of Low
Activity Dwarfs
Authors: Saar, Steven
1999hst..prop.8143S Altcode: 1999hst..prop.4477S
Recent observations cast doubt on the importance of acoustic waves
for chromospheric heating, at least in inactive giant stars, and
have set small upper limits to their contribution to upper layers of
the Solar chromosphere. These findings contradict the widely accepted
picture that acoustic heating accounts for a significant fraction, the
“basal component”, of chromospheric heating in inactive stars across
the HR diagram. To help resolve this issue, we propose to observe
an extremely inactive {basal} dwarf star {Tau Ceti} to search for
specific signatures of upward propagating acoustic waves: blue-shifts
and enhanced blue wings in chromospheric lines. Solar data show that the
strength of blue-shift can be used to estimate the acoustic contribution
to chromospheric heating. We will also analyze archival HST data of
an active dwarf of the same spectral type, and solar spectra from
the SUMER instrument on SOHO, for comparison with the new data. Lack
of a significant acoustic signature in Tau Ceti would indicate that
magnetic heating generated by a local {turbulent, non- cycling} dynamo
is responsible for the basal component of chromospheric heating in
main sequence stars. Tau Cet may be in a phase analogous to the solar
Maunder minimum, and HST spectra might serve as a proxy for the solar
spectrum in this state. The spectra will also be used for emission
measure analysis differentially between the Sun and solar-like stars.

---------------------------------------------------------
Title: Optical and ultraviolet observations of a strong flare in
the young, single K2 dwarf LQ Hya
Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C.
1999MNRAS.305...45M Altcode: 1998astro.ph.11452M
We present high-resolution optical echelle spectra and IUE observations
during a strong flare on 1993 December 22 in the very active, young,
rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive
phase of the flare, which started sometime between 2:42 ut and 4:07
ut, was characterized by strong optical continuum enhancement and
blueshifted emission lines with broad wings. The optical chromospheric
lines reached their maximum intensity at ~ 5:31 ut, by which time the
blueshift vanished and the optical continuum enhancement had sharply
decreased. Thereafter, the line emission slowly decreased and the lines
redshift in a gradual phase that lasted at least two more hours. The
Mg II lines behaved similarly. Quiescent C IV flux levels were not
recovered until 21 h later, though a data gap and a possible second
flare make the interpretation uncertain. In addition to the typically
flare-enhanced emission lines (e.g., H alpha and H beta), we observe
He I D_3 going into emission, plus excess emission (after subtraction
of the quiescent spectrum) in other He I and several strong neutral
metal lines (e.g., Mg I b). Flare enhancement of the far-ultraviolet
continuum generally agrees with an Si I recombination model. We
estimate the total flare energy, and discuss the broad components,
asymmetries and Doppler shifts seen in some of the emission lines.

---------------------------------------------------------
Title: Parent Stars of Extrasolar Planets. IV. 14 Herculis, HD 187123,
and HD 210277
Authors: Gonzalez, Guillermo; Wallerstein, George; Saar, Steven H.
1999ApJ...511L.111G Altcode:
Spectroscopic analyses of 14 Her, HD 187123, and HD 210277, recently
reported to harbor planets, reveal that these stars are metal
rich. We find [Fe/H]=0.50+/-0.05, 0.16+/-0.05, and 0.24+/-0.05 for
14 Her, HD 187123, and HD 210277, respectively. This is the first
spectroscopic analysis of HD 187123; our results for 14 Her and HD
210277 are in agreement with published studies. It is shown that
14 Her and ρ1 Cnc are nearly identical in their bulk
physical characteristics. This result, combined with their extreme
metallicities, suggests that their physical parameters have been
affected by the process that formed their planets. These two stars join
a group of about half a dozen stars in the solar neighborhood with
[Fe/H]&gt;=0.4. It is also shown that 51 Peg and HD 187123, which
have companions with similar orbital periods and masses, are nearly
identical. We find vsini~2.0 km s-1 for HD 210277 from a
high-resolution spectrum. Based on observations obtained at the
W. M. Keck Observatory, which is operated jointly by the University of
California and the California Institute of Technology, and the National
Solar Observatory, Tucson, AZ, administered by AURA, Inc., for the NSF.

---------------------------------------------------------
Title: Time Evolution of the Magnetic Activity Cycle Period: Results
for an Expanded Stellar Sample
Authors: Saar, S. H.; Brandenburg, A.
1998AAS...193.4404S Altcode: 1998BAAS...30S1315S
We explore non-dimensional relationships between the magnetic dynamo
cycle period P_cyc, the rotational period P_rot, the activity level
(as observed in Ca ii HK), and other stellar properties using a
large stellar sample including Ca ii, photometric and other cycles
in dwarfs, evolved stars, active binaries, and the secondaries of
CV systems. We confirm that most stars with age t ga 0.3 Gyr occupy
two roughly parallel branches, separated by a factor of ~ 6 in P_cyc,
with P_rot/P_cyc ~ Ro(-0.5) , where Ro is the Rossby number. Using the
simple model of Brandenburg, Saar, &amp; Turpin (1998 ApJ 498, L51),
this result implies that the alpha effect increases with mean magnetic
field B, and that alpha and omega_cyc decrease with age along these
branches. Stars are not strictly segregated onto one or the other branch
by activity level, though the high P_rot/P_cyc branch is primarily
composed of inactive stars. The expanded dataset suggests that for t
ga 1 Gyr, stars can have P_cyc on one or both branches (double P_cyc
stars), though among older stars, those with higher mass (F) tend to
have their primary P_cyc on the low P_rot/P_cyc branch, while lower
mass (K) stars occupy the high P_rot/P_cyc branch. The sun's ~ 80 year
Gleissberg cycle agrees with this scenario, suggesting that long-term
“trends" in many stars may be segments of long (P_cyc ~ 50-100 yr)
cycles not yet resolved by the data. Most extremely active stars
(P_rot &lt; 3 days) appear to occupy a third branch with P_rot/P_cyc ~
Ro(0.4) , where some kind of alpha -quenching may be operating. Many RS
CVn variables lie in a transition region between the two most active
branches. We discuss implications for dynamo theory and evolution,
and compare our results with various other models. The results are also
used to predict P_cyc for stars with long-term HK trends, a sample of
young open cluster members, and a group which may be in the stellar
analog of the Maunder minimum.

---------------------------------------------------------
Title: Properties of Flares and Microflares in the RS CVn Variable
II Peg
Authors: Herczeg, G. J.; Saar, S. H.; Daw, A.
1998AAS...193.9901H Altcode: 1998BAAS...30.1395H
We have analyzed two orbits of HST GHRS rapid-readout data of the
active RS CVn subgiant II Peg. About 30 min of data were taken at
medium resolution centered at C IV apparently during the late decay of
a flare. These show strong symmetric C IV lines composed of a narrow
(50 km/s FWHM) and a broad (150 km/s FWHM) component. About 45 min
of data taken at low resolution show both quiescent emission and a
flare. In the quiescent state we detect a wide range of lines including
O V (1371 Angstroms) and (possibly) Fe XXI (1354 Angstroms); analysis
of density sensitive lines (O IV) imply an electron density of n_e ~
10(12) cm(-3) in the transition region (TR) at T~10(5) K. Analysis of
the time-arrival distribution of photons in the quiescent data suggests
an excess at high counts over that expected by Poisson statistics;
thus the data can be modeled by a steady-state quiescent (Poisson)
process, plus a stochastic process probably due to weak flares and
microflares. By fitting the maximum possible Poisson component, we
estimate that in the “quiescent” state, at least 11% of the flux
in TR lines and at least 5% in the chromospheric lines comes from
microflare heating. Analysis of the main flare shows it is dominated by
continuum emission, which reaches a blackbody temperature of 22,000 K
some 2.5 min into the flare. The continuum emission does not appear to
be consistent with Si I recombination suggested previously; rather,
we suggest reprocessed X-rays are a more likely source. The flare
generated red-shifted line emission which rapidly reached +120 km/s
and remained constant thereafter. Higher T lines (C IV and Si IV)
were more enhanced and changed more rapidly than chromospheric lines
(C II). There is some evidence for compression followed by explosive
evaporation in the TR during the initial phases of the flare, but the
density diagnostics give conflicting results.

---------------------------------------------------------
Title: Two-Component Chromosphere Models for K Dwarf Stars: The
Chromospheric Emission --- Stellar Rotation Relationship
Authors: Cuntz, M.; Musielak, Z. E.; Ulmschneider, P.; Rammacher,
W.; Saar, S. H.
1998AAS...193.4402C Altcode: 1998BAAS...30.1315C
We present two-component theoretical chromosphere models for K dwarf
stars with different levels of magnetic activity. The two components
are: a nonmagnetic component heated by acoustic waves, and a magnetic
component heated by longitudinal tube waves. The filling factor for
the magnetic component is determined from an observational relationship
between the stellar rotation rate and the measured coverage of stellar
surface by magnetic fields. The chromosphere models are constructed by
performing state-of-the-art calculations of the generation of acoustic
and magnetic energy in stellar convection zones, the propagation and
dissipation of this energy at the different atmospheric heights,
and the formation of specific chromospheric emission lines, which
are then compared to the observational data. In all these steps, the
two-component structure of stellar photospheres and chromospheres is
fully taken into account. We find that due to the presence of magnetic
flux tubes, the heating and chromospheric emission is significantly
increased in the magnetic component. The heating and chromospheric
emission is found to be the strongest in flux tubes with small
spreading factors which are expected to be present in fast rotating
stars. For stars with very slow rotation we are able to reproduce
the basal flux limit of chromospheric emission previously identified
as due to pure acoustic heating. Most importantly, however, we find
that the relationship between the Ca II H+K emission and the stellar
rotation rate deduced from our models is consistent with the empirical
relationship given by observations.

---------------------------------------------------------
Title: Measurements of Starspot Parameters on Active Stars using
Molecular Bands in Echelle Spectra
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.
1998ApJ...507..919O Altcode:
We present results from a study of starspot areas (fS)
and temperatures (TS), primarily on active, single-lined
spectroscopic binaries, determined using molecular absorption
bands. Expanding upon our previous studies, we have analyzed multiorder
echelle spectra of eight systems to simultaneously measure several
different molecular bands and chromospheric emission lines. We
determined starspot parameters by fitting the molecular bands of
interest, using spectra of inactive G and K stars as proxies for the
nonspotted photosphere of the active stars, and using spectra of M
stars as proxies for the spots. At least two bands with different
Teff sensitivities are required. We found that fitting
bands other than the TiO 7055 and 8860 Å features does not greatly
extend the temperature range or sensitivity of our technique. The 8860
Å band is particularly important because of its sharply different
temperature sensitivity. We did not find any substantial departures
from fS or TS that we have measured previously
based on single-order spectra. We refined our derived spot parameters
using contemporaneous photometry where available. We found that using M
giants as spot proxies for subgiant active stars often underestimates
fS needed to fit the photometry; this is presumably
due to the increase in strength of the TiO bands with decreasing
gravity. We also investigated correlations between fS and
chromospheric emission, and we developed a simple method to measure
nonspot temperature (TQ) solely from our echelle spectra.

---------------------------------------------------------
Title: Spectroscopic Evidence for Nonuniform Starspot Properties on
II Pegasi
Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E.
1998ApJ...501L..73O Altcode:
We present spectroscopic evidence for multiple spot temperatures on
the RS CVn star II Pegasi (HD 224085). We model the strengths of the
7055 and 8860 Å TiO absorption bands in the spectrum of II Peg using
weighted sums of inactive comparison spectra: a K star to represent the
nonspotted photosphere and an M star to represent the spots. The best
fit yields independent measurements of the starspot filling factor
(fS) and mean spot temperature (&lt;TS&gt;)
averaged over the visible hemisphere of the star. During three-fourths
of a rotation of II Peg in late 1996, we measure a constant
fS~55%+/-5%. However, &lt;TS&gt; varies from
3350+/-60 to 3550+/-70 K. We compute &lt;TS&gt; for two
simple models: (1) a star with two distinct spot temperatures, and
(2) a star with different umbral/penumbral area ratios. The changing
&lt;TS&gt; correlates with emission strengths of Hα and the
Ca II infrared triplet in the sense that cooler &lt;TS&gt;
accompanies weaker emission. We explore possible implications of these
results for the physical properties of the spots on II Peg and for
stellar surface structure in general.

---------------------------------------------------------
Title: Time Evolution of the Magnetic Activity Cycle Period
Authors: Brandenburg, Axel; Saar, Steven H.; Turpin, Christen R.
1998ApJ...498L..51B Altcode:
We propose a new interpretation of the relationships between the
dynamo cycle period (Pcyc) as observed in Ca II H and K,
the rotational period (Prot), the activity level, and other
stellar properties. Viewed within this framework, the data suggest
that the dynamo α-parameter increases with magnetic field strength,
contrary to the conventional idea of α-quenching. The data also
suggest a possibly discontinuous dependence of the ratio of cycle
to rotation frequency, ωcyc/Ω, as a function of Rossby
number, Ro (or equivalently, activity or age). Stars evolve with
ωcyc/Ω~t-0.35 (or Ro-0.7), until
age t~2-3 Gyr (roughly at the Vaughan-Preston gap), where a sharp
transition occurs, in which ωcyc/Ω increases by a factor
of ~6. Thereafter, evolution with ωcyc/Ω~t-0.35
continues. The age at which transition occurs may be mass dependent,
with K stars making the transition first.

