Author name code: sobotka ADS astronomy entries on 2022-09-14 author:"Sobotka, Michal" ------------------------------------------------------------------------ Title: Horizontal motions in sunspot penumbrae Authors: Sobotka, Michal; Puschmann, Klaus G. Bibcode: 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.
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.
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.
Results: In the inner penumbra, PGs move towards the umbra (inwards) with a mean speed of −0.7 km s−1. 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−1. 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−1. High outward speeds, 3.6 km s−1 on average, are observed in dark bodies of penumbral filaments.
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.

Movies associated to Fig. 1 are available at https://www.aanda.org 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. Bibcode: 2021A&A...653A.165K Altcode: 2021arXiv210711116K
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.
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).
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.
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. 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. Bibcode: 2021A&A...648A..28A Altcode: 2021arXiv210208678A
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.
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.
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%.
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. 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 Bibcode: 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.
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.
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.
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. 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. Bibcode: 2020A&A...642A..52A Altcode: 2020arXiv200802688A
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.
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.
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.
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. 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. Bibcode: 2020A&A...639A..19V Altcode: 2020arXiv200503966V
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.
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.
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.
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.

Movies are available at https://www.aanda.org 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 Bibcode: 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. 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. Bibcode: 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-1 next to the pores and to 4 km s-1 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. 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. Bibcode: 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). 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. Bibcode: 2018A&A...614A...2V Altcode: 2018arXiv180103686V
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.
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.
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.
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. Title: Václav Bumba (1925 - 2018) Authors: Kotrč, Pavel; Heinzel, Petr; Sobotka, Michal; Ambrož, Pavel; van Driel-Gesztelyi, Lidia Bibcode: 2018SoPh..293...40K Altcode: No abstract at ADS Title: The Temperature - Magnetic Field Relation in Observed and Simulated Sunspots Authors: Sobotka, Michal; Rezaei, Reza Bibcode: 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″ 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. 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. Bibcode: 2017A&A...608A.117K Altcode: 2017arXiv170906861K
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.
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.
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-1. 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.
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.

The movie associated to Fig. 2 is available at http://www.aanda.org 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. Bibcode: 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. 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 Bibcode: 2017psio.confE.104D Altcode: No abstract at ADS 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. Bibcode: 2017psio.confE.105B Altcode: No abstract at ADS 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. Bibcode: 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. Bibcode: 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-1. 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.

Movies associated to Figs. 1 and 2 are available at http://www.aanda.org 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. Bibcode: 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.
Aims: We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra.
Methods: We investigated the magnetic field at log τ5 = 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.
Results: At log τ5 = 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. Bibcode: 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-1 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. Bibcode: 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.
Aims: We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface.
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.
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. Bibcode: 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.
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.
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.
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-1 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. Bibcode: 2016A&A...596A...8J Altcode: 2016arXiv160801988J
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.
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.
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.
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. Bibcode: 2016A&A...596A...7S Altcode: 2016arXiv160707094S Context. The various mechanisms of magneto-convective energy transport determine the structure of sunspots and active regions.
Aims: We characterise the appearance of light bridges and other fine-structure details and elaborate on their magneto-convective nature.
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.
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.
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. Bibcode: 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.
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.
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).
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.
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. Bibcode: 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. Bibcode: 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.
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.
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.
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.

Movies associated to Figs. 2 and 13 are available at http://www.aanda.org 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. Bibcode: 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.
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.
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.
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. Bibcode: 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-1 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1. 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 2014A&A...564A..91J Altcode: 2014arXiv1402.6558J
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.
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.
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.
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.

A movie attached to Fig. 11 is available in electronic form at http://www.aanda.org Title: An Estimate of Chromospheric Heating by Acoustic Waves Authors: Sobotka, M.; Švanda, M.; Jurčak, J.; Heinzel, P.; Del Moro, D.; Berrilli, F. Bibcode: 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. Bibcode: 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.
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.
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.
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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:
· Radiative and dynamical properties of Photospheric Bright Points versus their magnetic field concentration.
· Close up analysis of magnetic, velocity and temperature field in a solar pore.
· 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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.
Aims: Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (Deff = 8''.5) are analysed to provide observational constraints on theoretical models and numerical simulations.
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.
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 Bhor is more extended than the vertical component Bz. The temperature linearly decreases with increasing Bz, by about - 300 K kG-1 in the photosphere and - 800 K kG-1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for Bz > 1200 G. Granular upflows dominate in regions with Bz < 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 Bhor > 1000 G. Horizontal motions of granules start to be damped for Bz > 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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.
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-1. Features faster than 0.4 km s-1 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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1 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. Bibcode: 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.

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.

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.

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.

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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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-1 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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.
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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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

correlation tracking algorithm when tracing supergranules in full-disc dopplergrams. The method was developed using synthetic data.

The data are transformed during the data processing into a suitable coordinate system, the noise is removed, and finally the velocity field is

calculated. Resulting velocities are compared with the model velocities and the calibration is done. From our results it becomes clear that

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. Bibcode: 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 −1 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 −1) 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 (Jz). The increase of Jz 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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-1 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-1) 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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-1), 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. Bibcode: 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. Bibcode: 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-1) than the neighbouring granules. Title: Velocity fields in an irregular sunspot Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 arcsec2 at the disc centre to 2 arcsec2 at mu =0.6 in the lambda 0.8 mu m images and from 1.24 arcsec2 to 1.85 arcsec2 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. Bibcode: 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. Bibcode: 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 Tb(1.55 μm) and Tb(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 Bibcode: 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. Bibcode: 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-1 to 2.7%deg;h-1. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 7.6deg h-1 to 2.7deg h-1. 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. Bibcode: 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 Tb(1.55μm)-Tb(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. Bibcode: 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. Bibcode: 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 (Iphot). 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-1 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. Bibcode: 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-1. 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-1. 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Tb (1.55 μm) and Tb (0.80 μm) were computed for the best pairs of images. In the scatter plots Tb (1.55) versus Tb (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 Tb(1.55)-Tb(0.80) in faculae is lower than that in the quiet photosphere but increases with decreasing Tb 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (Jmin/Iphot = 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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).

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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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).

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:

The most important photometric parameter of the UCs is the mean intensity of their DB (mean background intensity ‾Iback). 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 ‾Iback 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 ‾Iback rather than in terms of variations of UD filling factor.

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.

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 ‾Iback. 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.

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.

On the basis of the obtained spectral profiles, working models of temperature stratification are presented for UDs, their adjacent DB, and DNs.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1989BAICz..40..196P Altcode: No abstract at ADS Title: Spectroscopic Observations and Models of Umbral Light Bridges Authors: Sobotka, M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1987PAICz..66...33S Altcode: 1987eram....1...33S On the basis of spectroscopic observations in the lines Fe I 543.5 nm and Na I D2 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 Bibcode: 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. Bibcode: 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. Bibcode: 1986Rise...67..204S Altcode: No abstract at ADS Title: Semi-empirical models of sunspots in various phases of evolution Authors: Sobotka, M. Bibcode: 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. Bibcode: 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. Bibcode: 1985SvA....29..576S Altcode: No abstract at ADS Title: An Analysis of Spectral Lines in Sunspot Umbrae Authors: Sobotka, M. Bibcode: 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. Bibcode: 1985Rise...66..226S Altcode: No abstract at ADS Title: Stray light determination in small sunspots. Authors: Sobotka, M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1977ASSL...65...96S Altcode: 1977nrst.conf...96S No abstract at ADS