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Author name code: sobotka
ADS astronomy entries on 2022-09-14
author:"Sobotka, Michal"
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Title: Horizontal motions in sunspot penumbrae
Authors: Sobotka, Michal; Puschmann, Klaus G.
2022A&A...662A..13S Altcode: 2022arXiv220503171S
Context. A model of penumbral filaments represented by magnetoconvective
cells was derived recently from spectropolarimetric observations. This
model resolves many of the inconsistencies found in the relations
between intensity, magnetic, and velocity patterns in sunspot
penumbrae. <BR /> Aims: High-resolution observations of horizontal
motions in the penumbra are needed to complement the concept of
penumbrae obtained from spectropolarimetry. Time series of intensity
images of a large sunspot in AR 10634 acquired with the Swedish
Solar Telescope in the G band and red continuum are analysed. The
two simultaneous time series last six hours and five minutes. <BR />
Methods: Horizontal motions of penumbral grains (PGs), structures in
dark bodies of filaments, the outer penumbral border, and G-band bright
points are measured in time slices that cover the whole width of the
penumbra and the neighbouring granulation. The spatial and temporal
resolutions are 90 km and 20.1 s, respectively. <BR /> Results:
In the inner penumbra, PGs move towards the umbra (inwards) with
a mean speed of −0.7 km s<SUP>−1</SUP>. The direction of motion
changes from inwards to outwards at approximately 60% of the penumbral
width, and the mean speed increases gradually in the outer penumbra,
approaching 0.5 km s<SUP>−1</SUP>. This speed is also typical of
an expansion of the penumbra-granulation border during periods that
typically last one hour and are followed by a fast contraction. The
majority of the G-band bright points moves away from the sunspot,
with a typical speed of 0.6 km s<SUP>−1</SUP>. High outward speeds,
3.6 km s<SUP>−1</SUP> on average, are observed in dark bodies of
penumbral filaments. <BR /> Conclusions: According to the model
of penumbral filaments, it is suggested that the speeds detected
in the dark bodies of filaments are associated with the Evershed
flow and that the opposite directions of PG motions in the inner
and outer penumbrae may be explained by the interaction of rising
plasma in filament heads with a surrounding, differently inclined
magnetic field. <P />Movies associated to Fig. 1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243577/olm">https://www.aanda.org</A>
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Title: Multiple Stokes I inversions for inferring magnetic fields
in the spectral range around Cr I 5782 Å
Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.;
Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma,
M.; Kontogiannis, I.; Sobotka, M.
2021A&A...653A.165K Altcode: 2021arXiv210711116K
<BR /> Aims: In this work, we explore the spectral window containing
Fraunhofer lines formed in the solar photosphere, around the
magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0,
and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is
to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I,
Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer
the thermodynamic and magnetic properties in strongly magnetized
plasmas using an inversion code. <BR /> Methods: Our study is based
on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which
includes fast spectroscopic scans in the wavelength range around
the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all
spectral lines, as well as their response functions to temperature,
magnetic field, and Doppler velocity, were determined using the Stokes
Inversion based on Response functions (SIR) code. Snapshot 385 of the
enhanced network simulation from the Bifrost code serves to synthesize
all the lines, which are, in turn, inverted simultaneously with SIR to
establish the best inversion strategy. We applied this strategy to VTT
observations of a sunspot belonging to NOAA 12723 on 2018 September
30 and compared the results to full-disk vector field data obtained
with the Helioseismic and Magnetic Imager (HMI). <BR /> Results: The
15 simultaneously inverted intensity profiles (Stokes I) delivered
accurate temperatures and Doppler velocities when compared with the
simulations. The derived magnetic fields and inclinations achieve
the best level of accuracy when the fields are oriented along the
line-of-sight (LOS) and less accurate when the fields are transverse to
the LOS. In general, the results appear similar to what is reported in
the HMI vector-field data, although some discrepancies exist. <BR />
Conclusions: The analyzed spectral range has the potential to deliver
thermal, dynamic, and magnetic information for strongly magnetized
features on the Sun, such as pores and sunspots, even without the use
of polarimetry. The highest sensitivity of the lines is found in the
lower photosphere, on average, around log τ = −1. The multiple-line
inversions provide smooth results across the whole field of view
(FOV). The presented spectral range and inversion strategy will be
used for future VTT observing campaigns.
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Title: IRIS observations of chromospheric heating by acoustic waves
in solar quiet and active regions
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.; Liu,
W.; Mravcová, L.
2021A&A...648A..28A Altcode: 2021arXiv210208678A
<BR /> Aims: To study the heating of solar chromospheric magnetic and
nonmagnetic regions by acoustic and magnetoacoustic waves, the deposited
acoustic-energy flux derived from observations of strong chromospheric
lines is compared with the total integrated radiative losses. <BR />
Methods: A set of 23 quiet-Sun and weak-plage regions were observed in
the Mg II k and h lines with the Interface Region Imaging Spectrograph
(IRIS). The deposited acoustic-energy flux was derived from Doppler
velocities observed at two different geometrical heights corresponding
to the middle and upper chromosphere. A set of scaled nonlocal
thermodynamic equilibrium 1D hydrostatic semi-empirical models -
obtained by fitting synthetic to observed line profiles - was applied
to compute the radiative losses. The characteristics of observed waves
were studied by means of a wavelet analysis. <BR /> Results: Observed
waves propagate upward at supersonic speed. In the quiet chromosphere,
the deposited acoustic flux is sufficient to balance the radiative
losses and maintain the semi-empirical temperatures in the layers under
study. In the active-region chromosphere, the comparison shows that
the contribution of acoustic-energy flux to the radiative losses is
only 10−30%. <BR /> Conclusions: Acoustic and magnetoacoustic waves
play an important role in the chromospheric heating, depositing a main
part of their energy in the chromosphere. Acoustic waves compensate
for a substantial fraction of the chromospheric radiative losses in
quiet regions. In active regions, their contribution is too small to
balance the radiative losses and the chromosphere has to be heated by
other mechanisms.
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Title: Evolution and motions of magnetic fragments during the active
region formation and decay: A statistical study
Authors: Švanda, Michal; Sobotka, Michal; Mravcová, Lucia;
Výbošťoková, Tatiana
2021A&A...647A.146S Altcode: 2021arXiv210202807S
Context. The evolution of solar active regions is still not fully
understood. The growth and decay of active regions have mostly been
studied in case-by-case studies. <BR /> Aims: Instead of studying the
evolution of active regions case by case, we performed a large-scale
statistical study to find indications for the statistically most
frequent scenario. <BR /> Methods: We studied a large sample of active
regions recorded by the Helioseismic and Magnetic Imager instrument. The
sample was split into two groups: forming (367 members) and decaying
(679 members) active regions. We tracked individual dark features
(i.e. those that are assumed to be intensity counterparts of magnetised
fragments from small objects to proper sunspots) and followed their
evolution. We investigated the statistically most often locations
of fragment merging and splitting as well as their properties. <BR
/> Results: Our results confirm that statistically, sunspots form
by merging events of smaller fragments. The coalescence process is
driven by turbulent diffusion in a process similar to random-walk,
where supergranular flows seem to play an important role. The number
of appearing fragments does not seem to significantly correlate with
the number of sunspots formed. The formation seems to be consistent
with the magnetic field accumulation. Statistically, the merging occurs
most often between a large and a much smaller object. The decay of the
active region seems to take place preferably by a process similar to
the erosion.
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Title: Observational study of chromospheric heating by acoustic waves
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.;
García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis,
I.; Koza, J.; Korda, D.; Kuckein, C.
2020A&A...642A..52A Altcode: 2020arXiv200802688A
<BR /> Aims: Our aim is to investigate the role of acoustic and
magneto-acoustic waves in heating the solar chromosphere. Observations
in strong chromospheric lines are analyzed by comparing the deposited
acoustic-energy flux with the total integrated radiative losses. <BR
/> Methods: Quiet-Sun and weak-plage regions were observed in the Ca
II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and
in the Hα and Hβ lines with the echelle spectrograph attached
to the Vacuum Tower Telescope on 2018 December 11 and 2019 June
6. The deposited acoustic energy flux at frequencies up to 20 mHz
was derived from Doppler velocities observed in line centers and
wings. Radiative losses were computed by means of a set of scaled
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models obtained by fitting synthetic to observed line profiles. <BR />
Results: In the middle chromosphere (h = 1000-1400 km), the radiative
losses can be fully balanced by the deposited acoustic energy flux in
a quiet-Sun region. In the upper chromosphere (h > 1400 km), the
deposited acoustic flux is small compared to the radiative losses in
quiet as well as in plage regions. The crucial parameter determining
the amount of deposited acoustic flux is the gas density at a given
height. <BR /> Conclusions: The acoustic energy flux is efficiently
deposited in the middle chromosphere, where the density of gas is
sufficiently high. About 90% of the available acoustic energy flux in
the quiet-Sun region is deposited in these layers, and thus it is a
major contributor to the radiative losses of the middle chromosphere. In
the upper chromosphere, the deposited acoustic flux is too low, so that
other heating mechanisms have to act to balance the radiative cooling.
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Title: High-resolution spectroscopy of a surge in an emerging
flux region
Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar,
H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M.
2020A&A...639A..19V Altcode: 2020arXiv200503966V
<BR /> Aims: The regular pattern of quiet-Sun magnetic fields was
disturbed by newly emerging magnetic flux, which led a day later to
two homologous surges after renewed flux emergence, affecting all
atmospheric layers. Hence, simultaneous observations in different
atmospheric heights are needed to understand the interaction of
rising flux tubes with the surrounding plasma, in particular by
exploiting the important diagnostic capabilities provided by the
strong chromospheric Hα line regarding morphology and energetic
processes in active regions. <BR /> Methods: A newly emerged active
region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT)
at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High
spectral resolution observations using the echelle spectrograph in the
chromospheric Hαλ6562.8 Å line were obtained in the early growth
phase. Noise-stripped Hα line profiles yield maps of line-core and
bisector velocities, which were contrasted with velocities inferred
from Cloud Model inversions. A high-resolution imaging system recorded
simultaneously broad- and narrowband Hα context images. The Solar
Dynamics Observatory provided additional continuum images, line-of-sight
(LOS) magnetograms, and UV and extreme UV (EUV) images, which link the
different solar atmospheric layers. <BR /> Results: The active region
started as a bipolar region with continuous flux emergence when a new
flux system emerged in the leading part during the VTT observations,
resulting in two homologous surges. While flux cancellation at the
base of the surges provided the energy for ejecting the cool plasma,
strong proper motions of the leading pores changed the magnetic
field topology making the region susceptible to surging. Despite
the surge activity in the leading part, an arch filament system in
the trailing part of the old flux remained stable. Thus, stable
and violently expelled mass-loaded ascending magnetic structures
can coexist in close proximity. Investigating the height dependence
of LOS velocities revealed the existence of neighboring strong up-
and downflows. However, downflows occur with a time lag. The opacity
of the ejected cool plasma decreases with distance from the base of
the surge, while the speed of the ejecta increases. The location at
which the surge becomes invisible in Hα corresponds to the interface
where the surge brightens in He IIλ304 Å. Broad-shouldered and
dual-lobed Hα profiles suggests accelerated or decelerated and
highly structured LOS plasma flows. Significantly broadened Hα
profiles imply significant heating at the base of the surges, which
is also supported by bright kernels in UV and EUV images uncovered
by swaying motions of dark fibrils at the base of the surges. <BR />
Conclusions: The interaction of newly emerging flux with pre-existing
flux concentrations of a young, diffuse active region provided
suitable conditions for two homologous surges. High-resolution
spectroscopy revealed broadened and dual-lobed Hα profiles
tracing accelerated or decelerated flows of cool plasma along the
multi-threaded structure of the surge. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936762/olm">https://www.aanda.org</A>
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Title: Chromospheric Heating by Acoustic Waves Compared to Radiative
Cooling. II. Revised Grid of Models
Authors: Abbasvand, Vahid; Sobotka, Michal; Heinzel, Petr; Švanda,
Michal; Jurčák, Jan; del Moro, Dario; Berrilli, Francesco
2020ApJ...890...22A Altcode: 2020arXiv200103413A
Acoustic and magnetoacoustic waves are considered to be possible
agents of chromospheric heating. We present a comparison of deposited
acoustic energy flux with total integrated radiative losses in the
middle chromosphere of the quiet Sun and a weak plage. The comparison
is based on a consistent set of high-resolution observations acquired
by the Interferometric Bidimensional Spectrometer instrument in the
Ca II 854.2 nm line. The deposited acoustic-flux energy is derived
from Doppler velocities observed in the line core and a set of 1737
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models, which also provide the radiative losses. The models are obtained
by scaling the temperature and column mass of five initial models by
Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to
observed profiles. We find that the deposited acoustic-flux energy in
the quiet-Sun chromosphere balances 30%-50% of the energy released by
radiation. In the plage, it contributes by 50%-60% in locations with
vertical magnetic field and 70%-90% in regions where the magnetic
field is inclined more than 50° to the solar surface normal.
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Title: Spectropolarimetric Observations of an Arch Filament System
with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
2019ASPC..526..217B Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s<SUP>-1</SUP> next
to the pores and to 4 km s<SUP>-1</SUP> at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.
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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
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Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
2018A&A...614A...2V Altcode: 2018arXiv180103686V
<BR /> Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings. <BR /> Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines. <BR /> Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h. <BR /> Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.
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Title: Václav Bumba (1925 - 2018)
Authors: Kotrč, Pavel; Heinzel, Petr; Sobotka, Michal; Ambrož,
Pavel; van Driel-Gesztelyi, Lidia
2018SoPh..293...40K Altcode:
No abstract at ADS
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Title: The Temperature - Magnetic Field Relation in Observed and
Simulated Sunspots
Authors: Sobotka, Michal; Rezaei, Reza
2017SoPh..292..188S Altcode: 2017arXiv171109821S
Observations of the relation between continuum intensity and magnetic
field strength in sunspots have been made for nearly five decades. This
work presents full-Stokes measurements of the full-split (g =3 ) line
Fe I 1564.85 nm with a spatial resolution of 0.5<SUP>″</SUP> obtained
with the GREGOR Infrared Spectrograph in three large sunspots. The
continuum intensity is corrected for instrumental scattered light, and
the brightness temperature is calculated. Magnetic field strength and
inclination are derived directly from the line split and the ratio of
Stokes components. The continuum intensity (temperature) relations to
the field strength are studied separately in the umbra, light bridges,
and penumbra. The results are consistent with previous studies, and it
was found that the scatter of values in the relations increases with
increasing spatial resolution thanks to resolved fine structures. The
observed relations show trends common for the umbra, light bridges, and
the inner penumbra, while the outer penumbra has a weaker magnetic field
than the inner penumbra at equal continuum intensities. This fact can
be interpreted in terms of the interlocking comb magnetic structure of
the penumbra. A comparison with data obtained from numerical simulations
was made. The simulated data generally have a stronger magnetic field
and a weaker continuum intensity than the observations, which may
be explained by stray light and limited spatial resolution of the
observations, and also by photometric inaccuracies of the simulations.
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Title: Ca II 8542 Å brightenings induced by a solar microflare
Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma,
M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka,
M.; Denker, C.
2017A&A...608A.117K Altcode: 2017arXiv170906861K
<BR /> Aims: We study small-scale brightenings in Ca II 8542 Å
line-core images to determine their nature and effect on localized
heating and mass transfer in active regions. <BR /> Methods:
High-resolution two-dimensional spectroscopic observations of a solar
active region in the near-infrared Ca II 8542 Å line were acquired
with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR
telescope. Inversions of the spectra were carried out using the NICOLE
code to infer temperatures and line-of-sight (LOS) velocities. Response
functions of the Ca II line were computed for temperature and LOS
velocity variations. Filtergrams of the Atmospheric Imaging Assembly
(AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI)
were coaligned to match the ground-based observations and to follow the
Ca II brightenings along all available layers of the atmosphere. <BR />
Results: We identified three brightenings of sizes up to 2” × 2”
that appeared in the Ca II 8542 Å line-core images. Their lifetimes
were at least 1.5 min. We found evidence that the brightenings belonged
to the footpoints of a microflare (MF). The properties of the observed
brightenings disqualified the scenarios of Ellerman bombs or Interface
Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some
common properties with flaring active-region fibrils or flaring arch
filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric
and coronal layers according to the AIA channels; and (2) both show
flaring arches with lifetimes of about 3.0-3.5 min and lengths of
20” next to the brightenings. The inversions revealed heating by
600 K at the footpoint location in the ambient chromosphere during
the impulsive phase. Connecting the footpoints, a dark filamentary
structure appeared in the Ca II line-core images. Before the
start of the MF, the spectra of this structure already indicated
average blueshifts, meaning upward motions of the plasma along the
LOS. During the impulsive phase, these velocities increased up to -
2.2 km s<SUP>-1</SUP>. The structure did not disappear during the
observations. Downflows dominated at the footpoints. However, in
the upper photosphere, slight upflows occurred during the impulsive
phase. Hence, bidirectional flows are present in the footpoints
of the MF. <BR /> Conclusions: We detected Ca II brightenings that
coincided with the footpoint location of an MF. The MF event led to
a rise of plasma in the upper photosphere, both before and during the
impulsive phase. Excess mass, previously raised to at most chromospheric
layers, slowly drained downward along arches toward the footpoints
of the MF. <P />The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731319/olm">http://www.aanda.org</A>
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Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
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Title: Center-to-limb variation of the velocity field in and around
a sunspot with light-bridges
Authors: Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke,
Andrea; González Manrique, S. J.; Löhner-Böttcher, Johannes;
Kuckein, Christoph; Sobotka, Michal
2017psio.confE.104D Altcode:
No abstract at ADS
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Title: Velocity fields in sunspots derived from observations with
the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Denker, C.; Diercke, A.; González Manrique,
S. J.; Kuckein, C.; Louis, R. E.; Verma, M., Löhner-Böttcher, J.;
Sobotka, M.
2017psio.confE.105B Altcode:
No abstract at ADS
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Title: A study on Ca II 854.2 nm emission in a sunspot umbra using
a thin cloud model
Authors: Hamedivafa, H.; Sobotka, M.; Bellot Rubio, L.; Esteban
Pozuelo, S.