---------------------------------------------------------
Title: Magnetic Activity-related Radial Velocity Variations in Cool
Stars: First Results from the Lick Extrasolar Planet Survey
Authors: Saar, Steven H.; Butler, R. Paul; Marcy, Geoffrey W.
1998ApJ...498L.153S Altcode:
The discovery of the radial velocity (vr) signatures of
planets around several solar-like stars highlights the importance
of exploring the sources of vr variations intrinsic
to the stars themselves. We study the stars in the Lick planetary
survey for vr variations related to stellar activity: the
rotation of starspots and convective inhomogeneities and their temporal
evolution. We study the relationships between the weighted vr
dispersion, σ'v (which has first been corrected
for the orbital contribution from known planets and the mean internal
error), and spectral type, rotation, and activity (as measured by
Ca II H and K). We find that the largest σ'v
values occur among both the coolest (dMe) and the warmest (active
F) stars. Values of σ'v increase with H
and K emission and scale proportional to vsini in G and K stars
and proportional to (vsini)1.3 in F stars. For a G star
with vsini ~ 8-10 km s-1 (age ~0.3 Gyr), for example, 20 m
s-1&lt;~σ'v&lt;~45 m s-1,
roughly consistent with the predicted σ'v levels
due to magnetic activity (Saar &amp; Donahue). All the stars with
proposed planetary companions show σ'v values
typical for their spectral type, activity, and/or rotation. However,
before the planetary vr perturbations are removed, these
stars show significantly enhanced σ'v values. We
develop a simple model that can predict the σ'v
expected for a given star (within ~40%) as a function of vsini,
spectral type, photometric variability, and macroturbulent velocity. The
implications for extrasolar planet searches are discussed.

---------------------------------------------------------
Title: Physical properties of active stars and stellar systems
Authors: Osten, R. A.; Saar, S. H.
1998MNRAS.295..257O Altcode:
We study spectra of 18 active stars and stellar systems, drawn from
lists of known active binaries or newly discovered extreme-ultraviolet
and soft X-ray sources. Using spectral synthesis and template
modelling, we measure (often for the first time) a variety of physical
properties of the stars, including spectral types, luminosities and
vsini values. We report direct observation of previously undetected
secondary components in three systems, and refine the orbital elements
for two of these (HR 7275 and HD 217344).

---------------------------------------------------------
Title: PZ Mon - An Active Evolved Star
Authors: Saar, Steven H.
1998IBVS.4580....1S Altcode:
An Hipparcos parallax and new high-resolution spectra show that PZ Mon,
long considered a spotted UV Ceti flare star, is actually a distant
active giant (K1III+?), probably an RS CVn, with km s

---------------------------------------------------------
Title: Non-Radiative Heating in “Flat Activity” Stars
Authors: Saar, S. H.
1998ASPC..154..211S Altcode: 1998csss...10..211S
The Mount Wilson Ca ii program has identified a group of stars with
very low level, non-variable chromospheric emission over the ~25 year
survey. Many of these stars are very likely in the stellar analog
of the solar Maunder minimum --- a period when the normal cyclic
(alpha Omega) dynamo was in temporary quiescence. I study UV and X-ray
emission for a sample of these “flat activity” stars. While their
chromospheric Ca ii and C ii emission is consistent with “basal”
(possibly acoustic) flux levels, and increase with T_eff, their
transition region (TR) and coronal fluxes 1) are lower than in normal
cyclic stars, 2) increase towards cooler T_eff, and 3) are independent
of rotation. The TR and coronal fluxes thus appear to be formed by a
largely non-acoustic process which is weak, non-variable, and depends
on mass (convection zone depth) rather than rotation. These properties
are consistent with magnetic heating due to a turbulent, distributed,
convection zone dynamo. Turbulent dynamos thus likely operate at some
level in all cool stars. I discuss implications of these results for
dynamos and magnetic activity in late-type stars.

---------------------------------------------------------
Title: The Contribution of Flares to Transition Region Heating in
Active G and K Dwarfs
Authors: Saar, S. H.; Bookbinder, J. A.
1998ASPC..154.1560S Altcode: 1998csss...10.1560S
We present the preliminary results of an analysis of HST GHRS rapid
readout spectra covering the region 1380 AA - 1670 AA for two active
dwarfs of approximately Pleiades age: HD 129333 (G0V, P_rot ~2.8 days)
and LQ Hya (K2V, P_rot ~1.6 days). Both were observed for &gt;= 4
orbits at 1 second time resolution (total exposure time &gt; 13,000 s
each). The time series of the transition region (TR) fluxes (the sum
of C iv + Si iv) shows many low-level flares in both stars, making
the quiescent level somewhat difficult to identify. We assume that TR
heating in the stars is a combination of a steady background (due to
e.g., MHD wave heating) plus superimposed flares. The distribution of TR
photons per unit time, N(n_TR), should thus have a component at the low
counts which can be fit by a Poisson function. The best-fit Poisson to
the low count end of N(n_T) then defines the the average background TR
heating rate (from the Poisson mean), and an upper limit to the total
steady heating unaffected by flares (from the Poisson amplitude). Our
analysis suggests that at least 8% of TR flux of HD 129333 and 11%
of TR flux of LQ Hya arose from flares during our observations. We
also discuss the flare rates as a function of energy. This represents
the first detailed information on flare heating rates for active G
and K dwarfs.

---------------------------------------------------------
Title: II Peg: Spectroscopic Evidence for Multiple Starspot
Temperatures
Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E. Neff
1998ASPC..154.1439O Altcode: 1998csss...10.1439O
We present spectroscopic evidence for multiple spot temperatures on
the RS CVn star II Pegasi (HD 224085). We fit the strengths of the 7055
AAg and 8860 AAg TiO absorption bands in the spectrum of an active star
using weighted sums of comparison spectra: the spectrum of an inactive
K star to represent the non-spotted photosphere and the spectrum of
an M star to represent the spots. We can thus independently measure
starspot filling factor (fspot) and temperature (tspot). During
3/4 of a rotation of II Peg in Sept.-Oct. 1996, we measure fspot
approximately constant at 55+/-5%. However, tspot varies from 3350 K
to 3500 K. Since our method yields one derived tspot integrated over
the visible hemisphere of the star, we present the results of simple
models of a star with two distinct spot temperatures and compute the
tspot we would derive in those cases. The changing tspot correlates
with emission strengths of Hα and the Ca 2 infrared triplet, in the
sense that cooler \tspot accompanies weaker emission. We explore the
consequences of these results for the physical properties of the spots
on II Peg and for stellar surface structure in general.

---------------------------------------------------------
Title: A Strong Flare on the K Dwarf LQ Hya
Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C.
1998ASPC..154.1508M Altcode: 1998csss...10.1508M
We present high resolution optical echelle spectra and IUE SWP
observations during a strong flare on 1993 December 22 in the very
active, young, rapidly rotating, single K2 dwarf LQ Hya. The temporal
evolution of the flare consists of an initial impulsive phase,
characterized by strong continuum enhancement, which started between
02:42 UT (quiescent spectrum) and 04:36 UT (first spectrum with a strong
increase in the chromospheric lines). The chromospheric lines reached
their maximum intensity ~55 min later, by which time the continuum
enhancement had sharply decreased. Thereafter, the line emission slowly
decreased in a gradual phase that lasted at least until the end of
the observation (07:29 UT). IUE data indicate that quiescent C iv flux
levels were not recovered after ~4 UT on the following day. We describe
the variation of the continuum enhancement, the optical and the UV lines
during the flare. In addition to the emission lines that show strong
flare enhancement (e.g., Hα and Hβ), we observe He i D3
going into emission. After subtraction of the quiescent spectrum,
we also observe excess emission in He i lines at 4921.9, 5015.7, and
6678.1AA, and in other metal lines such as the Na i D1 and
D2, the Mg i b triplet and several Fe i and Fe ii lines. We
estimate the energy release during the flare, and analyze the broad
components and asymmetries seen in some of the emission lines.

---------------------------------------------------------
Title: Eclipse Mapping the Chromosphere of the M4 Ve Binary CM Dra:
First Results
Authors: Saar, S. H.; Bookbinder, J. A.
1998ASPC..154.2042S Altcode: 1998csss...10.2042S
We present a preliminary analysis of HST FOS rapid readout spectra
(1 s resolution) of Mg ii during two secondary eclipses in the dM4e
binary CM Dra. Several flares were observed in both the Mg ii line and
in the nearby continuum, which we use to estimate the contribution of
flares to atmospheric heating. After removing the flares, we study the
shape of the eclipse in Mg ii. The Mg ii lightcurve during the first
eclipse shows subtle differences between ingress and egress, implying
a non-uniform chromosphere. Larger differences between eclipses suggest
that short-term evolution may be significant. We discuss the prospects
for inverting the lightcurve to produce maps of Mg ii variations across
the stellar surface. Analysis of a FUV spectrum of CM Dra reveals C ii,
Si iv and C iv emission for the first time.

---------------------------------------------------------
Title: Further Evidence for Activity-Related Radial Velocity
Variations in Cool Stars
Authors: Saar, S. H.; Butler, R. P.; Marcy, G. W.
1998ASPC..154.1895S Altcode: 1998csss...10.1895S
The discovery of planets around several solar-like stars by means
of high precision radial velocity (vr) measurements
makes it important to explore sources of vr variations
intrinsic to the stars themselves. Such studies guard against false
planet detections, and can guide planet searches towards stars
with low vr “noise" levels. We explore vr
variations related to stellar activity - the rotation and temporal
evolution of starspots and convective inhomogeneities - by studying
the weighted RMS of vr variations (= sigma_v) for stars
in the Lick planetary survey. After removing vr effects
of known planets and binaries, and correcting sigma_v for the mean
internal error (thus removing measurement RMS to first order), we
study relationships between sigma_v and spectral type, rotation,
and activity. Excluding binaries and evolved stars in the sample,
we find sigma_v decreases with decreasing Teff, increases
with activity level, and scales propto v sin i. For a G star with v
sin i ~8-10 km s^{-1} (age ~0.3 Gyr), for example, sigma_v ~20-45 m
s^{-1}, roughly consistent with the predictions of Saar &amp; Donahue
(1997). Implications for planet searches are discussed.

---------------------------------------------------------
Title: High-resolution Infrared Spectroscopy of Starspots on RS
CVn Stars
Authors: O'Neal, D.; Neff, J. E.; Saar, S. H.
1997AAS...191.4515O Altcode: 1997BAAS...29.1283O
We present results from a study of magnetically active stars using
the PHOENIX infrared spectrograph at KPNO. We constrain starspot
coverages on RS CVn stars using high-resolution observations of two
temperature-sensitive OH lines near 1.563mu m (6397 cm(-1) ). The use
of these features holds two advantages over the TiO bands that we have
used previously: the OH lines are visible in spots up to ~ 4500 K;
and spots are much brighter, relative to the unspotted photosphere,
in the infrared than in the visible. These properties also make these
OH lines excellent candidates for the first Doppler imaging study to
use high-resolution observations of infrared spectral features. Using
the OH lines, we also search for previously unknown secondary stars in
“single-lined” RS CVn binary systems, including II Pegasi (HD 224085).

---------------------------------------------------------
Title: HeI D3 absorption and its relation to rotation and activity
in G and K dwarfs.
Authors: Saar, S. H.; Huovelin, J.; Osten, R. A.; Shcherbakov, A. G.
1997A&A...326..741S Altcode:
We have obtained high resolution, high S/N spectra of the He I D3
line (5876 Å) for 53 stars. Combining these data with previous
measurements, we investigate correlations between the flux absorbed
by D3, F_D3_, rotation and other stellar activity indicators for a
set of 76 G and K dwarfs. We find that F_D3_{prop.to}P_rot_^-1.2^
for P_rot_&gt;=4days. For P_rot_&lt;4days, F_D3_ behaviour depends on
spectral type, either remaining roughly constant (G stars), decreasing
(K stars), or even going into emission (a few late K stars). We study
correlations between D3 and chromospheric (Ca II HK), transition region
(C IV 1550Å) and coronal emission, and find, for P_rot_&gt;4days,
F_D3_{prop.to}{DELTA}F_HK_^1.5^, F_D3_{prop.to}F_CIV_^0.7^, and
F_D3_{prop.to}F_X_^0.6^, respectively. Thus, D3 has a response
intermediate between Ca II HK and C IV in low to moderate
activity stars, consistent with its formation in the upper
chromosphere. Our data suggest that the maximum flux absorbed by D3 is
F_D3_{prop.to}T_eff_^9.3^=~2x10^5^erg/cm^2^/s in G stars (equivalent
widths Wlambda_&lt;=80mÅ), and about 40% of that value
(or Wlambda_&lt;=50mÅ) in K stars, less than predicted
by current theoretical models. We discuss the implications of our
results for stellar activity and He I line formation, and suggest
future avenues of study.

---------------------------------------------------------
Title: Activity-Related Radial Velocity Variation in Cool Stars
Authors: Saar, Steven H.; Donahue, Robert A.
1997ApJ...485..319S Altcode:
Planets have been detected orbiting several solar-type stars
with the use of high-precision radial velocity (vr)
measurements. While changes in vr can be measured with
an accuracy of a few meters per second, there has been relatively
little study of how other astrophysical processes, such as magnetic
activity, may affect the observed velocities. In this paper, we
use published data and simple models to explore the contributions
to vr from two activity-related sources, starspots and
convective inhomogeneities, as these features rotate across the
disk and evolve in time. Radial velocity perturbations due to
both of these sources increase with rotation and the level of surface
activity. Our models indicate that for solar-age G stars, the amplitude
of perturbations due to spots is AS &lt;~ 5 m s-1,
increasing to AS ~ 30-50 m s-1 for Hyades-age G
stars. If fS is the starspot area coverage, we find that
AS~f0.9Sv sin i. The effects of
convective inhomogeneities (as observed in line bisector variations)
appear to depend on both rotation and spectral type. Young (active)
F and G dwarfs can have convective vr perturbations with
amplitudes AC &lt;~ 50 m s-1, while vr
amplitudes are reduced for stars with lower v sin i and cooler
Teff. We show that vr data from the literature
display similar trends with v sin i and Teff. AS
and AC will be strongest at or near timescales related to
magnetic activity variations: rotation, active region growth and decay,
and activity cycles. Thus, knowledge of these timescales and typical
AS and AC values are important in searching for
extrasolar planets, especially those around younger, more active stars
or those with small vr reflex amplitudes (i.e., &lt;~20 m
s-1). We discuss implications of our results for current
planet detections and planet search strategies.

