Author name code: balthasar ADS astronomy entries on 2022-09-14 author:"Balthasar, Horst" ------------------------------------------------------------------------ Title: An Interactive Virtual Hiking Map for the Mars 2020 Perseverance Landing Site, Jezero Crater Authors: Walter, S. H. G.; Neu, D.; Gross, C.; Neesemann, A.; Balthasar, H.; Jaumann, R.; Postberg, F. Bibcode: 2022LPICo2678.1921W Altcode: We welcome you to explore the landing site of the Mars 2020 rover in an interactive hiking map loaded with orbital imagery, terrain data, and 3D panoramic views! Title: Observational evidence for two-component distributions describing solar magnetic bright points Authors: Berrios Saavedra, Gerardine; Utz, Dominik; Vargas Domínguez, Santiago; Campos Rozo, José Iván; González Manrique, Sergio Javier; Gömöry, Peter; Kuckein, Christoph; Balthasar, Horst; Zelina, Peter Bibcode: 2022A&A...657A..79B Altcode: 2021arXiv211012404B Context. High-resolution observations of the solar photosphere reveal the presence of fine structures, in particular the so-called Magnetic Bright Points (MBPs), which are small-scale features associated with strong magnetic field regions of the order of kilogauss (kG). It is especially relevant to study these magnetic elements, which are extensively detected in all moments during the solar cycle, in order to establish their contribution to the behavior of the solar atmosphere, and ultimately a plausible role within the coronal heating problem.
Aims: Characterisation of size and velocity distributions of MBPs in the solar photosphere in two different datasets of quiet Sun images acquired with high-resolution solar instruments i.e. Solar Optical Telescope SOT/Hinode and the High-resolution Fast Imager HiFI/GREGOR, in the G-band (4308 Å).
Methods: In order to detect the MBPs, an automatic segmentation and identification algorithm is used. Next, the identified features were tracked to measure their proper motions. Finally, a statistical analysis of hundreds of MBPs is carried out, generating histograms for areas, diameters and horizontal velocities.
Results: This work establishes that areas and diameters of MBPs display log-normal distributions that are well-fitted by two different components, whereas the velocity vector components follow Gaussians and the vector magnitude a Rayleigh distribution revealing again for all vector elements a two component composition.
Conclusions: The results can be interpreted as due to the presence of two different populations of MBPs in the solar photosphere one likely related to stronger network magnetic flux elements and the other one to weaker intranetwork flux elemens. In particular this work concludes on the effect of the different spatial resolution of GREGOR and Hinode telescopes, affecting detections and average values. Title: Velocity Difference of Ions and Neutrals in Solar Prominences Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H.; Bianda, M. Bibcode: 2021ApJ...920...47W Altcode: 2021arXiv210813103W Marked velocity excesses of ions relative to neutrals are obtained from two time series of the neighboring emission lines He I 5015 Å and Fe II 5018 Å in a quiescent prominence. Their Doppler shifts show time variations of quasi-periodic character where the ions are faster than the neutrals, 1.0 ≤ Vmacro(Fe II)/Vmacro(He I) ≤ 1.35 in series A and ≤1.25 in series B. This "ratio excess" confirms our earlier findings of a 1.22 ion velocity excess, but the present study shows a restriction in space and time of typically 5 Mm and 5 minutes. The ratio excess is superposed by a time- and velocity-independent "difference excess" of -0.3 ≤ Vmacro(Fe II)-Vmacro(He I) ≤ +0.7 km s-1 in series A (also indicated in series B). The high repetition rate of 3.9 s enables the detection of high-frequency oscillations with several damped 22 s periods in series A. These show a ratio excess with a maximum of 1.7. We confirm the absence of a significant phase delay of He neutrals with respect to the Fe ions. 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: Properties of the inner penumbra boundary and temporal evolution of a decaying sunspot (Corrigendum) Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry, P.; Kuckein, C.; Jurčák, J. Bibcode: 2021A&A...652C...7B Altcode: No abstract at ADS Title: Evidence For Two-component Distributions Describing Magnetic Bright Points In The Solar Photosphere Authors: Vargas Domínguez, S.; Berrios Saavedra, G.; Utz, D.; Campos Rozo, J. I.; González Manrique, S.; Gömöry, Peter; Kuckein, Christoph; Balthasar, Horst; Zelina, Peter Bibcode: 2021AAS...23811310V Altcode: High-resolution observations of the Sun reveal the presence of Magnetic Bright Points (MBPs), which are small-scale features associated with strong magnetic field regions, that are found all over the solar photosphere. In this work, we characterize some physical properties and dynamics of MBPs in a quiet Sun region by using time series of images acquired with the High-resolution Fast Imager HiFI/GREGOR and Solar Optical Telescope SOT/Hinode in the G-band (4308 Angstrom). An automated segmentation algorithm is used to identify the MBPs and track their evolution. The results show observational evidence for two-component distributions of areas, diameters and velocities, that can be interpreted as corresponding to different populations of MBPs. Title: High-Precision Topographic Map of the Mars 2020 Landing Site as Part of the MC-13E Syrtis Major Quadrangle Digital Terrain Model. Authors: Neesemann, A.; Walter, S. H. G.; Gross, C.; Jaumann, R.; Gwinner, K.; Michael, G. G.; Schreiner, B. P.; Zuschneid, W.; Neu, D.; Balthasar, H.; Rabethge, C.; Riedel, C.; Kersten, E.; Tirsch, D. Bibcode: 2021LPI....52.2509N Altcode: For more than 17 years, the HRSC on board Mars Express has acquired image data of the Red Planet on a global scale and at high resolution. Here, we present the only recently finished MC-13E Syrtis Major HRSC-based DTM covering the Mars 2020 Perseverance rover landing site. Title: Looking Back to 17 Successful Years of High Resolution Stereo Camera Image Release on ESA's Mars Express Mission Authors: Gross, C.; Balthasar, H.; Dumke, A.; Neu, D.; Schreiner, B.; Walter, S.; Jaumann, R. Bibcode: 2021LPI....52.1480G Altcode: During the past 17 years, the experiment has collected image data from more than 21.000 orbits, resulting in a steadily increasing set of image, mosaic, and movie releases. Altogether more than 1.273 high quality image PR products have been created. Title: Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke, Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert; Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S. Bibcode: 2021ApJ...907...54V Altcode: 2020arXiv201113214V The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions. 