2016arXiv161206636H Altcode:
In the present work, we introduce and explain a method of solution
of the radiative transfer equation based on a thin cloud model. The
efficiency of this method to retrieve dynamical chromospheric parameters
from Stokes I profiles of Ca II 854.2 nm line showing spectral emission
is investigated. The analyzed data were recorded with the Crisp
Imaging Spectro-Polarimeter (CRISP) at Swedish 1-m Solar Telescope
on La Palma on 2012 May 5 between 8:11 - 9:00 UT. The target was a
large decaying sunspot (NOAA 11471) at heliocentric position W 15
deg S 19 deg. This sunspot has a large umbra divided into two umbral
cores (UCs). One of these UCs shows steady spectral emission in both
Ca II 854.2 nm and H-alpha lines, where downflows prevail. The other
UC shows intermittent spectral emission only in Ca II 854.2 nm, when
umbral flashes are propagating. The statistics of the obtained Doppler
velocities in both UCs is discussed.
---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. <P />Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. <BR /> Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. <BR /> Methods:
We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
= 0 we find no evidence of regions with dynamically weak (B<
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.
---------------------------------------------------------
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
---------------------------------------------------------
Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F Altcode: 2016arXiv160800513F
Context. A significant part of the penumbral magnetic field returns
below the surface in the very deep photosphere. For lines in the
visible, a large portion of this return field can only be detected
indirectly by studying its imprints on strongly asymmetric and
three-lobed Stokes V profiles. Infrared lines probe a narrow layer
in the very deep photosphere, providing the possibility of directly
measuring the orientation of magnetic fields close to the solar
surface. <BR /> Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
datasets from Hinode and from the GREGOR infrared spectrograph. We
inferred the quality and polarimetric accuracy of the infrared data
after applying several reduction steps. Techniques of spectral
inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral
area covered by reversed-polarity and three-lobed Stokes V profiles for
sunspots at disk center. We determined the amount of reversed-polarity
and three-lobed Stokes V profiles in visible and infrared data of
sunspots at various heliocentric angles. From the results, we computed
center-to-limb variation curves, which were interpreted in the context
of existing penumbral models. <BR /> Results: Observations in visible
and near-infrared spectral lines yield a significant difference in the
penumbral area covered by magnetic fields of opposite polarity. In
the infrared, the number of reversed-polarity Stokes V profiles is
smaller by a factor of two than in the visible. For three-lobed Stokes
V profiles the numbers differ by up to an order of magnitude.
---------------------------------------------------------
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. <BR />
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. <BR /> Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. <BR />
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.
---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
<BR /> Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. <BR /> Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. <BR /> Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.
---------------------------------------------------------
Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
T.; Kneer, F.; Nicklas, H.; Sobotka, M.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. <BR />
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. <BR /> Methods: We present speckle-reconstructed images taken
with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
486 nm and 589 nm bands. We estimate the spatial resolution from the
noise characteristics of the image bursts and obtain 0.08″ at 589
nm. We describe structure details in individual best images as well
as the temporal evolution of selected features. <BR /> Results: We
find branched dark lanes extending along thin (≈1″) light bridges
in sunspots at various heliocentric angles. In thick (≳ 2″) light
bridges the branches are disconnected from the central lane and have a Y
shape with a bright grain toward the umbra. The images reveal that light
bridges exist on varying intensity levels and that their small-scale
features evolve on timescales of minutes. Faint light bridges show
dark lanes outlined by the surrounding bright features. Dark lanes are
very common and are also found in the boundary of pores. They have a
characteristic width of 0.1″ or smaller. Intergranular dark lanes of
that width are seen in active region granulation. <BR /> Conclusions: We
interpret our images in the context of magneto-convective simulations
and findings: while central dark lanes in thin light bridges are
elevated and associated with a density increase above upflows, the dark
lane branches correspond to locations of downflows and are depressed
relative to the adjacent bright plasma. Thick light bridges with central
dark lanes show no projection effect. They have a flat elevated plateau
that falls off steeply at the umbral boundary. There, Y-shaped filaments
form as they do in the inner penumbra. This indicates the presence of
inclined magnetic fields, meaning that the umbral magnetic field is
wrapped around the convective light bridge.
---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. <BR /> Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. <BR /> Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. <BR />
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. <BR /> Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. <BR /> Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. <BR /> Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. <BR /> Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: Chromospheric Heating by Acoustic Waves Compared to Radiative
Cooling
Authors: Sobotka, M.; Heinzel, P.; Švanda, M.; Jurčák, J.; del Moro,
D.; Berrilli, F.
2016ApJ...826...49S Altcode: 2016arXiv160504794S
Acoustic and magnetoacoustic waves are among the possible candidate
mechanisms that heat the upper layers of the solar atmosphere. A weak
chromospheric plage near the large solar pore NOAA 11005 was observed
on 2008 October 15, in the Fe I 617.3 nm and Ca II 853.2 nm lines of
the Interferometric Bidimemsional Spectrometer attached to the Dunn
Solar Telescope. In analyzing the Ca II observations (with spatial
and temporal resolutions of 0.″4 and 52 s) the energy deposited by
acoustic waves is compared to that released by radiative losses. The
deposited acoustic flux is estimated from the power spectra of Doppler
oscillations measured in the Ca II line core. The radiative losses
are calculated using a grid of seven one-dimensional hydrostatic
semi-empirical model atmospheres. The comparison shows that the
spatial correlation of the maps of radiative losses and acoustic flux
is 72%. In a quiet chromosphere, the contribution of acoustic energy
flux to radiative losses is small, only about 15%. In active areas
with a photospheric magnetic-field strength between 300 and 1300 G
and an inclination of 20°-60°, the contribution increases from 23%
(chromospheric network) to 54% (a plage). However, these values have
to be considered as lower limits and it might be possible that the
acoustic energy flux is the main contributor to the heating of bright
chromospheric network and plages.
---------------------------------------------------------
Title: Temporal Evolution of Magnetic Field and Intensity Properties
of Photospheric Pores
Authors: Dorotovič, I.; Rybanský, M.; Sobotka, M.; Lorenc, M.;
Barandas, M.; Fonseca, J. M.
2016ASPC..504...37D Altcode:
We describe conditions of pore formation in relation to the
configuration and intensity of magnetic field, using observations
of the SDO/HMI instrument, which observes the photosphere in the
visible continuum and simultaneously the magnetic field with a
spatial resolution of better than 1”. An area with a diameter of 35”
containing 6 pores during the period from October 10, 2013, 22:01:30
UT to October 11, 2013, 20:01:30 UT is selected from the HMI full-disk
images. We analyze the temporal evolution of the area and brightness
of the pores (time step 15 minutes), their statistics, and in parallel
a time-sequence of the line-of-sight magnetic field intensity and its
correlation with the area and brightness. We find that the pores become
visible when their intensity decreases below 0.85 of the photospheric
surrounding intensity and the magnetic field increases to 650 G in the
HMI measurements. We determine the mean synodical rotational speed of
the pores to be 14.44°/24 hours, which is 1° more than the tabular
value. Positions of maximum magnetic field precede the positions of
the pores in the direction of rotation for the positive polarity and
lag behind it for the negative polarity.
---------------------------------------------------------
Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.
2016IAUS..320...68S Altcode:
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5-m GREGOR telescope, using a 0.1 nm Ca II H interference
filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show
that the ribbon is a part of a larger one that extends through the
neighboring positive polarities and also participates in several
other flares within the active region. A 140 second long time series
of Ca II H images was reconstructed by means of the Multi-Frame
Blind Deconvolution method, giving the respective spatial and
temporal resolutions of 0”.1 and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
providing evidence for the presence of slipping reconnection at small
spatial scales.
---------------------------------------------------------
Title: White-light continuum emission from a solar flare and plage
Authors: Berlicki, Arkadiusz; Awasthi, Arun Kumar; Heinzel, Petr;
Sobotka, Michal
2016IAUS..320..268B Altcode: 2016arXiv160404186B
Observations of flare emissions in the optical continuum are very
rare. Therefore, the analysis of such observations is useful and
may contribute to our understanding of the flaring chromosphere and
photosphere. We study the white light continuum emission observed
during the X6.9 flare. This emission comes not only from the flare
ribbons but also form the nearby plage area. The main aim of this work
is to disentangle the flare and plage (facula) emission. We analyzed
the spatial, spectral and temporal evolution of the flare and plage
properties by analyzing multi-wavelength observations. We study
the morphological correlation of the white-light continuum emission
observed with different instruments. We found that some active region
areas which produce the continuum emission correspond rather to plages
than to the flare kernels. We showed that in some cases the continuum
emission from the WL flare kernels is very similar to the continuum
emission of faculae.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, Michal; Dudik, Jaroslav; Denker, Carsten; Balthasar,
Horst; Jurcak, Jan; Liu, Wenjuan; GREGOR Team
2015IAUGA..2246841S Altcode:
A small flare ribbon above a sunspot with a light bridge was observed on
7 November 2014 around 12:00 UT in the blue imaging channel of GREGOR,
using a 0.1 nm Ca II H interference filter. Context observations from
SDO/AIA, Hinode/SOT and IRIS show that the ribbon is a part of a larger
ribbon extending through the neighbouring negative polarities that also
participates in several other flares within the active region. A 140
s long time series of Ca II H images was reconstructed by means of the
Multi Frame Blind Deconvolution method, giving the respective spatial
and temporal resolutions of 0.1" and 1 s. Light curves and horizontal
velocities of small-scale brightenings in the flare ribbon located
above an umbral core were measured. Some of them are stationary but
three brightenings move in opposite directions along the ribbon with
speeds of 7 - 11 km/s. Expecting that the brightenings correspond to
footpoints of flare loops, their motions can be interpreted in terms
of the slipping reconnection model.
---------------------------------------------------------
Title: Moat Flow System around Sunspots in Shallow Subsurface Layers
Authors: Švanda, Michal; Sobotka, Michal; Bárta, Tomáš
2014ApJ...790..135S Altcode: 2014arXiv1406.2482S
We investigate the subsurface moat flow system around McIntosh
H-type symmetrical sunspots and compare it to the flow system within
supergranular cells. Representatives of both types of flows are
constructed by means of the statistical averaging of flow maps obtained
by time-distance helioseismic inversions. We find that moat flows around
H-type sunspots replace supergranular flows but there are two principal
differences between the two phenomena: the moat flow is asymmetrical,
probably due to the proper motion of sunspots with respect to the
local frame of rest, while the flow in the supergranular cell is highly
symmetrical. Furthermore, the whole moat is a downflow region, while the
supergranule contains the upflow in the center, which turns into the
downflow at about 60% of the cell radius from its center. We estimate
that the mass downflow rate in the moat region is at least two times
larger than the mass circulation rate within the supergranular cell.
---------------------------------------------------------
Title: Orphan penumbrae: Submerging horizontal fields
Authors: Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M.
2014A&A...564A..91J Altcode: 2014arXiv1402.6558J
<BR /> Aims: We investigate the properties of orphan penumbrae,
which are photospheric filamentary structures observed in active
regions near polarity inversion lines that resemble the penumbra of
regular sunspots but are not connected to any umbra. <BR /> Methods:
We use Hinode data from the Solar Optical Telescope to determine the
properties of orphan penumbrae. Spectropolarimetric data are employed
to obtain the vector magnetic field and line-of-sight velocities in
the photosphere. Magnetograms are used to study the overall evolution
of these structures, and G-band and Ca ii H filtergrams are to
investigate their brightness and apparent horizontal motions. <BR />
Results: Orphan penumbrae form between regions of opposite polarity in
places with horizontal magnetic fields. Their magnetic configuration
is that of Ω-shaped flux ropes. In the two cases studied here,
the opposite-polarity regions approach each other with time and the
whole structure submerges as the penumbral filaments disappear. Orphan
penumbrae are very similar to regular penumbrae, including the existence
of strong gas flows. Therefore, they could have a similar origin. The
main difference between them is the absence of a "background" magnetic
field in orphan penumbrae. This could explain most of the observed
differences. <BR /> Conclusions: The fast flows we detect in orphan
penumbrae may be caused by the siphon flow mechanism. Based on the
similarities between orphan and regular penumbrae, we propose that
the Evershed flow is also a manifestation of siphon flows. <P />A
movie attached to Fig. 11 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: An Estimate of Chromospheric Heating by Acoustic Waves
Authors: Sobotka, M.; Švanda, M.; Jurčak, J.; Heinzel, P.; Del Moro,
D.; Berrilli, F.
2014CEAB...38...53S Altcode:
Several mechanisms may heat the solar chromosphere: acoustic waves,
magnetoacoustic waves (slow, fast, and Alfvén waves), and small-scale
magnetic reconnections. Based on observations in the Ca II 854.2 nm
line, the contribution of acoustic waves to the heating of quiet and
plage regions in the chromosphere is discussed. The energy released
by radiative losses is compared with the energy deposited by acoustic
waves. Radiative losses are computed using a grid of six semi-empirical
models VAL A--F. The deposited acoustic flux is calculated using power
spectra of Doppler oscillations measured in the Ca~II line core. The
comparison shows that the spatial correlation of maps of radiative
losses and acoustic flux is 70 %. The deposited acoustic flux provides
at least 25--30~% of the energy radiated in the quiet chromosphere
and 50~% in plage regions.
---------------------------------------------------------
Title: Dynamics of the solar atmosphere above a pore with a light
bridge
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del Moro,
D.; Berrilli, F.
2013A&A...560A..84S Altcode: 2013arXiv1309.7790S
Context. Solar pores are small sunspots lacking a penumbra that have
a prevailing vertical magnetic-field component. They can include light
bridges at places with locally reduced magnetic field. Like sunspots,
they exhibit a wide range of oscillatory phenomena. <BR /> Aims:
A large isolated pore with a light bridge (NOAA 11005) is studied
to obtain characteristics of a chromospheric filamentary structure
around the pore, to analyse oscillations and waves in and around
the pore, and to understand the structure and brightness of the light
bridge. <BR /> Methods: Spectral imaging observations in the line Ca II
854.2 nm and complementary spectropolarimetry in Fe I lines, obtained
with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter,
were used to measure photospheric and chromospheric velocity fields,
oscillations, waves, the magnetic field in the photosphere, and
acoustic energy flux and radiative losses in the chromosphere. <BR />
Results: The chromospheric filamentary structure around the pore has
all important characteristics of a superpenumbra: it shows an inverse
Evershed effect and running waves, and has a similar morphology and
oscillation character. The granular structure of the light bridge in
the upper photosphere can be explained by radiative heating. Acoustic
waves leaking up from the photosphere along the inclined magnetic
field in the light bridge transfer enough energy flux to balance
the entire radiative losses of the light-bridge chromosphere. <BR />
Conclusions: A penumbra is not a necessary condition for the formation
of a superpenumbra. The light bridge is heated by radiation in the
photosphere and by acoustic waves in the chromosphere.
---------------------------------------------------------
Title: Atmosphere above a large solar pore
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del
Moro, D.
2013JPhCS.440a2049S Altcode: 2013arXiv1302.4893S
A large solar pore with a granular light bridge was observed on October
15, 2008 with the IBIS spectrometer at the Dunn Solar Telescope and a
69-min long time series of spectral scans in the lines Ca II 854.2 nm
and Fe I 617.3 nm was obtained. The intensity and Doppler signals in the
Ca II line were separated. This line samples the middle chromosphere
in the core and the middle photosphere in the wings. Although no
indication of a penumbra is seen in the photosphere, an extended
filamentary structure, both in intensity and Doppler signals, is
observed in the Ca II line core. An analysis of morphological and
dynamical properties of the structure shows a close similarity to a
superpenumbra of a sunspot with developed penumbra. A special attention
is paid to the light bridge, which is the brightest feature in the
pore seen in the Ca II line centre and shows an enhanced power of
chromospheric oscillations at 3-5 mHz. Although the acoustic power
flux in the light bridge is five times higher than in the "quiet"
chromosphere, it cannot explain the observed brightness.
---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.
---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.
---------------------------------------------------------
Title: IBIS: High-Resolution Multi-Height Observations and Magnetic
Field Retrieval
Authors: Del Moro, D. .; Berrilli, F.; Stangalini, M.; Giannattasio,
F.; Piazzesi, R.; Giovannelli, L.; Viticchiè, B.; Vantaggiato, M.;
Sobotka, M.; Jurčák, J.; Criscuoli, S.; Giorgi, F.; Zuccarello, F.
2012ASPC..463...33D Altcode:
IBIS (Interferometric BIdimensional Spectrometer) allows us to measure
the four Stokes parameters in several spectroscopic lines with high
spatial and spectral resolutions. With this information, we can
retrieve both the dynamics and the magnetic field at different layers
of the Photosphere and Chromosphere. The high spectral, spatial and
temporal resolutions and the polarimetric sensitivity of IBIS allows
us to study different phenomena taking place in the solar atmosphere
with new tools. As an example, we highlight some applications of
IBIS observations and analysis: <BR /> · Radiative and dynamical
properties of Photospheric Bright Points versus their magnetic field
concentration. <BR /> · Close up analysis of magnetic, velocity and
temperature field in a solar pore. <BR /> · MHD wave propagation from
the photosphere to the chromosphere in complex magnetic configuration.
---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.
---------------------------------------------------------
Title: Optimisation of solar synoptic observations
Authors: Klvaña, Miroslav; Sobotka, Michal; Švanda, Michal
2012SPIE.8448E..0AK Altcode:
The development of instrumental and computer technologies is
connected with steadily increasing needs for archiving of large data
volumes. The current trend to meet this requirement includes the
data compression and growth of storage capacities. This approach,
however, has technical and practical limits. A further reduction of
the archived data volume can be achieved by means of an optimisation
of the archiving that consists in data selection without losing the
useful information. We describe a method of optimised archiving of
solar images, based on the selection of images that contain a new
information. The new information content is evaluated by means of the
analysis of changes detected in the images. We present characteristics
of different kinds of image changes and divide them into fictitious
changes with a disturbing effect and real changes that provide a new
information. In block diagrams describing the selection and archiving,
we demonstrate the influence of clouds, the recording of images during
an active event on the Sun, including a period before the event onset,
and the archiving of long-term history of solar activity. The described
optimisation technique is not suitable for helioseismology, because it
does not conserve the uniform time step in the archived sequence and
removes the information about solar oscillations. In case of long-term
synoptic observations, the optimised archiving can save a large amount
of storage capacities. The actual capacity saving will depend on the
setting of the change-detection sensitivity and on the capability to
exclude the fictitious changes.