---------------------------------------------------------
Title: The Emergence of Magnetic Flux Loops in Sunlike Stars
Authors: DeLuca, Edward E.; Fan, Yuhong; Saar, Steven H.
1997ApJ...481..369D Altcode:
We explore the latitude of emergence of flux tubes at the surface
of G stars as a function of the rotation rate, magnetic flux,
and injection latitude at the bottom of the convective zone. Our
analysis is based on a thin flux tube evolution code that has been
developed to study the emergence of magnetic flux in the Sun and is
well calibrated by detailed comparisons with solar observations. We
study solar models with rotation rates between 1/3 and 10 times solar,
injection latitudes φI between 1° and 40°, and tubes
with a range of field strengths, B0, and fluxes. For
our range of input parameters, we find that the mean latitude of
emergence, &lt;φE&gt;, increases and its range decreases
with higher rotation rates, that φE &lt;= 45° for stars
with rotational periods &gt;=27 days, that φE increases
with B0 in rapid rotators, while the reverse is true for
slow rotators, that the dependence of φE on B0
decreases with increasing φI, that tubes with higher flux
emerge at larger φE, and that the footpoint separation
depends linearly on B0. We compare our results to other
calculations and with observations of magnetic features on stars and
suggest future observations and extensions of this research. Our results
suggest that for near-polar starspots to occur, either active stars
must have a larger range of φI than inferred for the Sun,
or differential rotation and meridional flows are more important for
magnetic flux redistribution in these stars. Our models also imply
that flux appearing near the equator of active stars may be generated
by a distributed, rather than a boundary layer, dynamo.

---------------------------------------------------------
Title: Rotation, turbulence and evidence for magnetic fields in
southern dwarfs
Authors: Saar, S. H.; Osten, R. A.
1997MNRAS.284..803S Altcode:
We model high-resolution spectra using a simple radiative transfer
analysis to derive projected rotational velocities (v sin i) and
macroturbulent velocity dispersions (v_mac) for 49 southern dwarf
stars (including many first-ever measurements). We compare our results
with previous values, and estimate rotation periods (P_rot) and sin i
values where possible. We confirm that v_mac generally decreases with
decreasing temperature for T_eff &gt;= 5000 K. Magnetically active stars
tend to show enhanced values of v_mac. This may be due to a difference
in the mean stellar convective properties, a change in the mean stellar
temperature structure, or a combination of both. We identify a group
of stars that exhibit correlations between the derived velocities and
line Lande g_eff values, implying the presence of significant surface
magnetic flux.

---------------------------------------------------------
Title: Magnetic field measurements on moderately active cool dwarfs.
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
1997A&A...318..429R Altcode:
We present a careful analysis of 13 high-quality optical spectra
of low to moderately active late-type dwarfs (G1-K5) aimed at
determining their magnetic parameters. Among our sample only one
star, ɛ Eri (spatially averaged field strength=~165+/-30G), exhibits
the unambiguous signature of a magnetic field, a few are candidates
and the remaining show no sign of a magnetic field in the observed
spectra. Our analysis is based on an inversion of the spectra using
detailed numerical solutions of the Unno-Rachkovsky equations, for
multiple spectral lines at different positions on the stellar disk,
and including magneto-optical effects. It gives results for ɛ Eri
which are in good agreement with the detailed analysis of infrared
spectra by Valenti et al. (1995ApJ...439..939V). However, the low
value of the spatially averaged field strength of these recent analyses
imply that most values of the magnetic flux determined previously for
moderately active stars are probably too large, often by considerable
amounts. We find that the magnetic flux can be reliably determined if
considerable care is taken in the analysis, but the magnetic field
strength and filling factor cannot be determined separately for
moderately active stars with optical spectra of spectral resolution
&lt;=10^5^ and S/N&lt;=250. In the case of ɛ Eri we are able to
constrain the temperature of the detected magnetic features, which we
find to be similar to or hotter than the non-magnetic surroundings,
providing the first direct evidence that the detected field is in the
form of plages. We also find that if an inversion approach is used,
which determines various line broadening parameters simultaneously
in a self-consistent manner, the presence of a magnetic field is not
as obvious as some previous analyses have suggested. In addition,
we determine fundamental parameters of the stellar sample.

---------------------------------------------------------
Title: Properties of Sun-like Stars with Planets: 51 Pegasi, 47
Ursae Majoris, 70 Virginis, and HD 114762
Authors: Henry, Gregory W.; Baliunas, Sallie L.; Donahue, Robert A.;
Soon, Willie H.; Saar, Steven H.
1997ApJ...474..503H Altcode:
Radial velocity variations have revealed planets orbiting 51 Peg,
47 UMa, and 70 Vir, and a low-mass companion orbiting HD 114762. We
analyze parallel records of photometric measurements in Strömgren
b and y and Johnson V, R, and I passbands and Ca II H and K fluxes
in those stars. In the case of 51 Peg, the high precision of the
differential photometric measurements made by the 0.75 m Automatic
Photoelectric Telescope and the nonvariability of the star would allow
the detection of a transit of a planet as small as Earth (corresponding
to an amplitude of 0.0001 mag) if its orbit were nearly coplanar with
our line of sight. No transits were observed. For 51 Peg and
70 Vir, the upper limit of nondetection of photometric variability
at their companion's orbital periods is Δ(b + y)/2 &lt; 0.0002 +/-
0.0002 mag. For HD 114762, it is ΔV &lt; 0.0007 +/- 0.0004 mag. Such
small amplitudes of photometric variability seem to eliminate periodic
velocity variations expected from p-mode oscillations. All four
stars are magnetically quiet; that is, they lack the typical Ca II and
photometric variability due to rotation and activity cycles expected
from surface magnetic activity in solar-type stars. Such quiescence
produces an interesting observational bias that favors the detection of
planets from low-amplitude radial velocity or photometric variations
by minimizing the contribution from intrinsic stellar variability. We
discuss the circumstances for which the probability of planet detections
is improved by the reduced level of variability from surface magnetic
activity in G and K stars. Stars with low variability in surface
activity should be the best candidates for planet searches using
radial velocity and photometric techniques. Searches for planets
around younger, more active stars will be impeded by variations in
velocity or brightness caused by time-varying surface features. The Ca II H and K fluxes indicate that all four stars are older
than 5 Gyr. Ages were estimated from the average levels of Ca II
H and K fluxes and an existing relationship of the decrease of Ca
II fluxes with age on the lower main sequence and were drawn from
previous results based on theoretical isochrone fitting. Values of the
projected rotational velocity, v sin i, are determined for 70 Vir and
47 UMa from high-resolution spectra. Based on observations made
at Mount Wilson Observatory, operated by the Mount Wilson Institute
under an agreement with the Carnegie Institution of Washington, and at
the National Solar Observatory, administered by AURA, Inc. for the NSF.

---------------------------------------------------------
Title: PHOENIX (IR) and Optical Observations of Magnetic Fields on
M Dwarfs
Authors: Valenti, J.; Johns-Krull, C. M.; Saar, S.; Hinkle, K.;
Joyce, D.
1996AAS...189.7804V Altcode: 1996BAAS...28.1377V
We compare high quality IR and optical spectra of EV Lac (M3.5 Ve)
and Gliese 725B (M3.5 V) to obtain new constraints on magnetic regions
on EV Lac. While EV Lac is very active (L_X/L_bol = -2.6), Gliese 725B
is rather inactive (L_X/L_bol = -5.2). Nonetheless, TiO line strengths
are similar in the two stars, making Gliese 725B an excellent inactive
reference. Using the Zeeman--broadened Fe{I} 8468.40 Angstroms line
and a temperature sequence of inactive standards, Johns--Krull &amp;
Valenti (1996) detected 3.8 +/- 0.5 kG magnetic fields covering 50 +/-
13% of EV Lac. Using this same line, we find similar field strengths in
several other active M dwarfs. We have also extended the EV Lac analysis
to include several other atomic lines. We generate synthetic spectra
using the latest Allard &amp; Hauschildt (1996) model atmospheres and
extensive atomic and TiO line lists. A generalized Feautrier technique
is used to solve the radiative transfer equation for all four Stokes
components. By comparing model and observed spectra, we show that
current TiO line lists have wavelength errors large enough to hinder
detailed analysis. For certain bands, we determined empirical wavelength
corrections from our data. Alternatively, dividing the EV Lac spectrum
by Gliese 725B empirically removes most TiO features, leaving only
the differences in Zeeman sensitive atomic lines. We successfully
determine magnetic parameters by fitting these ratio spectra. Unlike
M dwarfs, active G and K dwarfs typically have field strengths &lt;=
2 kG covering &lt; 10% of their surface. Detecting these weaker fields
in the optical has proven difficult, but they are measurable in the
IR because Zeeman splitting grows more quickly than line broadening
(Delta lambda (2) vs. Delta lambda ). In preparation for an IR
survey of magnetic properties in late-type stars, we obtained 2.2 mu
m Phoenix spectra (S/N = 100, R = 60,000) of EV Lac and Gliese 725B,
containing several Ti{I} lines that are potentially useful as magnetic
diagnostics. Quite surprisingly, we see broad absorption lines in both
stars, but lines in Gliese 725B also have a narrow component with no
apparent analog in EV Lac. We will discuss various interpretations
(both magnetic and nonmagnetic) of these data and assess the use of
these lines to measure magnetic fields.

---------------------------------------------------------
Title: Possible Detection of a Residual Non-Cyclic Distributed Dynamo
in “Maunder Minimum” Stars
Authors: Saar, S. H.; Deluca, E. E.; Baliunas, S. L.; Donahue, R. A.
1996AAS...189.8104S Altcode: 1996BAAS...28.1382S
We have analyzed HST and IUE ultraviolet spectra of five dwarfs which
have extremely low, non-variable levels of Ca II HK emission. These
stars appear to be in the stellar analog of the solar “Maunder
minimum” - a period when the normal cyclic magnetic dynamo went
into temporary quiescence. The stars all have very low levels of
chromospheric and transition region (TR) emission. The ratio of TR (Si
IV and C IV) to chromospheric emission (C II) is smaller than expected
from published estimates of the “basal” emission, and increases with
decreasing T_eff. This is in contrast to the lack of such a trend in
dwarfs with variable Ca II HK (“normal” operating magnetic dynamos)
and the reverse of the trend expected if the emission was acoustic in
origin. The existence of significant TR emission in “Maunder minimum”
stars suggests that they are still generating magnetic flux, but
it is apparently in some form which enhances chromospheric emission
relative to the TR. A possible explanation for the observations is
that a residual “Maunder minimum” magnetic flux is a generated
by a non-cyclic distributed-type dynamo (a less efficient mechanism
which operates throughout the convective zone, and thus grows with
increased convective zone depth). If this scenario is correct, our
data are the first observational evidence of such a dynamo operating
in a star which is not fully convective.

---------------------------------------------------------
Title: A Relationship between Mean Rotation Period in Lower
Main-Sequence Stars and Its Observed Range
Authors: Donahue, Robert A.; Saar, Steven H.; Baliunas, Sallie L.
1996ApJ...466..384D Altcode:
Chromospheric Ca II H and K fluxes have been measured in a
sample of ~100 stars on or near the main sequence at Mount Wilson
Observatory. Observations were made several times a week and span
more than ten years. Within an observing season, many stars show
periodic variations due to rotation. Thirty-six of the stars have
highly-significant periods in at least five seasons. We compute
the range in the observed period, Delta P, and suggest that it is a
measure of, and a lower limit to, the surface differential rotation
(SDR). Several physical and selection effects can affect the measured
Delta P value. An analysis of the cumulative variance distribution
at various time scales, however, demonstrates that Ca II variations
due to active region growth and decay are of longer period and smaller
amplitude than those due to rotation. We argue that other effects (e.g.,
multiple active regions, latitude bands) are either small, or primarily
act to reduce the measured Delta P relative to its true value. Including
results for the Sun, we find that Delta P depends on the mean seasonal
rotation period , such that Delta P is proportional to to
the power of 1.3 +/- 0.1, independent of mass. We briefly discuss this
in the context of dynamo models, and other observations of surface
differential rotation and active region structure.

---------------------------------------------------------
Title: Rapid UV Variability: the Contribution of Flare Heating in
the Atmospheres of Active, Evolved Stars
Authors: Saar, Steven
1996hst..prop.6676S Altcode: 1996hst..prop.3087S
The question of the contribution of flares and microflares tothe
non-radiatively heated outer atmospheres of late-typestars has been
studied with very limited success for over adecade using IUE, a variety
of X--ray satellites, and ground-based studies. HST presents the best
opportunity to place afirm lower limit on the fraction of the transition
region fluxresulting from short timescale events. Our analysis of
HSTdata on one M dwarf shows that up to 60% of the transitionregion flux
is directly attributable to stellar flares andmicroflares. This leaves
little room for the traditional“quiescent" emission. Such a result,
if confirmed for otherstars, promises to revitalize the study of their
outeratmospheres, with the recognition that they are far moredynamic
than static. We now propose to observe two active,evolved stars to
probe the importance of flare heating intheir outer atmospheres: the
RS CVn binary II Peg, and FKComae, a rapidly rotating single giant
(possibly the result ofa coalesced binary). It is important to make
theseobservations before STIS, since the even moderate flares onthese
stars could saturate the MAMA detectors in strong lines.