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 an Erupting Minifilament and Its Impact on the Nearby Chromosphere Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein, C.; Balthasar, H.; Denker, C. Bibcode: 2020ApJ...898..144K Altcode: 2020arXiv200701564K We study the evolution of a minifilament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high spectral resolution imaging spectroscopy in Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope, Tenerife, Spain; photospheric magnetic field observations from the Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. The Hα line profiles were noise-stripped using principal component analysis and then inverted to produce physical and cloud model parameter maps. The minifilament formed between small-scale, opposite-polarity magnetic features through a series of small reconnection events, and it erupted within an hour after its appearance in Hα. Its development and eruption exhibited similarities to large-scale erupting filaments, indicating the action of common mechanisms. Its eruption took place in two phases, namely, a slow rise and a fast expansion, and it produced a coronal dimming, before the minifilament disappeared. During its eruption, we detected a complicated velocity pattern, indicative of a twisted, thread-like structure. Part of its material returned to the chromosphere, producing observable effects on nearby low-lying magnetic structures. Cloud model analysis showed that the minifilament was initially similar to other chromospheric fine structures, in terms of optical depth, source function, and Doppler width, but it resembled a large-scale filament on its course to eruption. High spectral resolution observations of the chromosphere can provide a wealth of information regarding the dynamics and properties of minifilaments and their interactions with the surrounding atmosphere. 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: HRSC on Mars Express - Imaging for Public Outreach: Global Colour Mars View Authors: Schreiner, B. P.; Neu, D.; Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael, G. G. Bibcode: 2020LPI....51.2437S Altcode: Based on HRSC colour data, a single orbit global Mars view is presented. Title: The magnetic structure and dynamics of a decaying active region Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar, Horst; Denker, Carsten Bibcode: 2020IAUS..354...53K Altcode: We study the evolution of the decaying active region NOAA 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph (GRIS), spectral imaging time-series in the Na ID2 spectral line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context imaging in the Ca IIH and blue continuum by the High-resolution Fast Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) complements our dataset. The region under study contains one pore with a light-bridge, a few micro-pores and extended clusters of magnetic bright points. We study the magnetic structure from the photosphere up to the upper chromosphere through the spectropolarimetric observations in He II and Si I and through the magnetograms provided by the Helioseismic and Magnetic Imager (HMI). The high-resolution photospheric images reveal the complex interaction between granular-scale convective motions and a range of scales of magnetic field concentrations in unprecedented detail. The pore itself shows a strong interaction with the convective motions, which eventually leads to its decay, while, under the influence of the photospheric flow field, micro-pores appear and disappear. Compressible waves are generated, which are guided towards the upper atmosphere along the magnetic field lines of the various magnetic structures within the field-of-view. Modelling of the He i absorption profiles reveals high velocity components, mostly associated with magnetic bright points at the periphery of the active region, many of which correspond to asymmetric Si I Stokes-V profiles revealing a coupling between upper photospheric and upper chromospheric dynamics. Time-series of Na ID2 spectral images reveal episodic high velocity components at the same locations. State-of-the-art multi-wavelength GREGOR observations allow us to track and understand the mechanisms at work during the decay phase of the active region. Title: Coordinated observations between China and Europe to follow active region 12709 Authors: González Manrique, S. J.; Kuckein, C.; Gömöry, P.; Yuan, S.; Xu, Z.; Rybák, J.; Balthasar, H.; Schwartz, P. Bibcode: 2020IAUS..354...58G Altcode: 2020IAUS..354...58M; 2019arXiv191208611G We present the first images of a coordinated campaign to follow active region NOAA 12709 on 2018 May 13 as part of a joint effort between three observatories (China-Europe). The active region was close to disk center and enclosed a small pore, a tight polarity inversion line and a filament in the chromosphere. The active region was observed with the 1.5-meter GREGOR solar telescope on Tenerife (Spain) with spectropolarimetry using GRIS in the He i 10830 Å spectral range and with HiFI using two broad-band filter channels. In addition, the Lomnicky Stit Observatory (LSO, Slovakia) recorded the same active region with the new Solar Chromospheric Detector (SCD) in spectroscopic mode at Hα 6562 Å. The third ground-based telescope was located at the Fuxian Solar Observatory (China), where the active region was observed with the 1-meter New Vacuum Solar Telescope (NVST), using the Multi-Channel High Resolution Imaging System at Hα 6562 Å. Overlapping images of the active region from all three telescopes will be shown as well as preliminary Doppler line-of-sight (LOS) velocities. The potential of such observations are discussed. Title: Revisiting the building blocks of solar magnetic fields by GREGOR Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván; González Manrique, Sergio Javier; Balthasar, Horst; Gömöry, Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu; Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke, Andrea Bibcode: 2020IAUS..354...38U Altcode: The Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide range of spatial and temporal scales, starting on the larger end with active regions harbouring complex sunspots, via isolated pores, down to the smallest yet resolved elements - so-called magnetic bright points (MBPs). Here, we revisit the various manifestations of solar magnetic fields by the largest European solar telescope in operation, the 1.5-meter GREGOR telescope. We show images from the High-resolution Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS). Besides, we outline resolved convective features inside the larger structures - so-called light-bridges occurring on large to mid-sized scales. Title: Polarimetry with the GREGOR Fabry-Pérot Interferometer Authors: Balthasar, H.; Gisler, D.; González Manrique, S. J.; Kuckein, C.; Verma, M.; Denker, C. Bibcode: 2019spw..confE...3B Altcode: No abstract at ADS 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: 15 Years High Resolution Stereo Camera Observations with ESA's Mars Express Mission Authors: Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael, G.; Neu, D.; Schreiner, B.; Jaumann, R. Bibcode: 2019LPI....50.1537M Altcode: Within the last 15 years, HRSC has delivered a large quantity of images that build the basis for mosaic generation. Title: HRSC on Mars Express - Image Mosaicking for Public Outreach: Korolev Crater Authors: Schreiner, B. P.; Neu, D.; Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael, G. G. Bibcode: 2019LPI....50.2735S Altcode: Public outreach image mosaic of Korolev Crater and volume estimation of ice filling. Title: Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry, P.; Kuckein, C.; Jurčák, J. Bibcode: 2018A&A...620A.191B Altcode: 2018arXiv181013185B Context. It has been empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field.
