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Author name code: lopez-ariste
ADS astronomy entries on 2022-09-14
author:"Lopez Ariste, Arturo"
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Title: Three-dimensional imaging of convective cells in the
photosphere of Betelgeuse
Authors: López Ariste, A.; Georgiev, S.; Mathias, Ph.; Lèbre, A.;
Wavasseur, M.; Josselin, E.; Konstantinova-Antova, R.; Roudier, Th.
2022A&A...661A..91L Altcode: 2022arXiv220212011L
<BR /> Aims: Understanding convection in red supergiants and the
mechanisms that trigger the mass loss from these evolved stars are
the general goals of most observations of Betelgeuse and its inner
circumstellar environment. <BR /> Methods: Linear spectropolarimetry
of the atomic lines of the spectrum of Betelgeuse reveals information
about the three-dimensional (3D) distribution of brightness in its
atmosphere. We model the distribution of plasma and its velocities and
use inversion algorithms to fit the observed linear polarization. <BR
/> Results: We obtain the first 3D images of the photosphere of
Betelgeuse. Within the limits of the used approximations, we recover
vertical convective flows and measure the velocity of the rising plasma
at different heights in the photosphere. In several cases, we find
this velocity to be constant with height, indicating the presence of
forces other than gravity acting on the plasma and counteracting it. In
some cases, these forces are sufficient to maintain plasma rising at
60 km s<SUP>−1</SUP> to heights where this velocity is comparable
to the escape velocity. <BR /> Conclusions: Forces are present in the
photosphere of Betelgeuse that allow plasma to reach velocities close
to the escape velocity. These mechanisms may suffice to trigger mass
loss and sustain the observed large stellar winds of these evolved
stars. <P />Based on observations obtained at the Télescope Bernard
Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and Université
de Toulouse, France.
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Title: Precision requirements for the POLLUX-LUVOIR spectropolarimeter
Authors: Muslimov, Eduard; Bouret, Jean-Claude; Neiner, Coralie;
Ferrari, Marc; Lombardo, Simona; Lopez Ariste, Arturo; Le Gal, Maëlle
2020SPIE11444E..6GM Altcode:
POLLUX is a project of high-resolution UV spectropolarimeter for
the prospective LUVOIR space observatory. It will work in the range
of 90-400 nm with R >= 120000. The baseline design consists of 3
channels representing echelle spectrographs with dedicated polarimeters,
customized echelles and freeform-based concave holographic gratings. We
study the requirements for manufacturing and assembly precision. We
consider three performance criteria related to the spectral
resolving power, calibration stability, and the gratings diffraction
efficiency. We perform the tolerance analysis in corresponding modes
using raytracing and numerical methods of diffraction modelling in a
Monte-Carlo loop. We emphasize the most influential design parameters,
which may require high precision of manufacturing and alignment and
should be the subjects of further studies. We also briefly discuss
possible compensators for maintenance of the imaging performance.
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Title: Solar surveillance with CLIMSO: instrumentation, database
and on-going developments
Authors: Pitout, Frédéric; Koechlin, Laurent; López Ariste, Arturo;
Dettwiller, Luc; Glorian, Jean-Michel
2020JSWSC..10...47P Altcode:
CLIMSO is a suite of solar telescopes installed at Pic du Midi
observatory in the southwest of France. It consists of two refractors
that image the full solar disk in Hα and CaII K, and two coronagraphs
that capture the prominences and ejections of chromospheric matter
in Hα and HeI. Synoptic observations are carried out since 2007
and they follow those of previous instruments. CLIMSO, together
with its predecessors, offer a temporal coverage of several solar
cycles. With a direct access to its images, CLIMSO contributes
to real time monitoring of the Sun. For that matter, the national
research council for astrophysics (CNRS/INSU) has labelled CLIMSO as
a national observation service for "surveillance of the Sun and the
terrestrial space environment". Products, under the form of images,
movies or data files, are available via the CLIMSO DataBase. In this
paper, we present the current instrumental configuration; we detail
the available products and show how to access them; we mention some
possible applications for solar and space weather; and finally, we
evoke developments underway, both numerical to valorise our data,
and instrumental to offer more and better capabilities.
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Title: Modelling and observations: Comparison of the magnetic field
properties in a prominence
Authors: Mackay, D. H.; Schmieder, B.; López Ariste, A.; Su, Y.
2020A&A...637A...3M Altcode:
Context. Direct magnetic field measurements in solar prominences occur
infrequently and are difficult to make and interpret. As a consequence,
alternative methods are needed to derive the main properties of the
magnetic field that supports the prominence mass. This is important for
our understanding of solar prominences, but also for understanding how
eruptive prominences may affect space weather. <BR /> Aims: We present
the first direct comparison of the magnetic field strength derived
from spectro-polarimetric observations of a solar prominence, with
corresponding results from a theoretical flux rope model constructed
from on-disc normal component magnetograms. <BR /> Methods: We first
used spectro-polarimetric observations of a prominence obtained with
the magnetograph THEMIS operating in the Canary Islands to derive the
magnetic field of the observed prominence by inverting the Stokes
parameters measured in the He D3 line. Next, we constructed two
data-constrained non-linear force-free field (NLFFF) models of the
same prominence. In one model we assumed a strongly twisted flux rope
solution, and in the other a weakly twisted flux rope solution. <BR />
Results: The physical extent of the prominence at the limb (height
and length) is best reproduced with the strongly twisted flux rope
solution. The line-of-sight average of the magnetic field for the
strongly twisted solution results in a magnetic field that has a
magnitude of within a factor of 1-2 of the observed magnetic field
strength. For the peak field strength along the line of sight,
an agreement to within 20% of the observations is obtained for
the strongly twisted solution. The weakly twisted solution produces
significantly lower magnetic field strengths and gives a poor agreement
with the observations. <BR /> Conclusions: The results of this first
comparison are promising. We found that the flux rope insertion method
of producing a NLFFF is able to deduce the overall properties of the
magnetic field in an observed prominence.
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Title: Asymmetric shocks in χ Cygni observed with linear
spectropolarimetry
Authors: López Ariste, A.; Tessore, B.; Carlín, E. S.; Mathias, Ph.;
Lèbre, A.; Morin, J.; Petit, P.; Aurière, M.; Gillet, D.; Herpin, F.
2019A&A...632A..30L Altcode: 2019arXiv190903720L
<BR /> Aims: We derive information about the dynamics of the stellar
photosphere, including pulsation, from a coherent interpretation of the
linear polarisation detected in the spectral lines of the Mira star χ
Cyg. <BR /> Methods: From spectropolarimetric observations of χ Cyg,
we performed a careful analysis of the polarisation signals observed
in atomic and molecular lines, both in absorption and emission, using
radiative transfer in the context of polarisation produced through two
mechanisms: intrinsic polarisation and continuum depolarisation. We also
explain the observed line doubling phenomenon in terms of an expanding
shell in spherical geometry, which allows us to pinpoint the coordinates
over the stellar disc with enhanced polarisation. <BR /> Results: We
find that the polarised spectrum of χ Cyg is dominated by intrinsic
polarisation and has a negligible continuum depolarisation. The
observed polarised signals can only be explained by assuming that
this polarisation is locally enhanced by velocity fields. During the
pulsation, radial velocities are not homogeneous over the disc. We map
these regions of enhanced velocities. <BR /> Conclusions: We set an
algorithm to distinguish the origin of this polarisation in any stellar
spectra of linear polarisation and to find a way to increase the signal
by coherently adding many lines with an appropriated weight. Applied
to the Mira star χ Cyg, we reached the unexpected result that during
the pulsation, velocities are radial but not homogeneous over the
disc. The reason for these local velocity enhancements are probably
related to the interplay between the atmospheric pulsation dynamics and
the underlying stellar convection. <P />Based on observations obtained
at the Télescope Bernard Lyot (TBL) at Observatoire du Pic du Midi,
CNRS/INSU and Université de Toulouse, France.
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Title: Solar survey at Pic du Midi: Calibrated data and improved
images
Authors: Koechlin, Laurent; Dettwiller, Luc; Audejean, Maurice;
Valais, Maël; López Ariste, Arturo
2019A&A...631A..55K Altcode: 2019arXiv190206980K
Context. We carry out a solar survey with images of the photosphere,
prominences, and corona at Pic du Midi observatory. This survey, named
CLIMSO (for CLIchés Multiples du SOleil), is in the following spectral
lines: Fe XIII corona (1.075 μm), Hα (656.3 nm), and He I (1.083 μm)
prominences, and Hα and Ca II (393.4 nm) photosphere. All frames
cover 1.3 times the diameter of the Sun with an angular resolution
approaching one arcsecond. The frame rate is one per minute per channel
(weather permitting) for the prominences and chromosphere, and one per
hour for the Fe XIII corona. This survey started in 2007 for the disk
and prominences and in 2015 for the corona. We have almost completed one
solar cycle and hope to cover several more, keeping the same wavelengths
or adding others. <BR /> Aims: We seek to make the CLIMSO images
easier to use and more profitable for the scientific community. <BR />
Methods: At the beginning of the survey, the images that we sent to the
CLIMSO database were not calibrated. We have implemented a photometric
calibration for the present and future images, in order to provide
"science-ready" data. The old images have been calibrated. We have
also improved the contrast capabilities of our coronagraphs, which
now provide images of the Fe XIII corona, in addition to previous
spectral channels. We also implemented an autoguiding system based on
a diffractive Fresnel array for precise positioning of the Sun behind
coronagraphic masks. <BR /> Results: The data, including the images
and films, are publicly available and downloadable through virtual
observatories and dedicated websites (use "CLIMSO" and "IRAP" keywords
to find them). For the Hα and Ca II channels we calibrate the data into
physical units, independent of atmospheric or instrumental conditions;
we provide solar maps of spectral radiances in W m<SUP>-2</SUP>
sr<SUP>-1</SUP> nm<SUP>-1</SUP>. The instrumental improvements and
calibration process are presented in this paper.
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Title: Atmospheric circulation of Venus measured with visible imaging
spectroscopy at the THEMIS observatory
Authors: Gaulme, Patrick; Schmider, François-Xavier; Widemann,
Thomas; Gonçalves, Ivan; López Ariste, Arturo; Gelly, Bernard
2019A&A...627A..82G Altcode: 2019arXiv190511078G
Measuring the atmospheric circulation of Venus at different altitudes
is important for understanding its complex dynamics, in particular the
mechanisms driving super-rotation. Observationally, Doppler imaging
spectroscopy is in principle the most reliable way to measure wind
speeds of planetary atmospheres because it directly provides the
projected speed of atmospheric particles. However, high-resolution
imaging spectroscopy is challenging, especially in the visible domain,
and most knowledge about atmospheric dynamics has been obtained with
the cloud tracking technique. The objective of the present work is to
measure the global properties of the atmospheric dynamics of Venus at
the altitude of the uppermost clouds, which is probed by reflected solar
lines in the visible domain. Our results are based on high-resolution
spectroscopic observations with the long-slit spectrometer of the solar
telescope THEMIS. We present the first instantaneous "radial-velocity
snapshot" of any planet of the solar system in the visible domain, i.e.,
a complete radial-velocity map of the planet obtained by stacking data
on less than 10% of its rotation period. From this, we measured the
properties of the zonal and meridional winds, which we unambiguously
detect. We identify a wind circulation pattern that significantly
differs from previous knowledge about Venus. The zonal wind reveals a
"hot spot" structure, featuring about 200 m s<SUP>-1</SUP> at sunrise
and 70 m s<SUP>-1</SUP> at noon in the equatorial region. Regarding
meridional winds, we detect an equator-to-pole meridional flow
peaking at 45 m s<SUP>-1</SUP> at mid-latitudes, i.e., about
twice as large as what has been reported so far. <P />Tables
A.1-A.3 are 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/A82">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A82</A>
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Title: VUV test of a new polarimeter for spectropolarimetric
measurements on board space missions
Authors: Le Gal, Maelle; Pertenais, Martin; Lopez Ariste, Arturo;
Neiner, Coralie; Champion, Norbert; Younes, Youssef; Reess, Jean-Michel
2019arXiv190711549L Altcode:
High-resolution spectropolarimetry is a useful astronomical technique,
in particular to study stellar magnetic fields. It has been extensively
used in the past but mostly in the visible range. Space missions
equipped with high-resolution spectropolarimeters working in the
ultra-violet (UV) are now being studied. We propose a concept of a
polarimeter working with temporal modulation and allowing to perform
Stokes IQUV measurements over the full UV + Visible range. The purpose
of this article is to describe the polarimeter concept, two prototypes
and the bench developed to perform on ground testing to establish the
performances of this new polarimeter.
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Title: Far ultra-violet polarimeter by reflection for Pollux (LUVOIR)
Authors: Le Gal, Maëlle; López Ariste, Arturo; Neiner, Coralie
2019SPIE11180E..4VL Altcode: 2019arXiv190712281L
The ultra-violet (UV) high-resolution spectropolarimeter Pollux is
being studied in Europe under CNES leadership for the LUVOIR space
mission. LUVOIR is a projected 15-m telescope equipped with a suite of
instruments proposed to NASA. Pollux will perform spectropolarimetric
measurements from 90 to 400 nm with a resolution of 120000. The
spectrograph will be divided in three channels, each with its own
polarimeter: far UV (FUV, 90-124.5 nm), mid UV (MUV, 118.5-195 nm),
and near UV (NUV, 190-390 nm). We present here our FUV prototype and
our investigation to optimize this polarimeter (angle, materials,
coating…).
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Title: VizieR Online Data Catalog: Venus photometric flux and los
velocities (Gaulme+, 2019)
Authors: Gaulme, P.; Schmider, F. -X.; Widemann, T.; Goncalves, I.;
Lopez Ariste, A.; Gelly, B.
2019yCat..36270082G Altcode:
Two-dimension maps of Venus from data taken on September 14th, 16th and
17th, 2009. <P />Velocity data are provided for the data points that
are reliable, i.e., for all the point visible on Fig. 13 (middle panel),
whereas photometry is provided for out-of-mask regions, in case a user
would like to fit the complete photometric profile. <P />(3 data files).
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Title: Detection of the Linearly Polarised Spectrum of the Red
Supergiant Star α Ori
Authors: Tessore, B.; Tessore, B.; López Ariste, A.; Mathias, P.;
Josselin, E.; Lèbre, A.; Morin, J.; Josselin, E.
2019ASPC..526..249T Altcode:
At the solar limb, the observed linear polarisation is due to the
anisotropy of the radiation field induced by limb darkening. It is
maximal when it is seen parallel to the limb and it vanishes when it
is integrated over the spherically-symmetric solar disk. Therefore for
distant stars, that present spherical symmetry, linear polarisation
signatures are very difficult to observe. However, strong linear
polarisation features have been reported in the prototypical red
supergiant star α Ori (Betelgeuse). We propose to explain them with
an analytical model.
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Title: POLLUX, an innovative instrument providing a unique UV
spectropolarimetric capability to LUVOIR
Authors: Ferrari, Marc; Bouret, Jean-Claude; Neiner, Coralie; Muslimov,
Eduard; Le Gal, Maelle; Lopez Ariste, Arturo
2019AAS...23314809F Altcode:
The Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR) is one of
four large mission concept studies led by NASA for the 2020 Decadal
Survey. Under the leadership of French Institutes and French Space
Agency, European institutes have come together to propose an instrument,
POLLUX, that would be onboard the 15-meter primary mirror option
of LUVOIR. POLLUX will operate over a broad spectral range (90 to
400 nm), at high spectral resolution (R >=120,000), with a unique
spectropolarimetric capability. It is designed to address a range of
questions at the core of the LUVOIR Science portfolio. The working range
is split into 3 channels: Far (90-125 nm), Medium (119-200 nm), and Near
(200-400 nm) ultraviolet. MUV and NUV channel, separated by a dichroic
splitter, can be recorded simultaneously. The FUV channel is recorded
separately (temporal separation), using a dedicated flip-mirror. The
coatings on the optical elements of POLLUX are optimized for each
channel, to maximize the throughput. Each channel will include an
optimized echelle spectrograph integrating advanced technologies,
i.e. high groove densities, holographic recording on a freeform surface
for the cross-dispersors, etc. The polarimeters design were optimized
for each channel accounting for the technological feasibility. They
are retractable in the MUV and NUV to allow the pure spectroscopic
mode. The FUV modulator is retractable while the analyzer is kept in
the optical path to direct the beam towards the collimator. Detectors
will be delta-doped EMCCDs, combining the linearity of CCDs with
photon-counting ability, which is a key capability enabling detection
of faint UV signals. Furthermore, these detectors deliver high
quantum efficiency thus offering the possibility to reach very high
signal-to-noise ratios. CMOS are also considered as a viable option
in the development time-frame of POLLUX. The complete study will be
included as a dedicated POLLUX chapter in the document presenting
the final study of LUVOIR to the NASA decadal 2020 committee. In this
poster, we present the instrument concept, as well as the challenges
offered by the development of POLLUX.
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Title: Characterizing the photospheric convection of red supergiant
stars at high angular resolution
Authors: Montargès, M.; Norris, R.; Tessore, B.; López Ariste, A.;
Chiavassa, A.; Lèbre, A.
2018sf2a.conf..333M Altcode:
Over the past few years, our knowledge of red supergiant stars
has changed dramatically thanks to the development of high angular
resolution techniques (interferometry in both the optical and mm
domains, adaptive optics) and of numerical modeling. We present here our
last results on the observation of the photosphere of red supergiants
using near infrared interferometry and visible spectropolarimetry.
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Title: POLLUX, a high-resolution UV spectropolarimeter for LUVOIR
Authors: Bouret, J. -C.; Muslimov, E.; Neiner, C.; Le Gal, M.; Lopez
Ariste, A.; Ferrari, M.
2018sf2a.conf...61B Altcode:
POLLUX is a high-resolution, UV spectropolarimeter proposed for the
15-meter primary mirror option of LUVOIR. The instrument Phase 0 study
is supported by the French Space Agency (CNES) and performed by a
consortium of European scientists. POLLUX has been designed to deliver
high-resolution spectroscopy (R ≥ 120,000) over a broad spectral
range (90-400 nm). Its unique spectropolarimetric capabilities will
open-up a vast new parameter space, in particular in the unexplored UV
domain and in a regime where high-resolution observations with current
facilities in the visible domain are severely photon starved. In this
paper, we introduce the general context of LUVOIR, the design of POLLUX,
and the required technology development needed to achieve the desired
performances of the instrument.
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Title: Convective cells in Betelgeuse: imaging through
spectropolarimetry
Authors: López Ariste, A.; Mathias, P.; Tessore, B.; Lèbre, A.;
Aurière, M.; Petit, P.; Ikhenache, N.; Josselin, E.; Morin, J.;
Montargès, M.
2018A&A...620A.199L Altcode: 2018arXiv181110362L
<BR /> Aims: We assess the ability to image the photosphere of red
supergiants and, in particular Betelgeuse, through the modelling
of the observed linear polarization in atomic spectral lines. We
also aim to analyse the resulting images over time, to measure the
size and dynamics of the convective structures in these stars. <BR />
Methods: Rayleigh scattering polarizes the continuum and spectral lines
depolarize it. This depolarization is seen as a linear polarization
signal parallel to the radial direction on the stellar disk. Integrated
over the disk, it would result in a null signal, except if brightness
asymmetries/inhomogeneities are present. This is the basic concept
behind our imaging technique. Through several tests and comparisons, we
have tried to assess and extend its validity, and to determine what can
be learnt unambiguously through it. <BR /> Results: The several tests
and comparisons performed prove that our technique reliably retrieves
the salient brightness structures in the photosphere of Betelgeuse,
and should be relevant to other red supergiants. For Betelgeuse,
we demonstrate that these structures we infer are convective cells,
with a characteristic size of more than 60% of the stellar radius. We
also derive the characteristic upflow and downflow speeds, 22 and 10 km
s<SUP>-1</SUP>, respectively. We find weak magnetic fields concentrated
in the downflow lanes in between granules, similar to the quiet sun
magnetism. We follow those convective structures in time. Changes
happen on timescales of 1 week, but individual structures can be
tracked over 4 yr of observations. <BR /> Conclusions: The measured
characteristics of the convection in Betelgeuse confirm the predictions
of numerical simulations in both the strong, supersonic upflows and
the size of the convective cells. They also concur in the presence of
weak magnetic fields that are completely dominated by the convective
flows and constrained to the dark lanes of down-flowing plasma. <P
/>Based on observations obtained at the Télescope Bernard Lyot (TBL)
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.
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Title: UV Polarimeters for Pollux onboard LUVOIR
Authors: Le Gal, M.; López Ariste, A.; Pertenais, M.; Neiner, C.