---------------------------------------------------------
Title: Measurements of Starspot Area and Temperature on Five Active,
Evolved Stars
Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E.
1996ApJ...463..766O Altcode:
We resent results from a study of starspot areas and temperatures
on active stars using the 7055 and 8860 Å bands of the titanium
oxide molecule. Because the two bands have different temperature
sensitivities, the ratio of their strengths provides a measure of the
spot temperature, while their absolute strengths are a function of
total starspot area. We have analyzed the TiO bands of four active,
evolved, single-lined spectroscopic binaries (EI Eridani, σ Geminorum,
V1762 Cygni, and II Pegasi) and of the FK Comae star V1794 Cygni. Where
possible, we compare our results with contemporaneous photometry,
which is used to refine our estimate of the nonspotted photospheric
temperature. We find that, over multiple epochs of observation, the
spot filling factor ranges from below our detection threshold (≍8%)
to just under 60%. In some cases, we find that significant starspot
coverage was likely present at historical light maxima. Our results
suggest a possible correlation between increasing surface gravity
and the temperature difference between the spotted and nonspotted
photosphere. This might result from smaller starspot magnetic field
strengths on active stars of lower gravity and the corresponding
decrease in the pressure and temperature contrast between the
photosphere and the umbra.

---------------------------------------------------------
Title: Optical and X-Ray Characteristics of Stars Detected in the
Einstein Slew Survey
Authors: Schachter, Jonathan F.; Remillard, Ron; Saar, Steven H.;
Favata, Fabio; Sciortino, Salvatore; Barbera, Marco
1996ApJ...463..747S Altcode:
We detect X-rays for the first time from 63 cool (types AM) stars. These
stars are part of the 229 total stellar X-ray sources identified to
date in the Einstein Slew Survey (hereafter Slew). We also list new
X-ray data on one A star that may have a corona, five OB stars, and
report discoveries of two new T Tauri stars and two new cataclysmic
variables. The stellar content of the Slew high-latitude subset
(currently 93% identified for |b_II_| &gt; 20^deg^) is 26%. This agrees
well with the Einstein Extended Medium Sensitivity Survey (EMSS)
stellar sample, which only considered high latitudes. Because of
the large solid angle covered by the Slew, and its shallow limiting
flux, the sample will better probe the bright end of the stellar
X-ray luminosity function (L_X_ &gt; 10^30^ ergs s^-1^). Presently
(based on the 221 Slew stars with known spectral types), the sample
is dominated by late-type systems (cooler than F; 68%). These include
dMe's, BY Dra, RS CVn, and FK Comae systems. Based on the limiting
magnitudes of catalogs searched to date, the Slew is assessed to be
complete for spectral types earlier than K. Hence, K and M systems will
be prominent in the ~50 as yet unidentified stars. We have embarked
on an extensive program to (1) confirm the X-ray identifications with
the optical counterparts; (2) search for Ca II H and K and Balmer line
emission as activity signatures; and (3) search for supporting evidence
of magnetic activity by measuring rotational velocities and relating
them to X-ray luminosity level. Of 64 proposed coronal systems observed
to date, we have confirmed 44 active stars, while in the remaining 20
we have been unable to find definitive activity. We have confirmed
an additional 19 active stars from stellar database searches, and
reclassified nine systems as having nonstellar optical counterparts
from optical follow-up identification work and extragalactic database
searches. We discuss notable new discoveries. From the sample of single
active F7-MS Slew stars with measured ν sin i-values, we find a strong
(99.9% confidence level) linear correlation of X-ray luminosity with ν
sin i and with stellar radius (R). However, L_X_ is uncorrelated with
angular rotation speed at the 99% level. For the combined Slew and
EMSS single star F7-MS sample, we find the same 99.9% ν sin i-L_X_
and R-L_X_ correlations. The L_X_-ν sin i relation for the combined
sample appears to flatten with respect to the quadratic behavior seen
for optically selected stellar samples at rotational velocities in
excess of ~16 km s^-1^. For the unevolved subset of the Slew single
star sample, we also find a correlation between L_X_ and Rossby number
(R_0_; more than 99% confidence). A least-squares fit gives L_X_ ~
R_0_^-0.4^, which is similarly flatter than the quadratic dependence
seen in optical samples. Using the stellar surface X-ray flux F_X_
versus B - V diagram, we interpret these results as saturation of the
stellar surface by active regions at F_X_/F_bol_ ~ 10^-3^.

---------------------------------------------------------
Title: Deep SWP spectra of marginal by DRA stars and UV spectra of
the super-cycle star: HD 10780
Authors: Saar, Steven H.
1996sao..reptS....S Altcode:
A deep short wavelength prime (SWP) spectrum of the marginal BY Dra
star GL 256 shows no obvious C IV or other transition region line
emission. This is at odds with other members of the class and raises
the question of whether GL 256 is a bonafide member of this group. An
analysis of the optical high resolution spectra indicates that the
star is somewhat warmer than previously suspected. We suggest that GL
256 is in fact not a marginal BY Dra star. Two sets of International
Ultraviolet Explorer (IUE) observations of the star HD 10780 were
obtained in September 1992 and January 1993. An analysis of these data
indicates that the star appears to have confounded expectations and
does not have a simple, quasi-sinusoidal dynamo cycle.

---------------------------------------------------------
Title: The Age-related Properties of the HD 98800 System
Authors: Soderblom, David R.; Henry, Todd J.; Shetrone, Matthew D.;
Jones, Burton F.; Saar, Steven H.
1996ApJ...460..984S Altcode:
We present optical spectroscopy of the field K star system HD
98800, which has been found to have significant infrared emission
from circumstellar material. The lithium abundances of the stars
in HD 98800 are well above those of Pleiades of similar color, but
activity levels and rotation in these stars are at or below Pleiades
level. Thus, it is not yet possible to say whether HD 98800 is or is not
a pre-mainsequence system, and it is possible that its components are
on or near the zero-age main sequence. However, the two visible
objects that make up HD 98800 both have high levels of lithium and
activity, strongly suggesting that they are physically related to one
another. As shown by Torres and coworkers, having these stars physically
tied implies that their relative orbit is highly eccentric and highly
inclined to our line of sight, and it also means that we are viewing
the HD 98800 system at an unusual time in its orbit.

---------------------------------------------------------
Title: Recent magnetic fields measurements of stellar
Authors: Saar, S. H.
1996IAUS..176..237S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Recent Measurements of Stellar Magnetic Fields
Authors: Saar, S. H.
1996mpsa.conf..367S Altcode: 1996IAUCo.153..367S
No abstract at ADS

---------------------------------------------------------
Title: TiO Band Measurement of Starspot Temperature and Area on
Active Stars
Authors: O'Neal, D.; Neff, J. E.; Saar, S. H.
1996ASPC..109..621O Altcode: 1996csss....9..621O
No abstract at ADS

---------------------------------------------------------
Title: TiO Band Measurement of Starspot Temperature and Area on
Active Stars.
Authors: O'Neal, D.; Neff, J. E.; Saar, S. H.
1996ASPC..109..261O Altcode: 1996csss....9..261O
No abstract at ADS

---------------------------------------------------------
Title: Absolute Measurements of Starspot Area and Temperature:
II Pegasi in 1989 October
Authors: Neff, James E.; O'Neal, Douglas; Saar, Steven H.
1995ApJ...452..879N Altcode:
We are developing an empirical spectrum synthesis technique that yields
independent measurements of starspot filling factor, f5,
and starspot temperature, TS, by fitting TiO bands of
differing temperature sensitivity. The absolute depth of the TiO bands
constrains fS, while the ratio of their depths is a function
only of TS. One strength of this technique is its ability
to determine the spot parameters in traditionally difficult cases:
slowly rotating stars, uniformly spotted stars, and stars that always
have spots. For this initial study, we have used a simpler procedure
of measuring the band depths in the most spotted star in our survey
(the single-lined RS CVn binary system II Pegasi) and for a full grid
of comparison stars (inactive G, K, and M dwarfs and giants). This
yields TS and fS for a given assumed temperature
of the nonspotted photosphere, TQ. The latter was further
constrained by the use of simultaneous photometry. We have analyzed
a series of spectra of II Peg obtained throughout a single 6.7
day rotational cycle in 1989 October. We find that starspots on
II Peg are better modeled by comparison spectra of giants than by
dwarfs. Combining TiO analysis with contemporaneous photometry, we
find that cool starspots (TS ≍ 3500 K) are always visible,
with a fractional projected coverage of the visible hemisphere varying
from 54% to 64% as the star rotates. The nonspotted photosphere has a
temperature TQ ≍ 4800 K. Our results imply that even at
the historical light maximum of V = 7.2, at least 34% of II Peg was
covered by starspots.

---------------------------------------------------------
Title: Rapid UV Variability: the Contribution of Flare Heating in
Active Dwarf Atmospheres
Authors: Saar, Steven
1995hst..prop.5871S Altcode: 1995hst..prop.2344S
The question of the contribution of flares and microflares to the
non-radiatively heated outer atmospheres of late-type stars has been
studied with at best very limited success for over a decade using IUE,
a variety of X--ray satellites, and ground-based studies. However,
HST presents the possibility for being able to place a firm lower
limit on the fraction of the transition region flux that is the direct
result of short timescale events. Our analysis of HST data on one M
dwarf shows that up to 60 percent attributable to stellar flares and
microflares. This leaves little room for the traditional “quiescent"
emission. Such a result, if confirmed for other stars, promises to
revitalize the study of these atmospheres, with the recognition that
the atmospheres are far more dynamic than static. We are now proposing
to observe 3 new targets, including a very youthful solar analog and
a fully convective star.

---------------------------------------------------------
Title: Dead or Just Sleeping? Status of Magnetic Dynamos in ”maunder
Minumum” Stars
Authors: Saar, Steven
1995hst..prop.5870S Altcode: 1995hst..prop.2343S
The Maunder minimum (and similar episodes occurring every few centuries)
is a poorly understood 75 year period in which the normal solar magnetic
dynamo cycle was temporarily interrupted. Its study is important for
understanding the generation and evolution of solar/stellar magnetic
fields, and for the possible influence of magnetic flux on the Sun's
luminosity and hence on earth's climate. We propose to study the Maunder
mimimum state by obtaining HRS spectra of a sample of solar-like stars
which appear to be in the stellar analog of the Maunder minimum:
i.e., stars with weak, nonvariable Ca II emission and long periods
of rotation. Using transition region line emission as a proxy for
magnetic fields, we will determine the residual magnetic activity
levels of Maunder stars, the magnetic contribution to the total energy
budget of their outer atmospheres, and explore the relations between
Maunder activity levels and stellar mass and rotation. Only HST has
the sensitivity to detect or usefully constrain the very weak emission
seen in these stars. The results will be used to explore the evolution
of dynamos with time, define the dependence of Maunder minimum activity
on mass and rotation rate, test non-linear dynamo models, and estimate
what solar conditions are like during a Maunder episode.

---------------------------------------------------------
Title: Using TiO Spectroscopy to Further Constrain Doppler Imaging
Authors: O'Neal, D.; Neff, J. E.; Saar, S. H.
1995IAUS..176P..32O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Possible Relationship Between Starspot Temperature Deficit
and Surface Gravity
Authors: Saar, S. H.; O'Neal, D.; Neff, J. E.
1995IAUS..176P.105S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Starspot Areas and Temperatures on Active Stars from TiO Bands
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.
1994AAS...185.4507O Altcode: 1994BAAS...26.1380O
We present results from a study of starspot areas and temperatures on
active stars using the 7055 Angstroms and 8860 Angstroms absorption
bands of the titanium oxide (TiO) molecule. These two bands have
different temperature sensitivities, so the ratio of their strengths
in a spotted star spectrum constrains the spot temperature, while
the absolute strengths are a function of total starspot area. This
spectroscopic technique complements Doppler Imaging and light-curve
modeling studies because it can measure spot distributions on even
uniformly-spotted or slowly-rotating stars. We present results
for four active giant or subgiant stars: EI Eridani, V1794 Cygni,
Sigma Geminorum, and V1762 Cygni. In multiple epochs of observation,
the spot coverages we detected on those stars ranged from below our
sensitivity level to approximately 35%.

---------------------------------------------------------
Title: New Measurements of Rotational and Turbulent Velocities for
Southern Dwarfs
Authors: Osten, R. A.; Saar, S. H.
1994AAS...18512503O Altcode: 1995BAAS...27..760O
No abstract at ADS

---------------------------------------------------------
Title: Possible detection of a stellar flare-generated particle beam
in polarized light
Authors: Saar, S. H.; Martens, P. C. H.; Huovelin, J.; Linnaluoto, S.
1994A&A...286..194S Altcode:
We present broadband linear polarization measurements of the active
dK5e flare star, BD +26 730, which show a rapid change in polarization
amplitude and direction over a two hour period. We conclude that
impact polarization resulting from flare-generated particle beams
is the most likely cause of the polarization variations. If this
interpretation is correct, this event represents the most direct
evidence to date for flare-generated particle beams in a star other
than the Sun. With proton beams as the most probable source, energy
fluxes of the order of 10^9-10^ erg/cm2/s are required to power the
observed polarization changes. Using the non-flare polarization level
(likely produced by stellar magnetic regions) and simple models,
we estimate a lower limit of 7% for the inhomogeneous component of
the magnetic region area filling factor. We compare our results with
solar flares and suggest future observational and theoretical efforts.

---------------------------------------------------------
Title: Carbon Monoxide Fundamental Bands in Late-Type
Stars. III. Chromosphere or CO-mosphere?
Authors: Wiedemann, G.; Ayres, T. R.; Jennings, D. E.; Saar, S. H.
1994ApJ...423..806W Altcode:
The strong vibration-rotation lines of CO at 4.6 microns (Δυ = 1)
are unique diagnostics for the thermal conditions in the atmospheric
altitude range of late-type stars near and above the temperature
minimum in chromospheric models. Exploiting recent improvements in IR
instrumentation, we observed a number of cool stars with high spectral
resolution (R ≍ 100,000). The analysis of the spectra was based on
an earlier theoretical study which had established CO Δυ = 1 non-LTE
spectra as useful probes for stars of spectral type F, G, and K with
log g ≥ 1. No direct chromospheric indicators were detected
in the CO spectra. Stellar boundary (CO) temperatures were determined
for the program stars and temperature profiles were constructed for α
Tau, α Boo, β Gem and β Dra. The CO-based models feature a steady
decrease in temperature at the height where the temperature increases in
chromospheric models. Further comparison with chromospheric indicators
shows an increasing discrepancy between the temperatures determined
from CO measurements and those predicted from radiative equilibrium
models, respectively, with increasing chromospheric activity. Thermal
bifurcation of the stellar surfaces is proposed to reconcile the
contradicting scenarios derived based on different spectral diagnostics.