Aims: We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28-September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to prove the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots.
Methods: A spectral-line inversion technique was used to infer the magnetic field vector from the full-Stokes profiles. In total, eight maps were inverted and the variation of the magnetic properties in time were quantified using linear or quadratic fits.
Results: We find a linear decay of the umbral vertical magnetic field, magnetic flux, and area. The penumbra showed a linear increase of the vertical magnetic field and a sharp decay of the magnetic flux. In addition, the penumbral area quadratically decayed. The vertical component of the magnetic field is weaker on the umbra-penumbra boundary of the studied decaying sunspot compared to stable sunspots. Its value seem to be steadily decreasing during the decay phase. Moreover, at any time of the sunspot decay shown, the inner penumbra boundary does not match with a constant value of the vertical magnetic field, contrary to what is seen in stable sunspots.
Conclusions: During the decaying phase of the studied sunspot, the umbra does not have a sufficiently strong vertical component of the magnetic field and is thus unstable and prone to be disintegrated by convection or magnetic diffusion. No constant value of the vertical magnetic field is found for the inner penumbral boundary. Title: sTools - a software package for data reduction of GREGOR instruments and general data analysis Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva, Ekaterina; Kontogiannis, Ioannis; Shen, Zili Bibcode: 2018csc..confE.105K Altcode: The optical solar physics group at AIP is responsible for the GREGOR Fabry-Perot Interferometer (GFPI) and the large-format facility cameras (Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI)) at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since the »Early Science Phase« of the telescope in 2014, the group developed a data reduction pipeline for these two instruments. The pipeline »sTools« is based on the Interactive Data Language (IDL) and delivers reduced and image-restored data with a minimum of user interaction. Furthermore, it creates quick-look data and builds a webpage with an overview of the observations and their statistics (http://gregor.aip.de). However, during the last years, sTools continuously evolved and currently hosts many additional routines for data analysis: (1) A local correlation tracking (LCT) algorithm adapted for both high-resolution (GREGOR and Hinode) and synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e., a Background-subtracted Solar Activity Map (BaSAM), to assess and visualize the temporal variation of the photospheric magnetic field and the EUV 160 nm intensity. This method utilizes SDO data and is applicable to both full-disk observations and regions-of-interest. (3) Calibration of synoptic full-disk data from the Chromospheric Telescope (ChroTel) including extraction of Doppler velocities from He I 1083 nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed under a creative commons license and is freely available, after registration, at the abovementioned website. Title: Temporal evolution of arch filaments as seen in He I 10 830 Å Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker, C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg, A.; Diercke, A. Bibcode: 2018A&A...617A..55G Altcode: 2018arXiv180700728G
Aims: We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them.
Methods: We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS.
Results: We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 Å triplet. The arch filament expanded in height and extended in length from 13″ to 21″. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s-1. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s-1 in the chromosphere. The temporal evolution of He I 10 830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time.
Conclusions: We followed the arch filament as it carried plasma during its rise from the photosphere to the corona. The material then drained toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and aids in improving future models.