---------------------------------------------------------
Title: Magnetic and velocity fields of a solar pore
Authors: Sobotka, M.; Del Moro, D.; Jurčák, J.; Berrilli, F.
2012A&A...537A..85S Altcode:
Context. Solar pores are intermediate-size magnetic flux features
that emerge at the surface of the Sun. The absence of a filamentary
penumbra indicates that there is a relatively simple magnetic structure
with a prevailing vertical magnetic field. <BR /> Aims: Relations
between the magnetic field components, line-of-sight velocities,
and horizontal motions in and around a large pore (D<SUB>eff</SUB> =
8”.5) are analysed to provide observational constraints on theoretical
models and numerical simulations. <BR /> Methods: Spectropolarimetric
observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS
spectrometer attached to the Dunn Solar Telescope are inverted into
series of maps of thermal, magnetic, and velocity parameters using the
SIR code. Horizontal velocities are obtained from series of white-light
images by means of local correlation tracking. <BR /> Results: The
magnetic field B extends from the visible pore border of more than 3”.5
and has a radial structure in a form of spines that are co-spatial with
dark intergranular lanes. The horizontal component B<SUB>hor</SUB> is
more extended than the vertical component B<SUB>z</SUB>. The temperature
linearly decreases with increasing B<SUB>z</SUB>, by about - 300 K
kG<SUP>-1</SUP> in the photosphere and - 800 K kG<SUP>-1</SUP> in the
umbra. The temperature contrast of granulation increases with increasing
magnetic field strength and is then suppressed for B<SUB>z</SUB> >
1200 G. Granular upflows dominate in regions with B<SUB>z</SUB> <
600-700 G. Line-of-sight velocities are lower in stronger fields,
except for fast isolated downflows at the pore's border. The velocity
signature of granulation is suppressed completely for B<SUB>hor</SUB>
> 1000 G. Horizontal motions of granules start to be damped for
B<SUB>z</SUB> > 500 G and recurrently exploding granules appear
only in magnetic fields comparable to or weaker than the equipartition
field strength 400 G.
---------------------------------------------------------
Title: Solar synoptic telescope. Characteristics, possibilities,
and limits of design
Authors: Klvaňa, M.; Sobotka, M.; Švanda, M.
2011CoSka..41...92K Altcode:
A rapid evolution of electronics and information technologies makes
it possible to use new original designs of synoptic telescopes for
solar observations, to increase the demands on their functions, and
to fully automate the observation. However, there are hardware and
software limits that strongly influence the working capabilities of
synoptic telescopes. In this contribution, we analyze relationships
between the synoptic telescope's characteristics, the parameters of
image digitization, the control, the achievable degree of automation of
observations, and the possibilities to implement functions connected
with the solar activity monitoring and image archiving. The principles
listed above serve as a basis for the design study of the Auxiliary
Full-Disc Telescope for the European Solar Telescope (EST), a
pan-European project of a large 4-meter solar telescope.
---------------------------------------------------------
Title: Synoptic observations with the Coimbra spectroheliograph
Authors: Garcia, A.; Sobotka, M.; Klvaňa, M.; Bumba, V.
2011CoSka..41...69G Altcode:
Spectroheliograms in the Astronomical Observatory of the Coimbra
University (Portugal) have been photographed in the spectral line of Ca
II K continuously since 1926 and, since 1989, spectroheliograms in Hα
have been photographed as well. Since 2007, all the spectroheliograms
have been recorded using a CCD camera. Until July 2010, about 34 000
observations in total were acquired in the spectral bands Ca II K3, Ca
II K1, Hα, red continuum, and Hα Dopplergrams (since 2009), covering
a period of 85 years (Ca II K3 line). We describe the characteristics
of the photographic and digital spectroheliograms, the statistics of
the observations, and the utilization of Coimbra spectroheliograms by
the solar community.
---------------------------------------------------------
Title: The challenge of umbral dots
Authors: Sobotka, M.; Klvaňa, M.
2011CEAB...35...39S Altcode:
Recent numerical simulations of magnetoconvection in the umbra
reproduced not only the basic characteristics of central (CUDs) and
peripheral (PUDs) umbral dots but predicted also possible substructures
-- dark lanes in CUDs and tails connected to PUDs. Imaging of
these extremely small and faint substructures is at the limits of
contemporary solar telescopes and spectropolarimetry is currently
not feasible. Although the existence of these substructures has
been recently confirmed by observations, there are some differences
between the observed and predicted characteristics that need to be
clarified. The required spectropolarimetric observations with extremely
high spatial and temporal resolution and stability can be acquired only
with 4-m class telescopes equipped with multi-conjugate adaptive optics.
---------------------------------------------------------
Title: Vývoj celodiskového dalekohledu pro EST
---------------------------------------------------------
Title: Vývoj
celodiskového dalekohledu pro EST
---------------------------------------------------------
Title: Development of the full-disc
telescope for EST.
Authors: Sobotka, M.; Klvaňa, M.; Melich, Z.; Rail, Z.
2010nspm.conf..201S Altcode:
At present, a development study takes place of the 4-meter European
Solar Telescope (EST), the status of which is summarized in the
introduction of this contribution. A part of the study is the design
of the Auxiliary Full-Disc Telescope (AFDT), developed in the AI and
IPP of the AS CR. The telescope, 150 mm in diameter, will serve for
positioning the observer on the solar disc and in its surroundings,
steering the main EST telescope towards the selected object, accurate
coordinate measurements and EST coordinate system corrections. AFDT
will also be used as an autonomous robotic telescope for synoptic
observations of solar activity. In this paper we describe the current
status of the AFDT special mechanical design, optical system design,
and the principles of the telescope control system.
---------------------------------------------------------
Title: Spectroheliograms recorded using the new CCD camera in the
OAUC, Coimbra, Portugal
Authors: Garcia, A.; Klvaňa, M.; Sobotka, M.; Bumba, V.
2010nspm.conf..206G Altcode:
Spectroheliograms in the OAUC (Coimbra, Portugal) have been
photographed in the spectral line of Ca II continuously since 1926,
and since 1990 spectroheliograms in H-alpha have been photographed as
well. Since 2007, all the spectroheliograms are recorded using new CCD
camera. Specifications of the camera, including the new optical scheme
of the spectrograph, were presented in a previous paper (Klvana et al.,
2006). On the data recorded in 2010 we demonstrate the good quality
of spectroheliograms taken during standard observing conditions,
influence of the clouds and the effects introduced by filtering.
---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V
With the integration of a 1-meter Cesic primary mirror the GREGOR
telescope pre-commissioning started. This is the first time, that
the entire light path has seen sunlight. The pre-commissioning period
includes testing of the main optics, adaptive optics, cooling system,
and pointing system. This time was also used to install a near-infrared
grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5
meter primary mirror is installed, commissioning will be completed,
and an extended phase of science verification will follow. In the near
future, GREGOR will be equipped with a multi-conjugate adaptive optics
system that is presently under development at KIS.
---------------------------------------------------------
Title: Auxiliary full-disc telescope for the European Solar Telescope
Authors: Sobotka, Michal; Klvaña, Miroslav; Melich, Zbynék; Rail,
Zdenék; Bettonvil, Felix; Gelly, Bernard
2010SPIE.7735E..1ZS Altcode: 2010SPIE.7735E..67S
The Auxiliary Full-Disc Telescope (AFDT) will be used for the
orientation of the observer on the solar disc and in its surroundings,
for an easy guidance of the European Solar Telescope (EST) to a selected
target, and for precise coordinate measurements. AFDT can be used as an
autonomous robotic telescope for synoptic observations and records of
solar activity also when no observations are carried out at the EST main
telescope. The principal functions of AFDT and the related requirements
are summarised. The specific axial mechanical structure accommodating
the refractor optical system is outlined. The optical system and its
components are described. Two alternatives of the positional control
system - the active guiding system and the passive guiding system -
are described and their functionality is analysed.
---------------------------------------------------------
Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
D.; Strassmeier, K. G.
2010AN....331..624V Altcode:
The integration and verification phase of the GREGOR telescope
reached an important milestone with the installation of the
interim 1 m SolarLite primary mirror. This was the first time
that the entire light path had seen sunlight. Since then extensive
testing of the telescope and its subsystems has been carried out. The
integration and verification phase will culminate with the delivery and
installation of the final 1.5 m Zerodur primary mirror in the summer of
2010. Observatory level tests and science verification will commence in
the second half of 2010 and in 2011. This phase includes testing of the
main optics, adaptive optics, cooling and pointing systems. In addition,
assuming the viewpoint of a typical user, various observational modes
of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
Spectrograph (GRIS), and high-speed camera systems will be tested to
evaluate if they match the expectations and science requirements. This
ensures that GREGOR will provide high-quality observations with its
combination of (multi-conjugate) adaptive optics and advanced post-focus
instruments. Routine observations are expected for 2012.
---------------------------------------------------------
Title: Measurements of chromospheric velocity fields by means of
the Coimbra University spectroheliograph
Authors: Garcia, A.; Klvaňa, M.; Sobotka, M.
2010CEAB...34...47G Altcode:
The Coimbra University spectroheliograph produces high-quality
full-disc spectroheliograms in the lines Hα, Ca II K3, Ca II K1, and
adjacent continua. The reduction software was extended to enable the
measurement of velocity fields in Hα. We describe the instrument, the
data processing, present the first results of the velocity measurements,
and discuss the possibilities of improvement of their quality.
---------------------------------------------------------
Title: Dynamics of Active Regions Revealed by Tracking of Doppler
Features
Authors: Švanda, M.; Sobotka, M.; Klvaňa, M.; Bumba, V.
2010ASSP...19..410S Altcode: 2010mcia.conf..410S
We investigate the large-scale horizontal dynamics of active regions in
the 23rd solar cycle. The large-scale horizontal velocity fields were
measured applying the local correlation tracking (LCT) algorithm to the
processed high-cadence full-resolution full-disc MDI Dopplergrams. We
performed the selection of NOAA active regions in the available dataset
and followed their individual evolution in time. The statistical study
of this sample gives us a unique opportunity to study the dynamics
of active regions at various stages of their evolution. In few cases,
we found behavior that is consistent with the dynamical disconnection
of sunspots from the magnetic roots.
---------------------------------------------------------
Title: Evolution of Umbral Dots and Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
2010ASSP...19..507S Altcode: 2010mcia.conf..507S
On 27 February 2007, Hinode SOT/SP acquired a time series of full-Stokes
spectra of a regular, medium-sized sunspot NOAA 10944 located near
the center of the solar disk. The inversion code SIR (Ruiz Cobo and
del Toro Iniesta 1992, ApJ 398, 375) was applied to these data and a
3-h long time series of 34 spatial 3D maps of plasma parameters in the
umbra and penumbra were computed. The temporal and spatial resolutions
are 5.5 min and 0 :0032, respectively. A simultaneous series of SOT/BFI
G-band images was utilized for complementary measurements of horizontal
motions and sizes of small-scale features.
---------------------------------------------------------
Title: Transport of Supergranules and their Vertical Coherence
Authors: Švanda, M.; Kosovichev, A. G.; Klvaňa, M.; Sobotka, M.;
Duvall, T. L., Jr.
2009ASPC..416..547S Altcode:
In recent papers, we have introduced a method for measuring the
photospheric flow field that is based on the tracking of supergranular
structures. Here, in combination with helioseismic data, we are
able to estimate the depth in the solar convection envelope to
which the detected large-scale flow field is coherent. We show that
the upper 10 Mm in the convection zone depicts similar features in
horizontal velocity. Our interpretation of this observation is that
the supergranulation is a coherent structure 10 Mm deep and is subject
to large-scale transport by the underlying velocity field.
---------------------------------------------------------
Title: Large-scale horizontal flows in the solar
photosphere. V. Possible evidence for the disconnection of bipolar
sunspot groups from their magnetic roots
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.
2009A&A...506..875S Altcode: 2009arXiv0908.3183S
In a recent paper (Švanda et al. 2008, A&A, 477, 285) we pointed
out that, based on the tracking of Doppler features in the full-disc
MDI Dopplergrams, the active regions display two dynamically different
regimes. We speculated that this could be a manifestation of the
sudden change in the active regions dynamics, caused by the dynamic
disconnection of sunspots from their magnetic roots as proposed by
Schüssler & Rempel (2005, A&A, 441, 337). Here we investigate
the dynamic behaviour of the active regions recorded in the high-cadence
MDI data over the last solar cycle in order to confirm the predictions
in the Schüssler's & Rempel's paper. We find that, after drastic
reduction of the sample, which is done to avoid disturbing effects,
a large fraction of active regions displays a sudden decrease in the
rotation speed, which is compatible with the mechanism of the dynamic
disconnection of sunspots from their parental magnetic structures.
---------------------------------------------------------
Title: Morphology and evolution of umbral dots and their substructures
Authors: Sobotka, M.; Puschmann, K. G.
2009A&A...504..575S Altcode: 2009arXiv0907.4236S
Context: Substructures - dark lanes and tails - of umbral dots (UDs)
were predicted by numerical simulations of magnetoconvection and have
been detected later in some observations. <BR />Aims: To provide
constraints for realistic theoretical models of sunspot umbrae, we
describe the observed properties and evolutionary characteristics of
UDs (including their substructure) and of other umbral structures. <BR
/>Methods: We analyse a 6 h 23 min time series of broadband images
of a large umbra in the active region NOAA 10634, acquired with the
1-m Swedish Solar Telescope, in the wavelength band around 602 nm. A
43 min part of this series was reconstructed with the MFBD method,
reaching a spatial resolution of 0.14 arcsec. With the help of image
segmentation, feature tracking, and local correlation tracking,
we measured brightness, size, lifetime, and horizontal velocities
of various umbral structures. <BR />Results: Large structures in the
umbra - strong and faint light bridges (LBs) and an extended penumbral
filament - evolve on time scales of hours. Most (90%) of UDs and bright
point-like features in faint LBs split and merge, and their median
lifetimes are 3.5 or 5.7 min, depending on whether the split or merge
event is considered as the end of their life. Both UDs and features in
faint LBs that do not split or merge are clearly smaller (0.15 arcsec)
than the average size (0.17 arcsec) of all features. Horizontal motions
of umbral bright small-scale features are directed either into the
umbra or along faint LBs with mean horizontal velocities of 0.34 km
s<SUP>-1</SUP>. Features faster than 0.4 km s<SUP>-1</SUP> appear
mostly at the periphery of the umbra. The motion of peripheral UDs
(PUDs) seems to be the continuation of the motion of penumbral grains
(PGs). The intensity of dark lanes, measured in four bright central UDs
(CUDs), is by a factor 0.8 lower than the peak intensity of CUDs. The
width of dark lanes is probably less than the resolution limit 0.14
arcsec. The characteristic time of substructure changes of UDs is ~4
min. We observe narrow (0.14 arcsec) bright and dark filaments connected
with PUDs. The bright filaments are 0.06 I_ph brighter than the dark
ones. Usually one dark and two bright filaments form a 0.4 arcsec
wide tail attached to one PUD, resembling a short dark-cored penumbral
filament. <BR />Conclusions: Our results indicate the similarity between
PUDs and PGs located at the tips of bright penumbral filaments. The
features seen in numerical MHD simulations are consistent with our
observations of dark lanes in CUDs and tails attached to PUDs.
---------------------------------------------------------
Title: Examples of Science Cases and Requirements for EST
Authors: Sobotka, M.; Heinzel, P.; Kašparová, J.
2009ASPC..405..455S Altcode:
We present various suggestions for the study of flares (fast emission
variations, heating mechanisms), prominences (fine structure, magnetic
field, energy balance), and sunspots (umbral structure, heating
mechanisms, depth and structure of the penumbra, Evershed flow). From
these cases we derive the requirements for the future European Solar
Telescope: spectropolarimetric capabilities, high signal-to-noise ratio,
multi-line spectroscopy, high spatial and temporal resolution.
---------------------------------------------------------
Title: Large-scale horizontal flows in the solar photosphere IV. On
the vertical structure of large-scale horizontal flows
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.; Kosovichev, A. G.;
Duvall, T. L.
2009NewA...14..429S Altcode: 2008arXiv0812.1971S
In the recent papers, we introduced a method utilised to measure
the flow field. The method is based on the tracking of supergranular
structures. We did not precisely know, whether its results represent
the flow field in the photosphere or in some subphotospheric
layers. In this paper, in combination with helioseismic data, we
are able to estimate the depths in the solar convection envelope,
where the detected large-scale flow field is well represented by
the surface measurements. We got a clear answer to question what
kind of structures we track in full-disc Dopplergrams. It seems that
in the quiet Sun regions the supergranular structures are tracked,
while in the regions with the magnetic field the structures of the
magnetic field are dominant. This observation seems obvious, because
the nature of Doppler structures is different in the magnetic regions
and in the quiet Sun. We show that the large-scale flow detected by
our method represents the motion of plasma in layers down to ∼10
Mm. The supergranules may therefore be treated as the objects carried
by the underlying large-scale velocity field.
---------------------------------------------------------
Title: Evolution of Physical Characteristics of Umbral Dots and
Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
2009ApJ...694.1080S Altcode:
A time series of full-Stokes spectropolarimetric observations of
the sunspot NOAA 10944, acquired with HINODE/SOT in 2007 February, is
analyzed. The data were inverted using the code SIR into a series of 34
maps covering 3 hr of umbra and penumbra evolution. The retrieved maps
of plasma parameters show the spatial distribution of temperature,
line-of-sight velocity, magnetic field strength, and inclination
in two different ranges of optical depths corresponding to the low
and high photosphere. In these maps, the evolution of central and
peripheral umbral dots (CUDs and PUDs) and penumbral grains (PGs) was
traced. While CUDs do not show any excess of line-of-sight velocity
and magnetic field inclination with respect to the surrounding umbra,
upflows of 400 m s<SUP>-1</SUP> and a more horizontal magnetic field
are detected in the low photospheric layers of PUDs. PGs have even
stronger upflows and magnetic field inclination in the low photosphere
than PUDs. The absolute values of these parameters decrease when PGs
evolve into PUDs. It seems that PGs and PUDs are of a similar physical
nature. Both classes of features appear in regions with a weaker and
more horizontal magnetic field and their formation height reaches
the low photosphere. On the other hand, CUDs appear in regions with
a stronger and more vertical magnetic field and they are formed too
deep to detect upflows and changes in magnetic field inclination.