---------------------------------------------------------
Title: Simultaneous SPOT and Chromosphere Maps of FK Comae
Authors: Piskunov, N. E.; Huenemoerder, D.; Saar, S. H.
1994ASPC...64..658P Altcode: 1994csss....8..658P
Maps of the local T_eff and chromospheric intensity (from He I D3)
from a surface imaging analysis of 51 echelle spectra of FK Comae show
a complex relationship between spots and activity.

---------------------------------------------------------
Title: Are Magnetic Features on epsilon ERI Cold or Hot?
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
1994ASPC...64..465R Altcode: 1994csss....8..465R
We analyse high-quality spectra of epsilon Eri with the aim of
determining its magnetic and thermal parameters. From a careful analysis
we conclude that it is not possible to separate the field strength
and filling factor of this star based on data obtained in the visible
spectral range. The data do suggest, however, that the magnetic field
of the star is concentrated in cool, starspot-like structures.

---------------------------------------------------------
Title: How Accurate Are Stellar Magnetic Field
Measurements? II. Analysis of Disk-Integrated Flux Tube Models
Authors: Saar, S. H.; Buente, M.; Solanki, S. K.
1994ASPC...64..474S Altcode: 1994csss....8..474S
We analyze disk-integrated line profiles generated in atmospheres
embedded with fluxtubes to test the accuracy of simple radiative
transfer (RT) analyses in determining stellar magnetic parameters.

---------------------------------------------------------
Title: Spatial and Temporal Activity Variations on AD Leo
Authors: Saar, S. H.; Morgan, M. R.; Bookbinder, J. A.; Neff, J. E.;
Walter, F. M.; Valenti, J.; Misch, T.; Bopp, B. W.; Hale, A.
1994ASPC...64..471S Altcode: 1994csss....8..471S
Multiwavelength measurements of AD Leo show rotational modulation
of magnetic and quiescent C IV fluxes, and UV emission variability
on all timescales 1 s &lt; t &lt; 60 s. Si IV flux arises from
quiescent:microflare:flare heating in approximately a 35:25:40 ratio.

---------------------------------------------------------
Title: Stellar Dynamo Models: From F to K
Authors: Brandenburg, A.; Saar, S. H.; Moss, D.; Tuominen, I.
1994ASPC...64..357B Altcode: 1994csss....8..357B
We extend the two-dimensional solar dynamo models to stars of different
spectral types. Dynamo action is restricted to the overshoot layer.

---------------------------------------------------------
Title: The Evolution of Stellar Dynamo Variations.
Authors: Saar, S. H.; Brandenburg, A.; Donahue, R. A.; Baliunas, S. L.
1994ASPC...64..468S Altcode: 1994csss....8..468S
No abstract at ADS

---------------------------------------------------------
Title: Measurements of Starspot Area and Temperature on II Peg
Authors: O'Neal, D.; Neff, J. E.; Saar, S. H.
1994ASPC...64..726O Altcode: 1994csss....8..726O
We are developing an empirical spectral synthesis technique that will
yield independent measurements of starspot area and temperature. We
have tested this technique on a series of spectra of the single-lined
spectroscopic binary II Pegasi (HD 224085). II Peg is an RS CVn star
from which evidence for magnetic activity has been observed in many
wavelength bands.

---------------------------------------------------------
Title: The Variability of Magnetic Fields, Related Surface Structures,
and Activity
Authors: Saar, S. H.
1994svsp.coll..147S Altcode: 1994IAUCo.143P.147S
I review information from a variety of sources, including magnetic
field measurements, Doppler imaging, and various photometric and
spectroscopic survey and monitoring programs for clues concerning the
physical properties, spatial structure, variability and evolution of
magnetic regions and associated activity on cool stars. Based on these
data, I sketch a scenario of what the surfaces of cool stars look like
as a function of spectral type and age/rotation/activity level.

---------------------------------------------------------
Title: The Relationship Between Radiative and Magnetic Fluxes on
Three Active Solar-type Dwarfs
Authors: Linsky, J. L.; Andrulis, C.; Saar, S. H.; Ayres, T. R.;
Giampapa, M. S.
1994ASPC...64..438L Altcode: 1994csss....8..438L
We present some preliminary results from our coordinated campaign of
IUE and McMath Telescope magnetic field measurements of three active
solar-type dwarf stars: 59 Vir, xi Boo A, and HD 131511. We observed
the three stars nearly every day from May 9 to May 25, 1993, covering
between 1 and 3 rotations. We explore the functional and spatial
relationship between magnetic and radiative fluxes.

---------------------------------------------------------
Title: The Time Evolution of Magnetic Flux, Dynamos, and Surface
Structures on Cool Stars
Authors: Saar, S. H.
1994ASPC...64..319S Altcode: 1994csss....8..319S
I briefly summarize recent observations related to the time evolution
of magnetic flux, associated surface features (spots and network/plage),
and the dynamo mechanism which produces them.

---------------------------------------------------------
Title: Infrared Measurements of Stellar Magnetic Fields
Authors: Saar, S. H.
1994IAUS..154..437S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New Infrared Measurements of Magnetic Fields on Cool Stars
Authors: Saar, S. H.
1994IAUS..154..493S Altcode:
I review the advantages, techniques, and results of measurement of
magnetic fields on cool stars in the infrared (IR). These measurements
have generated several important results, including: the first data
on the magnetic parameters of dMe and RS CVn variables; evidence for
field strength confinement by photospheric gas pressure; support for
the correlation between magnetic flux and rotation, with possible
saturation at high rotation rates; indications of horizontal and/or
vertical magnetic field structure; and evidence of spatial variations
in B over a stellar surface. I discuss these results in detail, and
suggest future directions for IR magnetic field research.

---------------------------------------------------------
Title: Multiepoch Magnetic Surface Images of LQ Hya
Authors: Saar, S. H.; Piskunov, N. E.; Tuominen, I.
1994ASPC...64..661S Altcode: 1994csss....8..661S
We study several epochs of magnetic surface images of the active single
dwarf LQ Hya to explore the surface differential rotation (SDR) rate
and the correlation between magnetic flux Phi_B and T_eff.

---------------------------------------------------------
Title: Measurements of Starspot Area and Temperature on II Pegasi
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.
1993AAS...183.1505O Altcode: 1993BAAS...25.1313O
We are developing an empirical technique that yields independent
measurements of starspot area and starspot temperature on active
stars. Our technique involves fitting observed spectra near TiO
absorption bands with synthetic spectra derived for various combinations
of starspot and non-spot temperatures and starspot filling factors. Our
comparison grid is generated from observed spectra of inactive G and K
stars and of M dwarfs and giants. The absolute depth of the TiO bands in
the spectra of active stars is a measure of the starspot filling factor,
while the relative strength of different bands constrains the starspot
temperature. We have analyzed a series of spectra of the single-lined
spectroscopic binary system II Pegasi (HD 224085), K2 IV-V, P=6.7d. We
find that cool starspots (Teff ~ 3400K) are always visible,
covering from 35% to 50% as the star rotates. However, the absolute
and relative depths of TiO bands are not by themselves sufficient to
establish the temperature of the non-spot photosphere. When coupled
with a temperature difference provided by multi-color photometry,
this technique will enable us to uniquely determine temperatures and
relative filling factors of both the spot and non-spot components of
spotted stars.

---------------------------------------------------------
Title: The interchange instability of stellar magnetic flux tubes
Authors: Bunte, M.; Saar, S. H.
1993A&A...271..167B Altcode:
We investigate the stability of magnetic flux tubes in the surface
layers of late-type stars, concentrating on the interchange (fluting)
instability. Flux tubes on low gravity stars (log g ≲ 3.5) are
generally unaffected by this instability. On stars with higher surface
gravity, tubes are stable if their magnetic flux exceeds 1019
- 1021 Mx (the precise value depending on Teff
and log g). Smaller structures on these stars may be stabilized by a
sufficient external whirl flow. The magnitude of the required whirl
flow shows only weak dependence on Teff but increases
sharply with log g. In some stars, the whirl velocities needed for
stabilization are larger than extant photo spheric velocities. In
these cases, stable tubes are possibly separated into two regimes of
permitted fluxes. Consequences for the field structure on the surfaces
of late-type stars are discussed.

---------------------------------------------------------
Title: Broad-band Linear Polarization in Cool Stars. II. Amplitude
and Wavelength Dependence for Magnetic and Scattering Regions
Authors: Saar, Steven H.; Huovelin, Juhani
1993ApJ...404..739S Altcode:
We have developed a model to estimate the amplitude and wavelength
dependence of broad-band linear polarization (BLP) from magnetic regions
on cool stars. The model includes corrections both for line blends and
for the partial cancellation of polarization in the vector sum over the
stellar disk. Our results agree with recent calculations of BLP in the
red, but show larger amplitudes and a different wavelength dependence
in the blue. We find that the detailed wavelength dependence of the
polarization is complex and varies with effective temperature and
gravity due to changes in line blanketing. The BLP amplitudes depend
strongly on field strength, blanketing, and magnetic region filling
factor and geometry. We make rough estimates of the maximum BLP for
stars of various spectral types and demonstrate a method for deriving
a lower limit to the filling factor from the maximum observed BLP. This
lower limit is related to the fractional area covered by the spatially
asymmetric component of magnetic regions.

---------------------------------------------------------
Title: Magnetic Doppler Imaging and UV Emission of an Active K Dwarf
Authors: Saar, Steven H.
1993iue..prop.4584S Altcode:
Our objective is to determine, for the first time ever, the functional
and spatial relationships between magnetic flux, outer atmospheric
emission, and temperature inhomogeneities on the surface of an active
cool dwarf star. We have developed and successfully tested a new
method, magnetic doppler imaging, for mapping the surface temperature
and magnetic field distributions on rapid rotators. We will apply
this method to the young, rapidly rotating, spotted K2 dwarf,
HD 82558, covering the star with a phase resolution of 0.1 over
two full rotations. The second rotation is crucial for separating
out the effects of flares and/or active region evolution. The UV
spectra will be combined with EUVE and ROSAT data to determine the
longitudinal extent and the brightness of stellar active regions from
the photosphere to the corona. These surface brightness maps will be
directly compared with the magnetic flux and temperature maps to study
stellar plage/spot properties, and serve as a basis for more realistic
two-component models (quiet +plage/spot) for the outer atmospheres of
active solar-like dwarfs.

---------------------------------------------------------
Title: Absolute measurements of starspot area and temperature
Authors: Neff, J. E.; O'Neal, D.; Saar, S. H.
1993ASPC...40..193N Altcode: 1993ist..proc..193N; 1993IAUCo.137..193N
No abstract at ADS

---------------------------------------------------------
Title: Accretion Disk Chromospheres and the Star-Disk Connection
Authors: Horne, K.; Saar, S. H.; Marsh, T. R.
1993AnIPS..10..123H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Surface Images of the BY DRA Star HD 82558
Authors: Saar, S. H.; Piskunov, N. E.; Tuominen, I.
1992ASPC...26..255S Altcode: 1992csss....7..255S
We present preliminary results of a new analysis method applied
to spectra of the BY Dra star HD 82558. We invert a time series of
unpolarized line profiles with different Lande g_eff values to derive
both temperature and magnetic field maps of the star. We find strong
fields (B &gt; 2 kG) near cool spots and weaker fields elsewhere,
with &lt;B&gt; ~ 1 kG.

---------------------------------------------------------
Title: The Star-Disk Connection
Authors: Horne, K.; Saar, S. H.; Marsh, T. R.
1992ASPC...26..273H Altcode: 1992csss....7..273H
No abstract at ADS

---------------------------------------------------------
Title: Evidence for a Complex Distribution of Magnetic Field Strengths
on the Flare Star AD Leo
Authors: Saar, S. H.
1992ASPC...26..252S Altcode: 1992csss....7..252S
I present a preliminary analysis of four Ti I lines from a high S/N IR
spectrum of the flare star AD Leo. The lines show consistent evidence
for a complex magnetic field distribution, and may be fit with either
(a) fields arising from a single atmospheric component but having
a large vertical gradient, or (b) a two component field with B_1 ~
2 x B_2.

---------------------------------------------------------
Title: The Magnetic Cycle of Kappa Ceti
Authors: Saar, S. H.; Baliunas, S. L.
1992ASPC...27..197S Altcode: 1992socy.work..197S
Observations of chromospheric Mg II and Ca II fluxes and photospheric
magnetic flux (spanning 10, 22, and 6 years, respectively) of the
active G5 dwarf, Kappa Ceti, show long-term variations analogous
to the solar cycle. Ca II emission varies with a period of P_cyc =
5.6 yr, and we detect a decrease in magnetic flux (~ fB) during the
declining phase of a recent cycle (1984-1988) of the form: Delta F_HK ~
(fB)^{0.4 +/- 0.2}. This is the first direct evidence for a magnetic
cycle on a star other than the Sun.