2018sf2a.conf...65L Altcode:
Pollux, the European high-resolution spectropolarimeter designed
for LUVOIR, will work from 90 to 400 nm. In order to optimize its
efficiency, the range is divided in 3 channels: far ultra-violet (FUV)
from 90 to 124.5 nm, mid-UV (MUV) from 118.5 to 195 nm and near-UV
(NUV) from 190 to 400 nm. Optical materials' properties being different
between channels, each one will benefit from its own polarimeter
adapted to its wavelength range. All polarimeters will use temporal
modulation and will be composed by a modulator and an analyzer. The
NUV polarimeter is similar to the one often used in in visible range:
it uses waveplates and a polarizer and works thus in transmission. The
FUV polarimeter has to be innovative because no birefringent material
transmits light at these wavelengths. It will use mirrors and work by
reflexion. The MUV polarimeter will benefit from the design of the two
others so that it will be the most efficient possible. This proceeding
presents these three polarimeters designed for Pollux.
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Title: Venus' winds measured with visible imaging-spectroscopy at
the THEMIS observatory
Authors: Gaulme, Patrick; Schmider, François Xavier; Widemann,
Thomas; Gonçalves, Ivan; Lopez Ariste, Arturo; Gelly, Bernard
2018EPSC...12..275G Altcode:
The objective of the present work is to measure the global properties
of Venus' atmospheric dynamics, through the obtention of a complete
radial-velocity map of Venus at the altitude of the uppermost
cloud layer. Our results are based on high-resolution spectroscopic
observations of Venus performed in the visible domain with the long
slit spectrometer of the solar telescope THEMIS (Spain). We present
the first instantaneous “radial-velocity snapshot” of any planet
of the solar system in the visible domain, i.e., a complete RV map
of the planet obtained by stacking data on less than 10 % of its
rotation period. From this, we measure the properties of the zonal
and meridional winds, which we unambiguously detect. We identify
a wind circulation pattern that significantly differs from what we
know about Venus. The zonal wind displays a “hot spot” structure,
featuring about 200 m s<SUP>-1</SUP> at sunrise and 70 m s<SUP>-1</SUP>
at noon in the equatorial region. Regarding meridional winds, we detect
an equator-to-pole meridional flow peaking at 45 m s<SUP>-1</SUP>
at mid latitudes, i.e., which is about twice as large as what was
reported so far.
---------------------------------------------------------
Title: VUV test of a new polarimeter for spectropolarimetric
measurements on board space missions
Authors: Le Gal, Maëlle; Pertenais, Martin; López Ariste, Arturo;
Neiner, Coralie; Champion, Norbert; Younes, Youssef; Reess, Jean-Michel
2018SPIE10706E..1ML Altcode:
High-resolution spectropolarimetry is a useful astronomical technique,
in particular to study stellar magnetic fields. It has been extensively
used in the past but mostly in the visible range. Space missions
equipped with high-resolution spectropolarimeters working in the
ultra-violet (UV) are now being studied. We propose a concept of a
polarimeter working with temporal modulation and allowing to perform
Stokes IQUV measurements over the full UV + Visible range. The purpose
of this article is to describe the polarimeter concept, two prototypes
and the bench developed to perform on ground testing to establish the
performances of this new polarimeter.
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Title: Superoscillations in solar MHD waves and their possible role
in heating coronal loops
Authors: López Ariste, A.; Facchin, M.
2018A&A...614A.145L Altcode: 2018arXiv180108330L
<BR /> Aims: We aim to study the presence of superoscillations in
coronal magnetoacoustic (MHD) waves and their possible role in heating
coronal loops through the strong and localised gradients that they
generate on the wave. <BR /> Methods: An analytic model is built
for the transition between sausage and kink wave modes propagating
along field lines in the corona. We compute in this model the local
frequencies, the wave gradients, and the associated heating rates due
to compressive viscosity. <BR /> Results: We find superoscillations
associated with the transition between wave modes accompanying the wave
dislocation that shifts through the wave domain. Frequencies ten times
higher than the normal frequency are found. This means that a typical
three-minute coronal wave will oscillate locally in 10 to 20 s. Such
high frequencies bring up strong gradients that efficiently dissipate
the wave through compressive viscosity. We compute the associated
heating rates; locally, they are very strong, largely compensating
typical radiative losses. <BR /> Conclusions: We find a new heating
mechanism associated to magnetoacoustic waves in the corona. Heating
due to superoscillations only happens along particular field lines with
small cross sections, comparable in size to coronal loops, inside the
much larger magnetic flux tubes and wave propagation domain.
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Title: Prominence/Tornado plasma parameters
Authors: Schmieder, Brigitte; Mein, Pierre; Zapior, Maciej; Labrosse,
Nicolas; Lopez Ariste, Arturo
2018cosp...42E3025S Altcode:
We present a comparison of the plasma physical parameters in prominences
and tornadoes using IRIS data and ground based polarimetry measurements
obtained with THEMIS. Mg II lines give a good diagnostics of the
temperature and optical thickness of the structures. The Stokes
parameters from the He D3 line allow to distinguish the behaviour
of the magnetic field in typical prominences and atypical prominences
(e.g. bubbles, eruptive prominence). We concentrate on the Dopplershifts
in a tornado observed in transition region lines and in Halpha. Our
results support the existence of oscillations in tornadoes but not
rotation.A reconstruction of the 3D geometry of a helical prominence
obtained by following the trajectory of kernels yields surprising
results. The loops are shown to be quasi-horizontal structures with
no curvature.We conclude that it is important to take into account the
3D structure of the prominence to study the dynamics of the prominence
plasma.
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Title: Evolution of the magnetic field of Betelgeuse from 2009-2017
Authors: Mathias, P.; Aurière, M.; López Ariste, A.; Petit, P.;
Tessore, B.; Josselin, E.; Lèbre, A.; Morin, J.; Wade, G.; Herpin,
F.; Chiavassa, A.; Montargès, M.; Konstantinova-Antova, R.; Kervella,
P.; Perrin, G.; Donati, J. -F.; Grunhut, J.
2018A&A...615A.116M Altcode: 2018arXiv180401831M
Context. Betelgeuse is an M-type supergiant that presents a circularly
polarized (Stokes V) signal in its line profiles, interpreted in
terms of a surface magnetic field. <BR /> Aims: The weak circular
polarization signal has been monitored over 7.5 years in order to
follow its evolution on different timescales, and eventually to
determine its physical origin. Linear polarization measurements have
also been obtained regularly in the last few years. <BR /> Methods:
We used both the ESPaDOnS and Narval spectropolarimeters to obtain
high signal-to-noise ratio spectra, which were processed by means
of the least-squares deconvolution method. In order to ensure the
reality of the very weak circular polarization, special care has been
taken to limit instrumental effects. In addition, several tests were
performed on the Stokes V signal to establish its stellar and Zeeman
origin. <BR /> Results: We confirm the magnetic nature of the circular
polarization, pointing to a surface magnetic field of the order of 1
G. The Stokes V profiles present variations over different timescales,
the most prominent one being close to the long secondary period (LSP;
around 2000 d for Betelgeuse) often invoked in red evolved stars. This
long period is also dominant for all the other Stokes parameters. The
circular polarization is tentatively modeled by means of magnetic
field concentrations mimicking spots, showing in particular that the
velocity associated with each "spot" also follows the long timescale,
and that this signal is nearly always slightly redshifted. <BR />
Conclusions: From the coupled variations of both linear and circular
polarization signatures in amplitude, velocity and timescale, we favour
giant convection cells as the main engine at the origin of polarization
signatures and variations in all the Stokes parameters. This strengthens
support for the hypothesis that large convective cells are at the origin
of the LSP. <P />Based on observations obtained at the Télescope
Bernard Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and
Université de Toulouse, France, and at the Canada-France-Hawaii
Telescope (CFHT) which is operated by the National Research Council
of Canada, CNRS/INSU and the University of Hawaii.
---------------------------------------------------------
Title: POLLUX: a UV spectropolarimeter for the LUVOIR space telescope
project
Authors: Muslimov, Eduard; Bouret, Jean-Claude; Neiner, Coralie;
López Ariste, Arturo; Ferrari, Marc; Vivès, Sébastien; Hugot,
Emmanuel; Grange, Robert; Lombardo, Simona; Lopes, Louise; Costeraste,
Josiane; Brachet, Frank
2018SPIE10699E..06M Altcode: 2018arXiv180509067M
The present paper describes the current baseline optical design
of POLLUX, a high-resolution spectropolarimeter for the future
LUVOIR mission. The instrument will operate in the ultraviolet
(UV) domain from 90 to 390 nm in both spectropolarimetric and pure
spectroscopic modes. The working range is split between 3 channels -
far (90-124.5 nm), medium (118.5-195 nm) and near (195-390 nm) UV. Each
of the channels is composed of a polarimeter followed by an echelle
spectrograph consisting of a classical off-axis paraboloid collimator,
echelle grating with a high grooves frequency and a cross-disperser
grating operating also as a camera. The latter component integrates
some advanced technologies: it is a blazed grating with a complex
grooves pattern formed by holographic recording, which is manufactured
on a freeform surface. One of the key features underlying the current
design is the large spectral length of each order 6 nm, which allows to
record wide spectral lines without any discontinuities. The modelling
results show that the optical design will provide the required spectral
resolving power higher than R 120,000 over the entire working range
for a point source object with angular size of 30 mas. It is also shown
that with the 15-m primary mirror of the LUVOIR telescope the instrument
will provide an effective collecting area up to 38 569 cm<SUP>2</SUP>
. Such a performance will allow to perform a number of groundbreaking
scientific observations. Finally, the future work and the technological
risks of the design are discussed in details.
---------------------------------------------------------
Title: POLLUX: A UV High-Resolution Spectropolatimeter for LUVOIR
Authors: Bouret, Jean-Claude; Neiner, Coralie; Lopez Ariste, Arturo;
Vivès, Sébastien; Muslimov, Eduard; Lopes, Louise; Costeraste,
Josiane; Brachet, Frank; POLLUX Consortium
2018AAS...23141901B Altcode:
The Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR) is one of
four large mission concept studies led by NASA for the 2020 Decadal
Survey. A versatile suite of instruments is envisioned for LUVOIR,
to advance our understanding of the origin and evolution of galaxies,
stars and planets that make up our Universe, and the life within it. We
present POLLUX, a high-resolution spectropolarimeter, operating at
UV wavelengths, designed for the 15-meter primary mirror option of
LUVOIR. POLLUX study is supported by the French Space Agency (CNES)
and developed by a European consortium of scientists.POLLUX will
operate over a broad spectral range (98 to 390 nm), at high spectral
resolution (R = 120,000). This will permit to resolve narrow UV
emission and absorption lines, thus to follow the baryon cycle over
cosmic time, from galaxies forming stars out of interstellar gas and
grains, and stars forming planets, to the various forms of feedback
into the interstellar and intergalactic medium (ISM and IGM), and
active galactic nuclei (AGN).The most innovative characteristic
of POLLUX is its unique spectropolarimetric capability, that will
enable detection of the polarized light reflected from Earth-like
exoplanets or from their circumplanetary material, and moons, and
characterization of the magnetospheres of stars and planets, and their
interactions. The magnetospheric properties of planets in the solar
system will be accessible to exquisite level of details, while the
influence of magnetic fields at the galactic scale and in the IGM will
be measured. UV circular and linear polarisation will provide a full
picture of magnetic field properties and impact for a variety of media
and objects, from AGN outflows to all types of stars. It will probe
the physics of accretion disks around young stars and white dwarfs,
or supermassive black holes in AGNs, and constrain the properties,
especially sphericity, of stellar ejecta and explosions. Since the
parameter space opened by POLLUX is essentially uncharted territory,
its potential for ground-breaking discoveries is high.We introduce
the science case and the instrument concept, as well as the challenges
offered by the development of this instrument.
---------------------------------------------------------
Title: Reconstruction of a helical prominence in 3D from IRIS spectra
and images
Authors: Schmieder, B.; Zapiór, M.; López Ariste, A.; Levens, P.;
Labrosse, N.; Gravet, R.
2017A&A...606A..30S Altcode: 2017arXiv170608078S
Context. Movies of prominences obtained by space instruments e.g. the
Solar Optical Telescope (SOT) aboard the Hinode satellite and the
Interface Region Imaging Spectrograph (IRIS) with high temporal
and spatial resolution revealed the tremendous dynamical nature
of prominences. Knots of plasma belonging to prominences appear
to travel along both vertical and horizontal thread-like loops,
with highly dynamical nature. <BR /> Aims: The aim of the paper
is to reconstruct the 3D shape of a helical prominence observed
over two and a half hours by IRIS. <BR /> Methods: From the IRIS
Mg II k spectra we compute Doppler shifts of the plasma inside
the prominence and from the slit-jaw images (SJI) we derive the
transverse field in the plane of the sky. Finally we obtain the
velocity vector field of the knots in 3D. Results.We reconstruct the
real trajectories of nine knots travelling along ellipses. <BR />
Conclusions: The spiral-like structure of the prominence observed
in the plane of the sky is mainly due to the projection effect of
long arches of threads (up to 8 × 10<SUP>4</SUP> km). Knots run
along more or less horizontal threads with velocities reaching 65 km
s<SUP>-1</SUP>. The dominant driving force is the gas pressure. <P
/>Movies associated to Figs. 1, 9, 10, and 13 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730839/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Comparing UV/EUV line parameters and magnetic field in a
quiescent prominence with tornadoes
Authors: Levens, P. J.; Labrosse, N.; Schmieder, B.; López Ariste,
A.; Fletcher, L.
2017A&A...607A..16L Altcode: 2017arXiv170804606L
Context. Understanding the relationship between plasma and the
magnetic field is important for describing and explaining the
observed dynamics of solar prominences. <BR /> Aims: We determine
if a close relationship can be found between plasma and magnetic
field parameters, measured at high resolution in a well-observed
prominence. <BR /> Methods: A prominence observed on 15 July 2014 by
the Interface Region Imaging Spectrograph (IRIS), Hinode, the Solar
Dynamics Observatory (SDO), and the Télescope Héliographique pour
l'Étude du Magnétisme et des Instabilités Solaires (THEMIS) is
selected. We perform a robust co-alignment of data sets using a 2D
cross-correlation technique. Magnetic field parameters are derived
from spectropolarimetric measurements of the He I D<SUB>3</SUB> line
from THEMIS. Line ratios and line-of-sight velocities from the Mg II h
and k lines observed by IRIS are compared with magnetic field strength,
inclination, and azimuth. Electron densities are calculated using Fe xii
line ratios from the Hinode Extreme-ultraviolet Imaging Spectrometer,
which are compared to THEMIS and IRIS data. <BR /> Results: We find
Mg II k/h ratios of around 1.4 everywhere, similar to values found
previously in prominences. Also, the magnetic field is strongest (
30 G) and predominantly horizontal in the tornado-like legs of the
prominence. The k<SUB>3</SUB> Doppler shift is found to be between
±10 km s<SUP>-1</SUP> everywhere. Electron densities at a temperature
of 1.5 × 10<SUP>6</SUP> K are found to be around 10<SUP>9</SUP>
cm<SUP>-3</SUP>. No significant correlations are found between the
magnetic field parameters and any of the other plasma parameters
inferred from spectroscopy, which may be explained by the large
differences in the temperatures of the lines used in this study. <BR />
Conclusions: This is the first time that a detailed statistical study of
plasma and magnetic field parameters has been performed at high spatial
resolution in a prominence. Our results provide important constraints
on future models of the plasma and magnetic field in these structures.
---------------------------------------------------------
Title: Prominence and tornado dynamics observed with IRIS and THEMIS
Authors: Schmieder, Brigitte; Levens, Peter; Labrosse, Nicolas; Mein,
Pierre; Lopez Ariste, Arturo; Zapior, Maciek
2017SPD....4820104S Altcode:
Several prominences were observed during campaigns in September 2013 and
July 2014 with the IRIS spectrometer and the vector magnetograph THEMIS
(Tenerife). SDO/AIA and IRIS provided images and spectra of prominences
and tornadoes corresponding to different physical conditions of the
transition region between the cool plasma and the corona. The vector
magnetic field was derived from THEMIS observations by using the He
D3 depolarisation due to the magnetic field. The inversion code (PCA)
takes into account the Hanle and Zeeman effects and allows us to compute
the strength and the inclination of the magnetic field which is shown
to be mostly horizontal in prominences as well as in tornadoes. Movies
from SDO/AIA in 304 A and Hinode/SOT in Ca II show the highly dynamic
nature of the fine structures. From spectra in Mg II and Si IV lines
provided by IRIS and H-alpha observed by the Multi-channel Subtractive
Double Pass (MSDP) spectrograph in the Meudon Solar Tower we derived
the Doppler shifts of the fine structures and reconstructed the 3D
structure of tornadoes. We conclude that the apparent rotation of AIA
tornadoes is due to large-scale quasi-periodic oscillations of the
plasma along more or less horizontal magnetic structures.
---------------------------------------------------------
Title: Spectral Characteristics of the He I D<SUB>3</SUB> Line in
a Quiescent Prominence Observed by THEMIS
Authors: Koza, Július; Rybák, Ján; Gömöry, Peter; Kozák, Matúš;
López Ariste, Arturo
2017SoPh..292...98K Altcode: 2017arXiv171209255K
We analyze the observations of a quiescent prominence acquired by
the Téléscope Heliographique pour l'Étude du Magnetisme et des
Instabilités Solaires (THEMIS) in the He I 5876 Å (He I D<SUB>3</SUB>)
multiplet aiming to measure the spectral characteristics of the He
I D<SUB>3</SUB> profiles and to find for them an adequate fitting
model. The component characteristics of the He I D<SUB>3</SUB> Stokes I
profiles are measured by the fitting system by approximating them with
a double Gaussian. This model yields an He I D<SUB>3</SUB> component
peak intensity ratio of 5.5 ±0.4 , which differs from the value of
8 expected in the optically thin limit. Most of the measured Doppler
velocities lie in the interval ± 5 km s<SUP>−1</SUP>, with a standard
deviation of ± 1.7 km s<SUP>−1</SUP> around the peak value of 0.4
km s<SUP>−1</SUP>. The wide distribution of the full-width at half
maximum has two maxima at 0.25 Å and 0.30 Å for the He I D<SUB>3</SUB>
blue component and two maxima at 0.22 Å and 0.31 Å for the red
component. The width ratio of the components is 1.04 ±0.18 . We show
that the double-Gaussian model systematically underestimates the blue
wing intensities. To solve this problem, we invoke a two-temperature
multi-Gaussian model, consisting of two double-Gaussians, which
provides a better representation of He I D<SUB>3</SUB> that is free
of the wing intensity deficit. This model suggests temperatures of
11.5 kK and 91 kK, respectively, for the cool and the hot component
of the target prominence. The cool and hot components of a typical He
I D<SUB>3</SUB> profile have component peak intensity ratios of 6.6
and 8, implying a prominence geometrical width of 17 Mm and an optical
thickness of 0.3 for the cool component, while the optical thickness of
the hot component is negligible. These prominence parameters seem to
be realistic, suggesting the physical adequacy of the multi-Gaussian
model with important implications for interpreting He I D<SUB>3</SUB>
spectropolarimetry by current inversion codes.
---------------------------------------------------------
Title: Detection of the linearly polarised spectrum of the red
supergiant star alpha Ori
Authors: Tessore, Benjamin; Lòpez-Ariste, Arturo; Mathias, Philippe;
Lèbre, Agnès; Morin, Julien; Josselin, Eric
2017arXiv170202002T Altcode:
In the solar limb, linear polarisation is due to anisotropy of the
radiation field induced by limb darkening. It is maximal when it is
seen parallel to the limb and it vanishes when it is integrated over
the spherically-symmetric solar disk. Therefore for distant stars,
that present spherical symmetry, linear polarisation signatures are
very difficult to observe. However strong linear polarisation features
have been reported in the prototypical red supergiant star alpha Ori
(Betelgeuse). With an analytical model we propose to explain them.
---------------------------------------------------------
Title: Space-weather assets developed by the French space-physics
community
Authors: Rouillard, A. P.; Pinto, R. F.; Brun, A. S.; Briand, C.;
Bourdarie, S.; Dudok De Wit, T.; Amari, T.; Blelly, P. -L.; Buchlin,
E.; Chambodut, A.; Claret, A.; Corbard, T.; Génot, V.; Guennou, C.;
Klein, K. L.; Koechlin, L.; Lavarra, M.; Lavraud, B.; Leblanc, F.;
Lemorton, J.; Lilensten, J.; Lopez-Ariste, A.; Marchaudon, A.; Masson,
S.; Pariat, E.; Reville, V.; Turc, L.; Vilmer, N.; Zucarello, F. P.
2016sf2a.conf..297R Altcode:
We present a short review of space-weather tools and services developed
and maintained by the French space-physics community. They include
unique data from ground-based observatories, advanced numerical
models, automated identification and tracking tools, a range of space
instrumentation and interconnected virtual observatories. The aim of
the article is to highlight some advances achieved in this field of
research at the national level over the last decade and how certain
assets could be combined to produce better space-weather tools
exploitable by space-weather centres and customers worldwide. This
review illustrates the wide range of expertise developed nationally
but is not a systematic review of all assets developed in France.
---------------------------------------------------------
Title: Magnetic Field in Atypical Prominence Structures: Bubble,
Tornado, and Eruption
Authors: Levens, P. J.; Schmieder, B.; López Ariste, A.; Labrosse,
N.; Dalmasse, K.; Gelly, B.