The movie associated to Fig. 3 is available at https://www.aanda.org/ Title: The Problem of the Height Dependence of Magnetic Fields in Sunspots Authors: Balthasar, Horst Bibcode: 2018SoPh..293..120B Altcode: 2018arXiv180806426B To understand the physics of sunspots, it is important to know the properties of their magnetic field, and especially its height stratification plays a substantial role. There are mainly two methods to assess this stratification, but they yield different magnetic gradients in the photospheric layers. Determinations based on the several spectral lines of different formation heights and the slope of their profiles result in gradients of −2 to −3 G km−1, or even steeper. This is similar for the total magnetic field strength and for the vertical component of the magnetic field. The other option is to determine the horizontal partial derivatives of the magnetic field, and with the condition divB =0 also the vertical derivative is known. With this method, gradients of −0.5 G km−1 and even shallower are obtained. Obviously, these results do not agree. If chromospheric spectral lines are included, only shallow gradients around −0.5 G km−1 are obtained. Shallow gradients are also found from gyro-resonance measurements in the radio wave range 300 - 2000 GHz. 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: High-cadence Imaging and Imaging Spectroscopy at the GREGOR Solar Telescope—A Collaborative Research Environment for High-resolution Solar Physics Authors: Denker, Carsten; Kuckein, Christoph; Verma, Meetu; González Manrique, Sergio J.; Diercke, Andrea; Enke, Harry; Klar, Jochen; Balthasar, Horst; Louis, Rohan E.; Dineva, Ekaterina Bibcode: 2018ApJS..236....5D Altcode: 2018arXiv180210146D In high-resolution solar physics, the volume and complexity of photometric, spectroscopic, and polarimetric ground-based data significantly increased in the last decade, reaching data acquisition rates of terabytes per hour. This is driven by the desire to capture fast processes on the Sun and the necessity for short exposure times “freezing” the atmospheric seeing, thus enabling ex post facto image restoration. Consequently, large-format and high-cadence detectors are nowadays used in solar observations to facilitate image restoration. Based on our experience during the “early science” phase with the 1.5 m GREGOR solar telescope (2014-2015) and the subsequent transition to routine observations in 2016, we describe data collection and data management tailored toward image restoration and imaging spectroscopy. We outline our approaches regarding data processing, analysis, and archiving for two of GREGOR’s post-focus instruments (see http://gregor.aip.de), i.e., the GREGOR Fabry-Pérot Interferometer (GFPI) and the newly installed High-Resolution Fast Imager (HiFI). The heterogeneous and complex nature of multidimensional data arising from high-resolution solar observations provides an intriguing but also a challenging example for “big data” in astronomy. The big data challenge has two aspects: (1) establishing a workflow for publishing the data for the whole community and beyond and (2) creating a collaborative research environment (CRE), where computationally intense data and postprocessing tools are colocated and collaborative work is enabled for scientists of multiple institutes. This requires either collaboration with a data center or frameworks and databases capable of dealing with huge data sets based on virtual observatory (VO) and other community standards and procedures. Title: Image Quality in High-resolution and High-cadence Solar Imaging Authors: Denker, C.; Dineva, E.; Balthasar, H.; Verma, M.; Kuckein, C.; Diercke, A.; González Manrique, S. J. Bibcode: 2018SoPh..293...44D Altcode: 2018arXiv180200760D Broad-band imaging and even imaging with a moderate bandpass (about 1 nm) provides a photon-rich environment, where frame selection (lucky imaging) becomes a helpful tool in image restoration, allowing us to perform a cost-benefit analysis on how to design observing sequences for imaging with high spatial resolution in combination with real-time correction provided by an adaptive optics (AO) system. This study presents high-cadence (160 Hz) G-band and blue continuum image sequences obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter GREGOR solar telescope, where the speckle-masking technique is used to restore images with nearly diffraction-limited resolution. The HiFI employs two synchronized large-format and high-cadence sCMOS detectors. The median filter gradient similarity (MFGS) image-quality metric is applied, among others, to AO-corrected image sequences of a pore and a small sunspot observed on 2017 June 4 and 5. A small region of interest, which was selected for fast-imaging performance, covered these contrast-rich features and their neighborhood, which were part of Active Region NOAA 12661. Modifications of the MFGS algorithm uncover the field- and structure-dependency of this image-quality metric. However, MFGS still remains a good choice for determining image quality without a priori knowledge, which is an important characteristic when classifying the huge number of high-resolution images contained in data archives. In addition, this investigation demonstrates that a fast cadence and millisecond exposure times are still insufficient to reach the coherence time of daytime seeing. Nonetheless, the analysis shows that data acquisition rates exceeding 50 Hz are required to capture a substantial fraction of the best seeing moments, significantly boosting the performance of post-facto image restoration. 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: sTools - a data reduction pipeline for the GREGOR Fabry-Pérot Interferometer and the High-resolution Fast Imager at the GREGOR solar telescope Authors: Kuckein, C.; Denker, C.; Verma, M.; Balthasar, H.; González Manrique, S. J.; Louis, R. E.; Diercke, A. Bibcode: 2017IAUS..327...20K Altcode: 2017arXiv170101670K A huge amount of data has been acquired with the GREGOR Fabry-Pérot Interferometer (GFPI), large-format facility cameras, and since 2016 with the High-resolution Fast Imager (HiFI). These data are processed in standardized procedures with the aim of providing science-ready data for the solar physics community. For this purpose, we have developed a user-friendly data reduction pipeline called ``sTools'' based on the Interactive Data Language (IDL) and licensed under creative commons license. The pipeline delivers reduced and image-reconstructed data with a minimum of user interaction. Furthermore, quick-look data are generated as well as a webpage with an overview of the observations and their statistics. All the processed data are stored online at the GREGOR GFPI and HiFI data archive of the Leibniz Institute for Astrophysics Potsdam (AIP). The principles of the pipeline are presented together with selected high-resolution spectral scans and images processed with sTools. 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: Flare-induced changes of the photospheric magnetic field in a δ-spot deduced from ground-based observations Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Veronig, A. M.; González Manrique, S. J.; Kučera, A.; Schwartz, P.; Hanslmeier, A. Bibcode: 2017A&A...602A..60G Altcode: 2017arXiv170406089G
Aims: Changes of the magnetic field and the line-of-sight velocities in the photosphere are being reported for an M-class flare that originated at a δ-spot belonging to active region NOAA 11865.