---------------------------------------------------------
Title: Recent Advances in Stellar Cycle Research
Authors: Saar, S. H.; Baliunas, S. L.
1992ASPC...27..150S Altcode: 1992socy.work..150S
We review recent work on stellar cycles, focusing on a preliminary
analysis of the first 25 years of data from the Mount Wilson Ca II
program. Cyclic variations are generally solar-like (rapid increase,
slow decline), but some stars show multiple cycle periods. About 10-15%
of the stars may be in the stellar equivalent of "Maunder minima":
epochs when cycles, but not all magnetic activity, temporarily
cease. Well-determined cycle periods show no clear dependence on
single stellar parameters, but do show correlations with more complex
formulations (e.g., alpha-Omega dynamo number) when normalized to the
magnetic diffusion timescale. The relation between this normalized cycle
frequency (Omega*_cyc) and dynamo number appears to change with activity
or age. Cycle amplitudes also correlate with Omega*_cyc, and tend to
increase with convection zone depth and P_rot. Giants in young clusters
also exhibit many of these phenomena, suggesting similar, dynamo-related
origins. Stellar differential rotation can differ markedly from the
Sun in both amplitude and form. Photometric variability increases
rapidly with increasing Ca II emission, first reversing, and eventually
eliminating the correlation between brightness and activity. Dynamos
of active stars thus appear to produce a larger spot-to-plage ratio
than inactive stars; more high-latitude spots are also seen. Surface
convective properties may also change during the cycle.

---------------------------------------------------------
Title: UV Spectra of the "Super-Cycle" Star: HD 10780
Authors: Saar, Steven H.
1992iue..prop.4308S Altcode:
HD 10780 is a moderately active K0 dwarf star with the largest known
dynamo cycle amplitude (as seen in the Ca II S index) of any known
dwarf. Its Ca II cycle amplitude is almost a factor of three higher
than the highest seen among normal dwarfs. In 1989, HD 10780 underwent
an extraordinary increase in activity, Delta S/S ~ 40%, from its cycle
minimum. There are only three previous IUE observations, all LWP, and
all of these spectra were taken before the recent "cycle outburst". The
stars' activity levels appear to have peaked, and may now be starting
a steep decline. We propose an extensive campaign to study the star
in detail, combining new IUE SWP and LWP observation, plus optical
spectroscopy, magnetic field and ROSAT X-ray measurements to, determine
(1) the activity characteristics of this unusual star near its cycle
maximum; and (2) any unusual characteristics of the star which may
explain its extraordinary behavior. Results will further understanding
of stellar activity, dynamos, and intermediate term variability.

---------------------------------------------------------
Title: Deep SWP Spectra of "Marginal" BY Dra Stars
Authors: Saar, Steven H.
1992iue..prop.4295S Altcode:
Recent optical and UV surveys of M dwarfs have resulted in the
discovery of a number of objects with intermediate activity levels
(H-alpha in weak emission but strong Ca, II and UV emission). Available
data suggest these stars have a level of chromospheric activity (and
perhaps an evolutionary status) midway between active BY Dra/dMe
stars and quiet dM's. These "marginal" BY Dra (mBY) stars provide
us with a class of objects rotating very near a "trigger velocity"
(about 5 km s^-1) which appears to divide active BY Dra stars from quiet
dM's. Unfortunately, only poor far UV spectra have been obtained to date
(&lt;= 5 hours). We propose to take about 20 hour SWP spectra of two
mBYs by combining an ESA shift with NASA US1 and US2 (first half). These
new spectra will allow us to accurately probe the upper chromospheres
and transition regions of these important transitional stars for the
first time. Infrared magnetic field measures will be used to explore
the connection between fieldstrength/filling-factor and atmospheric
heating. Comparison of these data with published information on active
dMe and quiet dM stars will yield information on the character of the
stellar dynamo as it makes a transition from "high" to "low" activity.

---------------------------------------------------------
Title: How Accurate are Stellar Magnetic Field Measurements?
Authors: Saar, S. H.; Solanki, S. K. .
1992ASPC...26..259S Altcode: 1992csss....7..259S
We study the accuracy of two magnetic analysis methods by applying
them to a large grid of lines computed using detailed 1.5-D radiative
transfer (RT) calculations in a variety of stellar atmospheres
imbedded with fluxtubes. We find errors of &lt; +/- 20% when using
the more realistic analysis method if the fluxtube and external quiet
atmospheres are similar; errors can increase substantially if this
condition is relaxed.

---------------------------------------------------------
Title: Characteristics of "Marginal" BY DRA Stars
Authors: Saar, S. H.; Bopp, B. W.
1992ASPC...26..288S Altcode: 1992csss....7..288S
We analyze new UV and optical spectra of "marginal" BY Dra stars,
and find support for the idea that they form a class of objects
intermediate in activity (and perhaps age) between dM and dMe stars.

---------------------------------------------------------
Title: Unfolding Mysteries of Stellar Cycles
Authors: Baliunas, S.; Saar, S.
1992Ast....20...42B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Absolute Starspot Area and Temperature Measurements on
Single-Lined RS CVn's
Authors: Neff, J. E.; Saar, S. H.
1991BAAS...23.1384N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Distribution of Magnetic Fields and Related Activity on
A'D Leo
Authors: Saar, S. H.; Bookbinder, J. A.; Neff, J.; Bromage, G.;
Bastian, T.
1991BAAS...23.1383S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Rotation and Emission Lines in Stars and Accretion Disks
Authors: Horne, Keith; Saar, Steven H.
1991ApJ...374L..55H Altcode:
In the accretion disks of quiescent dwarf novae, Doppler mapping studies
reveal that Balmer emission lines increase sharply toward the center
of the disk, with surface brightnesses scaling roughly as R exp -3/2
varies as Omega(Kep). Similarly, among chromospherically active stars
the H-alpha and Ca II H and K emission cores are stronger in the more
rapidly rotating stars, with surface brightnesses scaling again roughly
as Omega(rot). Since in both cases the emission lines scale linearly
with the rotation frequency, it is proposed that the mechanism powering
the emission lines in quiescent accretion disks is the same as that
in chromospherically active stars, namely, the emergence of magnetic
flux generated by the action of a dynamo, and its interaction with the
atmosphere. If this empirical connection between disks and stars is in
fact due to magnetic dynamos, the range of rotation rates available for
testing dynamo theories expands from a factor of 1000 to 10 to the 7th.

---------------------------------------------------------
Title: Broad-Band Linear Polarization in Cool Stars. I. Models and
Spatial Effects for Magnetic and Scattering Regions
Authors: Huovelin, Juhani; Saar, Steven H.
1991ApJ...374..319H Altcode:
We have developed models of broad-band linear polarization (BLP)
arising from magnetic regions on cool stars. The models include an
improved treatment of spatial effects in which the BLP is explicitly
integrated over the stellar surface. We find that for magnetic
region filling factors, f larger than ≍1% of a hemisphere, direct
disk-integration yields results which are often significantly different
from a simple linear scaling of BLP with region area, especially for
regions near the limb. In particular, the amplitude of the BLP reaches
a maximum for f ≍ 24%, which is a consequence of cancellation of
the polarization signal within the region itself. The line-of-sight
angle at which the region exhibits maximum polarization increases with
region size. We study the effects of bipolar pairs of regions,
and single regions with small-scale bipolarity. The most important
effect of bipolarity is the reduction in the influence of Faraday
rotation on the integrated polarization. Spatial effects become more
important as the size of the bipolar spot pair is increased. We
construct similar models for Rayleigh and Thomson scattering regions
in order to compare the signatures of BLP from these sources. Like
magnetic BLP, scattering-induced BLP shows a maximum in polarization
amplitude (at f ≍ 18%), but the line-of-sight angle of the maximum
first decreases (for f ≤ 10%) and then increases with increasing
region size. We also present approximate formulas for the scaling
of magnetically induced and scattering-induced polarization as a
function of f We discuss the importance of the differences found
in the rotational phase dependence for discerning the source of the
polarization. Use of the phase dependence requires detailed comparisons
of polarization observed at several rotational phases, with the success
of application depending on the specific geometry of the polarizing
regions. The general applicability of the models depends on the
accuracy in determining the instrumental and interstellar polarization
(in modeling of polarization degree P) and/or the orientation of the
stellar rotation axis on the plane of the sky (in modeling of Stokes
parameters PQ and PU)

---------------------------------------------------------
Title: Coordinated Observations of AD Leonis
Authors: Bookbinder, J.; Saar, S.
1991IAUC.5255....2B Altcode: 1991IAUC.5255....1B
J. Bookbinder and S. Saar, Center for Astrophysics, write: "We
have organized a major campaign to provide a comprehensive study
of the dynamics and energetics of stellar flares by utilizing high-
time-resolution spectroscopy and photometry. Observations of AD Leo
(R.A. = 10h16m52s.51 +/- 0s.03, Decl. = +20 07'17".2 +/- 0".5, equinox
1950.0, epoch 1991.4) are currently scheduled for May 8 and 9 UT with
the Hubble Space Telescope, IUE, ROSAT, GINGA, VLA, and at Arecibo and
many other ground-based facilities in the U.S. and Europe. We request
additional ground-based spectroscopy and photometry from all interested
parties. To standardize comparisons of results from ground-based
optical observations, please use the following stars as standards:
SAO 81296 = HD 89471 (R.A. = 10h17m09s.6, Decl. = +20 39'21", mv =
8.4), and SAO 81313 = HD 89772 (R.A. = 10h19m11s.5, Decl. = +20 18'23",
mv = 8.9). For more details on the planned observing, please contact
Bookbinder at telephone 617-495- 7058 (e-mail bookbind@cfa.harvard.edu)
or Saar at 617-495-7046 (SPAN e-mail 6702::saar)."

---------------------------------------------------------
Title: Linear Polarization and Magnetic Fields in Cool Stars
Authors: Huovelin, J.; Saar, S. H.
1991LNP...380..420H Altcode: 1991IAUCo.130..420H; 1991sacs.coll..420H
Observations and theoretical models of broadband linear polarization
(BLP) in cool stars are discussed. Two effects, 1) differential
saturation in magnetically sensitive absorption lines and, 2) Rayleigh
and Thomson scattering are considered as the possible causes of the
BLP. Results of theoretical models, and comparisons with observations
are summarized.

---------------------------------------------------------
Title: Recent Measurements of Stellar Magnetic Fields (With 3 Figures)
Authors: Huovelin, J.; Saar, S. H.
1991mcch.conf..273H Altcode: 1991mcch.conf..273S
I review recent measurements of magnetic fields on two interesting
cool stars: a nearly pole-on BY Dra variable (BD +26 730) and a
(possibly) very young K dwarf (HD 17925). These data are combined with
previous measurements to investigate correlations between magnetic,
chromospheric and coronal fluxes. Implications for atmospheric heating
are briefly discussed.

---------------------------------------------------------
Title: Long-Term Variability of Magnetic Structures on BD +26 730
Authors: Saar, Steven H.
1991iue..prop.4028S Altcode:
BD +26 730 , a rapidly rotating, BY Dra variable, is one of the most
magnetically active K dwarfs known, and is the most active of the few
stars with a known magnetic cycle period. The star is viewed nearly
poleon; thus, almost all variability results from the evolution of
activity in time, rather than rotational modulation. Direct measurement
of the magnetic field strength and area coverage of plages on the
star is possible. BD +26*730 thus presents a unique opportunity for
observing long-term, purely temporal variability due to a magnetic
cycle. IUE observations at two epochs already exist. We propose to
continue monitoring the longterm variability of this star, now nearing
starspot (and magnetic activity) maximum, with IUE in order to study the
time-variability of the chromospheric and transition-region activity
on long time-scales. Contemporaneous photometry, optical spectra,
linear polarization, and magnetic line broadening measurements will
be combined with the IUE data to explore the connections between
photospheric magnetic fields, and the structure and energy balance of
the hot, upper-atmospheric layers of the star. Comparison of the UV
fluxes with earlier epoch IUE spectra, some taken near activity minimum,
will allow us to investigate differences in stellar activity over the
magnetic cycle of the star, yielding fundamental data on the behavior
of stellar dynamos at high activity levels. Our study will be the first
investigation of strictly temporal evolution of magnetic fields and
related activity over the activity cycle on a star other than the Sun.

---------------------------------------------------------
Title: Recent Advances in the Observation and Analysis of Stellar
Magnetic Fields
Authors: Saar, Steven
1991LNP...380..389S Altcode: 1991sacs.coll..389S; 1991IAUCo.130..389S
There has been considerable progress recently in the study of magnetic
fields on late-type stars. Advances in the theory include investigation
of systematic effects, new and improved methods of analysis for
unpolarized and circularly polarized lines, new models of stellar
dynamos and of broadband linear polarization, and the first studies
of the thermodynamic nature of stellar magnetic regions and their
vertical structure. Observationally, there have been new measurements,
particularly of young and active stars (including the first detection
of a field on a pre-main sequence object, a new monitoring campaign,
the first indications of the relative temperatures in stellar plages,
and the first measurements of fields in a single stellar active
region. I discuss the results in the framework of stellar activity
and surface structure.

---------------------------------------------------------
Title: The Time Evolution of Magnetic Fields on Solar-Like Stars
Authors: Saar, Steven H.
1991suti.conf..848S Altcode:
Magnetic fields play a crucial role in governing the rotational
evolution of solarlike stars. Techniques for measuring stellar
magnetic fields are reviewed, and the most recent determinations of
magnetic-field strengths and surface-area coverages on cool stars are
analyzed for correlations with age. Tentative evidence for a decrease
in magnetic flux with age is found, primarily caused by a reduction
in the magnetic area filling factor with time.

---------------------------------------------------------
Title: Long-Term Variation of Magnetic and Chromospheric Flux on
κ Ceti
Authors: Saar, S. H.; Baliunas, S. L.
1990BAAS...22.1200S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Long- and short-timescale variability of magnetic activity
on the BY Dra star BD + 26°730
Authors: Saar, S. H.; Golub, L.; Bopp, B.; Herbst, W.; Huovelin, J.
1990ESASP.310..431S Altcode: 1990eaia.conf..431S
No abstract at ADS

---------------------------------------------------------
Title: Physical parameters for three chromospherically active
binaries.
Authors: Saar, S. H.; Nordstrom, B.; Andersen, J.
1990A&A...235..291S Altcode:
High-resolution spectroscopy, photoelectric radial-velocity
observations, and uvby photometry are reported for three southern
late-type binaries. Data obtained at ESO during 1988 and 1989 are
combined with previously published results in extensive tables and
graphs and analyzed in detail. HD 57853 is found to be at least a
triple system with period 122.2 d and components of strongly differing
luminosity; the primary component rotates rapidly (v sin i = 22 km/sec)
and has an age of about 80 Myr. HD 114630 comprises two components
of equal mass (at least 1.07 solar mass) and luminosity, with orbital
inclination about 90 deg, period 4.23 d, rotation v sin i = about 17
km/sec, and age about 2 Gyr. HD 119285 has rotational period 12.031
d, with a K2IVe primary rotating at v sin i = 6.5 km/sec and a very
low-mass secondary; its X-ray surface flux is estimated as 5.5 x 10
to the 6th erg/sq cm sec.