2016ApJ...826..164L Altcode: 2016arXiv160505964L
Spectropolarimetric observations of prominences have been obtained with
the THEMIS telescope during four years of coordinated campaigns. Our aim
is now to understand the conditions of the cool plasma and magnetism
in “atypical” prominences, namely when the measured inclination
of the magnetic field departs, to some extent, from the predominantly
horizontal field found in “typical” prominences. What is the role
of the magnetic field in these prominence types? Are plasma dynamics
more important in these cases than the magnetic support? We focus our
study on three types of “atypical” prominences (tornadoes, bubbles,
and jet-like prominence eruptions) that have all been observed by THEMIS
in the He I D<SUB>3</SUB> line, from which the Stokes parameters can
be derived. The magnetic field strength, inclination, and azimuth in
each pixel are obtained by using the inversion method of principal
component analysis on a model of single scattering in the presence of
the Hanle effect. The magnetic field in tornadoes is found to be more
or less horizontal, whereas for the eruptive prominence it is mostly
vertical. We estimate a tendency toward higher values of magnetic
field strength inside the bubbles than outside in the surrounding
prominence. In all of the models in our database, only one magnetic
field orientation is considered for each pixel. While sufficient
for most of the main prominence body, this assumption appears to be
oversimplified in atypical prominence structures. We should consider
these observations as the result of superposition of multiple magnetic
fields, possibly even with a turbulent field component.
---------------------------------------------------------
Title: Daytime sky polarization calibration limitations
Authors: Harrington, David M.; Kuhn, Jeffrey R.; López Ariste, Arturo
2016SPIE.9912E..6SH Altcode:
The daytime sky has been recently demonstrated as a useful
calibration tool for deriving polarization cross-talk properties of
large astronomical telescopes. The Daniel K Inouye Solar Telescope
(DKIST) and other large telescopes under construction can benefit from
precise polarimetric calibration of large off-axis mirrors. Several
atmospheric phenomena and instrumental errors potentially limit the
techniques accuracy. At the 3.67m AEOS telescope on Haleakala, we have
performed a large observing campaign with the HiVIS spectropolarimeter
to identify limitations and develop algorithms for extracting consistent
calibrations. Effective sampling of the telescope optical configurations
and filtering of data for several derived parameters provide robustness
to the derivedMueller matrix calibrations. Second-order scattering
models of the sky show that this method is relatively insensitive to
assumptions about telescope induced polarization provided the mirror
coatings are highly reflective. Zemax-derived polarization models show
agreement between predictions and on-sky calibrations.
---------------------------------------------------------
Title: New life for the THEMIS solar telescope
Authors: Gelly, Bernard; Langlois, Maud; Moretto, Gil; Douet, Richard;
Lopez Ariste, Arturo; Tallon, Michel; Thiébaut, Eric; Geyskens,
Nicolas; Lorgeoux, Guillaume; Léger, Johnathan; Le Men, Claude
2016SPIE.9906E..5AG Altcode:
The THEMIS solar telescope is building a classical adaptive optics
(AO) system to be operating on the Sun in 2017. To make compatible
its excellent dual beam spectropolarimetric features with the AO
also requires a major refurbishment of the relay optics starting at
the M2 and down to the spectrograph entrance. This paper presents
the design parameters and expected performances of our AO system,
and explains why and how we intend to control to a few percent the
Mueller matrix of the whole optical path from the prime focus to the
spectropolarimetric cameras. This project is co-funded by the European
Union SOLARNET Project Ref.:312495, and the Centre National de la
Recherche Scientifique.
---------------------------------------------------------
Title: Prominence plasma and magnetic field structure - A coordinated
observation with IRIS, Hinode and THEMIS
Authors: Schmieder, Brigitte; Labrosse, Nicolas; Levens, Peter;
Lopez Ariste, Arturo
2016cosp...41E1749S Altcode:
During an international campaign in 2014, utilising both space-based
(IRIS and Hinode) and ground-based (THEMIS) instruments, we focused
on observing prominences. We compare IRIS observations with those of
Hinode (EIS and SOT) in order to build a more complete picture of
the prominence structure for a quiescent prominence observed on 15
July 2014, identified to have tornado-like structure. THEMIS provides
valuable information on the orientation and strength of the internal
magnetic field. Here we find there is almost ubiquitously horizontal
field with respect to the local limb, with possibly a turbulent
component. The Mg II lines form the majority of our IRIS analysis,
with a mixture of reversed and non-reversed profiles present in the
prominence spectra. Comparing the differences between the Mg II data
from IRIS and the Ca II images from Hinode/SOT provides an intriguing
insight into the prominence legs in these channels. We present plasma
diagnostics from IRIS, with line of sight velocities of around 10
km/s in either direction along the magnetic loops of material in the
front of the prominence, and line widths comparable to those found
for prominences by previous authors (e.g. Schmieder et al. 2014). We
also take a look into the lines formed at higher, coronal plasma
temperatures, as seen by Hinode/EIS, to compare plasma structures at
a full range of temperatures.
---------------------------------------------------------
Title: Discovery of a complex linearly polarized spectrum of
Betelgeuse dominated by depolarization of the continuum
Authors: Aurière, M.; López Ariste, A.; Mathias, P.; Lèbre, A.;
Josselin, E.; Montargès, M.; Petit, P.; Chiavassa, A.; Paletou, F.;
Fabas, N.; Konstantinova-Antova, R.; Donati, J. -F.; Grunhut, J. H.;
Wade, G. A.; Herpin, F.; Kervella, P.; Perrin, G.; Tessore, B.
2016A&A...591A.119A Altcode: 2016arXiv160504702A
Context. <ASTROBJ>Betelgeuse</ASTROBJ> is an M supergiant that
harbors spots and giant granules at its surface and presents linear
polarization of its continuum. <BR /> Aims: We have previously
discovered linear polarization signatures associated with
individual lines in the spectra of cool and evolved stars. Here,
we investigate whether a similar linearly polarized spectrum exists
for <ASTROBJ>Betelgeuse</ASTROBJ>. <BR /> Methods: We used the
spectropolarimeter Narval, combining multiple polarimetric sequences
to obtain high signal-to-noise ratio spectra of individual lines, as
well as the least-squares deconvolution (LSD) approach, to investigate
the presence of an averaged linearly polarized profile for the
photospheric lines. <BR /> Results: We have discovered the existence
of a linearly polarized spectrum for <ASTROBJ>Betelgeuse</ASTROBJ>,
detecting a rather strong signal (at a few times 10<SUP>-4</SUP>
of the continuum intensity level), both in individual lines and in
the LSD profiles. Studying its properties and the signal observed for
the resonant Na I D lines, we conclude that we are mainly observing
depolarization of the continuum by the absorption lines. The linear
polarization of the Betelgeuse continuum is due to the anisotropy of
the radiation field induced by brightness spots at the surface and
Rayleigh scattering in the atmosphere. We have developed a geometrical
model to interpret the observed polarization, from which we infer the
presence of two brightness spots and their positions on the surface
of <ASTROBJ>Betelgeuse</ASTROBJ>. We show that applying the model
to each velocity bin along the Stokes Q and U profiles allows the
derivation of a map of the bright spots. We use the Narval linear
polarization observations of <ASTROBJ>Betelgeuse</ASTROBJ> obtained
over a period of 1.4 yr to study the evolution of the spots and of the
atmosphere. <BR /> Conclusions: Our study of the linearly polarized
spectrum of <ASTROBJ>Betelgeuse</ASTROBJ> provides a novel method
for studying the evolution of brightness spots at its surface and
complements quasi-simultaneous observations obtained with PIONIER at
the VLTI. <P />Based on observations obtained at the Télescope Bernard
Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and Université
de Toulouse, France.
---------------------------------------------------------
Title: Vortex waves in sunspots
Authors: López Ariste, A.; Centeno, R.; Khomenko, E.
2016A&A...591A..63L Altcode:
Context. Waves in the magnetized solar atmosphere are one of the
favourite means of transferring and depositing energy into the solar
corona. The study of waves brings information not just on the dynamics
of the magnetized plasma, but also on the possible ways in which the
corona is heated. <BR /> Aims: The identification and analysis of the
phase singularities or dislocations provide us with a complementary
approach to the magnetoacoustic and Aflvén waves propagating in the
solar atmosphere. They allow us to identify individual wave modes,
shedding light on the probability of excitation or the nature of the
triggering mechanism. <BR /> Methods: We use a time series of Doppler
shifts measured in two spectral lines, filtered around the three-minute
period region. The data show a propagating magnetoacoustic slow
mode with several dislocations and, in particular, a vortex line. We
study under what conditions the different wave modes propagating in
the umbra can generate the observed dislocations. <BR /> Results:
The observed dislocations can be fully interpreted as a sequence
of sausage and kink modes excited sequentially on average during
15 min. Kink and sausage modes appear to be excited independently
and sequentially. The transition from one to the other lasts less
than three minutes. During the transition we observe and model the
appearance of superoscillations inducing large phase gradients and
phase mixing. <BR /> Conclusions: The analysis of the observed wave
dislocations leads us to the identification of the propagating wave
modes in umbrae. The identification in the data of superoscillatory
regions during the transition from one mode to the other may be an
important indicator of the location of wave dissipation.
---------------------------------------------------------
Title: Magnetic Field and Plasma Diagnostics from Coordinated
Prominence Observations
Authors: Schmieder, B.; Levens, P.; Dalmasse, K.; Mein, N.; Mein,
P.; Lopez-Ariste, A.; Labrosse, N.; Heinzel, P.
2016ASPC..504..119S Altcode:
We study the magnetic field in prominences from a statistical point of
view, by using THEMIS in the MTR mode, performing spectropolarimetry
of the He I D<SUB>3</SUB> line. Combining these measurements with
spectroscopic data from IRIS, Hinode/EIS as well as ground-based
telescopes, such as the Meudon Solar Tower, we infer the temperature,
density, and flow velocities of the plasma. There are a number of
open questions that we aim to answer: - What is the general direction
of the magnetic field in prominences? Is the model using a single
orientation of magnetic field always valid for atypical prominences? %-
Does this depend on the location of the filament on the disk (visible
in Hα, in He II 304 Å) over an inversion line between weak or strong
network ? - Are prominences in a weak environment field dominated by
gas pressure? - Measuring the Doppler shifts in Mg II lines (with IRIS)
and in Hα can tell us if there are substantial velocities to maintain
vertical rotating structures, as has been suggested for tornado-like
prominences. We present here some results obtained with different
ground-based and space-based instruments in this framework.
---------------------------------------------------------
Title: The close circumstellar environment of
Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the
photosphere
Authors: Montargès, M.; Kervella, P.; Perrin, G.; Chiavassa, A.;
Le Bouquin, J. -B.; Aurière, M.; López Ariste, A.; Mathias, P.;
Ridgway, S. T.; Lacour, S.; Haubois, X.; Berger, J. -P.
2016A&A...588A.130M Altcode: 2016arXiv160205108M
Context. The mass-loss mechanism of cool massive evolved stars is
poorly understood. The proximity of Betelgeuse makes it an appealing
target to study its atmosphere, map the shape of its envelope,
and follow the structure of its wind from the photosphere out to
the interstellar medium. <BR /> Aims: A link is suspected between
the powerful convective motions in Betelgeuse and its mass loss. We
aim to constrain the spatial structure and temporal evolution of the
convective pattern on the photosphere and to search for evidence of
this link. <BR /> Methods: We report new interferometric observations
in the infrared H-band using the VLTI/PIONIER instrument. We monitored
the photosphere of Betelgeuse between 2012 January and 2014 November
to look for evolutions that may trigger the outflow. <BR /> Results:
Our interferometric observations at low spatial frequencies are
compatible with the presence of a hot spot on the photosphere that has a
characteristic width of one stellar radius. It appears to be superposed
on the smaller scale convective pattern. In the higher spatial frequency
domain, we observe a significant difference between the observations and
the predictions of 3D hydrodynamical simulations. <BR /> Conclusions:
We bring new evidence for the presence of a convective pattern in
the photosphere of red supergiants. The inferred hot spot is probably
the top of a giant convection cell although an asymmetric extension
of the star cannot be excluded by these interferometric observations
alone. The properties of the observed surface features show a stronger
contrast and inhomogeneity as predicted by 3D radiative hydrodynamical
simulations. We propose that the large observed feature is modifying the
signature of the convective pattern at the surface of the star in a way
that simulations cannot reproduce. <P />Based on observations made with
ESO telescopes at Paranal Observatory, under ESO programs 288.D-5035(A),
090.D-0548(A), 092.D-0366(A), 092.D-0366(B) and 094.D-0869 (A).
---------------------------------------------------------
Title: Detection of ultra-weak magnetic fields in Am stars: β Ursae
Majoris and θ Leonis
Authors: Blazère, A.; Petit, P.; Lignières, F.; Aurière, M.; Ballot,
J.; Böhm, T.; Folsom, C. P.; Gaurat, M.; Jouve, L.; Lopez Ariste,
A.; Neiner, C.; Wade, G. A.
2016A&A...586A..97B Altcode: 2016arXiv160101829B
Context. An extremely weak circularly polarized signature was recently
discovered in spectral lines of the chemically peculiar Am star
Sirius A. A weak surface magnetic field was proposed to account for
the observed polarized signal, but the shape of the phase-averaged
signature, dominated by a prominent positive lobe, is not expected
in the standard theory of the Zeeman effect. <BR /> Aims: We aim
at verifying the presence of weak circularly polarized signatures
in two other bright Am stars, β UMa and θ Leo, and investigating
the physical origin of Sirius-like polarized signals further. <BR />
Methods: We present here a set of deep spectropolarimetric observations
of β UMa and θ Leo, observed with the NARVAL spectropolarimeter. We
analyzed all spectra with the least squares deconvolution multiline
procedure. To improve the signal-to-noise ratio and detect extremely
weak signatures in Stokes V profiles, we co-added all available
spectra of each star (around 150 observations each time). Finally,
we ran several tests to evaluate whether the detected signatures are
consistent with the behavior expected from the Zeeman effect. <BR />
Results: The line profiles of the two stars display circularly polarized
signatures similar in shape and amplitude to the observations previously
gathered for Sirius A. Our series of tests brings further evidence of a
magnetic origin of the recorded signal. <BR /> Conclusions: These new
detections suggest that very weak magnetic fields may well be present
in the photospheres of a significant fraction of intermediate-mass
stars. The strongly asymmetric Zeeman signatures measured so far in Am
stars (featuring a dominant single-sign lobe) are not expected in the
standard theory of the Zeeman effect and may be linked to sharp vertical
gradients in photospheric velocities and magnetic field strengths.
---------------------------------------------------------
Title: Structure of Prominence Legs: Plasma and Magnetic Field
Authors: Levens, P. J.; Schmieder, B.; Labrosse, N.; López Ariste, A.
2016ApJ...818...31L Altcode: 2015arXiv151204727L
We investigate the properties of a “solar tornado” observed
on 2014 July 15, and aim to link the behavior of the plasma to the
internal magnetic field structure of the associated prominence. We
made multi-wavelength observations with high spatial resolution and
high cadence using SDO/AIA, the Interface Region Imaging Spectrograph
(IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT)
instrument. Along with spectropolarimetry provided by the Télescope
Héliographique pour l’Etude du Magnétisme et des Instabilités
Solaires telescope we have coverage of both optically thick emission
lines and magnetic field information. AIA reveals that the two legs
of the prominence are strongly absorbing structures which look like
they are rotating, or oscillating in the plane of the sky. The two
prominence legs, which are both very bright in Ca II (SOT), are not
visible in the IRIS Mg II slit-jaw images. This is explained by the
large optical thickness of the structures in Mg II, which leads to
reversed profiles, and hence to lower integrated intensities at these
locations than in the surroundings. Using lines formed at temperatures
lower than 1 MK, we measure relatively low Doppler shifts on the order
of ±10 km s<SUP>-1</SUP> in the tornado-like structure. Between the two
legs we see loops in Mg II, with material flowing from one leg to the
other, as well as counterstreaming. It is difficult to interpret our
data as showing two rotating, vertical structures that are unrelated
to the loops. This kind of “tornado” scenario does not fit with
our observations. The magnetic field in the two legs of the prominence
is found to be preferentially horizontal.
---------------------------------------------------------
Title: Polarimetric calibration of large mirrors
Authors: Lopez Ariste, A.
2015arXiv151103177L Altcode:
Aims: To propose a method for the polarimetric calibration of large
astronomical mirrors that does not require use of special optical
devices nor knowledge of the exact polarization properties of the
calibration target. Methods: We study the symmetries of the Mueller
matrix of mirrors to exploit them for polarimetric calibration under
the assumptions that only the orientation of the linear polarization
plane of the calibration target is known with certainty. Results:
A method is proposed to calibrate the polarization effects of single
astronomical mirrors by the observation of calibration targets with
known orientation of the linear polarization. We study the uncertainties
of the method and the signal-to-noise ratios required for an acceptable
calibration. We list astronomical targets ready for the method. We
finally extend the method to the calibration of two or more mirrors,
in particular to the case when they share the same incidence plane.
---------------------------------------------------------
Title: Polarimetric measurements in prominences and "tornadoe"
observed by THEMIS
Authors: Schmieder, Brigitte; López Ariste, Arturo; Levens, Peter;
Labrosse, Nicolas; Dalmasse, Kévin
2015IAUS..305..275S Altcode:
Since 2013, coordinated campaigns with the THEMIS spectropolarimeter in
Tenerife and other instruments (space based: Hinode/SOT, IRIS or ground
based: Sac Peak, Meudon) are organized to observe prominences. THEMIS
records spectropolarimetry at the He I D<SUB>3</SUB> and we use the
PCA inversion technique to derive their field strength, inclination
and azimuth.
---------------------------------------------------------
Title: On the nature of transverse coronal waves revealed by wavefront
dislocations
Authors: López Ariste, A.; Luna, M.; Arregui, I.; Khomenko, E.;
Collados, M.
2015A&A...579A.127L Altcode: 2015arXiv150503348L
Context. Coronal waves are an important aspect of the dynamics of the
plasma in the corona. Wavefront dislocations are topological features
of most waves in nature and also of magnetohydrodynamic waves. Are there
dislocations in coronal waves? <BR /> Aims: The finding and explanation
of dislocations may shed light on the nature and characteristics of the
propagating waves, their interaction in the corona, and in general on
the plasma dynamics. <BR /> Methods: We positively identify dislocations
in coronal waves observed by the Coronal Multi-channel Polarimeter
(CoMP) as singularities in the Doppler shifts of emission coronal
lines. We study the possible singularities that can be expected in
coronal waves and try to reproduce the observed dislocations in terms of
localization and frequency of appearance. <BR /> Results: The observed
dislocations can only be explained by the interference of a kink and
sausage wave modes propagating with different frequencies along the
coronal magnetic field. In the plane transverse to the propagation,
the cross-section of the oscillating plasma must be smaller than the
spatial resolution, and the two waves result in net longitudinal and
transverse velocity components that are mixed through projection onto
the line of sight. Alfvén waves can be responsible for the kink mode,
but a magnetoacoustic sausage mode is necessary in all cases. Higher
(flute) modes are excluded. The kink mode has a pressure amplitude
that is less than the pressure amplitude of the sausage mode, though
its observed velocity is higher. This concentrates dislocations on
the top of the loop. <BR /> Conclusions: To explain dislocations,
any model of coronal waves must include the simultaneous propagation
and interference of kink and sausage wave modes of comparable but
different frequencies with a sausage wave amplitude much smaller than
the kink one. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Magnetometry of Prominences
Authors: López Ariste, Arturo
2015ASSL..415..179L Altcode: 2015ASSL..415..179A
We describe the measurement of magnetic fields in prominences. Using
the He D<SUB>3</SUB> line as example we describe and illustrate the
computation of the polarization emitted by He atoms in the presence
of magnetic fields. The relatively weak magnetic fields expected in
prominences require taking into consideration a long series of quantum
coherences between the atomic levels of the He atom, coherences that
are critical for the sensitivity of the emitted radiation and its
polarization to the magnetic fields. But solving that quantum problem
is only half the task: the observed polarized profiles need to be
compared to the computed ones until a match is found. This inference
or inversion can only work when the appropriate numerical technicals
are put to work, techniques that help identify what magnetic field is
the best solution for an observed profile, that can make use of all
the available observables while being robust in front of noise and the
low brightness of prominences and filaments respect to the entouring
photosphere. These difficulties can be tackled but at the prixe of
some approximations that have to be kept in mind in the analysis of
prominence magnetic fields at the risk of serious mistakes on the
inferred magnetic fields. Improving upon those approximations marks
also the path for the future, with which description we will conclude
this chapter.
---------------------------------------------------------
Title: Open questions on prominences from coordinated observations
by IRIS, Hinode, SDO/AIA, THEMIS, and the Meudon/MSDP
Authors: Schmieder, B.; Tian, H.; Kucera, T.; López Ariste, A.;
Mein, N.; Mein, P.; Dalmasse, K.; Golub, L.