Methods: High-resolution ground-based near-infrared spectropolarimetric observations were acquired simultaneously in two photospheric spectral lines, Fe I 10783 Å and Si I 10786 Å, with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope (VTT) in Tenerife on 2013 October 15. The observations covered several stages of the M-class flare. Inversions of the full-Stokes vector of both lines were carried out and the results were put into context using (extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory (SDO).
Results: The active region showed high flaring activity during the whole observing period. After the M-class flare, the longitudinal magnetic field did not show significant changes along the polarity inversion line (PIL). However, an enhancement of the transverse magnetic field of approximately 550 G was found that bridges the PIL and connects umbrae of opposite polarities in the δ-spot. At the same time, a newly formed system of loops appeared co-spatially in the corona as seen in 171 Å filtergrams of the Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot exclude that the magnetic connection between the umbrae already existed in the upper atmosphere before the M-class flare and became visible only later when it was filled with hot plasma. The photospheric Doppler velocities show a persistent upflow pattern along the PIL without significant changes due to the flare.
Conclusions: The increase of the transverse component of the magnetic field after the flare together with the newly formed loop system in the corona support recent predictions of flare models and flare observations.

The movie associated to Figs. 4 and 5 is available at http://www.aanda.org 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: Flare induced changes of the photospheric magnetic field in a delta-spot deduced from ground-based observations Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Kuĉera, A.; González Manrique, S. J.; Schwartz, P.; Veronig, A. M.; Hanslmeier, A. Bibcode: 2017psio.confE.107G Altcode: No abstract at ADS 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: NLTE modeling of a small active region filament observed with the VTT Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry, P.; Rybák, J.; Heinzel, P.; Kučera, A. Bibcode: 2016AN....337.1045S Altcode: An active region mini-discretionary-filament was observed with the Vacuum Tower Telescope (VTT) in Tenerife simultaneously in the He I infrared triplet using the Tenerife Infrared Polarimeter 1 (TIP 1), in Hα with the TESOS Fabry-Pérot interferometer, and in Ca II 8542 Å with the VTT spectrograph. The spectropolarimetric data were inverted using the HAZEL code and Hα profiles were modelled by solving a NLTE radiative transfer in a simple isobaric and isothermal 2D slab irradiated both from its bottom and sides from the solar surface. It was found that the mini-discretionary-filament is composed of horizontal fluxtubes, along which the cool plasma of T∼10 000 K can flow with very large, even supersonic, velocities. 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: 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: 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: 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: Non-LTE Inversion of Spectropolarimetric and Spectroscopic Observations of a Small Active-region Filament Observed at the VTT Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry, P.; Rybák, J.; Kučera, A.; Heinzel, P. Bibcode: 2016ASPC..504..205S Altcode: An active region mini-filament was observed by VTT simultaneously in the He<small>I</small> 10 830 Å triplet by the TIP 1 spectropolarimeter, in Hα by the TESOS Fabry-Pérot interferometer, and in Ca <small>II</small> 8542 Å by the VTT spectrograph. The spectropolarimetric data were inverted using the HAZEL code and Hα profiles were modelled solving a NLTE radiative transfer in a simple isobaric and isothermal 2D slab irradiated both from bottom and sides. It was found that the mini-filament is composed of horizontal fluxtubes, along which the cool plasma of T∼10 000 K can flow by very large - even supersonic - velocities. 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: 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: The Magnetic Configuration of a δ-Spot Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C. Bibcode: 2014ASPC..489...39B Altcode: 2013arXiv1312.5128B Sunspots, which harbor both magnetic polarities within one penumbra, are called δ-spots. They are often associated with flares. Nevertheless, there are only very few detailed observations of the spatially resolved magnetic field configuration. We present an investigation performed with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope in Tenerife. We observed a sunspot with a main umbra and several additional umbral cores, one of them with opposite magnetic polarity (the δ-umbra). The δ-spot is divided into two parts by a line along which central emissions of the spectral line Ca <font size=2>II 854.2 nm appear. The Evershed flow comming from the main umbra ends at this line. In deep photospheric layers, we find an almost vertical magnetic field for the δ-umbra, and the magnetic field decreases rapidly with height, faster than in the main umbra. The horizontal magnetic field in the direction connecting main and δ-umbra is rather smooth, but in one location next to a bright penumbral feature at some distance to the δ-umbra, we encounter a change of the magnetic azimuth by 90° from one pixel to the next. Near the δ-umbra, but just outside, we encounter a blue-shift of the spectral line profiles which we interpret as Evershed flow away from the δ-umbra. Significant electric current densities are observed at the dividing line of the spot and inside the δ-umbra. Title: Overview of Outreach Activities of the Planetary Sciences and Remote Sensing Group at Freie Universität Berlin Authors: Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael, G.; Neu, D.; Platz, T.; Rosenberg, H.; Schreiner, B.; Walter, S. H. G.; van Gasselt, S. Bibcode: 2014EPSC....9..545M Altcode: Planetary Sciences teach us how special our homeplanet is in the solar system. Incorporating a broad variety of natural science topics they count to the most fundamental branches of scientific research with a strong interdisciplinary character. However, since planetary sciences are not a school subject, children as well as adults are often lacking an overall awareness and understanding of that field. The mission of planetary education has to be fulfilled by research institutions. With several platforms and activities our group is engaged to address this topic. The Planetary Sciences and Remote Sensing Group at Freie