---------------------------------------------------------
Title: Tracking of Supergranules - Does It Make Any Sense?
Authors: Svanda, M.; Klvaòa, M.; Sobotka, M.
2008ESPM...12.2.10S Altcode: 2008arXiv0809.4757S
The motions of the plasma and structures in and below the solar
photosphere is not well understood. The results obtained using various
methods cannot be in general considered as consistent, especially in
details. In this contribution we show a summary of the results obtained
by the method we have developed recently. <P />To study the photospheric
dynamics we apply the local correlation tracking algorithm to the
series of full-disc Dopplergrams obtained by Michelson Doppler Imager
(MDI) on-board the SoHO observatory. The dominant structures recorded
in the Dopplergrams are supergranules. Under the assumtion that the
supergranules are carried by the flow field of the larger scale, we
study properties of this underlying velocity field. The methodology
consists of an extensive data processing of primary data in order to
suppress disturbing effects such as p-modes of solar oscillations
or instrumental issues. Aditional coordinate transformations
are also needed to make the data suitable for tracking. <P />We
perform comparative tests with synthetic data with known properties
and with results of time-distance helioseismology with a great
success. Correlation coeficients of the comparison of mean components
of the flow field are larger than 0.8, for the comparison of details
in the vector velocity field the correlation coeficient is larger than
0.6. <P />The results of the method applied to the real data agree
well with well-known features detected in the photospheric velocity
fields and reported by many other authors. With the proposed method
we detect differential rotation, meridional circulation, torsional
oscillations, and other features. A few case studies are shown to
demonstrate the performance of the method. <P />As a conclusion
let's answer the question in the title. We believe that tracking of
supergranules makes a perfect sense when studying the large-scale
flows in the solar photosphere. The method we demonstrate is suitable
to detect large-scale velocity field with effective resolution of 60"
and random error of 15 m/s. We believe that our method may provide a
powerful tool for studies related to the dynamic behaviour of plasmas
in the solar photosphere.
---------------------------------------------------------
Title: The Conception of the Full-disc Telescope for EST Instrument
Authors: Klvana, M.; Sobotka, M.; Svanda, M.
2008ESPM...12.2.73K Altcode:
In year 2008 European Association for Solar Telescopes (EAST)
started to carry out the project of the European Solar Telescope (EST)
instrument. The main telescope of EST is expected to have a diameter of
4 m and therefore it will become one of the biggest solar telescopes
in the world. The main telescope will be connected to the smaller
full-disc solar telescope, the development of which is carried out by
our group. <P />In this contribution we present optical and mechanical
demands of the telescope, its optical design and the description of
the basic operation regimes. We analyse the possibilities of inclusion
of this full-disc telescope in the general EST controlling system. We
show that the small telescope can be used for alignment of the main
telescope and for the determination of the changing instrumental
constants of the instrument during a long-term run.
---------------------------------------------------------
Title: Differences between Central and Peripheral Umbral Dots
Authors: Sobotka, M.; Jurcak, J.
2008ESPM...12.2.23S Altcode:
A time series of full-Stokes spectropolarimetric observations of the
sunspot NOAA 10944, acquired with Hinode SOT/SP in February 2007,
is analysed. The data were inverted using the code SIR into a series
of 33 maps covering 3 hours of the umbra and penumbra evolution. Each
map describes the spatial distribution of temperature, line-of-sight
velocity, and magnetic field vector in two different ranges of optical
depths corresponding to lower and upper photosphere. In these maps,
several long-lived central (CUDs) and moving peripheral (PUDs)
umbral dots were selected and their evolution was traced. While CUDs
show only a very weak signature of LOS velocity and magnetic field
inclination, in the low layers of PUDs were detected upflows of 500
m/s and an enhanced field inclination with respect to the surrounding
umbra. These parameters decrease gradually during the evolution of
PUDs. Hence, concerning the physical characteristics, PUDs resemble
rather penumbral grains (from which they often originate) than CUDs.
---------------------------------------------------------
Title: Large-scale horizontal flows in the solar
photosphere. II. Long-term behaviour and magnetic activity response
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.; Bumba, V.
2008A&A...477..285S Altcode: 2007arXiv0710.2693S
We have developed a method to map large-scale horizontal velocity
fields in the solar photosphere. The method was developed, tuned, and
calibrated using synthetic data. Now, we apply the method to the series
of Michelson Doppler Imager (MDI) Dopplergrams covering almost one
solar cycle to generate the information about the long-term behaviour
of surface flows. Our method clearly reproduces the widely accepted
properties of mean flow field components, such as torsional oscillations
and a pattern of meridional circulation. We also performed a period
analysis, however due to the data series length and large gaps we did
not detect any significant periods. The relation between the magnetic
activity and the mean zonal motion is studied. We found evidence
that the emergence of compact magnetic regions locally accelerates
the rotation of the supergranular pattern in their vicinity and that
the presence of magnetic fields generally decelerates the rotation in
the equatorial region. Our results show that active regions in the
equatorial region emerge, exhibiting a constant velocity (faster by
60 ± 9 m s<SUP>-1</SUP> than the Carrington rate), suggesting that
they emerge from the base of the surface radial shear at 0.95 R_⊙,
disconnect from their magnetic roots, and slow down during their
evolution.
---------------------------------------------------------
Title: Kinematics of Umbral Fine Structure
Authors: Sobotka, M.; Puschmann, K. G.; Hamedivafa, H.
2008CEAB...32..125S Altcode:
A 2-hour long series of white-light images of a large sunspot acquired
in June 2004 with the 1-m Swedish Solar Telescope at La Palma is
utilized to study the evolution and motions of small-scale umbral
structures - umbral dots and features in faint light bridges. For
this purpose, a newly improved feature-tracking code is applied. The
small-scale structures move with average speeds of 0.34 km s^{-1} either
into the umbra or along the faint light bridges. Structures that do not
split or merge are smaller (0.15 arcsec) than the average size (0.17
arcsec). Brightness and size variations of individual non-split/merge
structures are positively correlated during their evolution.
---------------------------------------------------------
Title: The Use of Spectro-Polarimetric Measurements to determine
the Plasma Heating
Authors: Jurčák, J.; Martinez Pillet, V.; Sobotka, M.
2007ASPC..369..171J Altcode:
We present the possible use of spectro-polarimetric measurements on
a set of data recorded with La Palma Stokes Polarimeter attached to
the Swedish Vacuum Solar Telescope. The stratification over the solar
atmosphere of different physical parameters is retrieved from these data
using the Stokes Inversion based on Response functions (SIR). We derive
the vertical component of electric current density coming out from the
stratification of the magnetic field strength and orientation of the
magnetic field vector. We also found spatial and height correlation
between the temperature enhancement and increase of electric current
density, this could be caused by the energy dissipation stored in the
magnetic field configuration.
---------------------------------------------------------
Title: Properties of sunspot moats derived from horizontal motions
Authors: Sobotka, M.; Roudier, T.
2007A&A...472..277S Altcode:
Context: Sunspots in late phases of evolution are usually surrounded by
annular moats, regions where systematic horizontal flows are observed
to be directed radially away from the spot. These flows are considered
to be a manifestation of the sub-photospheric convection. <BR />Aims:
The characteristics of moats are derived at two different heights
in the solar atmosphere from horizontal motions around sunspots of
different sizes, shapes, and phases of evolution. We also study the
temporal evolution of moats. <BR />Methods: Local correlation tracking
is applied to approximately 70-min long time series of white-light
and 1600 Å images, acquired by the satellite TRACE, to analyse the
horizontal motions of photospheric granules and C IV emission structures
in the vicinity of 32 sunspots. Moat regions are defined by means of
radially-oriented, outward velocities. <BR />Results: Relations between
sunspot types and the occurrence, areas, and horizontal velocities of
moats in the photosphere and transition region are described. Moats do
not show substantial changes during the period of about 12 h. Observed
asymmetries in moat shapes and velocities are related to the height in
the atmosphere, to sunspot age, and to proper motion. It is suggested
that the sub-photospheric convective flows around sunspots may be
influenced by the spots' proper motion through the convection zone.
---------------------------------------------------------
Title: Joint Discussion 3 Solar active regions and 3D magnetic
structure
Authors: Choudhary, Debi Prasad; Sobotka, Michal
2007HiA....14..139C Altcode:
Keeping in view of the modern powerful observing tools, among
others Hinode (formerly SOLAR-B), STEREO and Frequency-Agile Solar
Radiotelescope, and sophisticated modelling techniques, Joint Discussion
3 during the IAU General Assembly 2006 focused on the properties of
magnetic field of solar active regions starting in deep interior of
the Sun, from where they buoyantly rise to the coronal heights where
the site of most explosive events are located. Intimately related with
the active regions, the origin and evolution of the magnetic field
of quiet Sun, the large scale chromospheric structures were also the
focal point of the Joint Discussion. The theoretical modelling of the
generation and dynamics of magnetic field in solar convective zone show
that the interaction of the magnetic field with the Coriolis force
and helical turbulent convection results in the tilts and twists in
the emerging flux. In the photosphere, some of these fluxes appear in
sunspots with field strengths up to about 6100 G. Spectro-polarimetric
measurements reveal that the line of sight velocities and magnetic
field of these locations are found to be uncombed and depend on depth in
the atmosphere and exhibit gradients or discontinuities. The inclined
magnetic fields beyond penumbra appear as moving magnetic features
that do not rise above upper photospheric heights. As the flux rises,
the solar chromosphere is the most immediate and intermediary layer
where competitive magnetic forces begin to dominate their thermodynamic
counterparts. The magnetic field at these heights is now measured
using several diagnostic lines such as Ca II 854.2 nm, H I 656.3 nm,
and He I 1083.0 nm. The radio observations show that the coronal
magnetic field of post flare loops are of the order of 30 G, which
might represent the force-free magnetic state of active region in the
corona. The temperatures at these coronal heights, derived from the
line widths, are in the range from 2.4 to 3.7 million degree. The same
line profile measurements indicate the existence of asymmetric flows
in the corona. The theoretical extrapolation of photospheric field
into coronal heights and their comparison with the observations show
that there exists a complex topology with separatrices associated to
coronal null points. The interaction of these structures often lead to
flares and coronal mass ejections. The current MHD modelling of active
region field shows that for coronal mass ejection both local active
region magnetic field and global magnetic field due to the surrounding
magnetic flux are important. Here, we present an extended summary of
the papers presented in Joint Discussion 03 and open questions related
to the solar magnetic field that are likely to be the prime issue with
the modern observing facilities such as Hinode and STEREO missions.
---------------------------------------------------------
Title: GREGOR: the New German Solar Telescope
Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.;
Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.;
Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier,
K.; Wittmann, A.
2007ASPC..368..605B Altcode: 2007arXiv0704.2693B
GREGOR is a new open solar telescope with an aperture of 1.5 m. It
replaces the former 45-cm Gregory Coudé telescope on the Canary island
Tenerife. The optical concept is that of a double Gregory system. The
main and the elliptical mirrors are made from a silicon-carbide material
with high thermal conductivity. This is important to keep the mirrors
on the ambient temperature avoiding local turbulence. GREGOR will be
equipped with an adaptive optics system. The new telescope will be ready
for operation in 2008. Post-focus instruments in the first stage will be
a spectrograph for polarimetry in the near infrared and a 2-dimensional
spectrometer based on Fabry-Pérot interferometers for the visible.
---------------------------------------------------------
Title: Horizontal Motions in the Vicinity of Sunspots
Authors: Sobotka, M.; Roudier, T.
2007ASPC..368..259S Altcode:
Many sunspots in late phases of evolution are surrounded by an annular
“moat”, where systematic horizontal flows radially away from the
sunspot are observed. Applying the local correlation tracking technique
to series of white-light and 1600 Å images acquired by the satellite
TRACE, we use photospheric granules and C IV emission structures to
track horizontal motions in the vicinity of sunspots of different
sizes, shapes, and phases of evolution. We define the moat regions on
the basis of horizontal motions. We present preliminary results about
the relations between the sunspot types and the occurrence, areas, and
velocities of the moats in the photosphere and chromosphere. Further
we analyze observed asymmetries in moat shapes and velocities and
their relation to the sunspot age and proper motion.
---------------------------------------------------------
Title: Observational Evidence for Rising Penumbral Flux Tubes?
Authors: Jurčák, J.; Sobotka, M.
2007SoPh..241..223J Altcode:
On 13 May 2000 parts of a penumbra were observed in an active region
NOAA 8990 with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification over the solar atmosphere of
different physical parameters is retrieved from these data by using the
Stokes inversion based on response functions. The results confirm the
previous findings of the penumbral structure. In general, the magnetic
field becomes weaker and more horizontal with increasing distance from
the umbra and the line-of-sight velocities are increasing towards the
outer boundary of the penumbra. The results also suggest the existence
of the unresolved fine structure of the penumbra. The stratifications
of the temperature and of the magnetic field strength indicate the
presence of rising flux tubes, which were predicted theoretically by
Schlichenmaier, Jahn and Schmidt (1998, Astron. Astrophys.337, 897).
---------------------------------------------------------
Title: New high resolution solar telescope GREGOR
Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.;
Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier,
K.; Wittmann, A. D.
2007msfa.conf...39V Altcode:
The 1.5m solar telescope GREGOR is being constructed at Tenerife,
Spain. Its purpose is to observe with high spatial and spectral
resolution small-scale dynamic magnetic features on the Sun. The
telescope is completely open with retractable dome and actively cooled
primary mirror made of silicon carbide to minimize thermal effects
on the image quality. After completion it will be one of the most
powerful solar telescopes. This paper presents a general overview of
the telescope characteristics and the current status.
---------------------------------------------------------
Title: The observational counterpart of the rising flux tube model?
Authors: Jurčák, J.; Sobotka, M.
2007msfa.conf..225J Altcode:
An analysis of Stokes observations of a penumbra in active region NOAA
8990 is presented. The observations were recorded with the La Palma
Stokes Polarimeter attached to the 1-m Swedish Solar Telescope. The
stratification in the solar atmosphere of different physical parameters
is retrieved from these data using the Stokes Inversion based on
Response functions (SIR). Our results confirm previous findings,
that with increasing distance from the umbra the magnetic field
becomes weaker and more horizontal and the line-of-sight velocities
increase. The results suggest the existence of unresolved filamentary
structure in the spatial distributions of temperature, magnetic field
strength and inclination. The maps of temperature and magnetic field
strength along the vertical cuts through the penumbra indicate the
presence of rising flux tubes, predicted theoretically by Schlichenmaier
et al. (1998).
---------------------------------------------------------
Title: Fine structure in a dark umbra
Authors: Sobotka, M.; Puschmann, K. G.
2007msfa.conf..205S Altcode:
An excellent-quality time series of images of a large dark umbra of
the leading sunspot of NOAA 10634 was acquired on 18 June 2004 with the
1-m Swedish Solar Telescope at La Palma, simultaneously in blue, red,
and G-band channels. The temporal and spatial resolutions are 20 s and
0".14. A 2-hour long series of the red continuum images is analysed,
showing the faintest umbral fine structures. In addition to umbral dots,
often clustered to more stable "granules" or aligned to short chains,
we observe large, low-intensity elongated structures with dark central
channels, resembling extremely faint light bridges. At the periphery
of the umbra, bright umbral dots move inwards, showing a similarity
to penumbral grains. Kinematic properties of umbral fine structures
are studied.
---------------------------------------------------------
Title: Large-scale horizontal flows in the solar
photosphere. I. Method and tests on synthetic data
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.
2006A&A...458..301S Altcode: 2006astro.ph..8443S
We propose a useful method for mapping large-scale velocity
fields in the solar photosphere. It is based on the local <P
/>correlation tracking algorithm when tracing supergranules in
full-disc dopplergrams. The method was developed using synthetic
data. <P />The data are transformed during the data processing into
a suitable coordinate system, the noise is removed, and finally the
velocity field is <P />calculated. Resulting velocities are compared
with the model velocities and the calibration is done. From our results
it becomes clear that <P />this method could be applied to full-disc
dopplergrams acquired by the Michelson Doppler Imager (MDI) onboard
the Solar and Heliospheric Observatory (SoHO).
---------------------------------------------------------
Title: Dynamics of Magnetic Bright Points in an Active Region
Authors: Möstl, C.; Hanslmeier, A.; Sobotka, M.; Puschmann, K.;
Muthsam, H. J.
2006SoPh..237...13M Altcode: 2006SoPh..tmp....2M
A high-quality 80-minute time series of a part of a sunspots moat
(18 ″ × 23 ″) in the G-band (4308.64 Å) has been analysed
to measure the horizontal velocities of Magnetic Bright Points
(MBPs). The observations were carried out in June 2004 at the new
1-meter Swedish Solar Telescope in La Palma. Spatial resolution was
estimated to be 0.17 ″ or 125 km on the Sun, and images were taken
in a frame selection mode in a 20-seconds interval. Individual feature
tracking of MBPs with manual selection and automated tracking has been
performed. The intensity of MBPs increases with size. The mean value
in a MBP-velocity histogram was found to be 1.11 km s <SUP>−1</SUP>
and it shows good accordance with an abnormal granulation-velocity
histogram. MBP velocity histograms as presented here can be taken
as an input for coronal heating models in an active region. However,
MBPs move slower in an active region than in the network (presumably
because of the higher active region magnetic flux) and hence, a process
that includes dissipation of MHD waves through fast MBP motions (>2
km s <SUP>−1</SUP>) may not alone explain the observed properties
of the corona.
---------------------------------------------------------
Title: The magnetic canopy above light bridges
Authors: Jurčák, J.; Martínez Pillet, V.; Sobotka, M.