2014A&A...569A..85S Altcode: 2014arXiv1407.3171S
Context. A large prominence was observed by multiple instruments on the
ground and in space during an international campaign on September 24,
2013, for three hours (12:12 UT -15:12 UT). Instruments used in the
campaign included the newly launched (June 2013) Interface Region
Imaging Spectrograph (IRIS), THEMIS (Tenerife), the Hinode Solar
Optical Telescope (SOT), the Solar Dynamic Observatory's Atmospheric
Imaging Assembly (SDO/AIA), and the Multichannel Subtractive Double
Pass spectrograph (MSDP) in the Meudon Solar Tower. The movies obtained
in 304 Å with the EUV imager SDO/AIA, and in Ca II line by SOT show
the dynamic nature of the prominence. <BR /> Aims: The aim of this
work is to study the dynamics of the prominence fine structures in
multiple wavelengths to understand their formation. <BR /> Methods:
The spectrographs IRIS and MSDP provided line profiles with a high
cadence in Mg II h (2803.5 Å) and k (2796.4 Å) lines along four
slit positions (IRIS), and in Hα in a 2D field of view (MSDP). The
spectropolarimetry of THEMIS (Tenerife) allowed us to derive the
magnetic field of the prominence using the He D<SUB>3</SUB> line
depolarization (Hanle effect combined with the Zeeman effect). <BR />
Results: The magnetic field is found to be globally horizontal with
a relatively weak field strength (8-15 Gauss). On the other hand,
the Ca II movie reveals turbulent-like motion that is not organized in
specific parts of the prominence. We tested the addition of a turbulent
magnetic component. This model is compatible with the polarimetric
observations at those places where the plasma turbulence peaks. On the
other hand, the Mg II line profiles show multiple peaks well separated
in wavelength. This is interpreted by the existence of small threads
along the line of sight with a large dispersion of discrete values of
Doppler shifts, from 5 km s<SUP>-1</SUP> (a quasi-steady component) to
60-80 km s<SUP>-1</SUP>. Each peak corresponds to a Gaussian profile,
and not to a reversed profile as was expected by the present non-LTE
radiative transfer modeling. This is a very surprising behavior for
the Mg II line observed in prominences. <BR /> Conclusions: Turbulent
fields on top of the macroscopic horizontal component of the magnetic
field supporting the prominence give rise to the complex dynamics of
the plasma. The plasma with the high velocities (70 km s<SUP>-1</SUP> to
100 km s<SUP>-1</SUP> if we take into account the transverse velocities)
may correspond to condensation of plasma along more or less horizontal
threads of the arch-shape structure visible in 304 Å. The steady
flows (5 km s<SUP>-1</SUP>) would correspond to a more quiescent plasma
(cool and prominence-corona transition region) of the prominence packed
into dips in horizontal magnetic field lines. The very weak secondary
peaks in the Mg II profiles may reflect the turbulent nature of parts
of the prominence. <P />Movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201423922/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Erratum: "Propagating Waves Transverse to the Magnetic Field
in a Solar Prominence" <A href="/abs/2013ApJ...777..108S">(2013,
ApJ, 777, 108)</A>
Authors: Schmieder, B.; Kucera, T. A.; Knizhnik, K.; Luna, M.;
Lopez-Ariste, A.; Toot, D.
2014ApJ...781..129S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Propagating waves transverse to the magnetic field in a
solar prominence
Authors: Kucera, Therese; Schmieder, Brigitte; Knizhnik, Kalman;
Lopez-Ariste, Arturo; Luna, Manuel; Toot, David
2014IAUS..300..435K Altcode:
We have observed a quiescent prominence with the Hinode Solar Optical
Telescope (SOT) (Ca II and Hα lines), Sacramento Peak Dunn Solar
Telescope using the Universal Birefringent Filter (DST/UBF, in Hα,
Hβ and Sodium-D lines), THEMIS (Télescope Héliographique pour l
Etude du Magnétisme et des Instabilités Solaires/MTR (Multi Raies)
spectromagnetograph (He D<SUB>3</SUB>), and the Solar Dynamics
Observatory Atmospheric Imaging Assembly (SDO/AIA) in EUV over a 4
hour period on 2012 October 10. The small fields of view of the SOT,
DST, and MTR are centered on a large prominence footpoint extending
towards the surface. This feature appears in the larger field of view
of the AIA/304 Å filtergram as a large, quasi-vertical pillar with
loops on each side. The THEMIS/MTR data indicate that the magnetic
field in the pillar is essentially horizontal and the observations in
the optical domain show a large number of horizontally aligned features
in the pillar. The data are consistent with a model of cool prominence
plasma trapped in the dips of horizontal field lines. The SOT and DST
data show what appear to be moving wave pulses. These pulses, which
include a Doppler signature, move vertically, perpendicular to the
field direction, along quasi-vertical columns of horizontal threads in
the pillar. The pulses have a velocity of propagation of about 10 km/s,
a wavelength about 2000 km in the plane of the sky, and a period about
280 sec. We interpret these waves in terms of fast magnetosonic waves.
---------------------------------------------------------
Title: Dynamics of a prominence observed in Mg II lines by IRIS
Authors: Schmieder, Brigitte; Mein, Pierre; Dalmasse, Kévin; Tian,
Hui; Kucera, Therese; Lopez-Ariste, Arturo
2014cosp...40E2927S Altcode:
In September 2013 several prominences were observed with the IRIS
spectrograph during a 60 day-long international program. We will present
one set of observations obtained using multiple instruments on September
24. SDO/AIA and IRIS slit jaws provided images of the prominence
corresponding to different physical conditions of the transition
region between the cool plasma and the corona. The vector magnetic
field was derived from THEMIS (Tenerife) observations using the He D3
depolarisation due to the magnetic field. The inversion code (CPA) takes
into account the Hanle and the Zeeman effects. Movies from SDO/AIA in
304 A and Hinode/SOT in Ca II show the dynamics of the fine structures
in the plane of the sky. From Mg II and Si IV line spectra observed by
IRIS and H-alpha observed by the Multi-channel subtractive spectrograph
(MSDP) in the Meudon solar tower we derived the Dopplershifts of the
fine structures. The profiles of the Mg II lines are narrow (FHWM =0.15
A) and not reversed, contrary to the predictions of the theoretical
models (Paletou et al 1993). We could resolve the velocity of several
structures along the LOS with Dopplershifts as high as 60 km/s.
---------------------------------------------------------
Title: Propagating Waves Transverse to the Magnetic Field in a
Solar Prominence
Authors: Schmieder, B.; Kucera, T. A.; Knizhnik, K.; Luna, M.;
Lopez-Ariste, A.; Toot, D.
2013ApJ...777..108S Altcode: 2013arXiv1309.1568S
We report an unusual set of observations of waves in a large prominence
pillar that consist of pulses propagating perpendicular to the
prominence magnetic field. We observe a huge quiescent prominence with
the Solar Dynamics Observatory Atmospheric Imaging Assembly in EUV on
2012 October 10 and only a part of it, the pillar, which is a foot or
barb of the prominence, with the Hinode Solar Optical Telescope (SOT;
in Ca II and Hα lines), Sac Peak (in Hα, Hβ, and Na-D lines), and
THEMIS ("Télescope Héliographique pour l' Etude du Magnétisme et des
Instabilités Solaires") with the MTR (MulTi-Raies) spectropolarimeter
(in He D<SUB>3</SUB> line). The THEMIS/MTR data indicates that
the magnetic field in the pillar is essentially horizontal and the
observations in the optical domain show a large number of horizontally
aligned features on a much smaller scale than the pillar as a whole. The
data are consistent with a model of cool prominence plasma trapped in
the dips of horizontal field lines. The SOT and Sac Peak data over
the four hour observing period show vertical oscillations appearing
as wave pulses. These pulses, which include a Doppler signature,
move vertically, perpendicular to the field direction, along thin
quasi-vertical columns in the much broader pillar. The pulses have
a velocity of propagation of about 10 km s<SUP>-1</SUP>, a period of
about 300 s, and a wavelength around 2000 km. We interpret these waves
in terms of fast magnetosonic waves and discuss possible wave drivers.
---------------------------------------------------------
Title: Dislocations in Magnetohydrodynamic Waves in a Stellar
Atmosphere
Authors: López Ariste, A.; Collados, M.; Khomenko, E.
2013PhRvL.111h1103L Altcode: 2013arXiv1308.0145L
We describe the presence of wave front dislocations in
magnetohydrodynamic waves in stratified stellar atmospheres. Scalar
dislocations such as edges and vortices can appear in Alfvén waves, as
well as in general magnetoacoustic waves. We detect those dislocations
in observations of magnetohydrodynamic waves in sunspots in the solar
chromosphere. Through the measured charge of all the dislocations
observed, we can give for the first time estimates of the modal
contribution in the waves propagating along magnetic fields in solar
sunspots.
---------------------------------------------------------
Title: Improved Search of Principal Component Analysis Databases
for Spectro-polarimetric Inversion
Authors: Casini, R.; Asensio Ramos, A.; Lites, B. W.; López Ariste, A.
2013ApJ...773..180C Altcode: 2013arXiv1307.0061C
We describe a simple technique for the acceleration of
spectro-polarimetric inversions based on principal component analysis
(PCA) of Stokes profiles. This technique involves the indexing of the
database models based on the sign of the projections (PCA coefficients)
of the first few relevant orders of principal components of the
four Stokes parameters. In this way, each model in the database can
be attributed a distinctive binary number of 2<SUP>4n </SUP> bits,
where n is the number of PCA orders used for the indexing. Each of
these binary numbers (indices) identifies a group of "compatible"
models for the inversion of a given set of observed Stokes profiles
sharing the same index. The complete set of the binary numbers so
constructed evidently determines a partition of the database. The
search of the database for the PCA inversion of spectro-polarimetric
data can profit greatly from this indexing. In practical cases it
becomes possible to approach the ideal acceleration factor of 2<SUP>4n
</SUP> as compared to the systematic search of a non-indexed database
for a traditional PCA inversion. This indexing method relies on the
existence of a physical meaning in the sign of the PCA coefficients
of a model. For this reason, the presence of model ambiguities and of
spectro-polarimetric noise in the observations limits in practice the
number n of relevant PCA orders that can be used for the indexing.
---------------------------------------------------------
Title: Propagating Waves Transverse to the Magnetic Field in a
Solar Prominence
Authors: Kucera, Therese A.; Knizhnik, K.; Lopez Ariste, A.; Luna
Bennasar, M.; Schmieder, B.; Toot, D.
2013SPD....4410403K Altcode:
We have observed a quiescent prominence with the Hinode Solar Optical
Telescope (SOT, in Ca II and H-alpha lines), Sacramento Peak Observatory
(in H-alpha, H-beta and Sodium-D lines), and THEMIS/MTR (Télescope
Héliographique pour l'Étude du Magnétisme et des Instabilités
Solaires/MulTi Raies, providing vector magnetograms), and SDO/AIA (Solar
Dynamics Observatory Atmospheric Imaging Assembly, in EUV) over a 4 hour
period on 2012 October 10. The small fields of view of SOT, Sac Peak
and THEMIS are centered on a large pillar-like prominence footpoint
extending towards the surface. This feature appears in the larger
field of view of the 304 Å band, as a large, quasi-vertical column
with material flowing horizontally on each side. The THEMIS/MTR data
indicate that the magnetic field in the pillar is essentially horizontal
and the observations in the optical wavelengths show a large number of
horizontally aligned features on a much smaller scale than the pillar
as a whole. The data are consistent with a model of cool prominence
plasma trapped in the dips of horizontal field lines. The SOT and Sac
Peak data show what appear to be moving wave pulses. These pulses,
which include a Doppler signature, move vertically, perpendicular to
the field direction, along quasi-vertical columns. The pulses have
a velocity of propagation of about 10 km/s, a period about 260 sec,
and a wavelength around 2000 km. We interpret these waves in terms of
fast magneto-sonic waves and discuss possible wave drivers.
---------------------------------------------------------
Title: Mercury exosphere. III: Energetic characterization of its
sodium component
Authors: Leblanc, Francois; Chaufray, Jean-Yves; Doressoundiram,
Alain; Berthelier, Jean-Jacques; Mangano, Valeria; López-Ariste,
Arturo; Borin, Patrizia
2013Icar..223..963L Altcode:
Mercury's sodium exosphere has been observed only few times with high
spectral resolution from ground based observatories enabling the
analysis of the emission spectra. These observations highlighted
the energetic state of the sodium exospheric atoms relative to
the surface temperature. More recently, the Doppler shift of the
exospheric Na atoms was measured and interpreted as consistent with
an exosphere moving outwards from the subsolar point (Potter, A.E.,
Morgan, T.H., Killen, R.E. [2009]. Icarus 204, 355-367). Using THEMIS
solar telescope, we observed Mercury's sodium exosphere with very high
spectral resolution at two opposite positions of its orbit. Using
this very high spectral resolution and the scanning capabilities of
THEMIS, we were able to reconstruct the 2D spatial distributions of
the Doppler shifts and widths of the sodium atomic Na D<SUB>2</SUB>
and D<SUB>1</SUB> lines. These observations revealed surprisingly
large Doppler shift as well as spectral width consistent with previous
observations. Starting from our 3D model of Mercury Na exosphere
(Mercury Exosphere Global Circulation Model, Leblanc, F., Johnson,
R.E. [2010]. Icarus 209, 280-300), we coupled this model with a 3D
radiative transfer model described in a companion paper (Chaufray,
J.Y., Leblanc, F. [2013]. Icarus, submitted for publication) which
allows us to properly treat the non-maxwellian state of the simulated
sodium exospheric population. Comparisons between THEMIS observations
and simulations suggest that the previously observed energetic state
of the Na exosphere might be essentially explained by a state of
the Na exospheric atoms far from thermal equilibrium along with the
Doppler shift dispersion of the Na atoms induced by the solar radiation
pressure. However, the Doppler shift of the spectral lines cannot be
explained by our modelling, suggesting either an exosphere spatially
structured very differently than in our model or the inaccuracy of
the spectral calibration when deriving the Doppler shift.
---------------------------------------------------------
Title: Towards Measuring the Magnetic Energy Spectrum at
Sub-Resolution Scales
Authors: López Ariste, A.; Sainz Dalda, A.
2012ASPC..463..243L Altcode:
Area asymmetries in the Stokes V profile of the Zeeman-sensitive Fe
I line at 630.25 nm shed light on gradients of velocity and magnetic
field along the photon path. We use that information on observations
of Hinode-SOT/SP of the quiet sun at different heliocentric angles
to further investigate turbulent field models in those regions. The
relationship between the asymmetry value and a correlation length
scale for the field strength in the framework of stochastic radiative
transfer for polarized light allows us to identify in the data
subresolution scales of change of the magnetic field. From these we
make a crude first attempt to determine the energy spectrum of the
turbulent magnetic field down to the km scale as a proof-of-concept
of the potential of this technique.
---------------------------------------------------------
Title: Beyond the Solar Corona: Mercury's Magnetic Fields seen with
Large Solar Telescopes
Authors: López Ariste, A.; Leblanc, F.
2012ASPC..463..275L Altcode:
Solar telescopes have a potential in non-solar observations thanks to
their instrumentation and their ability to observe in daylight, and
despite their smaller mirror size compared to night-time telescopes. We
review, as an illustration, THEMIS observations of Mercury's exosphere
including the polarization of exospheric emission lines, and speculate
that through analysis of this polarization made possible by the large
photon-collecting capabilities of the upcoming large solar telescope
we may expect to map Mercury's magnetosphere.
---------------------------------------------------------
Title: Multi-purpose grating spectrograph for the 4-meter European
Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Gelly, B.; Grauf, B.;
Hirzberger, J.; López Ariste, A.; Lopez, R. L.; Mein, P.; Sayéde, F.
2012SPIE.8446E..6TC Altcode:
This communication presents a family of spectrographs designed for
the European Solar Telescope. They can operate in four different
configurations: a long slit standard spectrograph (LsSS), two devices
based on subtractive double pass (TUNIS and MSDP) and one based on
an integral field, multi-slit, multi-wavelength configuration. The
combination of them composes the multi-purpose grating spectrograph of
EST, focused on supporting the different science cases of the solar
photosphere and chromosphere in the spectral range from 3900 Å to
23000 Å. The different alternatives are made compatible by using
the same base spectrographs and different selectable optical elements
corresponding to specific subsystems of each configuration.
---------------------------------------------------------
Title: Resonance scattering polarization in the magnetosphere
of Mercury
Authors: López Ariste, A.; Leblanc, F.; Casini, R.; Manso Sainz,
R.; Gelly, B.; Le Men, C.
2012Icar..220.1104L Altcode:
The conditions of the exosphere of Mercury constitute a prime example
of a magnetosphere subject to space weather. We aim at improving the
diagnostic of the physical conditions of Na atoms in the exosphere of
Mercury, with particular emphasis in the possibility of inferring the
magnetic field through polarimetry of the Na D emission lines. We
performed spectropolarimetry of the Na D emission lines in the
exosphere of Mercury at two different ranges of phases of the planet
and interpreted them under present models of resonance scattering
polarization applied to the Na atom. We measured successfully the
polarization of the Na D<SUB>2</SUB> line while no polarization
was seen in D<SUB>1</SUB>, as expected. The measured polarization
varies with the phase angle but it is roughly a factor two smaller
than expected from an isolated emitting atom. Depolarization due to
the presence of optical depth explains this factor two and is the
most probable explanation for this discrepancy. A framework for the
observation of polarization in the emission lines of the exosphere and
its interpretation is laid. This opens the possibility to use these
measurements for diagnostic of the physical conditions in the exosphere
of Mercury, and eventually to infer the magnetic field of Mercury and
its variability from observations made with ground telescopes.
---------------------------------------------------------
Title: Scales of the magnetic fields in the quiet Sun
Authors: López Ariste, A.; Sainz Dalda, A.
2012A&A...540A..66L Altcode: 2012arXiv1202.5436L
Context. The presence of a turbulent magnetic field in the quiet Sun has
been unveiled observationally using different techniques. The magnetic
field is quasi-isotropic and has field strengths weaker than 100
G. It is pervasive and may host a local dynamo. <BR /> Aims: We aim to
determine the length scale of the turbulent magnetic field in the quiet
Sun. <BR /> Methods: The Stokes V area asymmetry is sensitive to minute
variations in the magnetic topology along the line of sight. Using
data provided by Hinode-SOT/SP instrument, we performed a statistical
study of this quantity. We classified the different magnetic regimes
and infer properties of the turbulent magnetic regime. In particular
we measured the correlation length associated to these fields for the
first time. <BR /> Results: The histograms of Stokes V area asymmetries
reveal three different regimes: one organized, quasi-vertical and
strong field (flux tubes or other structures of the like); a strongly
asymmetric group of profiles found around field concentrations; and a
turbulent isotropic field. For the last, we confirm its isotropy and
measure correlation lengths from hundreds of kilometers down to 10 km,
at which point we lost sensitivity. A crude attempt to measure the
power spectra of these turbulent fields is made. <BR /> Conclusions: In
addition to confirming the existence of a turbulent field in the quiet
Sun, we give further prove of its isotropy. We also measure correlation
lengths down to 10 km. The combined results show magnetic fields with
a large span of length scales, as expected from a turbulent cascade.
---------------------------------------------------------
Title: Laboratory determination of Landé factors for the molecular
radical FeH
Authors: Crozet, P.; Tourasse, G.; Ross, A.; Paletou, F.; López
Ariste, A.
2012EAS....58...63C Altcode:
We report laboratory measurements of the Zeeman response of lines in the
0-0 Wing-Ford band of the F-X system (λ ~ 1 μm) of FeH, measured in
magnetic fields 0.3 - 0.5 Tesla. New Landé factors are used to deduce
the magnetic field in sunspots from Stokes V profiles recorded at the
solar telescope THEMIS. The magnetic field deduced from atomic lines
(Ti, Fe) is slightly higher than that found from FeH.
---------------------------------------------------------
Title: Spectropolarimetric Comparison Between SDO/HMI and
Hinode-SOT/SP Through THEMIS/MTR
Authors: Sainz Dalda, A.; Lopez Ariste, A.; Gelly, B.; Tarbell, T. D.;
Centeno, R.; DeRosa, M. L.; Hoeksema, J. T.
2011AGUFMSH31A1986S Altcode:
In the golden age of solar spacecraft observatories, the use of similar
instruments observing same targets offers us the possibility to get
more accurate information of the physical processes taking place on
them. We present a comparison between the vector magnetic field and
thermodynamic quantities obtained by three different spectropolarimetric
instruments. We have used the simultaneous multi-wavelength capabilities
of THEMIS/MTR as bridge between the observations at Fe I 6173 Å
provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP
observations. The official inversion codes for these instruments (PCA
based-on, VFISV and MERLIN respectively) have been used with the data
properly arranged for them. Therefore, we compare the final products
usually offered to the community, i.e. after the inversion, using
different codes and these different wavelengths. The cross-calibration
of these products shall allow us to go forward from one instrument
result to other one in an easy, convenient way.
---------------------------------------------------------
Title: Double-pass spectroimaging with spectral multiplexing: TUNIS
Authors: López Ariste, A.; Le Men, C.; Gelly, B.