Universität Berlin (FUB) is involved in space missions such as Mars Express with the High Resolution Stereo Camera (HRSC), Cassini to Saturn, and Dawn to the asteroids Vesta and Ceres. Moreover, we participate in developing a planetary X-ray fluorescence spectrometer. Information of our planetary research activities can be found on our institutes website [1]. Our outreach activities include press releases, an image download hub, permanent and special exhibition support, 3D-HD-animation production, science fairs, workshops, hands-on courses, public talks at observatories and schools, as well as media appearances in radio, press and TV. Title: High Resolution Stereo Camera (HRSC) on Mars Express — A Decade of PR/EO Activities at Freie Universität Berlin Authors: Balthasar, H.; Musiol, S.; van Gasselt, S.; PR Team Bibcode: 2014LPI....45.2099B Altcode: The Planetary Sciences and Remote Sensing Group supports web-based data access and educational outreach events for HRSC data dissemination. Title: The association between sunspot magnetic fields and superpenumbral fibrils Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.; Puschmann, K. G.; Denker, C. Bibcode: 2014AN....335..161L Altcode: 2013arXiv1312.1879L Spectropolarimetric observations of a sunspot were carried out with the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife, Spain. Maps of the physical parameters were obtained from an inversion of the Stokes profiles observed in the infrared Fe I line at 15 648 Å. The regular sunspot consisted of a light bridge which separated the two umbral cores of the same polarity. One of the arms of the light bridge formed an extension of a penumbral filament which comprised weak and highly inclined magnetic fields. In addition, the Stokes V profiles in this filament had an opposite sign as the sunspot and some resembled Stokes Q or U. This penumbral filament terminated abruptly into another at the edge of the sunspot, where the latter was relatively vertical by about 30o. Chromospheric H\alpha and He II 304 Åfiltergrams revealed three superpenumbral fibrils on the limb-side of the sunspot, in which one fibril extended into the sunspot and was oriented along the highly inclined penumbral counterpart of the light bridge. An intense, elongated brightening was observed along this fibril that was co-spatial with the intersecting penumbral filaments in the photosphere. Our results suggest that the disruption in the sunspot magnetic field at the location of the light bridge could be the source of reconnection that led to the intense chromospheric brightening and facilitated the supply of cool material in maintaining the overlying superpenumbral fibrils. Title: Near-infrared spectropolarimetry of a δ-spot Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C. Bibcode: 2014A&A...562L...6B Altcode: 2014arXiv1401.4386B Sunspots harboring umbrae of both magnetic polarities within a common penumbra (δ-spots) are often but not always related to flares. We present first near-infrared observations (Fe i λ1078.3 nm and Si i λ1078.6 nm spectra) obtained with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope in Tenerife on 2012 June 17, which afford accurate and sensitive diagnostics to scrutinize the complex fields along the magnetic neutral line of a δ-spot within active region NOAA 11504. We examined the vector magnetic field, line-of-sight (LOS) velocities, and horizontal proper motions of this rather inactive δ-spot. We find a smooth transition of the magnetic vector field from the main umbra to that of opposite polarity (δ-umbra), but a discontinuity of the horizontal magnetic field at some distance from the δ-umbra on the polarity inversion line. The magnetic field decreases faster with height by a factor of two above the δ-umbra. The latter is surrounded by its own Evershed flow. The Evershed flow coming from the main umbra ends at a line dividing the spot into two parts. This line is marked by the occurrence of central emission in the Ca iiλ854.2 nm line. Along this line, high chromospheric LOS-velocities of both signs appear. We detect a shear flow within the horizontal flux transport velocities parallel to the dividing line. Title: Sunspot splitting triggering an eruptive flare Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard; Balthasar, Horst; Denker, Carsten Bibcode: 2014A&A...562A.110L Altcode: 2013arXiv1311.5054L
Aims: We investigate how the splitting of the leading sunspot and associated flux emergence and cancellation in active region NOAA 11515 caused an eruptive M5.6 flare on 2012 July 2.
Methods: Continuum intensity, line-of-sight magnetogram, and dopplergram data of the Helioseismic and Magnetic Imager were employed to analyse the photospheric evolution. Filtergrams in Hα and He I 10830 Å of the Chromospheric Telescope at the Observatorio del Teide, Tenerife, track the evolution of the flare. The corresponding coronal conditions were derived from 171 Å and 304 Å images of the Atmospheric Imaging Assembly. Local correlation tracking was utilized to determine shear flows.
Results: Emerging flux formed a neutral line ahead of the leading sunspot and new satellite spots. The sunspot splitting caused a long-lasting flow towards this neutral line, where a filament formed. Further flux emergence, partly of mixed polarity, as well as episodes of flux cancellation occurred repeatedly at the neutral line. Following a nearby C-class precursor flare with signs of interaction with the filament, the filament erupted nearly simultaneously with the onset of the M5.6 flare and evolved into a coronal mass ejection. The sunspot stretched without forming a light bridge, splitting unusually fast (within about a day, complete ≈6 h after the eruption) in two nearly equal parts. The front part separated strongly from the active region to approach the neighbouring active region where all its coronal magnetic connections were rooted. It also rotated rapidly (by 4.9° h-1) and caused significant shear flows at its edge.
Conclusions: The eruption resulted from a complex sequence of processes in the (sub-)photosphere and corona. The persistent flows towards the neutral line likely caused the formation of a flux rope that held the filament. These flows, their associated flux cancellation, the emerging flux, and the precursor flare all contributed to the destabilization of the flux rope. We interpret the sunspot splitting as the separation of two flux bundles differently rooted in the convection zone and only temporarily joined in the spot. This explains the rotation as the continued rise of the separating flux, and it implies that at least this part of the sunspot was still connected to its roots deep in the convection zone.