2006A&A...453.1079J Altcode:
An analysis of high-resolution Stokes observations of two light
bridges in active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification over the solar atmosphere
of different physical parameters is retrieved from these data using
the Stokes inversion based on response functions (SIR). Our results
confirm previous observations of features such as the decrease in
magnetic field strength and the increase in inclination in the light
bridges. We also confirm a temperature increase in these structures
with respect to the surrounding umbrae. The maps of the magnetic field
strength and of the orientation of the magnetic field vector indicate
the presence of a canopy structure above the light bridges. We derive
the vertical component of electric current density (J_z) from the
configuration of the magnetic field. The increased temperature found
in the upper layers is studied in the context of the proposed canopy
topology and could also explain the recently observed chromospheric
heating processes found above light bridges.
---------------------------------------------------------
Title: The new 1.5m solar telescope GREGOR: first light and start
of commissioning
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald;
Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus;
Sobotka, Michal; Klvana, Miroslav; Collados, Manuel
2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V
The integration of the three main silicon carbide mirrors into the new
1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
during 2006. We expect first light at the end of 2006. A progress
report about integration of the optics and mechanics and planning of
the commissioning phase of the telescope and post focus instruments
will be presented at the meeting. The GREGOR telescope is build by a
consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
Gottingen and additional national and international Partners.
---------------------------------------------------------
Title: The Canopy Structure above Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
2006CEAB...30...55J Altcode:
An analysis of high-resolution Stokes observations of two light bridges
in the active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification of different physical
parameters is retrieved using the Stokes Inversion based on Response
functions (SIR). Our results confirm the decrease of magnetic field
strength and the increase of inclination in light bridges. We find a
complex temperature stratification in these structures Coming out from
the stratification of the magnetic field strength and the orientation
of the magnetic field vector, we suggest a canopy structure above the
light bridge. We derive the vertical component of electric current
density (J<SUB>z</SUB>). The increase of J<SUB>z</SUB> corresponds to
temperature enhancements that might be caused by the energy dissipation
stored in the magnetic field.
---------------------------------------------------------
Title: The Magnetic Configuration in Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
2005ESASP.600E...8J Altcode: 2005dysu.confE...8J; 2005ESPM...11....8J
No abstract at ADS
---------------------------------------------------------
Title: Mapping of Large-Scale Photospheric Velocity Fields
Authors: Švanda, M.; Klvaňa, M.; Sobotka, M.
2005ESASP.600E..71S Altcode: 2005ESPM...11...71S; 2005dysu.confE..71S
No abstract at ADS
---------------------------------------------------------
Title: The structure of a penumbral connection between solar pores
Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.;
Puschmann, K. G.; Sobotka, M.
2005A&A...442.1079H Altcode:
High resolution 2D-spectro-polarimetric observations have been used
to analyse the magnetic field and flow topologies of a penumbral
connection between two opposite polarity solar pores. A filamentary
structured Evershed-like material flow from one pore to the other
along the magnetic field lines has been detected. The flow channels
are co-spatial with bright penumbral filaments close to the pore which
feeds the flow and the clear brightness-velocity relation vanishes close
to the pore which represents the sink of the flow. The boundary between
umbra and penumbra of the two pores show significant differences: bright
comet-like penumbral grains represent endings of penumbral filaments
at the flow sources whereas no such grains were found at the sinks of
the flow. Furthermore, a systematic variation of the asymmetries of
measured Stokes V profiles across the penumbral connection have been
found. The obtained results are in accordance with the widely-accepted
uncombed penumbra hypothesis and the moving flux tube model.
---------------------------------------------------------
Title: Photometry of umbral dots
Authors: Sobotka, M.; Hanslmeier, A.
2005A&A...442..323S Altcode:
Until now, the size of umbral dots has been considered to be below the
resolution limit of large solar telescopes. We analyze observations
of two sunspots and two pores, acquired in September 2003 with the
new 1-m Swedish Solar Telescope, La Palma. White-light images with a
resolution better than 0.15 arcsec were taken simultaneously in blue
(451 nm) and red (602 nm) wavelength bands. They were corrected for
scattered light and restored for the instrumental profile of the
telescope. Intensities, diameters and positions of umbral dots were
measured in aligned pairs of images in the blue and red wavelength
band. We find that observed intensities of umbral dots are correlated
with local intensities of umbral background. On average, UDs are by
about 1000 K hotter than the coolest area in the umbra and by 500-1000
K cooler than the undisturbed photosphere. Individual UDs may reach or
exceed the average photospheric brightness and temperature. Histograms
of observed diameters peak at 0.23 arcsec (170 km). This indicates
that the majority of umbral dots are spatially resolved with the 1-m
telescope. The mean nearest-neighbour distance between umbral dots is
0.4 arcsec and their average observed filling factor is 9%. The method
of two-colour photometry is discussed and applied to obtain average
"true" intensities and diameters. About 50% of umbral dots are brighter
than the quiet photosphere and the average "true" diameter of umbral
dots is 100 km. However, the latter results might be influenced by
systematic errors of the method.
---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V Altcode:
The telescope structure including control system and the complete
retractable dome of the new 1.5 m solar telescope GREGOR were
assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
telescope is build by a consortium of the Kiepenheuer Institut fuer
Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
fuer Astrophysik Goettingen and additional national and international
Partners. Pointing, tracking and thermal tests were made to verify
the proposed performance. The results of these tests and a progress
report of the project will be presented.
---------------------------------------------------------
Title: Phase diversity restoration of sunspot images. II. Dynamics
around a decaying sunspot
Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.;
Roudier, Th.
2005A&A...430.1089B Altcode:
Two time series, taken simultaneously in the G-band and in white-light,
and corrected for telescope aberrations and turbulence perturbations
using the method of phase diversity, are employed to study the motions
of granules and G-band bright points (GBPs) in the moat of an old
regular sunspot. Local correlation tracking and feature tracking have
been utilized for this purpose. A large-scale radial outflow with
a mean velocity of 0.51 km s<SUP>-1</SUP> has been measured in the
sunspot moat. Centres of diverging horizontal motions, identified
with families of granules formed by repeatedly splitting granules,
move away from the sunspot. Most of the GBPs in the moat also move
outwards through radially orientated “channels” (confined between
the borders of adjacent families) with velocities comparable to those
of the adjacent granules. However, 6% of the GBPs move faster (>1.4
km s<SUP>-1</SUP>) than the neighbouring granules. GBPs in the moat
are not regularly distributed but they are less frequent on its solar
centre side.
---------------------------------------------------------
Title: Velocity Fields in an Irregular Sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
2005ASSL..320..227J Altcode: 2005smp..conf..227J
No abstract at ADS
---------------------------------------------------------
Title: Motions of Supergranular Structures on the Solar Surface
Authors: Švanda, M.; Klnaňa, M.; Sobotka, M.
2005HvaOB..29...39S Altcode:
We present a method used to study motions of supergranular structures
in the solar photosphere. It is based on the local correlation
tracking method applied to full-disk dopplergrams measured by
SoHO/MDI. In primary dopplergrams, there is a plenty of noise
originating mostly from oscillations and morphological changes of
the shape of supergranules. We describe a method used to suppress
such noise. To demonstrate the suggested technique and properties of
computed velocity fields, we processed a few-day period during the
time of minimum of solar activity. The obtained vector velocity fields
are drawn using streamlines in the Carrington's coordinate system. We
discuss the reproductivity of the obtained results and the connection
of the velocity field we found to the large-scale velocity field in
the upper part of the convection zone.
---------------------------------------------------------
Title: Observational evidence of Joule heating in some umbral dots
Authors: Hamedivafa, H.; Sobotka, M.
2004A&A...428..215H Altcode:
We investigate the effect of the Joule heating (JH) mechanism on the
brightness of umbral dots (UDs), proposed by Hamedivafa (\cite{H03},
A&A, 407, 761). Time series of high-resolution images of UDs in a
developed sunspot and in a large pore are used for this purpose. The
effect of the JH mechanism is characterized by a specific shape of
the temporal variations of UD brightness and area and it is observed
better in those UDs where the magnetic field strength is very weak
compared to their surroundings. In our observations, about 12% of UDs
in the sunspot and about 14% of UDs in the pore show indications of
the effective presence of the JH power.
---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V Altcode:
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
and other national and international Partners. The refurbishment of
the building is almost finished. The manufacturing of the telescope
structure and the optics is still in progress. After the integration of
the new complete retractable dome in July 2004 the telescope structure,
optic and post focus instruments will be assembled during the rest of
the year. First light is planned during May 2005.
---------------------------------------------------------
Title: The Thermal and Magnetic Structure of Umbral Dots from the
Inversion of High-Resolution Full Stokes Observations
Authors: Socas-Navarro, H.; Martínez Pillet, V.; Sobotka, M.;
Vázquez, M.
2004ApJ...614..448S Altcode:
This paper presents the analysis of high-resolution Stokes observations
of eight different umbral dots in a sunspot. The spectra were recorded
with the La Palma Stokes Polarimeter, attached to the Swedish Vacuum
Solar Telescope. The observed line profiles have been inverted to
yield the height stratifications of temperature, magnetic field,
and line-of-sight velocity, as well as their respective Wilson
depressions. We report on systematic differences in the properties of
umbral dots with respect to the nearby umbra, including small upflows
(~100 m s<SUP>-1</SUP>), higher temperatures (~1 kK), and weaker fields
(~500 G) with more horizontal orientations (~10°). The field weakening
is strongly correlated with the Wilson depression, suggesting that
it may be due to an opacity effect (as one is looking at higher
layers). The inclination excess, on the other hand, is real and
cannot be ascribed to formation height issues. The results obtained
from our semiempirical modeling are discussed within the context
of the currently existing scenarios for the subsurface structure of
sunspots. The observational signatures revealed by our analysis fit
well within both the “spaghetti” and the monolithic models.
---------------------------------------------------------
Title: Phase diversity restoration of sunspot images. I. Relations
between penumbral and photospheric features
Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.;
Tritschler, A.
2004A&A...423..737B Altcode: 2004astro.ph..5542B
We investigate the dynamics of and the relations between small-scale
penumbral and photospheric features near the outer penumbral
boundary: penumbral grains (PGs), dark penumbral fibrils, granules,
and photospheric G-band bright points. The analysis is based on a 2 h
time sequence of a sunspot close to disc center, taken simultaneously
in the G-band and in the blue continuum at 450.7 nm. Observations
were performed at the Swedish Vacuum Solar Telescope (La Palma)
in July 1999. A total of 2564 images (46 arcsec × 75 arcsec) were
corrected for telescope aberrations and turbulence perturbations by
applying the inversion method of phase diversity. Our findings can by
summarized as follows: (a) one third of the outward-moving PGs pass
through the outer penumbral boundary and then either continue moving
as small bright features or expand and develop into granules. (b)
Former PGs and G-band bright points next to the spot reveal a different
nature. The latter have not been identified as a continuation of PGs
escaping from the penumbra. The G-band bright points are mostly born
close to dark penumbral fibrils where the magnetic field is strong,
whereas PGs stem from the less-magnetized penumbral component and
evolve presumably to non-magnetic granules or small bright features.
---------------------------------------------------------
Title: Motions of photospheric features in a sunspot moat
Authors: Sobotka, M.; Bonet, J. A.; Márquez, I.; Muller R.;
Roudier, Th.
2004HvaOB..28...27S Altcode:
Two time series, taken simultaneously in the G-band and the blue
continuum, corrected for instrumental and atmospheric degradation
using the method of phase diversity, are employed to study the motions
of granules and G-band bright points (GBPs) in the moat of an old
regular sunspot. Centres of diverging horizontal motions, identified
with families of granules formed by recurrently splitting granules,
move away from the sunspot. Most of GBPs show radially oriented motions
in the same direction, with velocities comparable to those of adjacent
granules. However, 7 % of GBPs move faster (>1.4 km s<SUP>-1</SUP>)
than the neighbouring granules.
---------------------------------------------------------
Title: Velocity fields in an irregular sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
2003ESASP.535..109J Altcode: 2003iscs.symp..109J
Line-of-sight velocity fields in an irregular sunspot (NOAA 8990)
have been determined from Stokes-I spectra of the line Fe I 630.15
nm, obtained with the La Palma Stokes Polarimeter at the Swedish
Vacuum Solar Telescope on May 13, 2000. We show and discuss the
resulting velocity maps, the dependence of velocities on the
continuum intensities, and the correlation between velocities and
line asymmetries.
---------------------------------------------------------
Title: Dynamics of motions in the quiet photosphere
Authors: Svanda, M.; Klvana, M.; Sobotka, M.; Bumba, V.
2003ESASP.535..149S Altcode: 2003iscs.symp..149S
We determine the vector velocity fields describing the plasma motions
in the quiet solar photosphere, using the motions of the supergranular
structures, obtained by the analysis of series of Doppler measurements
of velocity fields of the whole solar disk. It turned out that
the studied vector velocity fields can be submerged under the noise
level, originating due to the strong variability of the supergranular
structures during their life time. We describe the method we used for
the suppressing of such noise, and we bring the criterions used by
the election of free parameters. We demonstrate examples of obtained
vector velocity fields and of the resulting motions of matter on the
visible photospheric surface. We discuss different factors influencing
the reproductivness of obtained results. We construct a graph of the
dependence of the differential rotation on the heliographic latitude
from the mean vector velocity field, we got for the solar disk without
expressive magnetic fields.
---------------------------------------------------------
Title: Current Status of the 1.5m Solar Telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkfeld, Thomas; Schmidt, Wolfgang; Soltau, Dirk; Nicklas,
Harald; Wiehr, Eberhardt; Wittman, Axel; Hofmann, Axel; Sobotka,
Michal; Klvana, Miroslav
2003ANS...324..112V Altcode: 2003ANS...324..P19V
No abstract at ADS
---------------------------------------------------------
Title: GREGOR: the new 1.5m solar telescope on Tenerife
Authors: Volkmer, Reiner; von der Luehe, Oskar; Kneer, Franz; Staude,
Juergen; Hofmann, Axel; Schmidt, Wolfgang; Sobotka, Michal; Soltau,
Dirk; Wiehr, Eberhardt; Wittmann, Axel; Berkefeld, Thomas
2003SPIE.4853..360V Altcode:
The new 1.5 m high resolution telescope will be build up on the reused
solar tower of the German 45 cm Gregory Coudé Telescope at the Teide
Observatory, Izaña, Tenerife. The new telescope is a Gregory type
with open telescope structure, alt-azimuth mount, complete retractable
dome, and a pool of well established and new developed post focus
instruments. An adaptive optics system provides the capability for
diffraction limited observations at visible wavelengths and the
polarimetry device in the secondary focus reduces the perturbation
due to instrumental polarization in an efficient way. We describe the
main optical characteristics and the focal plane instrumentation with
respect to the latest status of the project.
---------------------------------------------------------
Title: Infrared photometry of a sunspot near the disk center
Authors: Stangl, S.; Sobotka, M.; Bonet, J. A.; Vázquez, M.;
Hanslmeier, A.
2003AN....324..376S Altcode:
A time series of broadband images of a sunspot near the disk center
was obtained simultaneously in two wavelength bands at 0.56 mu m and
1.55 mu m at the German VTT on June 17, 1998. We computed intensity
difference images of the best frame pairs which reveal information
about the facular distribution in the present field of view. Faculae
are found around pores, in the quiet granulation and as well around
the sunspot penumbra.
---------------------------------------------------------
Title: A CCD-based guiding and control system for solar telescopes
Authors: Klvaňa, M.; Bumba, V.; Sobotka, M.
2003AN....324..305K Altcode:
We describe a system for guiding and control of motion of solar
telescopes based on a determination of the position of the full solar
disk on a CCD chip. The system computes the position of the disk center
and, according to the difference between the instantaneous and required
positions, it controls the motion of the telescope to compensate the
deviation. The instantaneous position of the disk center is the basic
input for the telescope's guiding and coordinate system. Brightness
inhomogeneities of the solar limb caused by clouds are checked in real
time. The function of the system can be suspended automatically if the
clouds degrade the accuracy of guiding. The system also makes possible
to check the correct focus and to evaluate the image quality.
---------------------------------------------------------
Title: System of coordinates for solar telescopes
Authors: Klvaňa, M.; Bumba, V.; Sobotka, M.
2003HvaOB..27..205K Altcode:
A system of coordinates for a solar telescope, based on the principle of
the CCD detection of the whole solar disk position, is described. The
system evaluates the position of the solar disk center and from this
position it calculates the coordinates of a point situated on the
optical axis of the telescope. The method of cloudiness testing,
as well as results of tests made, and algorithms for the coordinate
calculation in six coordinate systems are demonstrated. The function of
the system can be suspended automatically if the clouds would degrade
the accuracy of guiding.
---------------------------------------------------------
Title: Centre-to-limb variation of solar granulation in the infrared
Authors: Sánchez Cuberes, M.; Vázquez, M.; Bonet, J. A.; Sobotka, M.
2003A&A...397.1075S Altcode:
Broad-band images have been obtained at the extremes of the continuum
absorption coefficient of the solar atmosphere, at lambda 0.8 mu m
and lambda 1.55 mu m. Quiet regions have been observed for different
heliocentric angles. The centre-to-limb variation of granulation
contrast has been computed in both wavelength ranges and a steeper
decrease in the contrast is obtained for lambda 0.8 mu m than for
lambda 1.55 mu m. For positions near the solar limb the granulation
contrast shows a tendency to increase at both wavelengths. Mean
granular sizes vary from 1.25 arcsec<SUP>2</SUP> at the disc centre
to 2 arcsec<SUP>2</SUP> at mu =0.6 in the lambda 0.8 mu m images and
from 1.24 arcsec<SUP>2</SUP> to 1.85 arcsec<SUP>2</SUP> at lambda
1.55 mu m. Observations close to the limb detect granular structures
of 0.\arcsec 96 or even smaller at a distance from the limb of d=
0.\arcsec 32, equal to the diffraction limit of the telescope at
lambda 8000 Å. Using an Eddington-Barbier approximation this implies a
penetration of the temperature fluctuations associated with granulation
up to approximately z ~ 220 km, although the calculation of response
functions defines a broader interval.