2011CoSka..41...99L Altcode:
Solar observations would benefit from simultaneous imaging and
spectroscopy. To approach in an optimal manner such an ideal goal
we have designed and built in THEMIS a spectro-imager based upon
the concept of subtractive double pass through a diffraction grating
spectrograph called TUNIS. In its basic design it produces an image
at a wavelength which changes linearly in one of the directions of
the image. To improve the simultaneity of the spectral coverage,
we have implemented a spectral multiplexing, based upon Hadamard
spectroscopy. We present the first observations of TUNIS and give the
main specifications. TUNIS has been proposed for the European Solar
Telescope (EST) project.
---------------------------------------------------------
Title: The Polarization Optics for the European Solar Telescope
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2011ASPC..437..329B Altcode:
EST, the European Solar Telescope, is a 4-m class solar telescope,
which will be located at the Canary Islands. It is currently in the
conceptual design phase as a European funded project. In order to
fulfill the stringent requirements for polarimetric sensitivity
and accuracy, the polarimetry has been included in the design
work from the very beginning. The overall philosophy has been to
use a combination of techniques, which includes a telescope with
low (and stable) instrumental polarization, optimal full Stokes
polarimeters, differential measurement schemes, fast modulation
and demodulation, and accurate calibration, and at the same time not
giving up flexibility. The current baseline optical layout consists of a
14-mirror layout, which is polarimetrically compensated and non-varying
in time. In the polarization free F2 focus ample space is reserved for
calibration and modulators and a polarimetric switch. At instrument
level the s-, and p-planes of individual components are aligned,
resulting in a system in which eigenvectors can travel undisturbed
through the system.
---------------------------------------------------------
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2011ApJ...730L..37M Altcode: 2011arXiv1103.0145M
We present observational evidence for oscillations of magnetic flux
density in the quiet areas of the Sun. The majority of magnetic
fields on the solar surface have strengths of the order of or lower
than the equipartition field (300-500 G). This results in a myriad of
magnetic fields whose evolution is largely determined by the turbulent
plasma motions. When granules evolve they squash the magnetic field
lines together or pull them apart. Here, we report on the periodic
deformation of the shapes of features in circular polarization observed
at high resolution with SUNRISE. In particular, we note that the
area of patches with a constant magnetic flux oscillates with time,
which implies that the apparent magnetic field intensity oscillates
in antiphase. The periods associated with this oscillatory pattern
are compatible with the granular lifetime and change abruptly, which
suggests that these oscillations might not correspond to characteristic
oscillatory modes of magnetic structures, but to the forcing by granular
motions. In one particular case, we find three patches around the same
granule oscillating in phase, which means that the spatial coherence
of these oscillations can reach 1600 km. Interestingly, the same kind
of oscillatory phenomenon is also found in the upper photosphere.
---------------------------------------------------------
Title: Eigenpolarimetry: An Algebraic Approach to Polarization-free
Telescopes and Instruments
Authors: López Ariste, A.; Semel, M.
2011ASPC..437..403L Altcode:
We have developed new algebraic tools based upon the symmetries of
Mueller matrices that allow us to circumvent those problems while
keeping the adjective polarization-free for our telescopes and not
requiring expensive and delicate calibrations. The basic concept is
to modulate entrance polarization into the eigenvectors of the system
so that polarization information arrives unscathed at the analyzing
beamsplitters, placed at the instrument or detector level. I will
describe the basic concept, its application to THEMIS and the
propositions for EST.
---------------------------------------------------------
Title: Photospheric Hanle diagnostic of weak magnetic dipoles in stars
Authors: López Ariste, A.; Asensio Ramos, A.; González Fernández, C.
2011A&A...527A.120L Altcode: 2010arXiv1011.6288L
<BR /> Aims: We propose and explore a new diagnostic technique
based upon the linear polarization emitted in Hanle-sensitive lines
in disk-integrated stars where a dipolar magnetic field breaks the
rotational symmetry of the resonance scattering polarization <BR />
Methods: A star with a simple dipolar field and a 1-0 spectral line were
used to compute polarization amplitudes and angles. <BR /> Results:
Predicted amplitudes are low but within reach of present instruments
<BR /> Conclusions: A new application of the Hanle effect is proposed
and analyzed as a tool that allows measuring of some of the weakest
stellar magnetic fields.
---------------------------------------------------------
Title: Detecting photons with orbital angular momentum in extended
astronomical objects: application to solar observations
Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; López Ariste, A.;
Asensio Ramos, A.; Belenguer, T.; Manso Sainz, R.; Lemen, C.; Gelly, B.
2011A&A...526A..56U Altcode:
Context. The orbital angular momentum (OAM) of the photon is a
property of light from astronomical objects that has not yet been
measured. We propose a method of measuring the OAM spectrum of light
from an extended natural source, the Sun. Relating the OAM spectrum of
different solar areas to its structures could lead to a novel remote
sensing technique. <BR /> Aims: We present a method for measuring the
OAM spectrum of solar photons. <BR /> Methods: The THEMIS (Télescope
Héliographique pour l'Étude du Magnetisme et les Instabilités
Solaires is a 0.9 m solar telescope property of the French CNRS-INSU
at the Spanish Observatorio del Teide.) telescope is being used with
a novel phase-diversity technique. A spatial light modulator is placed
on one pupil image, and an ad-hoc optical setup allows the measurement
of two simultaneous phase-diverse images in the same CCD, with equal
optical paths. <BR /> Results: Preliminary results show that very good
seeing is mandatory for this kind of observation. The method works in
the laboratory, and good seeing conditions in the 2010 campaign are
being awaited.
---------------------------------------------------------
Title: The polarization optics for the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2010SPIE.7735E..6IB Altcode: 2010SPIE.7735E.214B
EST (European Solar Telescope) is a 4-m class solar telescope, which
is currently in the conceptual design phase. EST will be located at
the Canary Islands and aims at observations with the best possible
spectral, spatial and temporal resolution and best polarimetric
performance, of the solar photosphere and chromosphere, using a
suite of instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic
properties of the plasma over many scale heights, and ranging from
λ=350 until 2300 nm. In order to be able to fulfill the stringent
requirements for polarimetric sensitivity and accuracy, from the very
beginning the polarimetry has been included in the design work. The
overall philosophy has been to use a combination of techniques, which
includes a telescope with low (and stable) instrumental polarization,
optimal full Stokes polarimeters, differential measurement schemes,
fast modulation and demodulation, and accurate calibration. The
current baseline optical layout consists of a 14-mirror layout,
which is polarimetrically compensated and nonvarying in time. In the
polarization free F2 focus ample space is reserved for calibration and
modulators and a polarimetric switch. At instrument level the s-, and
p-planes of individual components are aligned, resulting in a system
in which eigenvectors can travel undisturbed through the system.
---------------------------------------------------------
Title: Image reconstruction with analytical point spread functions
Authors: Asensio Ramos, A.; López Ariste, A.
2010A&A...518A...6A Altcode: 2010arXiv1004.3278A
Context. The image degradation produced by atmospheric turbulence
and optical aberrations is usually alleviated using post-facto image
reconstruction techniques, even when observing with adaptive optics
systems. <BR /> Aims: These techniques rely on the development of the
wavefront using Zernike functions and the non-linear optimization of a
certain metric. The resulting optimization procedure is computationally
heavy. Our aim is to alleviate this computational burden. <BR />
Methods: We generalize the extended Zernike-Nijboer theory to carry
out the analytical integration of the Fresnel integral and present a
natural basis set for the development of the point spread function when
the wavefront is described using Zernike functions. <BR /> Results:
We present a linear expansion of the point spread function in terms
of analytic functions, which, in addition, takes defocusing into
account in a natural way. This expansion is used to develop a very
fast phase-diversity reconstruction technique, which is demonstrated
in terms of some applications. <BR /> Conclusions: We propose that
the linear expansion of the point spread function can be applied to
accelerate other reconstruction techniques in use that are based on
blind deconvolution.
---------------------------------------------------------
Title: Spectrograph capabilities of the European Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Grauf, B.;
Grivel-Gelly, C.; Hirzberger, J.; López Ariste, A.; López López,
R.; Mein, P.; Sayède, F.
2010SPIE.7735E..20C Altcode: 2010SPIE.7735E..68C
EST is a project for a 4-meter class telescope to be located in the
Canary Islands. EST will be optimized for studies of the magnetic
coupling between the photosphere and the chromosphere. This requires
high spatial and temporal resolution diagnostics tools of properties of
the plasma, by using multiple wavelength spectropolarimetry. To achieve
these goals, visible and near-IR multi-purpose spectrographs are being
designed to be compatible with different modes of use: LsSS (Long-slit
Standard Spectrograph), multi-slit multi-wavelength spectrograph with
an integral field unit, TUNIS (Tunable Universal Narrow-band Imaging
Spectrograph), and new generation MSDP (Multi-channel Subtractive
Double-pass Spectrograph). In this contribution, these different
instrumental configurations are described.
---------------------------------------------------------
Title: Double-pass spectro-imaging: TUNIS
Authors: López Ariste, A.; Le Men, C.; Gelly, B.; Asensio Ramos, A.
2010AN....331..658L Altcode:
We present TUNIS, a double-pass spectro-imager built in THEMIS as a
proof-of-concept for EST. Basic concepts and selected first results
are shown. We introduce the concept of a Hadamard spectral mask as
a proposition to move forward from the present implementation of a
single-wavelength per image pixel to a more general one of multiplexed
spectral information that improves the temporal coherence of the
spectral measurement.
---------------------------------------------------------
Title: The stochastic, intermittent nature of quiet Sun magnetism
Authors: Martinez González, M. J.; Manso Sainz, R.; López Ariste,
A.; Bellot Rubio, L. R.; Bianda, M.
2010iac..talk....1M Altcode: 2010iac..talk..153M
No abstract at ADS
---------------------------------------------------------
Title: Statistical Analysis of the very Quiet Sun Magnetism
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; López Ariste, A.; Bianda, M.
2010ApJ...711L..57M Altcode: 2010arXiv1001.4551M
The behavior of the observed polarization amplitudes with spatial
resolution is a strong constraint on the nature and organization
of solar magnetic fields below the resolution limit. We study the
polarization of the very quiet Sun at different spatial resolutions
using ground- and space-based observations. It is shown that 80% of the
observed polarization signals do not change with spatial resolution,
suggesting that, observationally, the very quiet Sun magnetism
remains the same despite the high spatial resolution of space-based
observations. Our analysis also reveals a cascade of spatial scales
for the magnetic field within the resolution element. It is manifest
that the Zeeman effect is sensitive to the microturbulent field usually
associated with Hanle diagnostics. This demonstrates that Zeeman and
Hanle studies show complementary perspectives of the same magnetism.
---------------------------------------------------------
Title: Compressive sensing for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; López Ariste, A.
2010A&A...509A..49A Altcode: 2009arXiv0909.4439A
We demonstrate, through numerical simulations with real data, the
feasibility of using compressive sensing techniques for the acquisition
of spectro-polarimetric data. This allows us to combine the measurement
and the compression process into one consistent framework. Signals are
recovered using a sparse reconstruction scheme from projections of
the signal of interest onto appropriately chosen vectors, typically
noise-like vectors. The compressibility properties of spectral lines
are analyzed in detail. The results shown in this paper demonstrate
that, thanks to the compressibility properties of spectral lines, it
is feasible to reconstruct the signals using only a small fraction of
the information that is measured nowadays. We investigate in depth
the quality of the reconstruction as a function of the amount of
data measured and the influence of noise. This change of paradigm
also allows us to define new instrumental strategies and to propose
modifications to existing instruments in order to take advantage of
compressive sensing techniques.
---------------------------------------------------------
Title: Multiline Zeeman signatures through line addition
Authors: Semel, M.; Ramírez Vélez, J. C.; Martínez González,
M. J.; Asensio Ramos, A.; Stift, M. J.; López Ariste, A.; Leone, F.
2009A&A...504.1003S Altcode: 2009arXiv0906.4226S
Context: To obtain a significant Zeeman signature in the polarised
spectra of a magnetic star, we usually “add” the contributions
of numerous spectral lines; the ultimate goal is to recover the
spectropolarimetric prints of the magnetic field in these line
additions. <BR />Aims: Here we want to clarify the meaning of these
techniques of line addition; in particular, we try to interpret the
meaning of the “pseudo-line” formed during this process and to
find out why and how its Zeeman signature is still meaningful. <BR
/>Methods: We create a synthetic case of line addition and apply well
tested standard solar methods routinely used in research on magnetism
in the Sun. <BR />Results: The results are convincing and the Zeeman
signatures well detected; Solar methods are found to be quite efficient
for stellar observations. We statistically compare line addition
with least-squares deconvolution and demonstrate that they both give
very similar results, as a consequence of the special statistical
properties of the weights. <BR />Conclusions: The Zeeman signatures
are unequivocally detected in this multiline approach. We suggest
that magnetic field detection is reliable well beyond the weak-field
approximation. Linear polarisation in the spectra of solar type stars
can be detected when the spectral resolution is sufficiently high.
---------------------------------------------------------
Title: Multi-Line Stokes Inversion for Prominence Magnetic-Field
Diagnostics
Authors: Casini, R.; López Ariste, A.; Paletou, F.; Léger, L.
2009ApJ...703..114C Altcode: 2009arXiv0906.2144C
We present test results on the simultaneous inversion of the Stokes
profiles of the He I lines at 587.6 nm (D<SUB>3</SUB>) and 1083.0 nm
in prominences (90° scattering). We created data sets of synthetic
Stokes profiles for the case of quiescent prominences (B < 200 G),
assuming a conservative value of 10<SUP>-3</SUP> of the peak intensity
for the polarimetric sensitivity of the simulated observations. In
this work, we focus on the error analysis for the inference of the
magnetic field vector, under the usual assumption that the prominence
can be assimilated to a slab of finite optical thickness with uniform
magnetic and thermodynamic properties. We find that the simultaneous
inversion of the two lines significantly reduces the errors on the
inference of the magnetic field vector, with respect to the case of
single-line inversion. These results provide a solid justification for
current and future instrumental efforts with multi-line capabilities
for the observations of solar prominences and filaments.
---------------------------------------------------------
Title: Variability of the polarization profiles of the Ba II D{2}
line in the solar atmosphere
Authors: López Ariste, A.; Asensio Ramos, A.; Manso Sainz, R.;
Derouich, M.; Gelly, B.
2009A&A...501..729L Altcode:
Resonance-scattering polarization and the Hanle effect are powerful
but seldom exploited probes into the magnetism of the quiet solar
atmosphere. They are also very interesting checks of the quantum theory
of atomic polarization. The Ba ii D2 line has been known for more than
20 years as presenting a conspicuous signal of resonance scattering
polarization thanks to its atomic configuration and the presence
of five different isotopes of Ba, two of which present a hyperfine
structure.A model that considers most of the known ingredients of the
atomic polarization of Ba ii related to the formation of the D2 line
was presented in 2007. We intend to observe all the variability of the
Stokes profiles of this line in conditions of resonance scattering
to verify the general validity of the model and to ascertain the
use of the model for magnetic field diagnostics in the quiet solar
chromosphere and in spicules. The new CCD cameras at THEMIS and the
recently commissioned tip-tilt tracking system gave us the opportunity
to perform the required observations with unprecedented precision
and reliability, resulting in data ready to confront the present
theory.The Stokes Q profiles, both off-limb and on disk, appear to
verify this theory in qualitative terms. The observed departures in
terms of overall signal amplitude and relative ratios among the three
spectral features point to a refinement of the theory for quantitative
purposes, perhaps including radiative-transfer effects. We observed,
on the other hand, anomalous Stokes V profiles in the absence of Zeeman
effect that remain unexplained.The qualitative agreement between the
theory and the observations encourages an increased effort to also
match the observations from a quantitative point of view, including
the observed anomalous Stokes V profiles.
---------------------------------------------------------
Title: Centre to Limb Variation of the Internetwork Magnetism
Authors: Martínez González, M. J.; Asensio Ramos, A.; López
Ariste, A.
2009ASPC..405..219M Altcode:
We analyse 1.5 μm spectropolarimetric observations of quiet
regions at different positions on the solar surface. Neither the
circular and linear polarization signals nor the area and amplitude
asymmetries present a clear trend with the position on the Sun. This
fact discards a network-like scenario for the internetwork magnetic
fields. An isotropically distributed magnetic field would reproduce the
observations, whatever its organisation (myriads of low-lying loops,
turbulent field, etc.).
---------------------------------------------------------
Title: Flux Cancellation in the Solar Photosphere: a near-IR Line
of Mn I as a Diagnostic Tool
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2009ASPC..405..215A Altcode:
Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR
line of Mn I at 15262.702 Å provides a new diagnostic window for
exploring the magnetism of the quiet Sun. In contrast with previously
considered Mn I lines located at visible wavelengths this near-IR
line has the advantage that the shape of its intensity profile is very
sensitive to the presence of magnetic fields. This enhanced magnetic
sensitivity is produced by the coincidence of two favorable facts:
the enhanced Zeeman sensitivity of near-IR lines and because this line
is subjected to particularly strong Paschen-Back perturbations due to
the hyperfine structure of manganese. Of great diagnostic interest is
that the intensity profile itself give us information on the unsigned
magnetic flux, while the polarization profiles are sensitive to the
net flux. An application to spectropolarimetric observations with the
Tenerife Infrared Polarimeter has allowed us to obtain the first flux
cancellation map in an enhanced network region.
---------------------------------------------------------
Title: Short-term variations of Mercury's Na exosphere observed with
very high spectral resolution
Authors: Leblanc, F.; Doressoundiram, A.; Schneider, N.; Massetti,
S.; Wedlund, M.; López Ariste, A.; Barbieri, C.; Mangano, V.;
Cremonese, G.
2009GeoRL..36.7201L Altcode: 2009GeoRL..3607201L
Short time variations of Mercury's exosphere cannot be tracked
easily from ground based observatories because of the difficulty
of distinguishing them from Earth atmospheric effects. On July 13th
2008, using THEMIS solar telescope, we were able to simultaneously
measure brightness, Doppler shift and width of the exospheric sodium
D<SUB>2</SUB> emission line during half a day with a resolving power
of ∼370,000. Mercury's exosphere displayed an emission brightness
peak in the Northern hemisphere which vanished in few hours and a
more persistent Southern Hemispheric peak. The bulk Doppler shift of
the exosphere suggests a period of strong escape from Mercury. The
global changes of the Doppler shift and of the Doppler width suggest
that a cloud of sodium atoms ejected before or at the beginning of our
sequence of observations passed through THEMIS field of view moving
anti-sunward. A preferentially southern ejection of sodium atoms leading
to the observed persistent southern emission peak is consistent with
the orientation of the Interplanetary Magnetic Field during that period.
---------------------------------------------------------
Title: Multiline Zeeman signatures as demonstrated through the
Pseudo-line
Authors: Semel, M.; Ramirez Velez, J. C.; Stift, M. J.; Martinez
Gonzalez, M. J.; Lopez Ariste, A.; Leone, F.
2008arXiv0810.3543S Altcode:
In order to get a significant Zeeman signature in the polarised spectra
of a magnetic star, we usually 'add' the contributions of numerous
spectral lines; the ultimate goal is to recover the spectropolarimetric
prints of the magnetic field in these line additions. Here we want to
clarify the meaning of these techniques of line addition; in particular,
we try to interpret the meaning of the 'pseudo-line' formed during
this process and to find out why and how its Zeeman signature is still
meaningful. We create a synthetic case of lines addition and apply
well tested standard solar methods routinely used in the research
on magnetism in our nearest star. The results are convincing and the
Zeeman signatures well detected; Solar methods are found to be quite
efficient also for stellar observations. The Zeeman signatures are
unequivocally detected in this multiline approach. We may anticipate
the outcome magnetic fields to be reliable well beyond the weak-field
approximation. Linear polarisation in the spectra of solar type stars
can be detected when the spectral resolution is sufficiently high.
---------------------------------------------------------
Title: Design and implementation of an image stabilization device
at the THEMIS solar telescope
Authors: Gelly, Bernard; Le Men, Claude; López Ariste, Arturo;
Delaigue, Cyril; Gónzalez Perez, Ruyman
2008ExA....22...67G Altcode: 2008ExA...tmp....1G
An image stabilizer has been inserted into the optical path of the
THEMIS solar telescope. THEMIS is a Ritchey Chretien reflector telescope
using an altazimuthal mount and closely tied to its spectrograph. The
optical and mechanical design, implementation and system tests are
described, and emphasis is put on the complexity of situations that this
stabilizer must accept, including the scanning of the solar surface
while stabilizing. The current closed-loop crossover frequency of the
device is 65 Hz at - 3 dB on all typical solar scenes.
---------------------------------------------------------
Title: High latitude peaks in Mercury's sodium exosphere: Spectral
signature using THEMIS solar telescope
Authors: Leblanc, F.; Doressoundiram, A.; Schneider, N.; Mangano, V.;
López Ariste, A.; Lemen, C.; Gelly, B.; Barbieri, C.; Cremonese, G.