---------------------------------------------------------
Title: Results of Coordinated Multiwavelength Observations of
Solar-Type Stars
Authors: Huovelin, J.; Saar, S. H.
1990IAUS..138..443H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Line Asymmetries in G and K Dwarfs - Dependence on Spectral
Type and Activity
Authors: Saar, Steven H.; Bruning, David H.
1990ASPC....9..168S Altcode: 1990csss....6..168S
Observations of photospheric line asymmetries in 12 G and 11 K dwarfs,
particularly the Fe I 6151.62 A line, are examined to determine the
amplitudes and shapes of the bisectors. Bisector shapes are compared
for magnetically inactive and active stars, and correlations between
the slope and the stellar angular velocity are investigated. G stars
have increasingly negative slopes with larger stellar angular velocity
while K-star slopes become more positive, an effect which is shown to
be consistent with recent hydrodynamical models.

---------------------------------------------------------
Title: The Wavelength Dependence of Broadband Linear Polarization
in Cool Stars
Authors: Saar, Steven H.; Huovelin, Juhani
1990ASPC....9...85S Altcode: 1990csss....6...85S
A model is developed to investigate the effect of wavelength dependence
of magnetically generated broadband linear polarization (BLP) in
late-type stars as a function of line blanketing, observation filters,
and other variables. Linear polarization is assumed to be a single
'average' line and the line opacity, magnetic area filling factor,
and continuum intensity are incorporated to establish an equation
for disk-generated BLP. The method is investigated by computing
special models for the flare star BY Dra and the sun which are
compared to previous calculations. The model is shown to agree
with the calculations of BLP, and the magnetic BLP dependent on
wavelengths varies significantly from the simple power law dependences
on wavelength. The model sets lower limits to the area occupied by
magnetic regions, and an upper limit to the expected BLP also results
from the formulation.

---------------------------------------------------------
Title: Magnetic Fields on Solar-like Stars: The First Decade
Authors: Saar, S. H.
1990IAUS..138..427S Altcode:
I review progress made over the last decade in the measurement of
magnetic fields on solar-like stars. I describe the evolution of
magnetic analysis techniques, summarize our current understanding
of stellar magnetic properties, and outline some future research
directions.

---------------------------------------------------------
Title: Models of Broadband Linear Polarization in Cool Stars
Authors: Huovelin, J.; Saar, S. H.
1990ASPC....9..174H Altcode: 1990csss....6..174H
No abstract at ADS

---------------------------------------------------------
Title: Spectroscopic measurements of magnetic fields on solar-like
stars : techniques and results.
Authors: Saar, Steven H.
1990MmSAI..61..559S Altcode:
This paper reviews the basic requirements for, and difficulties in,
measuring magnetic fields on cool stars. The main types of the analysis
methods are described, including methods that employ Fourier transforms;
line profile models; the Mathys and Solanki (1989) method based on the
difference between Fm and Fq (where Fm is the profile in nonmagnetic
regions and Fq is the profile in magnetic regions); and the Basri and
Marcy (1991) method based on the fact that, for optically thick lines,
Zeeman splitting will increase a line's equivalent width of the Fq. The
assumptions made in each case are examined and the results obtained
are summarized.

---------------------------------------------------------
Title: Studies of Intermediate Activity M Dwarfs
Authors: Saar, Steven H.
1990iue..prop.3754S Altcode:
Recent optical spectroscopic surveys of dwarf M stars have resulted in
the discovery of a number of objects with intermediate activity levels
(H-alpha in weak emission). Available optical data suggest these stars
have a level of chromospheric activity (and perhaps an evolutionary
status) midway between active BY Dra stars and quiet dM's. These
"marginal" BY Dra stars are single objects whose rotation velocities
parallel their chromospheric activity, i.e., higher than those of
quiet dM stars but below that of active BY Dra objects. The marginal
BY Dra stars provide us with a class of objects rotating very near a
"trigger velocity" (believed to be 5 km s^-1) which appears to divide
active BY Dra stars from quiet dM's. As only four "marginal" BY Dra
stars have been observed in the UV to date, we propose to considerably
enlarge the UV database for these objects. UV data on Mg II emission
fluxes and strength of transition region features such as C IV will
serve to fix activity levels in the marginal objects and determine
chromosphere and transition-region heating rates. Simultaneous optical
magnetic field measures will be used to explore the connection between
field-strength/filling-factor and atmospheric heating. Comparison of
these data with published information on active and quiet dM stars
will yield information on the character of the stellar dynamo as it
makes a transition from "low" to "high" activity.

---------------------------------------------------------
Title: Rotational Enhancement of Line Asymmetries in F9-G2 Dwarfs
Authors: Bruning, David H.; Saar, Steven H.
1990ASPC....9..165B Altcode: 1990csss....6..165B
Disk integration of solar intensity profiles suggests that rotation
enhances intermediate strength line asymmetries up to v sin i of
about 6 km/s, after which the slope of the line bisector remains
constant. Observed stellar line profiles do not show such a simple
relation. Fast rotators exhibit large variations, owing presumably to
stellar activity. Caution is advised with respect to the use of slow
rotating or inactive star line profiles to determine the broadening
of faster rotators.

---------------------------------------------------------
Title: First Evidence for Particle Beams in a Stellar Flare
Authors: Saar, S. H.; Martens, P.; Huovelin, J.
1989BAAS...21.1192S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Line Asymmetries in G and K Dwarfs
Authors: Bruning, D. H.; Saar, S. H.
1989BAAS...21.1116B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Active Chromosphere Binary HD 17433 (VY Arietis)
Authors: Bopp, Bernard W.; Saar, Steven H.; Ambruster, Carol; Feldman,
Paul; Dempsey, Robert; Allen, Morgan; Barden, Samuel C.
1989ApJ...339.1059B Altcode:
The sixth-magnitude K star HD 17433 (VY Ari) is shown to be an
active-chromosphere binary with an orbital period of 13.198 days. A
photometric (rotational) period of 17.4 days is indicated by the
existing photometry, implying that HD 17433 is not in synchronous
rotation. In the optical, H-alpha is seen in emission, with variable
profile and intensity; He I lambda-5876 is present in absorption. IUE
observations show chromospheric and transition-region emission lines
with surface fluxes up to 200 times greater than those observed in the
quiet sun. The luminosity and radius are appropriate for a subgiant,
and the kinematics suggest Pleiades group membership. The presence
of a lithium absorption feature indicates it may either be a young
object, possibly a pre-main sequence star or an evolved spotted RS CVn
system. Interpretations from the optical measurement of the magnetic
field strength of HD 17433 are given.

---------------------------------------------------------
Title: Relations between the Photospheric Magnetic Field and the
Emission from the Outer Atmospheres of Cool Stars. I. The Solar CA
II K Line Core Emission
Authors: Schrijver, C. J.; Cote, J.; Zwaan, C.; Saar, S. H.
1989ApJ...337..964S Altcode:
Observations of a solar active region complex and its surroundings are
used to establish a quantitative relation between the Ca II K line core
intensity and magnetic flux density. The Ca II K line core intensity
is transformed to a Ca II H + K line core flux density to facilitate
a comparison of solar and stellar data. A new absolute calibration for
the Mount Wilson Ca II H + K fluxes for G-type dwarfs is derived. The
minimum Ca II K flux, found in the centers of supergranulation cells
in quiet regions on the sun, is identical to the minimum flux that
is observed for solar-type stars. An expression is presented for the
nonlinear trend between the Ca II H + K line core excess flux density
and the absolute value of the magnetic flux density. Models that
explain the nonlinearity of the mean trend and the large intrinsic
scatter about it are discussed. The solar data define a relation that
is similar to the relation between stellar hemisphere-average magnetic
flux densities and Ca II H + K excess flux densities.

---------------------------------------------------------
Title: Line Asymmetries in Late-Type Dwarf Photospheres
Authors: Bruning, D. H.; Saar, S. H.
1989ASIC..263..145B Altcode: 1989ssg..conf..145B
No abstract at ADS

---------------------------------------------------------
Title: IUE Emission Line and Magnetic Field Variability of the Sub
Giant K Star HD 17433
Authors: Ambruster, C. W.; Saar, S.
1988BAAS...20..995A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Correlations Between He I D3 and Rotation for G and K Dwarfs
Authors: Saar, S. H.; Huovelin, J.; Shcherbakov, A. I.; Gustafsson,
B.; Andersen, J.
1988BAAS...20..997S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: C IV fluxes from the Sun as a star, and the correlation with
magnetic flux
Authors: Schrijver, C. J.; Linsky, J. L.; Bennett, J.; Brown, A.;
Saar, S. H.
1988jila.reptR....S Altcode:
A total of 144 C IV wavelength 1548 Solar Maximum Mission (SMM)-UVSP
spectroheliograms of solar plages were analyzed, some of which are
series of exposures of the same region on the same day. Also analyzed
were the C IV wavelength 1551 rasters of plages and C IV wavelength 1548
rasters of the quiet sun. The sample contained data on 17 different
plages, observed on 50 different days. The center-to-limb variations
of the active regions show that the optical thickness effects in the
C IV wavelength 1548 line can be neglected in the conversion from
intensity to flux density. As expected for the nearly optically thin
situation, the C IV wavelength 1548 line is twice as bright as the C
IV 1551 line. The average C IV wavelength 1548 flux density for a quiet
region is 2700 ergs/cm/s and, with surprisingly little scatter, 18,000
erg/cm/s for plages. The intensity histograms of rasters obtained at
disk center can be separated into characteristic plage and quiet sun
contributions with variable relative filling factors. The relationship
between the C IV and magnetic flux densities for spatially resolved
data is inferred to be almost the same, with only an additional factor
of order unity in the constant of proportionality.

---------------------------------------------------------
Title: C 4 fluxes from the sun as a star and the correlation with
magnetic flux
Authors: Schrijver, C. J.; Linsky, J. L.; Bennett, J.; Brown, A.;
Saar, S. H.
1988jila.reptQ....S Altcode:
A total of 144 C 4 wavelength 1548 SMM-UVSP spectroheliograms of
solar plages were analyzed, some of which are series of exposures of
the same region on the same day. Also analyzed were C 4 wavelength
1551 rasters of plages and C 4 1548 rasters of the quiet sun. The
sample contains data on 17 different plages, observed on 50 different
days. The center-to-limb variations of the active regions show that
the optical thickness effects in the C 4 wavelength 1548 line can be
neglected in the conversion from intensity to flux density. As expected
for the nearly optically thin situation, the C 4 1548 line is twice as
bright as the C 4 wavelength 1551 line. The average C 4 wavelength 1548
flux density for a quiet is 2700 erg/cm/s and, with surprisingly little
scatter, 18,000 erg/cm/s for plages. The intensity histograms of rasters
obtained at disk centers can be separated into characteristic plage and
quiet-sun contributions with variable relative filling factors. The
disk-averaged flux density in the C 4 doublet and the disk-averaged
magnitude of the magnetic flux density are related. The relationship
between the C 4 and magnetic flux densities for spatially resolved data
is inferred to be almost the same, with only an additional factor of
order unity in the constant of proportionality.

---------------------------------------------------------
Title: Relations between Broad-Band Linear Polarization and CA II
H and K Emission in Late-Type Dwarf Stars
Authors: Huovelin, Juhani; Saar, Steven H.; Tuominen, Ilkka
1988ApJ...329..882H Altcode:
The authors compare broad-band UBV linear polarization observations of a
sample of late-type (F5 - K5) dwarfs with contemporaneous measurements
of Ca II H and K line core emission. Various parameters representing
the degree of polarization are studied in relation to chromospheric
activity. A weighted average of the largest values of the polarization
degree appears to be the best parameter for activity diagnostics. The
authors suggest stellar magnetic fields and the resulting saturation in
the Zeeman-sensitive absorption lines to be the most probable source
of linear polarization in late-type main-sequence stars, consistent
with the weak trend found with Ca II flux and with inverse Rossby
number. The analysis of short term variability in nearly simultaneous
polarimetric and Ca-emission observations of ξ Boo A and HD 206860
suggests at least three active areas on both stars.

---------------------------------------------------------
Title: Spectral Line Asymmetries in Late-type Dwarf Photospheres
Authors: Bruning, D. H.; Saar, S. H.
1988BAAS...20..696B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Measurements of Magnetic Fields on Cool Stars
Authors: Saar, S. H.
1988IAUS..132..295S Altcode:
The author discusses some of the techniques used (and problems
involved) in measuring stellar magnetic fields on cool stars, and
details how these measurements are broadening our understanding of
stellar magnetic activity.

---------------------------------------------------------
Title: Improved Methods for the Measurement and Analysis of Stellar
Magnetic Fields
Authors: Saar, Steven H.
1988ApJ...324..441S Altcode:
The paper presents several improved methods for the measurement of
magnetic fields on cool stars which take into account simple radiative
transfer effects and the exact Zeeman patterns. Using these methods,
high-resolution, low-noise data can be fitted with theoretical line
profiles to determine the mean magnetic field strength in stellar
active regions and a model-dependent fraction of the stellar surface
(filling factor) covered by these regions. Random errors in the
derived field strength and filling factor are parameterized in terms
of signal-to-noise ratio, wavelength, spectral resolution, stellar
rotation rate, and the magnetic parameters themselves. Weak line blends,
if left uncorrected, can have significant systematic effects on the
derived magnetic parameters, and thus several methods are developed
to compensate partially for them. The magnetic parameters determined
by previous methods likely have systematic errors because of such
line blends and because of line saturation effects. Other sources
of systematic error are explored in detail. These sources of error
currently make it difficult to determine the magnetic parameters of
individual stars to better than about + or - 20 percent.