---------------------------------------------------------
Title: Solar activity II: Sunspots and pores
Authors: Sobotka, M.
2003AN....324..369S Altcode:
Sunspots and pores appear as a consequence of interactions
between strong magnetic fields and moving plasma. A wide variety of
small-scale features, presumably of convective origin, are observed in
photospheric layers of sunspots and pores: Umbral dots, light bridges,
penumbral filaments, and penumbral grains. Each type of features
has specific morphological, photometric, spectral, and kinematic
characteristics. Spots and pores modify velocity fields in adjacent
photosphere and sub-photospheric layers. Recent high-resolution
spectral, broad-band, and helioseismic observations of the structure,
dynamics, and magnetic fields of sunspots and pores, together with
theoretical interpretations, are discussed in this review.
---------------------------------------------------------
Title: Infrared photometric results of a sunspot
Authors: Stangl, S.; Hanslmeier, A.; Sobotka, M.; Bonet, J. A.;
Vázquez, M.
2002ESASP.506..473S Altcode: 2002ESPM...10..473S; 2002svco.conf..473S
We obtained simultaneously recorded time series of broadband
images of a sunspot close to the disk center at the German Vacuum
Tower Telescope, Tenerife, in two wavelength bands at 0.56 μm and
1.55 μm. Maps of brightness difference images T<SUB>b</SUB>(1.55
μm) and T<SUB>b</SUB>(0.56 μm) were computed for the best image
pairs. Furthermore, a scatter plot of the brightness temperatures
was made where five different magnetic and nonmagnetic regions -
quiet region (QR), faculae, pores, penumbra, and umbra - in the
field of view can be clearly distinguished. Pores as well as the
penumbra are surrounded by the facular regions consisting of several
single facular elements. However, facular regions are also found in
non-magnetic vicinity.
---------------------------------------------------------
Title: Photospheric layers of sunspots and pores
Authors: Sobotka, Michal
2002ESASP.506..381S Altcode: 2002svco.conf..381S; 2002ESPM...10..381S
Sunspots and pores appear as a consequence of interactions between
strong magnetic fields and moving plasma. A wide variety of small-scale
features, presumably of convective origin, are observed in photospheric
layers of sunspots and pores: Umbral dots, light bridges, penumbral
filaments, and penumbral grains. Each type of features has specific
morphological, photometric, spectral, and kinematic characteristics
due to a broad range of magnetic field strengths and inclinations in
umbrae and penumbrae. Spots and pores modify velocity fields in adjacent
photosphere and subphotospheric layers. Recent high-resolution spectral,
broad-band, and helioseismic observations of the structrure, dynamics,
and magnetic fields of sunspots and pores, together with theoretical
interpretations, are discussed in this review.
---------------------------------------------------------
Title: Evolution of small-scale structures in and around a large
solar pore
Authors: Dorotovič, I.; Sobotka, M.; Brandt, P. N.; Simon, G. W.
2002ESASP.506..435D Altcode: 2002ESPM...10..435D; 2002svco.conf..435D
The analysis of an 11-hour series of high resolution white light
observations of a large pore in the sunspot group NOAA 7519, observed
on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary
Islands, is described. We used a total of 1782 frames, with average
time interval of 22 s. Special attention was paid to the evolution of a
filamentary region attached to the pore, to horizontal motions around
the pore, and to small-scale morphological changes. The filamentary
region was observed to change its structure back and forth between
penumbra-like filaments and elongated granules. A clockwise rotation of
this region around the center of the pore was detected during the whole
observing period. This rotation had angular velocities decreasing with
time from 7.6°h<SUP>-1</SUP> to 2.7%deg;h<SUP>-1</SUP>. Motions inside
the filamentary region and around the pore, inclduding penetrations
of photospheric granules into the pore, were studied in detail using
local correlation and feature tracking algorithms. It was found that
the observed filamentary region, although having some typical penumbral
features, was different from a normal penumbra.
---------------------------------------------------------
Title: Properties of horizontal flows inside and outside a solar pore
Authors: Roudier, Th.; Bonet, J. A.; Sobotka, M.
2002A&A...395..249R Altcode:
Horizontal velocities and their temporal variations inside a large pore
and in the surrounding granulation are studied from a 73 min sequence
of white light frames, acquired at the Swedish Vacuum Solar Telescope
(La Palma). The local correlation tracking technique with high spatial
(0\farcs 31) and temporal (5 min) resolution was applied to binarized
images, yielding 14 independent velocity maps. A ring of divergence
centres around the pore was observed in all the maps. Motions directed
into the pore, deposited by the divergence centres, continue also within
the pore but with magnitudes smaller by factor of 2-3. A link between
the variations of large velocity amplitudes around the pore and the
brightness fluctuations of umbral dots is suggested. A phase delay
between velocity and intensity changes at the periphery of the pore,
probably related to the penetration of bright features inwards across
the pore's border, was observed.
---------------------------------------------------------
Title: Evolution of small-scale features at the penumbra-photosphere
border
Authors: Sobotka, M.; Muller, R.; Bonet, J. A.; Márquez, I.
2002ESASP.505..579S Altcode: 2002IAUCo.188..579S; 2002solm.conf..579S
Time series of images of a sunspot, acquired simultaneously
in blue light and in G-band at the SVST, La Palma, are used to
study horizontal motions of granules in the vicinity of the spot
and evolution of penumbral grains (PGs) near the outer penumbral
border. Local correlation tracking and feature tracking algorithms
have been utilized for this purpose. Around sunspots and pores we
can observe numerous centers of diverging local horizontal motions,
caused mostly by exploding granules. Around developed spots we find an
organized motion directed out from the penumbra. The divergence centers
are carried away from the spot by this motion. In the outer penumbra,
PGs move mostly outwards, toward the surrounding granulation. About 2/3
of PGs disappear near the penumbra-granulation border. The remaining
PGs move across the border, they transform either to granules or to
small bright features, and continue moving away from the sunspot.
---------------------------------------------------------
Title: Evolution and motions of small-scale photospheric structures
near a large solar pore
Authors: Dorotovič, I.; Sobotka, M.; Brandt, P. N.; Simon, G. W.
2002A&A...387..665D Altcode:
The analysis of an 11-hour series of high resolution white light
observations of a large pore in the sunspot group NOAA 7519, observed
on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary
Islands, is described. We used a total of 1782 frames, with average
time interval of 22 s. Special attention was paid to the evolution of a
filamentary region attached to the pore, to horizontal motions around
the pore, and to small-scale morphological changes. The filamentary
region was observed to change its structure back and forth between
penumbra-like filaments and elongated granules. A clockwise rotation
of this region around the center of the pore was detected during the
whole observing period. This rotation had angular velocities decreasing
with time from 7.6<SUP>deg</SUP> h<SUP>-1</SUP> to 2.7<SUP>deg</SUP>
h<SUP>-1</SUP>. Motions inside the filamentary region and around the
pore, including penetrations of photospheric granules into the pore,
were studied in detail using local correlation and feature tracking
algorithms. It was found that the observed filamentary region,
although having some typical penumbral features, was different from
a normal penumbra.
---------------------------------------------------------
Title: Infrared Photometry of Solar Photospheric
Structures. II. Center-to-Limb Variation of Active Regions
Authors: Sánchez Cuberes, M.; Vázquez, M.; Bonet, J. A.; Sobotka, M.
2002ApJ...570..886S Altcode:
Simultaneous broadband single images and time series of images have
been obtained at λ0.8 and λ1.55 μm, which are at the extremes of
the continuum absorption coefficient of the solar atmosphere. Active
regions have been observed for different heliocentric angles. Weighted
difference images between the two wavelength bands have been used
to identify faculae. Center-to-limb variations of facular relative
intensity distribution, facular size distribution, and facular
size-intensity relations have been obtained. At the spatial resolution
of the observations, faculae show no contrast at the disk center
at λ0.8 μm, while dark faculae are observed at λ1.55 μm. The
transition from dark to bright faculae occurs between μ=0.6 and
0.5 in λ1.55 μm images. The maximum of the mean facular relative
intensity is found at μ=0.3 for both wavelengths. However, the peak
of the facular relative intensity is greater and appears closer to
the limb the larger the faculae are. Brightness temperature maps
have been computed for the best pairs of images, and temperature
difference images have been derived. The temperature difference
T<SUB>b</SUB>(1.55μm)-T<SUB>b</SUB>(0.8μm) in pores is larger than
that in the quiet photosphere at the disk center, but smaller near
the limb. Faculae show smaller temperature differences than the quiet
photosphere at the disk center, but the temperature differences near
the limb are almost equal. Pores are surrounded by ringlike structures
of low temperature difference at the disk center. Near the limb these
ringlike structures appear bright in the brightness temperature maps and
show a temperature difference similar to that of the quiet photosphere.
---------------------------------------------------------
Title: Evolution of Filamentary Structures in and around a Large
Solar Pore
Authors: Simon, G. W.; Dorotovič, I.; Sobotka, M.; Brandt, P. N.
2002AAS...200.3803S Altcode: 2002BAAS...34..698S
We have studied evolution of a filamentary region attached to a pore,
horizontal motions around the pore, and small-scale morphological
changes, using an 11-hour series of 1782 high resolution white-light
images of a large pore in the sunspot group NOAA 7519, acquired on
5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary
Islands. We find that the structure of the region between the large pore
and an adjacent micropore was not always filamentary, but varied back
and forth in time between a filamentary structure and a granular one. A
clockwise rotation, at times exceeding 7 deg/h, of this filamentary
region around the center of the pore, was observed during the whole
run. Motions of fine structure around and within the pore were studied
in detail using local correlation and feature tracking. We conclude
that the filamentary region, while it had some typical penumbral
characteristics, was different from a normal penumbra. This research has
been funded by the USAF Research Lab, and by Emeritus Research Services.
---------------------------------------------------------
Title: Fine structure and dynamics in a light bridge inside a
solar pore
Authors: Hirzberger, J.; Bonet, J. A.; Sobotka, M.; Vázquez, M.;
Hanslmeier, A.
2002A&A...383..275H Altcode:
A photometric analysis of the sub-structure of a granular light
bridge in a large solar pore is performed. The data consist of a
66 min time series of white light images (lambda = 5425 Å,+/- 50
Å) of an active region NOAA 7886 obtained at the Swedish Vacuum
Solar Telescope on La Palma, Canary Islands. The light bridge can
be resolved into an assembly of small grains embedded in a diffuse
background with an intensity of about 85% of the mean photospheric
intensity (I<SUB>phot</SUB>). Following the temporal evolution of these
sub-structures in their irregular motions inside the light bridge,
proper motions with velocities up to 1.5 km s<SUP>-1</SUP> can be
detected. Their lifetime distribution shows a maximum at 5 min and a
second peak at approximately 20 min. The origin and the decay of these
sub-structures is very similar to those of granules, i.e. fragmentation,
merging and spontaneous origination from, and dissolution into, the
background can be observed. Some of them are able to escape from the
light bridge into the umbra where they cannot be distinguished from
adjacent umbral dots. Generally, this study presents evidence that
the observed phenomenon represents convective motions.
---------------------------------------------------------
Title: Fine structure in sunspots. IV. Penumbral grains in speckle
reconstructed images
Authors: Sobotka, M.; Sütterlin, P.
2001A&A...380..714S Altcode:
The properties of penumbral grains (PGs) in a large regular sunspot
are studied from a 70 min sequence of G-band images acquired on 20
September 1999 at the Dutch Open Telescope, La Palma. The frames were
processed using the speckle masking algorithm, resulting in an almost
diffraction-limited time series (30 s cadence), basically free of
atmospheric distortions. Applying feature tracking to a movie of 140
frames yields proper motions, intensities, and lifetimes for a set of
1058 PGs with lifetimes longer than 10 min. About 54% of the PGs move
toward the umbra and 46% toward the photosphere. The inward-moving
PGs are located mostly in the inner penumbra (up to 0.6 of the
distance from the umbra to the photosphere). Their average lifetime
and median speed are 50 min and 0.52 km s<SUP>-1</SUP>. Most of the
outward-moving PGs are observed in the outer penumbra and their average
lifetime and median speed are 31 min and 0.75 km s<SUP>-1</SUP>. These
measurements confirm the previous results published by Sobotka et
al. (\cite{sobotka99_AA348}).
---------------------------------------------------------
Title: Reconstruction of the HSFA telescopes
Authors: Klvaňa, M.; Kotrč, P.; Knížek, M.; Sobotka, M.; Heinze, P.
2001AN....322..371K Altcode:
At present, two large horizontal solar telescopes with spectrographs,
located at the Ondřejov Observatory, are undergoing an important
reconstruction. The original designation of these two identical
instruments will mostly be preserved. The telescope/spectrograph
HSFA1 will continue to be used for the measurement of solar magnetic
and velocity fields, while HSFA2 is in the process of rebuilding to a
multichannel spectrograph equipped with CCD cameras. The reconstruction
of the electronic control systems is the most important item. The
up-to-date electronic equipment will enable a remote control of all
functions of the instruments, will offer a large amount of automated
procedures and should resist to disturbances caused by atmospheric
electricity. The whole telescope/spectrograph control system is designed
to reduce and simplify the observer's work as much as possible.
---------------------------------------------------------
Title: A close look at sunspots
Authors: Sobotka, Michal
2001ESASP.493..361S Altcode: 2001sefs.work..361S
No abstract at ADS
---------------------------------------------------------
Title: Reconstruction of the Telescopes HSFA1 and HSFA2
Authors: Klvaňa, M.; Sobotka, M.; Bumba, V.
2001AGM....18S1002K Altcode:
At present, two large horizontal solar telescopes with spectrographs,
located at the Ondřejov Observatory, are undergoing an important
reconstruction. The original designation of these two identical
instruments will mostly be preserved. The telescope/spectrograph
HSFA1 will continue to be used for the measurement of solar magnetic
and velocity fields, while HSFA2 is in the process of rebuilding to a
multichannel spectrograph equipped with CCD cameras. The reconstruction
of the electronic control systems of both telescopes is the most
important item. The up-to-date electronic equipment will enable a remote
control of all functions of the instruments, will offer a large amount
of automated procedures and should be resistent to the disturbances
caused by atmospheric electricity. The whole telescope/spectrograph
control system is designed to reduce and simplify the observer's work as
much as possible. In this contribution we describe the characteristics
of both reconstructed instruments and the basics of their control.
---------------------------------------------------------
Title: Reconstruction of the Telescopes HSFA1 and HSFA2
Authors: Klvaňa, M.; Sobotka, M.; Bumba, V.
2001AGM....18.P220K Altcode:
At present, two large horizontal solar telescopes with spectrographs,
located at the Ondřejov Observatory, are undergoing an important
reconstruction. The original designation of these two identical
instruments will mostly be preserved. The telescope/spectrograph
HSFA1 will continue to be used for the measurement of solar magnetic
and velocity fields, while HSFA2 is in the process of rebuilding to a
multichannel spectrograph equipped with CCD cameras. The reconstruction
of the electronic control systems of both telescopes is the most
important item. The up-to-date electronic equipment will enable a remote
control of all functions of the instruments, will offer a large amount
of automated procedures and should be resistent to the disturbances
caused by atmospheric electricity. The whole telescope/spectrograph
control system is designed to reduce and simplify the observer's work as
much as possible. In this contribution we describe the characteristics
of both reconstructed instruments and the basics of their control.
---------------------------------------------------------
Title: Infrared Photometry of Solar Photospheric Structures. I. Active
Regions at the Center of the Disk
Authors: Sobotka, M.; Vázquez, M.; Sánchez Cuberes, M.; Bonet,
J. A.; Hanslmeier, A.
2000ApJ...544.1155S Altcode:
Simultaneous time series of broadband images of two active regions
close to the disk center were acquired at the Swedish Vacuum
Solar Telescope, La Palma, in the infrared bands at 1.55 and 0.80
μm, corresponding to the minimum and maximum continuum opacities,
respectively. Dark faculae are detected in images obtained as weighted
intensity differences between both wavelength bands. Maps of brightness
temperatures T<SUB>b</SUB> (1.55 μm) and T<SUB>b</SUB> (0.80 μm)
were computed for the best pairs of images. In the scatter plots
T<SUB>b</SUB> (1.55) versus T<SUB>b</SUB> (0.80), the elements of
quiet regions can be clearly distinguished from those of faculae and
pores, while the transition between faculae and pores is smooth. The
temperature difference T<SUB>b</SUB>(1.55)-T<SUB>b</SUB>(0.80) in
faculae is lower than that in the quiet photosphere but increases with
decreasing T<SUB>b</SUB> and is higher inside pores. Most of the pores
are surrounded by ringlike regions of low temperature difference. The
minimum intensity of pores at both wavelengths decreases with increasing
diameter. Maps of horizontal motions of dark faculae and pores were
derived from time series of intensity-difference images, using the
local correlation tracking technique. Velocities corresponding to
large-scale separation of polarities, an emergence of magnetic flux,
twist and contraction related to a pore formation, shear motions,
and a twist in dark faculae were measured.
---------------------------------------------------------
Title: Power-law spectra of 1-2 GHz narrowband dm-spikes
Authors: Karlický, Marian; Jiřička, Karel; Sobotka, Michal
2000SoPh..195..165K Altcode:
Twelve examples of clouds of narrowband dm-spikes, observed by the
Ondřejov radiospectrograph in the 1-2 GHz frequency range, are
analyzed. After transforming of the frequency scales to heights in
the solar atmosphere, the indices of the power-law power spectra are
determined. The derived power-law indices are scattered in a broad
range of values (−0.80-−2.85). In some cases they considerably
deviate from the previously found value of −5/3. A change of the
power-law index above log k≈2.5 was also found in some cases. In the
two longest events the time evolution of their power spectra as well as
their indices were studied. While in most parts of the radio spectra
the spectral index remains constant, in one part its absolute value
increases with the spike intensity increase. Finally, the results,
especially the broad range of power-law indices, are briefly discussed.
---------------------------------------------------------
Title: Infrared Photometry of Solar Active Regions
Authors: Sobotka, M.; Vázquez, M.; Cuberes, M. S.; Bonet, J. A.;
Hanslmeier, P.