2008GeoRL..3518204L Altcode:
We present the first combined intensity and temperature maps of sodium
in Mercury's exosphere, made possible by the use of the THEMIS solar
telescope on Tenerife in the Canary Islands. The intensity maps clearly
show high-latitude peaks, and temperatures inferred from spectral line
widths suggest that these regions are either slightly hotter than the
rest of the exosphere or much smaller than observed. These brighter,
warmer regions are also observed, for the first time, to appear within
few Earth hours which strongly suggest that they are produced by
solar wind sputtering. This highly capable instrument obtained these
data during daylight, highlighting the unique potential for THEMIS to
undertake continuous multi-hour and multi-day datasets in conjunction
with the MESSENGER mission to Mercury.
---------------------------------------------------------
Title: Venus wind map at cloud top level with the MTR/THEMIS visible
spectrometer, I: Instrumental performance and first results
Authors: Gaulme, Patrick; Schmider, François-Xavier; Grec, Catherine;
López Ariste, Arturo; Widemann, Thomas; Gelly, Bernard
2008P&SS...56.1335G Altcode: 2010arXiv1011.2680G
Solar light gets scattered at cloud top level in Venus' atmosphere,
in the visible range, which corresponds to the altitude of 67 km. We
present Doppler velocity measurements performed with the high resolution
spectrometer MTR of the Solar telescope THEMIS (Teide Observatory,
Canary Island) on the sodium D2 solar line (5890A˚). Observations
lasted only 49 min because of cloudy weather. However, we could assess
the instrumental velocity sensitivity, 31ms<SUP>-1</SUP> per pixel of
1 arcsec, and give a value of the amplitude of zonal wind at equator
at 151±16ms<SUP>-1</SUP>.
---------------------------------------------------------
Title: Strength distribution of solar magnetic fields in photospheric
quiet Sun regions
Authors: Ramírez Vélez, J. C.; López Ariste, A.; Semel, M.
2008A&A...487..731R Altcode: 2008arXiv0806.1326R
Context: The magnetic topology of the solar photosphere in its quietest
regions is hidden by the difficulties to disentangle magnetic flux
through the resolution element from the field strength of unresolved
structures. The observation of spectral lines with strong coupling with
hyperfine structure, like the observed Mn i line at 553.7 nm, allows
such differentiation. <BR />Aims: To analyse the distribution of field
strengths in the network and intranetwork of the solar photosphere
through inversion of the Mn i line at 553.7 nm. <BR />Methods: An
inversion code for the magnetic field using the principal component
analysis (PCA) has been developed. Statistical tests are run on
the code to validate it. The code has to draw information from the
small-amplitude spectral feature appearing in the core of the Stokes
V profile of the observed line for field strengths below a certain
threshold, coinciding with lower limit of the Paschen-Back effect in
the fine structure of the involved atomic levels. <BR />Results: The
inversion of the observed profiles, using the circular polarisation (V)
and the intensity (I), shows the presence of magnetic fields strengths
in a range from 0 to 2 kG, with predominant weak strength values. Mixed
regions with mean strength field values of 1130 and 435 Gauss are
found associated with the network and intranetwork, respectively. <BR
/>Conclusions: The Mn i line at 553 nm probes the field strength
distribution in the quiet sun and shows the predominance of weak,
hectoGauss fields in the intranetwork, and strong, kiloGauss fields in
the network. It also shows that both network and intranetwork are to be
understood at our present spatial resolutions as field distributions,
of which we hint at the mean properties.
---------------------------------------------------------
Title: Comet McNaught C/2006 P1: observation of the sodium emission
by the solar telescope THEMIS
Authors: Leblanc, F.; Fulle, M.; López Ariste, A.; Cremonese, G.;
Doressoundiram, A.; Sainz Dalda, A.; Gelly, B.
2008A&A...482..293L Altcode:
Comet McNaught C/2006 P1 was the brightest comet of the last forty
years when reaching its perihelion at an heliocentric distance of
0.17Â AU. Two days before this perihelion, at an heliocentric distance
of 0.2Â AU, Themis, a French-Italian solar telescope in the Canary
Islands, Spain, observed the Comet sodium emission of McNaught. The
measured maximum sodium brightness of the D2Â emission line peaked
at 900Â Mega-Rayleigh. The spatial distribution of the sodium
emission with respect to the nucleus of the comet is in agreement
with previous observations. It displays a clear sunward-tailward
asymmetry that suggests a dichotomy of the sodium sources between
a source close to the nucleus and an extended source most probably
corresponding to the dust tail. The spatial distribution along the
slit of the width and speed of the Doppler Na distribution also
suggests such a dichotomy. The sodium ejection rate inferred from this
observation agrees with the value of the ejection rate extrapolated
from comet Hale-Bopp, taking into account the heliocentric distance
of comet McNaught and its significantly larger dust release. If
we suppose a similar concentration of sodium atoms in both comets,
this observation suggests that the sodium ejection rate from comets
McNaught and Hale-Bopp is proportional to the solar flux. Therefore
the most probable ejection mechanisms are photo-sputtering, solar wind
sputtering, or cometary ion sputtering, and not thermal desorption.
---------------------------------------------------------
Title: Near-IR internetwork spectro-polarimetry at different
heliocentric angles
Authors: Martínez González, M. J.; Asensio Ramos, A.; López Ariste,
A.; Manso Sainz, R.
2008A&A...479..229M Altcode: 2007arXiv0710.5219M
Aims:The analysis of near infrared spectropolarimetric data at the
internetwork in different regions on the solar surface could offer
constraints that reject current modeling of these quiet areas. <BR
/>Methods: We present spectro-polarimetric observations of very
quiet regions for different values of the heliocentric angle for the
Fe i lines at 1.56 μm, from disc centre to positions close to the
limb. The spatial resolution of the data is 0.7{-}1”. We analyse
direct observable properties of the Stokes profiles as the amplitude
of circular and linear polarisation, as well as the total degree of
polarisation. The area and amplitude asymmetries are also studied. <BR
/>Results: We do not find any significant variation in the properties of
the polarimetric signals with the heliocentric angle. This means that
the magnetism of the solar internetwork remains the same regardless
of the position on the solar disc. This observational fact discards
the possibility of modeling the internetwork as a network-like
scenario. The magnetic elements of internetwork areas seem to be
isotropically distributed when observed at our spatial resolution.
---------------------------------------------------------
Title: Spectrophotometric analysis of Ellerman bombs in the Ca II,
Hα, and UV range
Authors: Pariat, E.; Schmieder, B.; Berlicki, A.; Deng, Y.; Mein,
N.; López Ariste, A.; Wang, S.
2007A&A...473..279P Altcode:
Context: Even if Ellerman bombs have been observed in the Hα line
within emerging magnetic flux regions since the early 20th century,
their origin and the mechanisms that lead to their formation have been
strongly debated. Recently, new arguments in favor of chromospheric
magnetic reconnection have been advanced. Ellerman bombs seem to be
the signature of reconnections that take place during the emergence
of the magnetic field. <BR />Aims: We have observed an active region
presenting emergence of magnetic flux. We detected and studied
Ellerman bombs in two chromospheric lines: Ca ii 8542 Å and Hα. We
investigated the link between Ellerman bombs and other structures and
phenomena appearing in an emerging active region: UV bright points,
arch filament systems, and magnetic topology. <BR />Methods: On August
3, 2004, we performed multi-wavelength observations of the active
region NOAA 10655. This active region was the target of SoHO Joint
Observation Program 157. Both SoHO/MDI and TRACE (195 Å and 1600 Å)
were used. Simultaneously, we observed in the Ca ii and Na D1 lines
with the spectro-imager MSDP mode of THEMIS. Alternately to the MSDP,
we used the MTR spectropolarimeter on THEMIS to observe in Hα and
in the Fe i doublet at 6302 Å. We derived the magnetic field vectors
around some Ellerman bombs. <BR />Results: We present the first images
of EBs in the Ca ii line and confirm that Ellerman bombs can indeed
be observed in the Ca ii line, presenting the same “moustache”
geometry profiles as in the Hα line, but with a narrower central
absorption in the Ca ii line, in which the peaks of emission are
around ±0.35 Å. We noticed that the Ellerman bombs observed in the
wings of Ca ii line have an elongated shape - the length about 50%
greater than the width. We derived mean semi-axis lengths of 1.4”
× 2.0”. In the UV time profiles of the Ellerman bombs, we noticed
successive enhanced emissions. The distribution of lifetimes of these
individual impulses presents a strong mode around 210 s. Study of the
magnetic topology shows that 9 out of the 13 EBs are located on the
inversion line of the longitudinal field and that some typical examples
might be associated with a bald patch topology. <BR />Conclusions: We
provide new arguments in favor of the reconnection origin of Ellerman
bombs. The different individual impulses observed in UV may be related
to a bursty mode of reconnection. We also show that this Ca ii 8542
Å chromospheric line is a good indicator of Ellerman bombs and can
bring new information about these phenomena.
---------------------------------------------------------
Title: What can We learn about Filaments from Vector Magnetograms?
Authors: Schmieder, B.; Aulanier, G.; Lopez Ariste, A.
2007ASPC..369..137S Altcode:
Theoretical MHD models of filaments have predicted the existence
of dips in magnetic field lines supporting the cool filament
plasma. Condensation would be one of the possible mechanism of filament
formation. The controversy is still alive. Filament fine structures are
of dynamical nature and injection of cold material (like surges) from
the photosphere would be the proposed mechanism. With the presence of
dips, the magnetic lines are predicted to be tangent to the photosphere,
near the barbs, footpoints of the prominences. The injection model
predicted nearly vertical structures of the barbs rooted in the
minority polarities. <P />Measurements of vector magnetic field in
filament channels can answer to these questions and will be possible
with Solar-B. <P />Recent results have been obtained with THEMIS vector
magnetograph in Tenerife, suggesting that dips are really present in
filament channel leading to the conclusion that the observed magnetic
topology in the photosphere fully supports models of prominences based
on dips.
---------------------------------------------------------
Title: Turbulent fields in the quiet sun from Hanle and Zeeman
effects with THEMIS
Authors: López Ariste, A.; Malherbe, J. M.; Manso Sainz, R.; Asensio
Ramos, A.; Ramírez Vélez, J. C.; Martínez González, M.
2007sf2a.conf..596L Altcode:
The measurement of the Sr I line with full polarimetry and spatial
resolution with THEMIS has provided the unexpected result of an apparent
correlation between the Hanle effect signals and the Zeeman effect
signals on this line. Traditionnally, Hanle effect signals in linear
polarisation have been interpreted as the signature of unorganized,
turbulent fields, while Zeeman effect signals -mostly in circular
polarisation- were interpreted as structured fields. The correlation
between both observed by THEMIS requires a change of mind respect to the
picture of the quiet sun, with fewer structured fields and a turbulent
field visible also in deep magnetograms. This picture is supported also
by recent results with Mn lines with strong coupling with its hyperfine
structure and of center-to-limb histograms of Zeeman amplitudes.
---------------------------------------------------------
Title: Chromospheric reversals in the emergence of an ephemeral region
Authors: Sainz Dalda, A.; López Ariste, A.
2007A&A...469..721S Altcode:
Context: The behaviour of both ephemeral regions and moving magnetic
features has been often described for the photospheric layer, but
not for the chromosphere. Both magnetic structures are related to the
decay of active regions, but their actual role is not yet clear. <BR
/>Aims: Our aim is to observe and understand the behaviour of these
structures in the chromosphere. <BR />Methods: We performed simultaneous
photospheric and chromospheric spectropolarimetric observations of an
ephemeral region and a moving magnetic feature. A new code developed
for the reduction of spectropolarimetric data of several wavelengths
observed simultaneously was used here for the first time and will be
described here for future reference. The resulting Stokes profiles are
analysed in detail. <BR />Results: The Stokes V profiles of Fe i 6301
and 6302 Å are reversed in polarity with respect to the chromospheric
Ca ii 8498 and 8542 Å in the cases shown. They reveal a reversed
magnetic field topology between these layers for both structures. The
time evolution of the ephemeral region results in a cancellation of
the chromospheric signal, while the ratio of Stokes V amplitudes of
Fe i 6301 and 6302 Å simultaneously informs us of a strengthening of
the photospheric field. A scenario of the evolution of the ephemeral
region is consequently suggested. <BR />Conclusions: The moving magnetic
feature reveals itself as an exclusively photospheric feature, similar
to the ephemeral region in the initial stages of its emergence. As
the loop emerges into the chromosphere it is slowed down and does not
reach the corona. Most probably, the opposite polarity background in
the chromosphere prevents ascent into corona.
---------------------------------------------------------
Title: Unveiling the Magnetic Field Topology of Prominences
Authors: López Ariste, A.; Aulanier, G.
2007ASPC..368..291L Altcode:
A renewed effort is being dedicated to infer magnetic fields in
prominences through spectropolarimetry of emission lines like the He
D<SUB>3</SUB> and 10830 Å lines. We will briefly review those present
observational efforts pointing at how do they improve or disregard past
attempts to measure magnetic fields in prominences and at how they try
to answer some of the standing questions from theoretical models. A
brief and gentle introduction to the Hanle effect and other subtle
quantum phenomena is given, as they are key to present diagnostic
techniques and, finally, an overview of future observational goals
and wishes is presented.
---------------------------------------------------------
Title: Spectrophotometry of Ellerman Bombs with THEMIS
Authors: Pariat, E.; Schmieder, B.; Berlicki, A.; López Ariste, A.
2007ASPC..368..253P Altcode:
During coordinated campaigns with THEMIS and space missions (TRACE,
SOHO) emerging flux was observed in multi-wavelengths. Ellerman bombs
(EBs) have been identified in TRACE 1600 Å and in chromospheric
lines. The Hα and Ca II 8542 Å lines present two enhanced emission
peaks respectively at 1 Å and at 0.35 Å which are signatures of
EBs. Vector magnetic field measured in the photosphere are consistent
with previous results indicating the presence of bald-patches under
the EBs and consequently the emergence of horizontal flux tubes from
below the photosphere.
---------------------------------------------------------
Title: The Intrinsic Dimensionality of Spectropolarimetric Data
Authors: Asensio Ramos, A.; Socas-Navarro, H.; López Ariste, A.;
Martínez González, M. J.
2007ApJ...660.1690A Altcode: 2007astro.ph..1604A
The amount of information available in spectropolarimetric data is
estimated. To this end, the intrinsic dimensionality of the data is
inferred with the aid of a recently derived estimator based on nearest
neighbor considerations and obtained applying the principle of maximum
likelihood. We show in detail that the estimator correctly captures the
intrinsic dimension of artificial data sets with known dimension. The
effect of noise in the estimated dimension is analyzed thoroughly,
and we conclude that it introduces a positive bias that needs to be
accounted for. Real simultaneous spectropolarimetric observations
in the visible 630 nm and the near-infrared 1.5 μm spectral regions
are also investigated in detail, showing that the near-infrared data
set provides more information of the physical conditions in the solar
atmosphere than the visible data set. Finally, we demonstrate that the
amount of information present in an observed data set is a monotonically
increasing function of the number of available spectral lines.
---------------------------------------------------------
Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the
Average Magnetic Energy in the Solar Photosphere
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2007ApJ...659..829A Altcode: 2006astro.ph.12389A
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 Å whose intensity and polarization profiles are
very sensitive to the presence of hyperfine structure. A theoretical
investigation of the magnetic sensitivity of this line uncovers several
interesting properties. The most important one is that the presence
of strong Paschen-Back perturbations due to the hyperfine structure
produces an intensity line profile whose shape changes according to the
absolute value of the magnetic field strength. A line ratio technique is
developed from the intrinsic variations of the line profile. This line
ratio technique is applied to spectropolarimetric observations of the
quiet solar photosphere in order to explore the probability distribution
function of the magnetic field strength. Particular attention is given
to the quietest area of the observed field of view, which was encircled
by an enhanced network region. A detailed theoretical investigation
shows that the inferred distribution yields information on the average
magnetic field strength and on the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field
strength and a tentative value of ~0.4" for the spatial scale at which
the observed magnetic field is horizontally organized.
---------------------------------------------------------
Title: Determination of field strengths in the quiet Sun
Authors: López Ariste, A.; Martínez González, M. J.; Ramírez
Vélez, J. C.
2007A&A...464..351L Altcode:
The magnetism in the quiet regions of the solar photosphere carries
information on the dynamo processes and its interaction with the
convection of the outer layers of the sun. Unfortunately, the scales
of the magnetic structures on these regions are mostly unresolved. It
is therefore instrumental to tell apart the intrinsic field strengths
in those regions from the flux through the resolution element. This
disentanglement has been far from obvious, leading to opposing views
of the magnetic topology in the unresolved structures of the quiet
Sun. Our study contributes to the disentanglement of field strength from
flux in the quiet Sun, at least, through the use of new observational
constrains in the form of spectropolarimetry of Mn i lines observed
in the solar spectrum.The chosen Mn lines present a strong coupling
with hyperfine structure resulting in spectral features, present or
absent as a function of field strength alone. We observe one of those
lines simultaneously and co-spatially with the Fe i lines at 630 nm,
at the core of the previous measurements.The inversion of the observed
Fe lines results in either strong or weak fields depending on the
initializations of the inversion algorithm. All the solutions show
nevertheless equally good values for the σ parameter and are therefore
equally valuable as solutions. The Mn however selects unambiguously
strong or weak fields, sometimes agreeing with the inversions of the Fe
lines, but half the time disagreeing with them.The Fe i lines at 630 nm,
in the conditions found in the quiet Sun, carry no binding information
on field strength. A proper analysis of quiet Sun magnetism should
necessarily pass through its simultaneous and co-spatial observation
with other lines imposing constraints on field strength, as the Mn i
lines here analyzed. Ultimately, the magnetic topology of the quiet Sun
shall arise from the coherent analysis of all these lines, sensitive
to the Zeeman effect.
---------------------------------------------------------
Title: Magnetic strength analysis in the quiet Sun regions using
the Mn I line at 553 nm.
Authors: Ramírez Vélez, J. C.; López Ariste, A.
2007MmSAI..78...54R Altcode:
In this work we present a quantitative analysis of the magnetic field
stength in quiet Sun regions using Mn I lines. The hyperfine structure
(HFS) of this atom results for its 553 nm line in a change of profile if
the magnetic strength is inferior to one kiloGauss. Spectropolarimetric
data obtained at the THEMIS telescope is presented and analysed. With
this purpose, we have developped and tested an inversion code based on
a Milne-Eddington atmospheric model. Close to half the total amount of
data shows enough signal in circular polarization (V) to be inverted. We
have found that quiet sun regions are dominated by weak magnetic
strengths (hG) but that strong intensities (kG) are not absent, being
these last ones close to one quarter of the total of inverted profiles.
---------------------------------------------------------
Title: Using reduction and inversion tools for THEMIS-MTR data:
chromospheric reversals of a moving magnetic feature and an ephemeral
region .
Authors: Sainz Dalda, A.; López Ariste, A.
2007MmSAI..78..154S Altcode:
New tools have been developed for THEMIS spectropolarimetric data. In
this paper we present how these tools work and can be used in order
to understand two interesting observed phenomena: a moving magnetic
feature and an ephemeral region.
---------------------------------------------------------
Title: THEMIS observational hits in 2006.
Authors: López Ariste, A.
2007MmSAI..78...27L Altcode:
We describe some of the most remarkable observational results reached
by THEMIS in 2006, stressing the instrumental improvements that
have allowed them, in particular the arrival of the new IXON CCD
detectors, and the T3 tip-tilt system. The selected observations are
the measurement of Na emission in Mercury's exosphere during daylight,
the polarimetry at 10<SUP>-5</SUP> on the 2nd solar spectrum, the
observation of the spatial variation over the photosphere in the
resonance scattering polarization of the SrI line and the simultaneous
observation of the two He lines D_3 and 10830 over prominences.
---------------------------------------------------------
Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006ASPC..358..193N Altcode:
We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
Å, that were candidates for use in the Helioseismic and Magnetic Imager
(HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
no blends that threaten performance. The higher Landé factor of Fe
I means its operational velocity range in regions of strong magnetic
field is smaller than for Ne I. Fe I performs better than Ni I for
vector magnetic field retrieval. Inversion results show that Fe I
consistently determines field strength and flux more accurately than
the Ni I line. Inversions show inclination and azimuthal errors are
recovered to ≈2° above 600 Mx/cm<SUP>2</SUP> for Fe I and above
1000 Mx/cm<SUP>2</SUP> for Ni I. The Fe I line was recommended, and
ultimately chosen, for use in HMI.
---------------------------------------------------------
Title: Quiet-Sun Magnetism Seen with a Mn Line: Km-Sized Magnetic
Structures
Authors: López Ariste, A.; Ramírez Vélez, J. C.; Tomczyk, S.;
Casini, R.; Semel, M.
2006ASPC..358...54L Altcode:
We observed Manganese lines with large hyperfine structure and used them
to disentangle strength from flux in the measurement of photospheric
magnetic fields. In observations of the quiet sun with both ASP and
THEMIS, we measure flux from the amplitude of Stokes V in Fe lines, and
the Mn line, crudely analyzed, places the field strength either above
or below a threshold of 600 G, which is set by the atomic structure. In
the case of THEMIS observations, having determined magnetic flux and
field strength for every pixel, one can estimate filling factors of
the magnetic field and determine characteristic scales. Structures at
scales smaller than 50 km are revealed.