---------------------------------------------------------
Title: The Magnetic Fields on Cool Stars and Their Correlation with
Chromospheric and Coronal Emission
Authors: Saar, S. H.
1988ASIC..249..139S Altcode: 1988htpa.conf..139S
No abstract at ADS

---------------------------------------------------------
Title: Multiwavelength observations of magnetic fields and related
activity on Xi Bootis A.
Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S.; Linsky, J. L.;
Jordan, C.
1988ASSL..143...45S Altcode: 1988acse.conf...45S
The authors present preliminary results of coordinated observations
of magnetic fields and related activity on the active dwarf, ξ Boo
A. Combining the magnetic fluxes with the linear polarization data,
a simple map of the stellar active regions has been constructed.

---------------------------------------------------------
Title: Temporal Variability of Magnetic Structures on BD +26 730
Authors: Saar, Steven H.
1988iue..prop.3175S Altcode:
BD +26 730 is perhaps the most magnetically active K dwarf known, a
rapidly rotating (P = 1.8 day) flare star with enormous chromospheric
and transition-region line emission, highly variable X-ray flux, and
large starspots with a known 60 year activity cycle period. Since
the star is viewed nearly pole-on, almost all variability will
be the result of the evolution of activity in time, rather than
rotational modulation. Direct measurement of the magnetic field
strength and fractional surface coverage of plages on the star is also
possible through the careful analysis of magnetic line broadening. We
propose to observe the star, now approaching starspot (and magnetic
activity) maximum, with the IUE at multiple phases in order to study
the time-variability of the chromospheric and transition-region
activity. Simultaneous measurements of photometric colors, linear
polarization, and magnetic line broadening will be combined with
the IUE data to study the growth and decay of active regions, and
explore the connections between photospheric magnetic fields, and the
structure and energy balance of the hot, upper-atmospheric layers of
the star. Comparison of the UV fluxes with earlier epoch IUE spectra
taken near activity minimum will allow us to investigate differences
in stellar activity at extremes in the magnetic cycle of the star. Our
study will be the first investigation of strictly temporal evolution
of magnetic fields and related activity on any star other than the Sun.

---------------------------------------------------------
Title: Comparison of Predicted vs. Measured Stellar Magnetic Fields
Authors: Quillen, A.; Golub, L.; Harnden, F. R., Jr.; Saar, S.
1987BAAS...19.1027Q Altcode:
No abstract at ADS

---------------------------------------------------------
Title: HD 1743 (VY Ari): A Young Chromospherically Active Binary
Authors: Bopp, B. W.; Saar, S.; Feldman, P. A.; Dempsey, R.; Allen,
M.; Ambruster, C.; Barden, S. P.
1987BAAS...19..709B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Spatial Distribution of Magnetic Fields on Xi Bootis A
Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S.
1987BAAS...19..703S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 4 meter FTS observations of photospheric magnetic fields on
M dwarfs.
Authors: Saar, Steven H.; Linsky, Jeffrey L.; Giampapa, Mark S.
1987LIACo..27..103S Altcode: 1987oahp.proc..103S
Much of the observed activity on M dwarfs (e.g., spots, flares,
chromospheric and coronal emission) has been attributed to the
interaction of magnetic fields with the stellar atmosphere. Since data
on the magnetic field parameters of M dwarfs can potentially reveal much
about the physical mechanisms behind these phenomena and, additionally,
about stellar dynamos and the evolution of stellar angular momentum,
the authors have begun a program to measure the mean magnetic field
strength in stellar active regions, and the surface filling factor of
these regions for a sample of M dwarfs. In this paper some preliminary
results of this survey are discussed.

---------------------------------------------------------
Title: The Photospheric Magnetic Fields of Cool Stars: Recent Results
of Survey and Time-Variability Programs (Invited review)
Authors: Saar, Steven H.
1987LNP...291...10S Altcode: 1987csss....5...10S; 1987LNP87.291...10S
The past decade has seen considerable advances in our ability to
measure magnetic fields on cool stars. New observational and analytical
techniques have been employed, producing a considerable body of data
on the mean magnetic field strength in stellar active regions (B) and
the fraction (filling factor = f) of the stellar surface covered by
these fields (f) for G, K, and M dwarfs. I focus on some of the recent
results of observational programs aimed at surveying magnetic parameters
on a broad range of stars and studying the time-variability of B and f.

---------------------------------------------------------
Title: Empirical Relations Between Magnetic Fluxes and Atmospheric
Radiative Losses for Cool Dwarf Stars
Authors: Saar, Steven H.; Schrijver, C. J.
1987LNP...291...38S Altcode: 1987csss....5...38S
We derive and discuss relations between magnetic, X-ray, and Ca II
H+K flux densities for a sample of G, K, and M dwarfs.

---------------------------------------------------------
Title: Observations and Analysis of the Photospheric Magnetic Fields
on Dwarf g, K and M Stars.
Authors: Saar, Steven Herbert
1987PhDT.........3S Altcode: 1987DiAbI..48.1385S
I have developed an improved technique for the analysis of magnetic
broadening in stellar absorption line profiles. Unlike previous methods,
the new technique is based on a model that includes radiative transfer
effects and the full Zeeman patterns. The effects of weak blends on the
profiles can be reduced by comparing identical lines in two stars of
the same spectral type, one of which is chromospheric inactive. After
adjusting for differences in line strength and doppler broadening,
the difference profile can be modeled to determine both the fraction
of the stellar surface covered by magnetic regions (f) and the mean
field strength in these regions (B). Accuracies of about 20% in B
and f are possible. I find that previous Zeeman analysis methods
systematically overestimate f, especially for cooler stars, due to
their neglect of line saturation and blends. I have applied the new
technique to two sets of high resolution, low noise spectra. The
first set consists of 29 stars, spanning spectral types from GO to
M4.5 and a broad range of rotational rates and ages. I have made the
first ever detection of photospheric magnetic fields on a BY Draconis
variable (EQ Vir) and a dMe flare star (AD Leo). Several major trends
are apparent from the results. The stellar magnetic field strength
is in pressure equilibrium with the photospheric gas pressure and is
thus a function of spectral type. The filling factor, f is a linear
function of angular velocity. The total magnetic flux on a star is thus
a function of the star's rotation rate, in agreement with simple dynamo
theories. A constant B and an f value decreasing with time explains
the observed decline in stellar rotational velocities and activity
levels with age. There is no correlation between f and B, or between
B and rotation. Contrary to some theoretical models, I find dM stars
have little magnetic flux. The highest filling factors are found on
flare stars. I have also used the new technique to study the spatial
and temporal behavior of f and B on the active star Epsilon Eri. Eleven
observations were made over two months with contemporaneous measurements
of the chromospheric Ca II emission flux. I find no correlation between
B and phase or Ca II flux. The filling factor, however, shows a weak
phase dependence and is linearly proportional to the Ca II emission,
consistent with many interpretations of the solar data.

---------------------------------------------------------
Title: Measurements of Stellar Magnetic Fields: Empirical Constraints
on Stellar Dynamo and Rotational Evolution Theories
Authors: Linsky, Jeffrey L.; Saar, Steven H.
1987LNP...291...44L Altcode: 1987LNP87.291...44L; 1987csss....5...44L
We explore the implications of empirical stellar magnetic parameters
for dynamo theories, stellar activity theories, and models of the
evolution of stellar angular momentum.

---------------------------------------------------------
Title: Broadband Linear Polarization and Chromospheric Ca II H and
K Emission in Late-Type Main Sequence Stars
Authors: Huovelin, J.; Saar, Steven H.; Tuominen, I.; Linnaluoto,
S.; Virtanen, H.
1987LNP...291...41H Altcode: 1987LNP87.291...41H; 1987csss....5...41H
We discuss correlations between broadband linear polarization, intrinsic
stellar parameters, and Ca 11 H+K emission in G and K dwarfs.

---------------------------------------------------------
Title: Carbon Monoxide Fundamental Bands in Late Type Stars
Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S.
1987LNP...291..374W Altcode: 1987csss....5..374W; 1987LNP87.291..374W
No abstract at ADS

---------------------------------------------------------
Title: Exploration of the CO Fundamental Bands in Late Type Stars
Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S.
1986BAAS...18..982W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Detailed Study of Photospheric Magnetic Fields on Late-type
Dwarfs
Authors: Saar, S. H.
1986BAAS...18R.961S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Magnetic Field of the BY Draconis Flare Star EQ Virginis
Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M.
1986ApJ...302..777S Altcode:
High resolution, high S/N-ratio line profiles of the BY Draconis-type
flare star EQ Vir obtained with the MMT are presently subjected to
a novel Zeeman analysis procedure which includes radiative transfer
effects and compensation for blends. A mean field of 2500 + or -
300 G covering 80 + or 15 percent of EQ Vir is determined. This
constitutes the first positive detection of a magnetic field in a BY
Draconis-type flare star, confirming that magnetic fields are present
on these stars. The value of 2500 G obtained for the photospheric field
strength is similar to the value derived by assuming equipartition of
magnetic and thermal energy densities in the photosphere and scaling
from the solar network fields, suggesting that equipartition may
determine the mean field strength in the nonspotted portion of the
flare star photosphere.

---------------------------------------------------------
Title: The Surface Magnetic Fields of dM and dMe Stars
Authors: Saar, S. H.; Linsky, J. L.; Giampapa, M. S.
1986BAAS...18..670S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New measurements of photospheric magnetic fields in late-type
stars and emerging trends
Authors: Saar, S. H.; Linsky, J. L.
1986AdSpR...6h.235S Altcode: 1986AdSpR...6..235S
We report on recent results of our program to measure photospheric
magnetic field strengths and filling factors from the analysis of
unpolarized high spectral resolution and S/N line profiles. We have
analyzed spectra obtained with the KPNO 4-m FTS, the MMT, and the
McMath Reticon Spectrograph. With the latter instrument we now have
an extensive data set through our synoptic and survey observing
programs. Photospheric magnetic field parameters are obtained by
comparison of observed and theoretical line profiles using an LTE
code that includes line saturation and the full Zeeman pattern. We
determine the nonmagnetic line broadening parameters for a star by
fitting profiles of low Landé g lines formed under conditions similar
to the high g lines which are used to infer magnetic fields. The
effects of line blending are cancelled to first order by fitting
profiles of the same high g lines in comparison inactive stars of
the same spectral type. We have measured field parameters (outside of
starspots) in dwarf stars of spectral type GO to dM3.5e (Ad Leo). We
find a trend of increasing field strength with later spectral type,
consistent with equal gas and magnetic pressure in the photosphere,
and a trend of increasing filling factor with activity. Our data are
inconsistent with the hypothesis of a constant number of magnetic flux
tubes on active stars. Staff Member, Quantum Physics Division,
National Bureau of Standards.

---------------------------------------------------------
Title: The Time Variability of Magnetic Fields on Epsilon Eridani
Authors: Saar, Steven H.; Linsky, Jeffrey L.; Duncan, Douglas K.
1986LNP...254..275S Altcode: 1986csss....4..275S
No abstract at ADS

---------------------------------------------------------
Title: The Detection of Magnetic Fields on Late Type Stars - Progress
Problems and Future Needs
Authors: Saar, S. H.
1986tswo.work...44S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Further Observations of Magnetic Fields on Active Dwarf Stars
Authors: Saar, Steven H.; Linsky, Jeffrev L.
1986LNP...254..278S Altcode: 1986csss....4..278S
No abstract at ADS

---------------------------------------------------------
Title: The photospheric magnetic field of the dM3.5e flare star
AD Leonis.
Authors: Saar, S. H.; Linsky, J. L.
1985ApJ...299L..47S Altcode:
A high-resolution infrared spectrum of the dM3.5e flare star AD Leo,
obtained with the Kitt Peak 4 m Fourier Transform Spectrometer, clearly
shows the presence of strong magnetic fields. Five absorption lines
in the 4400-4600 per cm region have been modeled, and it is inferred
that 73 percent + or - 6 percent of the surface of AD Leo is covered by
active regions outside of dark spots containing a mean field strength of
3800 + or - 260 G. If these active regions are brighter than the quiet
photosphere, the surface filling factor will be somewhat smaller. Since
simultaneous H-alpha observations exhibited no evidence of flares, the
observations probably represent the quiescent magnetic flux level. The
inferred field strength is consistent with equipartition of magnetic and
thermal pressures in the photosphere and is similar to values derived
using the scaling laws of Golub. The large observed filling factor is
consistent with efficient dynamo generation of magnetic flux in this
rapidly rotating star.

---------------------------------------------------------
Title: An extensive survey of photospheric magnetic fields in G and
K dwarfs.
Authors: Saar, S. H.; Linsky, J. L.
1985BAAS...17..879S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: An Extensive Survey of Photospheric Magnetic Fields in G and
K Dwarfs
Authors: Saar, S. H.; Linsky, J. L.
1985BAAS...17..751S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: First Measurement of Magnetic Fields on a BY Draconis Flare
Star: EQ Virginis
Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M.
1984BAAS...16Q.517S Altcode: 1984BAAS...16..517S
No abstract at ADS

---------------------------------------------------------
Title: A search for diffuse band profile variations in the rho
OPH cloud.
Authors: Snow, T. P.; Timothy, J. G.; Saar, S.
1982ApJ...262..611S Altcode:
(Previously announced in STAR as N82-30203)

---------------------------------------------------------
Title: The Profile of the λ4430 Diffuse Interstellar Band, Observed
with the MAMA Detector
Authors: Snow, T. P.; Timothy, J. G.; Saar, S.
1981BAAS...13..825S Altcode:
No abstract at ADS