2000JApA...21..289S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated MDI/TRACE/SVST Observations of Sunspots
Authors: Bush, R. I.; Shine, R. A.; Brandt, P.; Sobotka, M.;
Scharmer, G.
2000SPD....31.0122B Altcode: 2000BAAS...32R.804B
During the first two weeks of June 1999, coordinated observations
of sunspots were made by the MDI instrument on the SOHO spacecraft,
the TRACE satellite and the Swedish Vacuum Solar Tower (SVST) at La
Palma. The MDI instrument was operating in a "high resolution" mode
and was obtaining 1.2 arc-second resolution magnetograms and 2.4
arc-second resolution dopplergrams at a one minute cadence. TRACE
observations were made in Fe IX/X 171 Angstroms and/or Fe XII 195
Angstroms together with the 1600 Angstroms and continuum bands at a
1.0 arc-second resolution. The SVST data consist of filtergrams taken
with three 2Kx2K CCD cameras with about 0.4 arc-second resolution
operating in frame selection mode. The first camera used a fixed G
band (4305 Angstroms) filter, the second a fixed blue continuum filter
(4507 Angstroms), and the third a narrow band tunable filter which was
cycled through several positions in the Hα line and the 6302 Angstroms
Fe ~I line. The goal of this investigation is to detail the evolution
of stable sunspots in order to understand the detailed correlation of
photospheric flows and magnetic features. The high time and spatial
resolution of these measurements provides a unique opportunity to
explore the interactions of plasma and magnetic field at the solar
surface. This work was supported by NASA grant NAG5-3077 at Stanford
and NASA contract NAS5-38099 at Lockheed Martin.
---------------------------------------------------------
Title: Interaction of Convective Structures with the Magnetic Field
of Solar Pores
Authors: Sobotka, M.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A.
1999ASPC..184...60S Altcode:
Time series of high-resolution white-light images of solar pores are
analyzed. Granular motions in the vicinity of pores are driven by
mesogranular flows: Motions toward the pore dominate in the 2 arcsec
zone around the pore boundary, while at larger distances the granules
move away from the pore. Triggered by these motions, small granules
and granular fragments located close to the pore border penetrate into
the pore, where they move inwards as short-lived bright features very
similar to umbral dots. The formation of a transitory penumbra-like
structure at the border of a large pore was observed simultaneously
with a temporary reorganization of adjacent granular field to expanding
elongated granules separated by dark filaments.
---------------------------------------------------------
Title: Fine structure in sunspots. III. Penumbral grains
Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W.
1999A&A...348..621S Altcode:
The properties of penumbral grains (PGs) in a medium-size sunspot are
studied from a 4.5 hour observation series acquired on 5 June 1993 at
the Swedish Vacuum Solar Telescope, La Palma. The application of an
image segmentation procedure and a feature tracking algorithm on a movie
of 360 frames yields proper motions, intensities, and lifetimes for a
set of 469 PGs. Almost 3/4 of the PGs move toward the umbra and more
than 1/4 toward the photosphere. There appears to be a dividing line
(DL) in the penumbra, approximately 0.7 of the distance from the umbra
to the photosphere, such that most PGs outside this line move toward
the photosphere, and those inside move toward the umbra. For inward
moving PGs we find a typical proper motion speed of 0.4 km s(-1) and
a median lifetime of 29 minutes, for outward moving ones 0.5 km s(-1)
and 22 minutes. The average speed of inward moving PGs increases with
distance from the umbra with a maximum near the DL. Outward moving
PGs have maximum speed near the outer penumbral boundary. The measured
instantaneous velocities of individual PGs show only partial agreement
with theoretical model predictions. We find much shorter lifetimes than
earlier authors, and no pronounced dependence of lifetime on position
in the penumbra. We discuss possible reasons for the disagreement with
previous results.
---------------------------------------------------------
Title: Fine Structure in Sunspots, III: Penumbral Grains
Authors: Simon, G. W.; Sobotka, M.; Brandt, P. B.
1999AAS...194.5908S Altcode: 1999BAAS...31..919S
The properties of penumbral grains (PGs) in a medium-size sunspot are
studied from a 4.5 h observation series acquired on 1993 June 5 at the
Swedish Vacuum Solar Telescope, La Palma. The application of an image
segmentation procedure and a feature tracking algorithm on a movie of
360 frames yields proper motions, intensities, and lifetimes for a set
of 469 PGs. Almost 3/4 of the PGs move toward the umbra and more than
1/4 toward the photosphere. There appears to be a dividing line (DL)
in the penumbra, approximately 0.7 of the distance from the umbra to
the photosphere, such that most PGs outside this line move toward the
photosphere, and those inside move toward the umbra. For the inward
moving PGs we find a typical proper motion speed of 0.4 km/s and a
median lifetime of 29 minutes, for the outward moving ones 0.5 km/s
and 22 minutes. The average speed of inward moving PGs increases with
distance from the umbra and has a maximum near the DL. Outward moving
PGs have maximum speed near the outer penumbral boundary. Instantaneous
velocities of individual PGs were measured to compare them with
theoretical model predictions. We find much shorter lifetimes than
earlier authors, and no pronounced dependence of lifetime on position
in the penumbra. We discuss possible reasons for the disagreement in
results, and make some comments on the differences between human and
computer selection and tracking of features.
---------------------------------------------------------
Title: Temporal Evolution of Fine Structures in and around Solar Pores
Authors: Sobotka, Michal; Vázquez, Manuel; Bonet, José Antonio;
Hanslmeier, Arnold; Hirzberger, Johann
1999ApJ...511..436S Altcode:
Time series of high-resolution white-light images of six solar pores,
observed in 1993 and 1995 at the Swedish Vacuum Solar Telescope (La
Palma), are analyzed. The pores constitute an almost ideal laboratory
in which to study the interaction of a vertical magnetic field with
surrounding convective motions, without the perturbation of the inclined
magnetic field in the penumbra. Umbral dots observed in a large (D=8.9")
pore are similar to those in mature umbrae, but they live longer, are
brighter, and have a higher filling factor. Granular motions in the
vicinity of pores are driven by mesogranular flows. Motions toward the
pore dominate in the 2" zone around the pore boundary, while at larger
distances the granules move away from the pore. Pushed by these motions,
small granules and granular fragments located close to the pore border
sometimes penetrate into the pore, where they move inward as bright
short-lived features very similar to umbral dots. The capture of bright
features by the pore is probably a microscale manifestation of the
“turbulent erosion,” which results in the decay of the pore. Formation
of a transitory penumbra-like structure at the border of the large
pore was observed simultaneously with the appearance of expanding
elongated granules, separated by dark filaments, in an adjacent
granular field. These effects can be interpreted as a consequence of
emerging bipolar magnetic “loops” caused by a temporary protrusion
of opposite magnetic polarity.
---------------------------------------------------------
Title: Granulation in active regions as compared to quiet regions
Authors: Hirzberger, J.; Bonet, J. A.; Vázquez, M.; Hanslmeier, A.;
Sobotka, M.
1999AGAb...15...88H Altcode: 1999AGM....15..P09H
A comparative study of the statistical properties of granulation
in active and quiet regions is performed. The analysis is based on a
high-resolution time series of simultaneous white light (lambda5425 Å)
and G-band (lambda 4308 Å) images obtained at the Swedish Vacuum Solar
Telescope, La Palma, Canary Islands. The G-band images have been used
to discern quiet and active regions in the field of view, whereas the
white-light images were taken to analyze the photometry, size and time
evolution of granules in regions of different magnetic activity. Power
spectra confirm that the granular size decreases with increasing G-band
brightness. Granules with diameters below 0”.8 are systematically
brighter in the abnormal granulation than in quiet regions. These
small and bright elements are embedded in a diffuse background of
approximately mean photospheric brightness covering all the fields of
abnormal granulation. The granular lifetime decreases with increasing
G-band brighness. The conclusions about the behaviour of the granulation
have been decontaminated of the influence of magnetic elements (the
so-called Bright Points), that have been separated using criteria
of size (d < 0”.5) and lifetime (T > 6 min). A significant
fraction of them are concentrated in regions of high G-band activity,
an emerging flux region, and the rest are m ainly aligned outlining a
cellular pattern (the magnetic network formed by supergranular motions).
---------------------------------------------------------
Title: Fine Structures in Sunspots
Authors: Sobotka, M.
1999ASSL..239...71S Altcode: 1999msa..proc...71S
A review of the present knowledge on fine-scale features in sunspots
at the photospheric level is given. The principal aim is to summarize
and discuss the results of observations with high spatial resolution
but also several important theoretical models are briefly described.
---------------------------------------------------------
Title: Lifetimes and motions of penumbral grains.
Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W.
1999joso.proc...89S Altcode:
The properties of penumbral grains (PGs) are studied from a 4.5 hour
sunspot series observed on June 5, 1993 at the Swedish Vacuum Solar
Telescope, La Palma. The application of an image segmentation procedure
yields a set of 605 penumbral grains which are investigated by a feature
tracking algorithm. The authors find a dividing line between inward and
outward moving PGs and give results on their lifetime and proper motion.
---------------------------------------------------------
Title: Lifetime of dark nuclei.
Authors: Stupka, M.; Sobotka, M.
1999joso.proc..114S Altcode:
Preliminary results about the lifetime of dark nuclei in the umbra
of the leading spot NOAA 7882 are presented. From time-series of
white-light images obtained at the Swedish Vacuum Tower Telescope,
La Palma (on June 22 - 29, 1995), the authors estimated the
lifetime of three dark nuclei of a relatively bright sunspot
(J<SUB>min</SUB>/I<SUB>phot</SUB> = 0.30) to be in the range of 10 -
30 hours.
---------------------------------------------------------
Title: Lifetimes and Motions of Penumbral Grains-Preliminary Results
Authors: Sobotka, M.; Brandt, P.; Simon, G.
1999ASPC..183..116S Altcode: 1999hrsp.conf..116S
No abstract at ADS
---------------------------------------------------------
Title: Fine structure in sunspots. I. Sizes and lifetimes of
umbral dots
Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W.
1997A&A...328..682S Altcode:
The analysis of a 4 1/2 hour series of high resolution white light
observations of the umbra in a medium-size sunspot (NOAA 7519, observed
on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma) is
described. An automatic identification and tracking algorithm was
applied to umbral dots (UDs) observed in a destretched movie of 360
frames. In total, 662 UDs were tracked and their filling factor, sizes,
and lifetimes were measured. It was found that large (diameter >
0farcs 4) and long-lived (lifetime > 10 minutes) UDs appear mostly
in regions with enhanced umbral diffuse background intensity. UDs
do not have a “typical” size. Their number rapidly increases with
decreasing diameter down to the resolution limit. Similarly, UDs do
not have a “typical” lifetime, and their number rapidly increases
with decreasing lifetime. UDs with lifetimes below 10 minutes represent
about 2/3 of the population; the median lifetime is 5.9 minutes.
---------------------------------------------------------
Title: Fine structure in sunspots. II. Intensity variations and
proper motions of umbral dots
Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W.
1997A&A...328..689S Altcode:
Temporal intensity variations of umbral dots (UDs) and dark nuclei
(DNs), and proper motions of UDs, were analyzed in a 4 1/2 hour
time series of high resolution white light images of the umbra in a
medium-size sunspot (NOAA 7519). The observations were made on 5 June
1993 at the Swedish Vacuum Solar Telescope, La Palma. An identification
and tracking algorithm was applied to UDs observed in a destretched
movie of 360 frames. In total, 662 UDs were tracked, and their
intensities, positions, and proper motions were measured. Power
spectra of temporal intensity variations of UDs and DNs were
computed, and several typical periods were found. The histogram of
time-averaged intensities of UDs has two maxima; the UDs belonging to
the brighter part of the population are located mostly at or near the
umbral-penumbral boundary. The number of UDs decreases with increasing
magnitude of the proper motion velocity. Speeds of UDs are grouped
at 100 and 400 m/s. The observed spatial distribution of UDs with
different proper motion velocities is found to be in contradiction to
the generally accepted idea of moving “peripheral” and stationary
“central” UDs. Both “fast” and “slow” UDs are present in all
parts of the umbra. Thus velocity does not appear to be a good criterion
for separating UDs into “peripheral” and “central” ones.
---------------------------------------------------------
Title: Time Series of Solar Granulation Images. I. Differences
between Small and Large Granules in Quiet Regions
Authors: Hirzberger, J.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A.;
Sobotka, M.
1997ApJ...480..406H Altcode:
A 90 minute time series of high spatial resolution white-light images
of solar granulation, obtained at the Swedish Vacuum Solar Tower
(Observatorio del Roque de los Muchachos, La Palma), was analyzed
to study how the physical properties of the granules changed with
size. The observational material was corrected for global motions and
for the instrumental profile, and a subsonic filter was applied. A
definition of granular border was adopted using the inflection points
of the intensity of the images, and the granular cells were defined
as areas including, in addition to the granules, one-half of their
surrounding intergranular lanes. Using time series to investigate the
average behavior of solar granulation has three strong advantages:
the first is the possibility of removing the acoustic waves; second,
the possibility of estimating the effect of the variability of
seeing on our results; and, third, the opportunity to attain high
statistical significance in the analysis as a result of the large
number of extracted granules (61,138). <P />It is shown that the
granules of the sample can be classified according to their mean
and maximum intensities and their fractal dimension into two regimes,
with diameters smaller than and larger than 1.4", respectively. A broad
transition region in which both regimes coexist was found. The resolved
internal brightness structure of both the granules and the intergranular
lanes shows a linear increase of the number of substructures with the
granular and intergranular areas. The diameters of these substructures
range between our effective resolution limit (~0.3") and ~1.5",
with preferential sizes at 0.65" and 0.55", respectively. Moreover,
it seems that large and small granules are unevenly distributed with
respect to the large-scale vertical flows. Thus smaller granules are
more concentrated along downdrafts whereas larger ones preferentially
occupy the updrafts. Finally, a physical scenario compatible with the
existence of these two granular populations is discussed.
---------------------------------------------------------
Title: Sunspots Seen at High Spatial Resolution
Authors: Sobotka, M.
1997ASPC..118..155S Altcode: 1997fasp.conf..155S
Sunspots, if observed at high spatial resolution, display a complicated
pattern of fine structures, both in the penumbra (bright and dark
filaments, penumbral grains, dark cloud-like features) and in the
umbra (umbral dots, light bridges, dark nuclei, embedded in a diffuse
background). This review describes recent results of observations of
those fine-structure elements at the photospheric level. We discuss
the morphology, magnetic field, proper motions, and Doppler velocities
in sunspot penumbrae. We present the morphological classification
of light bridges and summarize the data about their evolution and
relations to other fine-structure elements, about the magnetic
field, and the results of an analysis of the internal structure of
strong granular light bridges. We review the present knowledge about
the general photometric characteristics and structure of sunspot
umbrae, dark nuclei, and umbral dots (brightness, size, lifetimes,
spatial distribution, proper motions, Doppler velocities, and magnetic
field). We also present original results, based on an exceptional 4.5
hour time-series of high-resolution images. Finally, we discuss some
interesting similarities and relations between the fine-structure
elements in different magnetic regions (umbrae, penumbrae, pores and
light bridges).
---------------------------------------------------------
Title: Fine structure in sunspots: sizes, lifetimes, motions, and
temporal variations.
Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W.
1997joso.proc...84S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Narrowband dm-Spikes in the 2 GHz Frequency Range and MHD
Cascading Waves in Reconnection Outflows
Authors: Karlický, Marian; Sobotka, Michal; Jiřička, Karel
1996SoPh..168..375K Altcode:
Two examples of clouds of narrowband dm-spikes, observed by the
Ondřejov radiospectrograph in the 1-2 GHz frequency range, are
analyzed. After transformation of the frequency scales to distances in
the solar atmosphere, the power spectra analysis of size scales reveals
a spectral index of −5/3, resembling that of Kolmogorov spectra of
turbulent cascades. The narrowband dm-spikes are interpreted as radio
emission from electrons accelerated in MHD cascading waves, probably
generated in plasma outflows from magnetic field reconnection.
---------------------------------------------------------
Title: Time evolution of solar granulation phenomena.
Authors: Hirzberger, J.; Bonet, J. A.; Hanslmeier, A.; Vázquez, M.;
Sobotka, M.
1996AGAb...12..160H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temporal evolution of fine-structures in sunspots.
Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W.
1996joso.proc..145S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Dynamics of Bright Features in Sunspot Umbrae
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel; Hanslmeier,
Arnold
1995ApJ...447L.133S Altcode:
Time series of white-light pictures of the sunspot NOAA 7522, obtained
at the Swedish Vacuum Solar Telescope (La Palma), were analyzed
to study the proper motion of bright features in sunspots. For the
first time, its relation with the dark nuclei present in the umbra is
investigated. The bright features are visible in the penumbra as bright
grains moving into the umbra. A few of them cross the penumbra/umbra
boundary, becoming peripheral umbral dots, which move farther into
the umbra until they meet dark nuclei, braking their motion and
disappearing. In some cases the encounter with a dark nucleus produces
a brightening of the central umbral dots placed on the opposite side
of the nucleus. A similar phenomenon is observed in the grains of a
faint light bridge, when bright penumbral grains collide with one of
the edges of the bridge.
---------------------------------------------------------
Title: Photometry of sunspot pores from partial eclipse observations.
Authors: Bonet, J. A.; Sobotka, M.; Vazquez, M.
1995A&A...296..241B Altcode:
White-light images, centered at λ6708A, were obtained at the Swedish
Solar Telescope, La Palma, on occasion of the 1994 May 10 partial solar
eclipse. From the recorded information, 5 frames showing several pores
together with the moon's limb were selected for detailed photometric
analysis. The observed intensity profile of the moon's limb projected
against the solar disk was used to derive, from each frame, the
Point Spread Function of the atmosphere + instrument to restore the
images. The characteristics of the obtained PSFs -low noise and precise
determination of the wings far away from the core- enabled us to avoid
arbitrary assumptions about analytical approximations. The FWHM of these
functions was typically 0.47". Several bright features were identified
in one of the pores. After determining the photometric parameters of
these fine umbral structures their link with the population of the
bright features in the umbra of evolved spots is discussed in the
framework of the dependence of sunspot properties on the spot size.