Movie available in electronic form at http://www.aanda.org Title: GREGOR Fabry-Pérot interferometer and its companion the blue imaging solar spectrometer Authors: Puschmann, Klaus G.; Denker, Carsten; Balthasar, Horst; Louis, Rohan E.; Popow, Emil; Woche, Manfred; Beck, Christian; Seelemann, Thomas; Volkmer, Reiner Bibcode: 2013OptEn..52h1606P Altcode: 2013arXiv1302.7157P The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-m GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and postfactum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectrometric and spectropolarimetric observations between 530-860 nm and 580-660 nm, respectively, and possesses a theoretical spectral resolution of R≈250,000. Large-format, high-cadence charged coupled device detectors with sophisticated computer hard- and software enable the scanning of spectral lines in time-spans equivalent to the evolution time of solar features. The field-of-view (FOV) of 50″×38″ covers a significant fraction of the typical area of active regions in the spectroscopic mode. In case of Stokes-vector spectropolarimetry, the FOV reduces to 25″×38″. The main characteristics of the GFPI including advanced and automated calibration and observing procedures are presented. Improvements in the optical design of the instrument are discussed and first observational results are shown. Finally, the first concrete ideas for the integration of a second FPI, the blue imaging solar spectrometer, are laid out, which will explore the blue spectral region below 530 nm. Title: Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop Authors: Gömöry, P.; Balthasar, H.; Puschmann, K. G. Bibcode: 2013A&A...556A...7G Altcode: 2013arXiv1306.3393G
Aims: We investigate the temporal evolution of magnetic flux emergence in the quiet-Sun atmosphere close to disk center.
Methods: We combined high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 Å channel to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere.
Results: We find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appeared first in the MDI magnetograms in form of an asymmetric bipolar element, i.e., the patch with negative polarity is roughly twice as weak as the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reached 1.6 × 1018 Mx, - 8.5 × 1017 Mx, and 55 Mx cm-2, -30 Mx cm-2, respectively. The spatial distance between the opposite polarity patches of the emerged feature increased from about 2.″5 to 5.″0 during the lifetime of the loop, which was 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurred ~9 min later than in the photospheric magnetograms. It consisted of a quasi-periodic sequence of time-localized brightenings visible in the 1216 Å TRACE channel for ~14 min that were co-spatial with the axis connecting the two patches of opposite magnetic polarity.
Conclusions: We identify the observed event as a small-scale magnetic loop emerging at photospheric layers that subsequently rose to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magnetic-field oscillations which propagate to the chromosphere in the form of waves. Title: Formation of a penumbra in a decaying sunspot Authors: Louis, R. E.; Mathew, S. K.; Puschmann, K. G.; Beck, C.; Balthasar, H. Bibcode: 2013A&A...552L...7L Altcode: 2013arXiv1303.3599L Context. Penumbrae are an important characteristic of sunspots, whose formation is intricately related to the nature of sub-photospheric magnetic fields.
Aims: We study the formation of a penumbra in a decaying sunspot and compare its properties with those seen during the development of a proto-spot.
Methods: High-resolution spectropolarimetric observations of active region NOAA 11283 were obtained from the spectro-polarimeter on board Hinode. These were complemented with full-disk filtergrams of continuum intensity, line-of-sight magnetograms, and dopplergrams from the Helioseismic and Magnetic Imager at high cadence.
Results: The formation of a penumbra in the decaying sunspot occurs after the coalescence of the sunspot with a magnetic fragment/pore, which initially formed in the quiet Sun close to an emerging flux region. At first, a smaller set of penumbral filaments develop near the location of the merger with very bright penumbral grains with intensities of 1.2 IQS, upflows of 4 km s-1, and a lifetime of 10 h. During the decay of these filaments, a larger segment of a penumbra forms at the location of the coalescence. These new filaments are characterized by nearly supersonic downflows of 6.5 km s-1 that change to a regular Evershed flow nearly 3 h later.
Conclusions: The coalescence of the pore with the decaying sunspot provided sufficient magnetic flux for the penumbra to form in the sunspot. The emerging flux region could have played a decisive role in this process because the formation occurred at the location of the merger and not on the opposite side of the sunspot.