---------------------------------------------------------
Title: Inference of the Magnetic Field in Spicules from
Spectro-Polarimetry of He I D<SUB>3</SUB>
Authors: López Ariste, A.; Casini, R.
2006ASPC..358..443L Altcode:
Spectro-polarimetric observations of the He I D<SUB>3</SUB> line in
spicules over the solar limb have been analyzed, and the magnetic field
direction determined. Up to a 90° ambiguity the field appears to be
aligned with the visible spicular structures. The anomalous broadening
of the observed line prevents the retrieval of other information at
this stage. The only further constraint we were able to place was on
the field strength: fields stronger than 40 G must be statistically
present in our observations, but not much stronger than that.
---------------------------------------------------------
Title: First observation of bald patches in a filament channel and
at a barb endpoint
Authors: López Ariste, A.; Aulanier, G.; Schmieder, B.; Sainz
Dalda, A.
2006A&A...456..725L Altcode:
The 3D magnetic field topology of solar filaments/prominences is
strongly debated, because it is not directly measureable in the
corona. Among various prominence models, several are consistent
with many observations, but their related topologies are very
different. We conduct observations to address this paradigm. We
measure the photospheric vector magnetic field in several small
flux concentrations surrounding a filament observed far from disc
center. Our objective is to test for the presence/absence of magnetic
dips around/below the filament body/barb, which is a strong constraint
on prominence models, and that is still untested by observations. Our
observations are performed with the THEMIS/MTR instrument. The four
Stokes parameters are extracted, from which the vector magnetic fields
are calculated using a PCA inversion. The resulting vector fields
are then deprojected onto the photospheric plane. The 180° ambiguity
is then solved by selecting the only solution that matches filament
chirality rules. Considering the weakness of the resulting magnetic
fields, a careful analysis of the inversion procedure and its error
bars was performed, to avoid over-interpretation of noisy or ambiguous
Stokes profiles. Thanks to the simultaneous multi-wavelength THEMIS
observations, the vector field maps are coaligned with the Hα image of
the filament. By definition, photospheric dips are identifiable where
the horizontal component of the magnetic field points from a negative
toward a positive polarity. Among six bipolar regions analyzed in the
filament channel, four at least display photospheric magnetic dips,
i.e. bald patches. For barbs, the topology of the endpoint is that of
a bald patch located next to a parasitic polarity, not of an arcade
pointing within the polarity. The observed magnetic field topology in
the photosphere tends to support models of prominence based on magnetic
dips located within weakly twisted flux tubes. Their underlying and
lateral extensions form photospheric dips both within the channel and
below barbs.
---------------------------------------------------------
Title: Quiet sun magnetic field diagnostics with a Mn line
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
2006A&A...454..663L Altcode:
Context: .The Mn line at 553 nm shows strong spectral features in both
intensity and polarization profiles due to the hyperfine structure of
the atom. These features, their presence or absence, are known to be
dependent on the magnetic regime to which the Mn atom is subject.<BR
/> Aims: .Our objective is to disentangle strong kilo-Gauss (kG)
fields from relatively weak hecto-Gauss (hG) fields in the quiet sun,
and compute relative filling factors on the resolution element.<BR />
Methods: .We observed the 553 nm Mn line in a quiet sun area with the
Advanced Stokes Polarimeter, and we introduce an in-line ratio between
different spectral features. Filling factors can be retrieved from
the measurement of this ratio and the total longitudinal flux.<BR />
Results: .In the photospheric network the kG dominate the magnetic flux,
although out of the higher concentration areas the hG fields dominate in
surface coverage. For the internetwork (granules and lanes confounded)
the hG are dominant both in surface and total flux. <BR />
---------------------------------------------------------
Title: Inversion of solar magnetic fields in photospheric quiet
regions.
Authors: Ramírez Vélez, J. C.; López Ariste, A.; Semel, M.
2006IAUJD...3E..13R Altcode:
Spectropolarymetric observational data and the correspondent
magnetic field inversion of the solar photosphere in quiet regions are
presented. The presence of atomic coupling between the nuclei momentum
(I) and total electron momentum ( J[LS]), known as hyperfine structure
atomic regime where the total momentum F = I + J, was founded in the
observed data for the atom MnI at 553.7 nm. The signature of these
hyperfine structure is clearly detected in circular polarisation in form
of protuberance in the central part of the profile. We have developed
an inversion code of the magnetic field using the Principal Component
Analysis (PCA). An statistical test is applied to the code obtaining
satisfactory inversion results. The inversion of the observed profiles,
using the circular polarisation (V) and the intensity (I), shows mixed
regions with values of |B| higher than 800 Gauss and lower than 600
Gauss associated with the network and internetwork respectively.
---------------------------------------------------------
Title: The THEMIS solar telescope in 2006: situation and perspectives
Authors: Gelly, B.; López Ariste, A.
2006sf2a.conf..539G Altcode:
Recent technical improvements like a new image stabilizer, coupled to a
set of comprehensive progress in data analysis and inversions software
and have quite significantly raised the level of performances achieved
at THEMIS. Spectropolarimetry at a relative precision of 10<SUP>-5</SUP>
is now accessible, opening whole new fields of discovery, and exceeding
by far the original specs of 10<SUP>-3</SUP>. In addition, and despite
a lack of background, speckle imaging has proven to be possible and
of obvious interest to couple with the current spectropolarimetry
capabilities.
---------------------------------------------------------
Title: Magnetic Fields Measured in Spicules.
Authors: López Ariste, A.; Casini, R.
2005ESASP.596E..21L Altcode: 2005ccmf.confE..21L
No abstract at ADS
---------------------------------------------------------
Title: Observational Evidence of Photoshperic Magnetic Dips in
Filament Channels
Authors: Schmieder, B.; López Ariste, A.; Aulanier, G.
2005ESASP.596E..19S Altcode: 2005ccmf.confE..19S
No abstract at ADS
---------------------------------------------------------
Title: Inference of the magnetic field in spicules from
spectropolarimetry of He I D3
Authors: López Ariste, A.; Casini, R.
2005A&A...436..325L Altcode:
We present observations of spicules in the He I D3 line with full-Stokes
spectropolarimetry, which were done with the Advanced Stokes Polarimeter
at the Dunn Solar Telescope of the Sacramento Peak Observatory. The line
profiles appear to be significantly broadened by non-thermal processes,
which we interpret using the hypothesis of a distribution of velocities
inside the spicule. The possibility of inferring the magnetic field
in those conditions is tested on synthetic data, and the results are
generalized to the interpretation of the observed data. We conclude
that the magnetic field is aligned with the visible structure of the
spicule, with strengths above 30 G in some cases (for heights between
3000 and 5000 km above the photosphere).
---------------------------------------------------------
Title: Principal Component Analysis of the He I D<SUB>3</SUB>
Polarization Profiles from Solar Prominences
Authors: Casini, R.; Bevilacqua, R.; López Ariste, A.
2005ApJ...622.1265C Altcode:
In this paper we discuss some general aspects of Stokes profile
inversion in prominences using principal component analysis
(PCA). First, we address the problem of departure of the formation of
He I D<SUB>3</SUB> from the optically thin approximation, dealing in
a heuristic way with the inversion of the two visible components of
the line, which are differently affected by radiative transfer. This
modified inversion does not alter recently published results on
the magnetic structure of quiescent prominences, in particular
confirming the presence of magnetic fields significantly larger than
average in limited regions. Second, we investigate the effect of
line-of-sight integration of the polarization signals from different
magnetic configurations, to determine whether PCA inversion could
interpret an observed signal in terms of a single magnetic model
with unrealistically large field strength. Our results show that this
possibility is not statistically significant, and in addition the few
models that are wrongly inverted show very peculiar geometries that
are not found in our inversion of real data. This result also supports
the reality of stronger than average fields in prominences. Finally,
we further investigated the importance of full Stokes inversion for
a correct diagnostic of magnetic fields in prominences. We show how
the exclusion of Stokes V induces the appearance of a 90° ambiguity
in the position angle of the magnetic field in the plane of the sky
(in addition to the well-known 180° ambiguity). Inclusion of Stokes V
proves to be important at all field strengths, even though Stokes Q and
U should in theory be sufficient to retrieve the complete vector field
information for field strengths in the Hanle depolarization regime. We
also show how the inversion noise determined by the discreteness of
the PCA database may be an additional source of the 90° ambiguity,
even in the presence of Stokes V, therefore imposing a lower bound on
the model density of the database.
---------------------------------------------------------
Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
J.; Balasubramaniam, K. S.
2005ApJ...621L.145L Altcode:
We report on spectropolarimetric observations of Hα in prominences
made with the Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires and the High Altitude Observatory/Advanced
Stokes Polarimeter. Stokes Q and U show the expected profile shape from
resonance scattering polarization and the Hanle effect. In contrast,
most of the time, Stokes V does not show the antisymmetric profile shape
typical of the Zeeman effect but a profile that indicates the presence
of strong atomic orientation in the hydrogen levels, to an extent that
cannot be explained by invoking the alignment-to-orientation transfer
mechanism induced by the prominence magnetic field. We found that the
largest signal amplitudes of Stokes V (comparable to that of Stokes
Q and U) could be produced by a process of selective absorption of
circularly polarized radiation from the photosphere, which requires
that the prominence be in the vicinity of an active region. Although
recent observations of active region filaments indicate such a
selective absorption mechanism as a plausible explanation of the
anomalous signals observed, the particular set of conditions that
must be met suggest that a different explanation may be required
to explain the almost ubiquitous symmetric V signal observed in Hα
prominences. Therefore, we speculate that an alternative mechanism
inducing strong atomic orientation at the observed level could be due
to the presence of electric fields inducing an electric Hanle effect
on Hα. Although we are still working toward a careful modeling of
this effect, including both electric and magnetic fields, we present
some preliminary considerations that seem to support this possibility.
---------------------------------------------------------
Title: PCA-Interpolation Methods for Inversion of Solar Stokes
Profiles. I. Inversion of Photospheric Profiles
Authors: Eydenberg, M. S.; Balasubramaniam, K. S.; López Ariste, A.
2005ApJ...619.1167E Altcode:
We present a method for the analysis of solar Stokes profiles based on
the technique of principal component analysis (PCA). We consider the
development of a PCA/interpolation technique for obtaining estimates of
the solar magnetic field vector when the underlying physical parameter
distribution is not well determined. Unlike previous applications
of PCA, we consider separate distributions of the PCA components as
applied to the source of the underlying plasma, namely, the umbra,
penumbra, and quiet photosphere. We also isolate the PCA for the Fe I
λ6301.5 line. In some previous work, PCA was applied to the entire
6300-6305 Å spectral region that includes the telluric lines. The
method is tested on photospheric (Fe I λ6301.5) observations of NOAA
Active Region 9240 and compared with the results of the traditional
High Altitude Observatory Milne-Eddington inversion code. We also
consider a PCA-perturbation analysis of the data and how it can assist
the interpretation of the results, discuss current challenges faced by
the inversion codes, and suggest important areas for future development.
---------------------------------------------------------
Title: An orthonormal set of Stokes profiles
Authors: del Toro Iniesta, J. C.; López Ariste, A.
2003A&A...412..875D Altcode:
A family of well-known orthonormal functions, the set of Hermite
functions, is proposed as a suitable basis for expanding the
Stokes profiles of any spectral line. An expansion series thus
provides different degrees of approximation to the Stokes spectrum,
depending on the number of basis elements used (or on the number
of coefficients). Hence, an usually large number of wavelength
samples, may be substituted by a few such coefficients, thus reducing
considerably the size of data files and the analysis of observable
information. Moreover, since the set of Hermite functions is an
universal basis, it promises to help in modern inversion techniques
of the radiative transfer equation that infer the solar physical
quantities from previously compiled look-up tables or artificial neural
networks. These features appear to be particularly important in modern
solar applications producing huge amounts of spectropolarimetric data
and on near-future, on-line applications aboard spacecrafts.
---------------------------------------------------------
Title: Magnetic maps of prominences
Authors: Casini, R.; Lopez Ariste, A.; Tomczyk, S.; Lites, B.
2003AGUFMSH42D..05C Altcode:
We present the first magnetic maps of a prominence obtained by applying
our PCA inversion approach to prominence spectropolarimetric data
in the He I D3 line. Our results indicate the presence of organized
structures in the prominence plasma embedded in magnetic field that are
significantly larger than average (50 G and higher). We reaffirm the
need for a Hanle-based diagnostics of prominence magnetism using full
Stokes spectropolarimetry, and the importance of improved, multi-line
observations, ideally involving both He I D3 and 10830.
---------------------------------------------------------
Title: Dynamo processes and activity cycles of the active stars AB
Doradus, LQ Hydrae and HR 1099
Authors: Donati, J. -F.; Collier Cameron, A.; Semel, M.; Hussain,
G. A. J.; Petit, P.; Carter, B. D.; Marsden, S. C.; Mengel, M.;
López Ariste, A.; Jeffers, S. V.; Rees, D. E.
2003MNRAS.345.1145D Altcode:
In this paper, we present new brightness and magnetic surface images of
the young K0 dwarfs AB Doradus and LQ Hydrae, and of the K1 subgiant
of the RS CVn system HR 1099 (=V711 Tauri), reconstructed from
Zeeman-Doppler imaging spectropolarimetric observations collected
at the Anglo-Australian Telescope during five observing campaigns
(totalling 50 nights), from 1998 January to 2002 January. Along with
the older images of the same stars (published in previous papers),
our complete data set represents the first long-term series on temporal
fluctuations of magnetic topologies of very active stars. <P />All of
the magnetic images presented here indicate that large regions with
predominantly azimuthal magnetic fields are continuously present at
the surfaces of these stars. We take this as further evidence that the
underlying dynamo processes that produce them are probably distributed
throughout the entire convective zone (and not confined at its base,
as in the Sun). We speculate that the radial and azimuthal field
maps that we recover correspond, respectively, to the poloidal and
toroidal components of the large-scale dynamo field. <P />We find, in
particular, that some signatures, for instance the relative fraction
of magnetic energy stored in the large-scale poloidal and toroidal
field components, and the polarity of the axisymmetric component of
the field, are variable with time, and provide potentially fruitful
diagnostics for investigating magnetic cycles in active stars other
than the Sun. We report here the detection of partial polarity switches
in some of the axisymmetric field components of two of our programme
stars (AB Dor and LQ Hya), suggesting that the dynamo operating in
these stars may be cyclic.
---------------------------------------------------------
Title: Magnetic Maps of Prominences from Full Stokes Analysis of
the He I D3 Line
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B. W.
2003ApJ...598L..67C Altcode:
We present the first magnetic maps of a prominence, derived from
inversion of spectropolarimetric data in He I D3 using the principal
component analysis of all four Stokes profiles. This prominence,
along with several others, was observed in 2002 May using the Dunn
Solar Telescope of the National Solar Observatory/Sacramento Peak
Observatory, equipped with the High Altitude Observatory Advanced
Stokes Polarimeter. The use of an unocculted instrument allowed us to
map the prominence magnetic fields down to the chromospheric limb. Our
analysis indicates that the average magnetic field in prominences
is mostly horizontal and varies between 10 and 20 G, thus confirming
previous findings. However, our maps show that fields significantly
stronger than average, even as large as 60 or 70 G, can often be found
in clearly organized plasma structures of the prominence.
---------------------------------------------------------
Title: The effect of atomic polarization on early estimates of
prominence magnetic field strengths
Authors: Brown, A.; López Ariste, A.; Casini, R.
2003SoPh..215..295B Altcode:
In this paper we present our results of the application of the
magnetograph formula to synthetic Stokes V profiles in prominences. We
investigate both the Zeeman and atomic-polarization signatures within
the V profile and question why previous attempts to determine magnetic
field strength, on average, were correct, even if the magnetograph
formula does not apply in general.
---------------------------------------------------------
Title: Polarimeter for the study of magnetic fields in prominences
Authors: Lopez Ariste, Arturo; Tomczyk, Steven; Semel, Meir;
Darnell, A.
2003SPIE.4853..235L Altcode:
We report on a new spectropolarimeter for the measurement of vector
magnetic fields on prominences using the HeD<SUB>3</SUB> line in the
Evans Solar Facility at the Sacramento Peak Observatory.
---------------------------------------------------------
Title: Quick-Look Polarization Inversion Using PCA Decomposition. The
Effect of Telluric Lines
Authors: Skumanich, A.; Toledano, O.; López Ariste, A.
2003ASPC..286...53S Altcode: 2003ctmf.conf...53S
No abstract at ADS
---------------------------------------------------------
Title: On the Invariance of PCA Quick-Look Polarization Analysis to
Different Magnetic Activity Samples
Authors: Skumanich, A.; López Ariste, A.
2003ASPC..307..109S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hyperfine Structure as a Diagnostic Tool of Solar Magnetic
Fields
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
2003ASPC..307..115L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) on SDO: Full Vector
Magnetography with a Filtergraph Polarimeter
Authors: Graham, J. D.; Norton, A.; López Ariste, A.; Lites, B.;
Socas-Navarro, H.; Tomczyk, S.
2003ASPC..307..131G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: PCA Inversion of Stokes Profiles in Solar Prominences
Authors: Casini, R.; López Ariste, A.
2003ASPC..307..109C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Paletou, F.; López Ariste, A.; Meunier, N.; Molodij, G.
2003sf2a.conf...97P Altcode: 2003sf2a.confE..30L
The Advanced Technology Solar Telescope (ATST) is a 4-m aperture solar
telescope project lead by the NSO and supported by all major solar US
research institutes. Also a European initiative gathering 17 countries,
so far, is currently being prepared in support of the project. ATST,
intended for first light in 2010, will provide the high-angular
resolution required for nowadays photospheric studies; but its large
aperture and controlled scattered-light design makes it also a very
promising tool for high sensitivity spectropolarimetric observations
needed throughout the whole solar atmosphere up to the corona, and in
spectral windows ranging from the visible to the thermal infrared.
---------------------------------------------------------
Title: Improved Estimate of the Magnetic Field in a Prominence
Authors: López Ariste, A.; Casini, R.
2003ApJ...582L..51L Altcode:
We present new results on the inversion of spectropolarimetric data
of the He I D3 line in a prominence. These data were taken with the
High Altitude Observatory Stokes II polarimeter on 1980 August 5. Full
Stokes profiles in I, Q, U, and V were recorded at 13 locations of a
prominence at the northeast limb. This prominence erupted 3 hr later,
giving rise to the day of year 218 Solar Maximum Mission coronal
transient. The data were originally analyzed in a paper by Querfeld
et al. Here we analyze the data using the new inversion algorithm
proposed by López Ariste & Casini based on pattern recognition
techniques. This method employs full Stokes profiles, and in tests
on synthetic data, it proved to be much more precise than previous
diagnostic procedures. When applied to the Stokes data of the prominence
under study, it gives magnetic field strengths at least 2 times larger
than previous estimates.
---------------------------------------------------------
Title: Estimating the Effects of JPEG Compression and Radiation on
the Accuracy of Vector Magnetic Fields Measurements for Solar-B
Authors: Lites, B.; Shine, R. A.; López Ariste, A.; Tarbell, T. D.
2002AGUFMSH52A0471L Altcode:
The Japanese Solar-B satellite, currently scheduled for launch in
September 2005, includes a spectro-polarimeter (SP) to precisely measure
the full Stokes polarization vector (I,Q,U,V) in the Fe I lines at
6302Å. These will be processed to produce vector magnetograms of the
solar surface using algorithms based on those for the Advanced Stokes
Polarimeter (ASP) as described in Skumanich, et al, 1997, ApJ Suppl
110. Accumulations of the raw images into time averaged I,Q,U,V images
will be done on board and the results will be 12 bit JPEG compressed to
make the best use of the available telemetry. Hence a single radiation
hit in a raw image affects the entire time average at that point. Also,
radiation spikes affect JPEG compression performance. Because of
concerns about these effects, we simulated them separately and in
combination using ASP data and radiation level measurements from the
TRACE satellite. Like TRACE, Solar-B will fly in a high inclination,
sun synchronous orbit and be exposed to radiation from the polar
radiation belts as well as the SAA. Since the SP detector will be
better shielded than that on TRACE, we hope that these will be an over
estimate of the effects. The results from the simulations are very
encouraging. We find that for active region magnetic fields we can use
JPEG to compress the data volume by more than a factor of 10 without
compromising the accuracy of the inferred magnetic field vector. The
radiation in the polar regions has little effect and even the much
stronger SAA radiation causes average perturbations that are less than
the formal errors for sunspot fields and about twice the formal errors
for plage fields. However, very weak field measurements will benefit
from less lossy compression and periods of low radiation. Of course,
the very strong radiation hits always produce artifacts. Compression
performance is affected only slightly so it will not be necessary to
avoid observations in the SAA because of excessive telemetry usage. This
work was supported by NASA contract NAS8-01002.