---------------------------------------------------------
Title: A High-Resolution Study of the Structure of Sunspot Light
Bridges and Abnormal Granulation
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel
1994ApJ...426..404S Altcode:
Strong light bridges (SLBs) represent an abrupt change in the physical
conditions of sunspot umbrae. They divide the umbra into separate units
(fragments, umbral cores) and very often show a granular structure. A
photometric and spectroscopic study of SLBs, and also of abnormal
granulation (AG) in a region of pores, is presented. Slit-jaw images
(bandpass 5425 +/- 50 A) and spectra (line Fe I 5434.5 A), with a
spatial resolution of 0.3 sec, were acquired during the period 1991 July
1-10 at the Swedish Solar Telescope at the Observatorio del Roque de
los Muchachos (La Palma). The power spectra of intensity fluctuations
in the slit-jaw images, were used as the primary diagnostic tool,
complemented by the analysis of line profiles. The following results
were obtained. 1. The structures present in SLBs and AG are generally
smaller than the granules in the quiet photosphere. The typical size
of SLB granules is 1.2 sec (in quiet granulation, 1.5 sec). In AG, the
distribution of power is more complex and is characterized by peaks
corresponding to scales of 2.5 sec, 1.3 sec, and 0.64 sec. 2. SLB
and AG power spectra show an excess of power (compared to quiet
granulation) at scales of 0.5 sec. This power enhancement reflects
the presence of small bright grains, clearly visible in SLBs and AG,
with a mean nearest neighbor distance of 0.5 sec. 3. Two of these small
bright grains, together with a dark lane between them, were resolved
spectroscopically in a SLB. The line shifts and bisector shapes suggest
a convective origin of these structures. 4. The SLB power spectra in
the log P/log k scale indicate the presence of a Kolmogorov turbulent
cascade in the structures between 1.7 sec and 0.64 sec. However, the
small bright grains do not pertain to the turbulent cascade. They
are particular phenomena, probably with a convective origin. The
power spectrum of AG does not give any indication of the presence of
a turbulent cascade. 5. Small bright features (umbral dots or bright
grains) can be found in unbral cores, light bridges, and AG regions as
well. <Their mean nearest neighbor distance, in the observed areas,
decreases with increasing brightness and decreasing magnetic field
strength. &We thus propose that they are a manifestation of altered
convection, which is modulated and maintained by the magnetic field.
---------------------------------------------------------
Title: Processing of Images Acquired at the Ondřejov Double Solar
Refractor
Authors: Klvaňa, M.; Bumba, V.; Sobotka, M.
1994ESOC...50..179K Altcode: 1994hadg.conf..179K
No abstract at ADS
---------------------------------------------------------
Title: Strong light bridges and abnormal granulation
Authors: Sobotka, M.; Bonet, J. A.; Vázquez, M.
1994smf..conf..197S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A High-Resolution Study of Inhomogeneities in Sunspot Umbrae
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel
1993ApJ...415..832S Altcode:
A detailed study of the brightness, size, spatial distribution,
and filling factor of the different umbral inhomogeneities is
presented. Many sunspots show multiple umbrae (separated by strong
light bridges, SLBs), which behave like independent units. These are
termed umbral cores (UCs). From the phenomenological point of view, UCs
show two components: (1) a dark area, formed by a diffuse background
(DB), with local intensity minima called dark nuclei (DNs), and (2)
bright features including umbral dots (UDs) and faint light bridges
(FLBs). <P />Slit-jaw images (bandpass 5425±50 Å) and spectra
(line Fe I 5434.5 Å) of seven sunspots with 13 separate UCs were
acquired using the Swedish Solar Telescope at the Observatorio
del Roque de los Muchachos (La Palma) with a spatial resolution of
0".3. Image restoration and inversion of the spectral line profile
were applied, with the following results: <P />The most important
photometric parameter of the UCs is the mean intensity of their DB
(mean background intensity ‾I<SUB>back</SUB>). It is well correlated
to the intensity minimum of the diffuse background and to the mean
brightness of UDs. The relation between the size of the UCs and their
‾I<SUB>back</SUB> is not straightforward, but UCs with radii <5"
are in general brighter than the larger ones. The differences in the
brightness of individual umbrae can be explained mainly by variations
of ‾I<SUB>back</SUB> rather than in terms of variations of UD filling
factor. <P />The linear relation between the peak intensity of UDs
and the intensity of the adjacent DB (local background intensity)
was confirmed in a sample of more than 1500 elements, and the
"true" peak-to-background ratio was estimated as 3. <P />The spatial
distribution of UDs is nonuniform. In DNs (whose size is comparable to
that of photospheric granules) UDs appear very rarely; they prefer to
form clusters and alignments outside the DNs. The mean nearest neighbor
distance decreases, and the density of UDs increases with increasing
‾I<SUB>back</SUB>. The filling factor of UDs is in the range 3%-10%,
and the size of UDs is similar in all UCs. The typical "true" size is
180-300 km, and it is uncorrelated to the peak brightness of UDs. <P
/>FLBs are composed of bright grains and dark spaces between them. The
bright grains are darker than photospheric granules. The size of the
bright grains is similar to that of UDs, and their relative area in
FLBs is very close to the fractional area granulum-intergranulum in the
quiet photosphere. <P />On the basis of the obtained spectral profiles,
working models of temperature stratification are presented for UDs,
their adjacent DB, and DNs. <P />On the basis of observational facts
the following is proposed: UDs and FLBs are probably demonstrations
of some kind of altered convection, with a cell size of about 0".5,
modulated by a smoothly varying magnetic field.
---------------------------------------------------------
Title: High Resolution Observations of Umbral Fine Structure
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
1993ASPC...46...20S Altcode: 1993mvfs.conf...20S; 1993IAUCo.141...20S
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic determination of intensities of umbral bright
features and adjacent background
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
1992A&A...260..437S Altcode:
Profiles of the Na I D doublet in three bright features (clusters
of umbral dots), located in a relatively dark umbra, were analyzed
by means of the 'local two-component modeling' to obtain the 'true'
continuum intensities and temperatures of the bright features and
their dark surroundings (background). The intensities of two central
and one peripheral bright feature were 0.31 (background 0.11), 0.33
(0.13), and 0.40 (0.17), respectively. For the ratio of the object and
background intensity (assumed to be constant, but unknown until now)
the value of 2.6 +/- 0.2 was obtained.
---------------------------------------------------------
Title: On the relation between the intensities of bright features
and the local background in sunspot umbrae
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
1992A&A...257..757S Altcode:
A photometric study of umbral bright features (umbral dots, clusters
of umbral dots, bright grains of light bridges) in sunspots is
presented. It is based on white-light images taken with a CCD video
camera driven by an automatic image selection system. A direct linear
relation between the observed brightness of the features and that
of the surrounding background areas has been found. To eliminate the
influence of the seeing on this result, the radiative fluxes, which
are much less sensitive to the image degradation, have been examined
and an analogous relation has been found. Finally, a possible physical
explanation is suggested.
---------------------------------------------------------
Title: Report from the Canary Islands.
Authors: Sobotka, M.
1991Rise...72..209S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photometry of the Umbral Structure of a Fast-developing Sunspot
Authors: Sobotka, M.; Simberova, S.; Bumba, V.
1991BAICz..42..250S Altcode:
A high-quality white-light photograph of an umbra of a large complex
spot was analyzed. Digital image processing methods were used. The
extensively inhomogeneous structure of the umbra, related to the fast
dynamics of development, displays many features (dark cores, bright
dots, light bridge, etc.), intensities and temperatures which were
studied in detail. In the dark cores a relatively low temperature was
obtained. A relation between the intensity of the individual bright
umbral dots and their dark surroundings was found.
---------------------------------------------------------
Title: Photometry of the Internal Structure of a Large Umbra
Authors: Bumba, V.; Sobotka, M.; Šimberová, S.
1990PDHO....7...84B Altcode: 1990ESPM....6...84B; 1990dysu.conf...84B
An analysis of a high-resolution white-light photograph of an umbra of a
large complex main spot was performed. Digital image processing methods
were used. The umbra was observed as a very inhomogeneous structure
with large differences in intensities of the individual elements
(dark cores, bright dots, light bridge, etc.). The temperatures of
these elements were derived. It is demonstrated that the intensity
of the individual bright umbral dots is related to the intensity of
their dark surroundings.
---------------------------------------------------------
Title: Book reviews
Authors: Sobotka, M.; Dyson, John
1989Ap&SS.162..175S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - 10TH European Regional Astronomical Meeting -
Prague - 1987AUG
Authors: Perek, L.; Hejna, L.; Sobotka, M.; Ceplecha, Z.; Pecina,
P.; Sidlichovsky, M.; Palous, J.; Harmanec, P.; Pecker, J. C.
1989BAICz..40..196P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic Observations and Models of Umbral Light Bridges
Authors: Sobotka, M.
1989SoPh..124...37S Altcode:
Profiles of the NaI D lines in two moderately bright umbral light
bridges are analyzed. A simple method of elimination of stray light
is presented. The corrected continuum intensities (λ ≈ 588 nm)
of the light bridges are 0.51 and 0.43. For each light bridge,
using optimization technique, a semi-empirical model is derived. The
models exhibit a steep temperature rise towards the subphotospheric
layers. Generally, the temperature of the light bridges under
investigation is lower than the temperature of the penumbra as well
as the temperature of bright umbral dots.
---------------------------------------------------------
Title: Two-component Models of Individual Sunspot Umbrae
Authors: Sobotka, M.
1988BAICz..39..236S Altcode:
Semiempirical two-component models of 11 umbrae differing in size
are presented and their general characteristics are discussed. The
models, based on the profiles of the Fe I 543.5 nm and Na I D2 lines
have bright components cooler than the undisturbed photosphere,
with a temperature down-scaling factor Delta Theta = 0.10 in most
cases. The temperature of dark components fluctuate in the range of
Delta Theta = 0.35 to 0.50. The filling factor of the bright component
remains practically constant in large umbrae whereas in small umbrae
it changes considerably. No dependence of the temperature of both
components as well as the filling factor on the phase of evolution of
the spot was observed.
---------------------------------------------------------
Title: Instrumental profile of the HSFA-type spectrograph in the
near infrared.
Authors: Sobotka, M.; Kotrc, P.
1987BAICz..38..272S Altcode:
A method of determining the instrumental profile of the horizontal
solar spectrograph (HSFA) using an infrared sensitized photographic
emulsion is described. Instrumental profiles, which include the effects
of the non-zero slit width, diffraction and photographic emulsion along
with possible distortions of the theoretical instrumental profile were
determined by numerical convolution and deconvolution.
---------------------------------------------------------
Title: Spectroscopic investigation of two-component umbral structure.
Authors: Sobotka, M.
1987PAICz..66...33S Altcode: 1987eram....1...33S
On the basis of spectroscopic observations in the lines Fe I 543.5 nm
and Na I D<SUB>2</SUB> the main characteristics of simple semi-empirical
two-component models of 11 umbrae differing in size (radii 2arcsec -
8arcsec) are studied.
---------------------------------------------------------
Title: The Sun. 10th European Regional Astronomy Meeting of the IAU,
held inPraha, Czechoslovakia, 24 - 29 August 1987. Proceedings,
Vol. 1.
Authors: Hejna, Ladislav; Sobotka, Michal
1987PAICz..66.....H Altcode: 1987eram....1.....H
Solar astronomy papers are presented, covering topics such as
the solar and stellar magnetic fields, the fine structure of solar
active regions, fragments in sunspots, photospheric granules, active
region fine structures, two-component umbral structure, bright
facular points in active regions, granulation variations with solar
latitude, the evolution and decay of active regions, the local dynamo
in sunspot groups, the extreme solar activity of February 1986, radial
differential rotation, 530.3 nm corona irradiance variations in cycle
21, and long-period components in solar wind velocities. Other topics
include electric current density in the photosphere, surges as tracers
of magnetic lines, magnetic turbulent diffusion, the relationship
of large-scale solar magnetic and velocity fields to solar active
phenomena, high flare activity and redistribution of solar magnetic
fields, the velocity field and solar activity, evershed flow, sunspot
rotation and electric currents, the effects of fluid viscosity and
electrical resistance on atmospheric Alfven waves, solar g modes, and
supergranular motions around a decaying sunspot. Additional subjects
include the physical structure of active regions, FIR solar images,
cool flare loops, the Ly-alpha line in the chromosphere, eruptive
prominences and coronal transients, chromospheric lines in sunspot
umbra and penumbra, flaring loop parameters, X-ray studies of active
regions, solar radio burst onset, the HXIS arches, magnetic field line
reconnection by localized enhancement of resistivity, optical and IR
spectrophotometry of quiescent prominences, continuum intensity and
magnetic flux of solar fluxtubes, microwave emission from sunspots,
and the S-component inside and outside of sunspots.
---------------------------------------------------------
Title: Infrared observations of quiescent prominences
Authors: Heinzel, P.; Kotrč, P.; Sobotka, M.; Zloch, F.; Scherbakova,
Z. A.
1986CoSka..15..171H Altcode:
The authors have developed a sophisticated numerical technique to
reduce infrared photographic spectra of quiescent prominences, taking
into account the influence of instrumental profiles, scattered light
and the noise. The reduced profiles were subsequently compared with
theoretical ones.
---------------------------------------------------------
Title: Solar physics. 12th regional consultation, Smolenice, May 1986.
Authors: Sobotka, M.
1986Rise...67..204S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Semi-empirical models of sunspots in various phases of
evolution
Authors: Sobotka, M.
1986CoSka..15..315S Altcode:
The characteristics of 10 semi-empirical models of umbrae of different
sizes and in various phases of evolution are studied, namely: 1) the
spectral distribution of the umbra/photosphere continuum intensity
ratio, 2) the dependence of the integral umbra/photosphere intensity
ratio on the umbral radius, 3) the variations of the integral contrast
of umbrae from the disk center to the limb. This study and earlier
ones indicate that the characteristics of the model depend mainly on
the umbral radius and do not depend on the phase of evolution.
---------------------------------------------------------
Title: Semiempirical models of sunspots
Authors: Sobotka, M.
1985AZh....62..995S Altcode:
On the basis of spectroscopic observations in the Mg I b1, Fe I 5434
A, and Na I D2 lines, 12 semiempirical models of sunspots of different
sizes (r umbral radius, 2-8 arcsec) are constructed for several stages
of their development. It is shown that the model of an umbra varies
greatly with an increase in umbral radius up to a limiting value of
3.5-4 arcsec (Su = 7.5 MSH), after which the changes are small, and
for a fixed umbral radius there is no significant difference between
the models of sunspots in different phases of their development.
---------------------------------------------------------
Title: Semiempirical Models of Sunspots
Authors: Sobotka, M.
1985SvA....29..576S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Analysis of Spectral Lines in Sunspot Umbrae
Authors: Sobotka, M.
1985BAICz..36..230S Altcode:
Spectroscopic observations of sunspots of different areas and in
various phases of evolution were performed with the horizontal
telescope-spectrograph in Ondřejov. A technique for obtaining a
semiempirical model of photospheric layers in the umbra from observed
line profiles (corrected for stray light) is described together with
a set of computational programs. Some preliminary results are presented.
---------------------------------------------------------
Title: Horizontal solar telescopes in Czechoslovakia.
Authors: Sobotka, M.
1985Rise...66..226S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stray light determination in small sunspots.
Authors: Sobotka, M.
1983PDHO....5..581S Altcode: 1984PDHO....5..581S
Correct analysis of spectral line profiles arising from the
spot requires a determination of the fraction α of photospheric
stray light. To do this, either an approximate formula derived
by Maltby, or the method introduced by Zwaan and Staveland can be
used. The latter method needs a determination of several blurring
and scattering parameters. In the case of the observations made
by a new horizontal solar telescope spectrograph in Ondřejov, the
scattering is negligible. The blurring parameters can be determined
from an observed photometric profile of the solar limb. According
to preliminary measurements of 12 sunspot spectra, the values of α,
computed by the above method, are on an average lower by a factor 0.85
as compared to those obtained from Maltby's approximate formula.
---------------------------------------------------------
Title: Physical conditions in sunspots.
Authors: Sobotka, M.
1983Rise...64..245S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopy of the Nova LV Vulpeculae (1968 No. 1)
Authors: Grygar, J.; Sobotka, M.; Stefl, S.
1981BAICz..32...88G Altcode:
Spectroscopic data of the fast nova LV Vul were obtained during the
28 April-15 October 1968 period. Fifty-one lines of nine elements
(H, He, C, N, O, Ca, Ti, Cr and Fe) at various ionization stages were
identified, including several forbidden lines of oxygen and iron. The
radial velocities of the emission peaks and of absorption components
were determined. Six distinct absorption systems were identified
and within each the course of the radial velocities with time was
approximated. The average acceleration for all systems was 0.20 plus
or minus 0.04 m/sq s. This is an order of magnitude greater than for
the slow nova HR Del. The linearity indicates that the driving force
was constant for a time period of 1-2 months after the initial outburst.
---------------------------------------------------------
Title: Spectroscopy of the Nova IIR Delphini in the Years 1967-1968
Authors: Sobotka, M.; Grygar, J.
1979BAICz..30..129S Altcode:
Twenty-five spectrograms of the nova HR Del are examined which were
obtained with dispersions of 0.8 to 8.6 nm/mm in the period between
October 1967 and December 1968. Some 225 lines of 19 elements in various
degrees of ionization are identified, radial velocities are determined
for the absorption and emission lines, and a detailed structural
analysis of the absorption systems in different phases is performed
separately for the Balmer lines, metal lines, and the He-C-N-O group. It
is found that changes in the expansion velocities for the individual
systems are caused by a very small acceleration (0.01 m/sec per sec)
of ejected material and that the systems in the primary spectrum began
to be accelerated at the end of March 1968. Changes in the appearance
of the spectrum over the period of observation are described.
---------------------------------------------------------
Title: Spectroscopy of the Nova Vulpeculae 1968 NO. (lv Vul)
Authors: Sobotka, M.; Stefl, S.; Grygar, G.
1977ASSL...65...96S Altcode: 1977nrst.conf...96S
No abstract at ADS