---------------------------------------------------------
Title: Hyperfine Structure as a Diagnostic of Solar Magnetic Fields
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
2002ApJ...580..519L Altcode:
We propose the use of the Zeeman effect of the hyperfine structure
(HFS) as a diagnostic of solar photospheric magnetic fields. The HFS
induces unique signatures in the polarized spectra of particular atoms,
which can be used to directly get information on the magnetic field
strength. To explore the effects of HFS, we adopt a numerical model of
line formation and radiative transfer of polarized light in a magnetized
Milne-Eddington atmosphere. We concentrate our studies on several lines
of Mn I, which show particularly striking HFS signatures in the solar
atlas. For these lines, anomalous Stokes profiles are produced for
fields in the range 0-1000 G. The presence of these unusual profiles
for weak magnetic fields constitutes a novel and potentially powerful
diagnostic of the strength of solar magnetic fields in the quiet
photosphere and plages.
---------------------------------------------------------
Title: Magnetic Fields in Prominences: Inversion Techniques for
Spectropolarimetric Data of the He I D<SUB>3</SUB> Line
Authors: López Ariste, A.; Casini, R.
2002ApJ...575..529L Altcode:
We propose the use of principal component analysis (PCA) to invert
spectropolarimetric data from prominences. Observation of the
full Stokes profiles in prominences is very important for a deeper
understanding of magnetic-field topology in these solar structures,
and for the testing of theoretical models. The line formation problem,
however, is complicated by the special conditions of prominences:
anisotropy of light, low magnetic intensities, temperature and density
ranges, etc. We created a code to solve this problem in the limit of
optically thin plasma and of a collisionless regime, and use it in
combination with PCA techniques to invert synthetic data. The results
show that inversion is feasible.
---------------------------------------------------------
Title: Inference of Solar Magnetic Field Parameters from Data with
Limited Wavelength Sampling
Authors: Graham, Jonathan D.; López Ariste, Arturo; Socas-Navarro,
Hector; Tomczyk, Steven
2002SoPh..208..211G Altcode:
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to explore
the possibility of inferring the magnetic field vector, its filling
factor, and the thermodynamics of model atmospheres when only a few
wavelength measurements are available. These simulations assume the
magnetic Sun to be represented by Milne-Eddington atmospheres. The
results indicate that two wavelength measurements are insufficient
to reliably determine the magnetic parameters, regardless of whether
magnetograph techniques or least-squares fitting inversions are
used. However, as few as four measurements analyzed with the inversion
technique provide enough information to retrieve the intrinsic magnetic
field with an accuracy better than 10% in most cases.
---------------------------------------------------------
Title: Inference of Solar Vector Magnetic Fields with Filtergraph
Instruments
Authors: Graham, J. D.; Lites, B. W.; López Ariste, A.; Norton, A.;
Socas-Navarro, H.; Tomczyk, S.
2002AAS...200.5611G Altcode: 2002BAAS...34..736G
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to
explore the possibility of inferring the magnetic field vector, its
filling factor, and the thermodynamics of model atmospheres when
only a few wavelength measurements are available. The simulations
assume the magnetic sun to be represented by Milne-Eddington (ME)
atmospheres. The results indicate that two wavelength measurements
are insufficient to reliably determine the magnetic parameters,
regardless of whether magnetograph techniques or least-squares fitting
inversions are used. However, as few as four measurements analyzed
with the inversion technique provide enough information to retrieve the
intrinsic magnetic field with an accuracy better than 10 generated by
more general models and ASP data passed through a simulated filtergraph.
---------------------------------------------------------
Title: The Physical Content of the Leading Orders of Principal
Component Analysis of Spectral Profiles
Authors: Skumanich, A.; López Ariste, A.
2002ApJ...570..379S Altcode:
We consider the principal component analysis (PCA) method of
expanding Stokes intensity and net polarization profiles in terms of
eigenfunctions (or principal components) of the spectral covariance
matrix. The expansion is ordered by the magnitude of the relevant
eigenvalue from largest to smallest. We find that the ordering
represents a perturbation expansion. This allows us to examine the
physical content of the first few orders of the basis set for 40,000
profiles for each Stokes parameter for a solar active region. For the
intensity profile, we find that the expansion represents a Taylor
series with the highest ranked, or first, eigenfunction being the
zeroth order term, the second as the (scaled) first derivative of
the zeroth term, and the third as the (scaled) second derivative
term. Thus, we can derive a velocity from the coefficients of the
first derivative term and a magnetic splitting parameter from those
of the second using the standard velocity perturbation and weak-field
expansion. For the net polarization profiles, we find that the zeroth
order terms yield, using the weak-field expansion, the vector magnetic
field. A comparison with a Stokes profile fitting inversion shows
that the thus-estimated velocity and magnetic parameters are in good
agreement with the more time-consuming profile fitting values, but
do show a roll-off, or saturation, for sufficiently large values. We
also find that the bright quiet-Sun points have an upflow signature,
while the dark regions have a downflow-one in good agreement with that
derived by traditional analysis.
---------------------------------------------------------
Title: On the Universality of the Leading Orders of PCA. Spectral
Eigenprofiles for the Sun.
Authors: Skumanich, A.; López Ariste, A.
2002AAS...200.5511S Altcode: 2002BAAS...34..733S
In a previous Principal Component Analysis (PCA) of the spectral
region containing the intensity profiles of the FeI λ630 .15 &
λ630 .25 nm lines for a solar active region, Ref(1), the issue of the
universality or invariance of the eigenprofiles (principal components)
to changes in the magnetic composition of the studied region was
raised. To address this issue we have performed a series of PCA studies
in which we incrementally increased the threshold Zeeman polarization
for the included profiles for a given region. This reduces the relative
roles of the various components such as the quiet sun and elements of
the active sun, viz. network, pores, plage and spot. We find that the
Taylor series representation of the highest ranked eigenprofiles in the
expansion of the intensity, which yield an estimate of the velocity and
magnetic splitting (first and second derivative terms respectively,
Ref(1)), continues to hold. However increased eigenprofile 'mixing'
occurs. Consequently to obtain eigenprofiles which represent the
derivatives of the zeroth order eigenprofile one requires significant
rotations of the basis in the PCA space. The implication for derived
velocity and magnetic parameters will be discussed. - Skumanich,
A. & López Ariste, A. 2002, "The Physical Content of the Leading
Orders of Principal Component Analysis of Spectral Profiles", ApJ
570. In press
---------------------------------------------------------
Title: New Polarization Diagnostics for the Solar Atmosphere
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B.
2002AAS...200.3403C Altcode: 2002BAAS...34..690C
We present relatively new diagnostics of “weak" magnetic fields in the
solar atmosphere. The first diagnostic is suggested by recent advances
in the inversion of Stokes profiles of lines formed by resonance
scattering in the weakly magnetized plasma of prominences (Hanle
effect and level-crossing; 0 to 100 G). Use of pattern recognition
techniques (PCA) in this field has marked a sensible progress with
respect to previous diagnostic procedures. The second diagnostic is
the modelling of hyperfine structured (HFS) lines that can be observed
in the spectrum of the quiet photosphere. This allows to investigate
relatively weak photospheric fields (200 G to 1000 G), in which regime
the HFS induces peculiar signatures in the Stokes profiles, including
the appearance of subcomponents and net circular polarization. The third
diagnostic is suggested by interesting polarization properties of the
Na I D1 line formed by resonance scattering: the atomic polarization
in the upper level of D1, which is responsible of a characteristic
antisymmetric (i.e., V-like) signature in the core of Stokes Q, is
rapidly suppressed for B > 10 G, irrespective of the magnetic field
direction. A common denominator of these three diagnostics is their
sensitivity to the actual strength of the magnetic field, instead
of the magnetic flux within the resolution element. Another common
aspect is that all require (or would profit from) high polarization
sensitivity, which will be one of the strengths of ATST. For the
diagnostics of prominence magnetic fields, the possibility of multiline
spectropolarimetry could be decisive. Simultaneous observations of
He I D3 (5876A) and 10830A, or of He I D3 and the Na I D lines (all
within a 20A spectral range!), would increase the inversion accuracy
of PCA. The high spatial resolution capabilities of ATST would be
advantageous mostly to diagnose weak photospheric fields, already at
the present time. Because of the complexity of radiative transfer in
complicated structures like prominences, high spatial resolution in
these structures is not the highest priority. However, we hope that
when ATST will become operative, this complicated problem will have
been attacked succesfully.
---------------------------------------------------------
Title: On the Asymmetry of Stokes Profiles
Authors: López Ariste, A.
2002ApJ...564..379L Altcode:
We find all the sources of asymmetries in Stokes profiles available for
a unidimensional line of sight. The analytical solution for the transfer
equation for polarized light obtained by López Ariste & Semel
is used for this purpose. Three sources of asymmetries are obtained:
the first is the well-known case of depth-dependent velocity fields;
the two others are due to wavelength asymmetries in the absorption
matrix and the emission vector. These emission vector asymmetries
can be produced by the presence of a polarized (but symmetric) source
function. Some formulae are derived describing the asymmetries owing
to depth-dependent velocity fields in Stokes V for the case of the
Zeeman effect in a multiplet, as well as for the net area of the
Stokes V profile, the so-called net circular polarization (NCP). An
implication of this last formula is that Milne-Eddington atmospheric
models, even when generalized to velocity and magnetic fields that
vary linearly with optical depth, cannot account for the observed NCPs.
---------------------------------------------------------
Title: Pattern recognition techniques and the measurement of solar
magnetic fields
Authors: Lopez Ariste, Arturo; Rees, David E.; Socas-Navarro, Hector;
Lites, Bruce W.
2001SPIE.4477...96L Altcode:
Measuring vector magnetic fields in the solar atmosphere using the
profiles of the Stokes parameters of polarized spectral lines split
by the Zeeman effect is known as Stokes Inversion. This inverse
problem is usually solved by least-squares fitting of the Stokes
profiles. However least-squares inversion is too slow for the new
generation of solar instruments (THEMIS, SOLIS, Solar-B, ...) which will
produce an ever-growing flood of spectral data. The solar community
urgently requires a new approach capable of handling this information
explosion, preferably in real-time. We have successfully applied pattern
recognition and machine learning techniques to tackle this problem. For
example, we have developed PCA-inversion, a database search technique
based on Principal Component Analysis of the Stokes profiles. Search is
fast because it is carried out in low dimensional PCA feature space,
rather than the high dimensional space of the spectral signals. Such
a data compression approach has been widely used for search and
retrieval in many areas of data mining. PCA-inversion is the basis of
a new inversion code called FATIMA (Fast Analysis Technique for the
Inversion of Magnetic Atmospheres). Tests on data from HAO's Advanced
Stokes Polarimeter show that FATIMA isover two orders of magnitude
faster than least squares inversion. Initial tests on an alternative
code (DIANNE - Direct Inversion based on Artificial Neural NEtworks)
show great promise of achieving real-time performance. In this paper
we present the latest achievements of FATIMA and DIANNE, two powerful
examples of how pattern recognition techniques can revolutionize data
analysis in astronomy.
---------------------------------------------------------
Title: Full-Stokes spectropolarimetry of solar prominences
Authors: Paletou, F.; López Ariste, A.; Bommier, V.; Semel, M.
2001A&A...375L..39P Altcode:
We report on first spectropolarimetric observations of solar prominences
made at THEMIS. Hereafter we shall emphasis on the preliminary analysis
of He I D<SUB>3</SUB> full-Stokes observations. Our measurements
clearly show manifestations of both the Hanle and Zeeman effects. More
generally, we demonstrate the very favourable performances of the THEMIS
multi-line spectropolarimetric mode for further new investigations of
the magnetic field in solar prominences. Based on observations made at
THEMIS, operated on the Island of Tenerife by CNRS-CNR in the Spanish
Observatorio del Teide of the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: Fast Inversion of Spectral Lines Using Principal Components
Analysis. II. Inversion of Real Stokes Data
Authors: Socas-Navarro, H.; López Ariste, A.; Lites, B. W.
2001ApJ...553..949S Altcode:
The principal components analysis (PCA) technique is used to develop
an extremely fast and stable Stokes inversion code, suitable for
application to large data sets from instruments that operate under
standard conditions. This paper provides some tips on reducing the
dimensionality of the problem, which are then used to develop a
practical implementation of PCA for the automatic analysis of Stokes
profiles. The resulting code is tested using real spectropolarimetric
observations of the pair of Fe I lines at 6302 Å at a sunspot.
---------------------------------------------------------
Title: The Physical Content of the Leading Orders of Principle
Component Analysis of Spectral Profiles
Authors: Skumanich, A.; Lopez Ariste, A.
2001AAS...198.0303S Altcode: 2001BAAS...33..786S
We consider the PCA (Principle Component Analysis) method of profile
analysis introduced by Ref (1). In this method one constructs a
covariance matrix C<SUB>ij</SUB> given by the product of the profile
amplitudes at wavelengths λ <SUB>i</SUB> and λ <SUB>j</SUB> averaged
over all profile samples (either over space or time). The matrix
is 'diagonalized' and ordered by Singular Value Decomposition. The
resulting orthonormal eigenfunctions over wavelength space are then
used as a basis for the expansion of the observed profiles at each
space(time) point. The eigenvalue ordering is by magnitude of the
mean square over space(time) of the expansion coefficients and is
given by the product of the frequency of occurrence of the particular
eigenfunction and its intrinsic mean square amplitude. An error based
truncation scheme yields a coefficient set which is a compression of
the original data set. We have applied the PCA method to the 40,000
profiles for each Stokes component for a Solar active region. In the
case of the intensity profile we find that the expansion appears to
be similar to a Taylor series with the 0th efunction being the zero
order term, the 1st efunction as the first derivative of the zero term
and the 2nd efunction as the second derivative term. Thus we derive a
line-of-sight velocity from the coefficients of the first derivative
term and a magnetic signature, using the weak field Milne-Eddington
approximation, from the second. A comparison with a Stokes profile
inversion shows that the thus estimated velocity and magnetic parameters
are in good agreement with the more time consuming profile fitting
values but do show a "roll-off" for sufficiently large values. One also
finds that the bright 'quiet' Sun points have an upflow while the dark
have a downflow similar to that derived by other analysis. 1) Rees,
D., López Ariste, A., Thatcher, J. & Semel, M. 2000, A & A,
355, 759 The National Center for Atmospheric Research is sponsored by
the National Science Foundation.
---------------------------------------------------------
Title: Observation of Linear Polarization in the Infrared Ca II
Triplet Lines during Umbral Flashes
Authors: López Ariste, A.; Socas-Navarro, H.; Molodij, G.
2001ApJ...552..871L Altcode:
We report on Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires (THEMIS)2 observations of linear polarization
events associated with umbral flashes observed in the Ca II infrared
(IR) triplet lines. The observed signals are usually delayed in time
and shifted in space when compared to the intensity and circular
polarization signals from the flash. The observations are compatible
with a scenario whereby flashes are produced by a perturbation
propagating along the magnetic field lines as they bend out toward
the penumbra. Only a fraction of the resolution element appears to
be emitting flashlike profiles, as if the waves were propagating only
within localized magnetic field lines. This localization, however, does
not impede the apparent propagation of the perturbation horizontally
within the umbra.
---------------------------------------------------------
Title: Group Theory Approach to the Transfer of Polarized Light
Authors: López Ariste, A.
2001ASPC..236..529L Altcode: 2001aspt.conf..529L
No abstract at ADS
---------------------------------------------------------
Title: Real-Time Inversion of Spectropolarimetric Data
Authors: López Ariste, A.
2001ASPC..248..621L Altcode: 2001mfah.conf..621L
No abstract at ADS
---------------------------------------------------------
Title: Current Ground-Based Stellar Spectropolarimeters and their
Use for Zeeman-Doppler Imaging
Authors: Semel, M.; López Ariste, A.
2001ASPC..248..575S Altcode: 2001mfah.conf..575S
No abstract at ADS
---------------------------------------------------------
Title: Inversion Codes based on Pattern Recognition
Authors: López Ariste, A.
2001ASPC..236..521L Altcode: 2001aspt.conf..521L
No abstract at ADS
---------------------------------------------------------
Title: Scattering Polarization Observations with the Tenerife Gregory
Coudé Telescope
Authors: Dittmann, O.; Trujillo Bueno, J.; Semel, M.; López Ariste, A.
2001ASPC..236..125D Altcode: 2001aspt.conf..125D
No abstract at ADS
---------------------------------------------------------
Title: Fast inversion of spectral lines using principal component
analysis. I. Fundamentals
Authors: Rees, D. E.; López Ariste, A.; Thatcher, J.; Semel, M.
2000A&A...355..759R Altcode:
This paper presents PCA inversion, a novel application of Principal
Component Analysis to the problem of spectral line inversion,
ie. solar/stellar atmospheric model parameter estimation from spectral
lines. For a given type of spectral line we compute a database of
synthetic spectral profiles using a large number of models. Inversion
of an observed profile to obtain an atmospheric model is equivalent
to a problem in pattern recognition, finding the nearest profile in
the synthetic profile database. To reduce dimensionality we use the
synthetic data as a PCA training set to decompose each synthetic (and
observed) profile into a sum of a small number of principal components,
or eigenprofiles. The coefficients of this decomposition can be regarded
as elements of a low-dimensional eigenfeature vector. The eigenfeatures
are smooth functions of model parameters, indicating that eigenfeatures
for parameters not in the training set could be easily estimated by
interpolation. Search for the nearest profile is fast because it is
done in the eigenfeature vector space. We illustrate the method using
several types of synthetic spectra: unpolarised intensity profiles of
a line formed in a Milne-Eddington model atmosphere; unpolarised Hα
flux profiles of a line formed in non-Local Thermodynamic Equilibrium
in the chromosphere of a cool star; and polarised Stokes parameter
profiles of a line split by the Zeeman effect in the presence of a
magnetic field. We also apply PCA to a set of Stokes data observed
in a sunspot region by the High Altitude Observatory Advanced Stokes
Polarimeter. PCA inversion is proposed as a fast alternative to
non-linear least squares inversion commonly used for solar magnetic
field measurements based on such Stokes data.
---------------------------------------------------------
Title: First results from THEMIS spectropolarimetric mode
Authors: López Ariste, A.; Rayrole, J.; Semel, M.
2000A&AS..142..137L Altcode:
We present here the very first spectropolarimetric results obtained with
the multiline spectroscopy mode (MTR) of THEMIS. The principal problems
found during the data analysis are exposed. A first characterisation
of the quality of this observing mode is given. Based on observations
made with THEMIS operated on the island of Tenerife by CNRS-CNR in
the Spanish Observatorio del Teide of the Instituto de Astrofísica
de Canarias.
---------------------------------------------------------
Title: La spectropolarimétrie en astrophysique. Application au
diagnostic des champs magnétiques solaires et stellaire.
Authors: Lopez Ariste, A.
1999JAF....60Q..40L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: DIAGONAL: A numerical solution of the Stokes transfer equation
Authors: López Ariste, A.; Semel, M.
1999A&AS..139..417L Altcode:
In a previous paper \cite[(Semel & López Ariste 1999]{art1},
hereafter referred to as Paper I) the authors found a new solution for
the integration of the radiative transfer equation for polarized light
(RTE). The present paper is a continuation of that work, and shows how
this solution has been incorporated into a new numerical code for the
integration of the RTE. This code, called DIAGONAL, is characterized
by an analytical handling of most model atmospheres, differing in that
from other codes. It gives exact solutions in new, non-trivial cases. In
the general case when no complete analytical solution is available,
the code resorts to a multi-layer technique, thus providing a solution
that combines an approximated analytical model and a minimized residual
treated linearly. The algorithm is shown both to be very stable and
to reach a high precision even for a small number of integration
layers. This results in a very fast code. A comparison with DELO has
been carried out. DIAGONAL is available, upon request to the authors.
---------------------------------------------------------
Title: Analytical solution of the radiative transfer equation for
polarized light
Authors: López Ariste, A.; Semel, M.
1999A&A...350.1089L Altcode: 1999astro.ph..9232A; 1999astro.ph..9232L
A new formalism is introduced for the transfer of polarized
radiation. Stokes parameters are shown to be four-vectors in a
Minkowski-like space and, most strikingly, the radiative transfer
equation (RTE) turns out to be an infinitesimal transformation under
the Poincaré (plus dilatations) group. A solution to the transfer
equation as a finite element of this group is proposed.
---------------------------------------------------------
Title: Integration of the radiative transfer equation for polarized
light: the exponential solution
Authors: Semel, M.; López Ariste, A.
1999A&A...342..201S Altcode: 1998astro.ph.11153S
The radiative transfer equation (RTE) for polarized light accepts a
convenient exponential solution when the absorption matrix commutes
with its integral. We characterize some of the matrix depth variations
which are compatible with the commutation condition. Eventually
the vector solution may be diagonalized and one may obtain four
independent scalar solutions with four optical depths, complex in
general. When the commutation condition is not satisfied, one must
resort to a determination of an appropriate evolution operator, which
is shown to be well determined mathematically, but whose explicit
form is, in general, not easy to apply in a numerical code. However,
we propose here an approach to solve a general case not satisfying
the commutation condition.
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Title: Exponential solutions to the radiative transfer equation for
polarized light
Authors: López Ariste, A.; Semel, M.
1999ASSL..243..157L Altcode: 1999sopo.conf..157L
No abstract at ADS