An animation of the HMI data is available in electronic form at http://www.aanda.org Title: Properties of a Decaying Sunspot Authors: Balthasar, H.; Beck, C.; Gömöry, P.; Muglach, K.; Puschmann, K. G.; Shimizu, T.; Verma, M. Bibcode: 2013CEAB...37..435B Altcode: 2013arXiv1301.1562B A small decaying sunspot was observed with the Vacuum Tower Telescope (VTT) on Tenerife and the Japanese Hinode satellite. We obtained full Stokes scans in several wavelengths covering different heights in the solar atmosphere. Imaging time series from Hinode and the Solar Dynamics Observatory (SDO) complete our data sets. The spot is surrounded by a moat flow, which persists also on that side of the spot where the penumbra already had disappeared. Close to the spot, we find a chromospheric location with downflows of more than 10 km s^{-1} without photospheric counterpart. The height dependence of the vertical component of the magnetic field strength is determined in two different ways that yielded different results in previous investigations. Such a difference still exists in our present data, but it is not as pronounced as in the past. 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: The GREGOR Fabry-Pérot Interferometer: A New Instrument for High-Resolution Spectropolarimetric Solar Observations Authors: Puschmann, K. G.; Balthasar, H.; Bauer, S. -M.; Hahn, T.; Popow, E.; Seelemann, T.; Volkmer, R.; Woche, M.; Denker, C. Bibcode: 2012ASPC..463..423P Altcode: 2011arXiv1111.5509P Fabry-Pérot interferometers have advantages over slit spectrographs because they allow fast narrow-band imaging and post-factum image reconstruction of the retrieved data. Temperature, plasma velocity, and magnetic field maps can be derived from inversions of spectral lines, thus, advancing our understanding of the dynamic Sun and its magnetic fields at the smallest spatial scales. The GREGOR Fabry-Pérot Interferometer (GFPI) is one of two first-light instruments of the 1.5-meter GREGOR solar telescope, which is currently being commissioned at the Observatorio del Teide, Tenerife, Spain. The GFPI operates close to the diffraction limit of GREGOR, thus, providing access to fine structures as small as 60 km on the solar surface. The field-of-view of 52″×40″ is sufficiently large to cover significant area fraction of active regions. The GFPI is a tuneable dual-etalon system in a collimated mounting. Equipped with a full-Stokes polarimeter, it records spectropolarimetric data with a spectral resolution of R ≍ 250,000 over the wavelength range from 530-860 nm. Large-format, high-cadence CCD detectors with powerful computer hard- and software facilitate scanning of spectral lines in time spans corresponding to the evolution time-scale of solar features. We present the main characteristics of the GFPI including the latest developments in software, mechanical mounts, and optics. 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: The GREGOR polarimetric calibration unit Authors: Hofmann, A.; Arlt, K.; Balthasar, H.; Bauer, S. M.; Bittner, W.; Paschke, J.; Popow, E.; Rendtel, J.; Soltau, D.; Waldmann, T. Bibcode: 2012AN....333..854H Altcode: The new Solar telescope GREGOR is designed to observe small-scale dynamic magnetic structures below a size of 70 km on the Sun with high spectral resolution and polarimetric accuracy. For this purpose, the polarimetric concept of GREGOR is based on a combination of post-focus polarimeters with pre-focus equipment for high precision calibration. The Leibniz-Institute for Astrophysics Potsdam developed the GREGOR calibration unit which is an integral part of the telescope. We give an overview of the function and design of the calibration unit and present the results of extensive testing series done in the Solar Observatory ``Einsteinturm'' and at GREGOR. Title: The GREGOR Fabry-Pérot Interferometer Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.; Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados, M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.; Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer, R.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..880P Altcode: 2012arXiv1210.2921P The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution of R ≈ 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. Title: Spectral Inversion of Multiline Full-Disk Observations of Quiet Sun Magnetic Fields Authors: Balthasar, H.; Demidov, M. L. Bibcode: 2012SoPh..280..355B Altcode: 2012arXiv1203.4522B; 2012SoPh..tmp...80B Spectral inversion codes are powerful tools for analyzing spectropolarimetric observations, and they provide important diagnostics of solar magnetic fields. Inversion codes differ according to numerical procedure, approximation of the atmospheric model, and description of radiative transfer. Stokes Inversion based on Response functions (SIR) is an implementation widely used by the solar physics community. It allows one to work with different atmospheric components, where gradients of different physical parameters are possible, e.g., magnetic field strength and velocities. The spectropolarimetric full-disk observations were carried out with the Stokesmeter of the Solar Telescope for Operative Prediction (STOP) at the Sayan Observatory on 3 February 2009, when neither an active region nor any other extended flux concentration was present on the Sun. In this study of quiet Sun magnetic fields, we apply the SIR code simultaneously to 15 spectral lines. A tendency is found that weaker magnetic field strengths occur closer to the limb. We explain this finding by the fact that, close to the limb, we are more sensitive to higher altitudes in an expanding flux tube, where the field strength should be smaller since the magnetic flux is conserved with height. Typically, the inversions deliver two populations of magnetic elements: i) high magnetic field strengths (1500 - 2000 G) and high temperatures (5500 - 6500 K) and ii) weak magnetic fields (50 - 150 G) and low temperatures (5000 - 5300 K). Title: The GREGOR Fabry-Perot interferometer: status report and prospects Authors: Puschmann, Klaus G.; Balthasar, Horst; Beck, Christian; Louis, Rohan E.; Popow, Emil; Seelemann, Thomas; Volkmer, Reiner; Woche, Manfred; Denker, Carsten Bibcode: 2012SPIE.8446E..79P Altcode: 2012arXiv1207.2084P The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and post-factum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic Sun and its magnetic field at spatial scales down to 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530-860 nm with a theoretical spectral resolution of R ≍ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful computer hard- and software enable the scanning of spectral lines in time spans equivalent to the evolution time of solar features. The field-of-view of 50''×38'' covers a significant fraction of the typical area of active regions. We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer, which will explore the blue spectral region below 530 nm. Title: On Multi-Line Spectro-Polarimetric Diagnostics of the Quiet Sun's Magnetic Fields. Statistics, Inversion Results and Effects on the SOHO/MDI Magnetogram Calibration Authors: Demidov, M. L.; Balthasar, H. Bibcode: 2012SoPh..276...43D Altcode: On the long way to establish reliable physical properties of the solar atmosphere from different kinds of magnetic field measurement, significant progress has been achieved, but many important issues are still waiting for solution. This is essential for the investigation of weak magnetic fields of the quiet Sun, which usually cover most of the solar surface. Weak magnetic fields significantly contribute to the formation of the interplanetary magnetic field. The problem of reliable diagnostics of such fields hardly ever has a simple solution using only single spectral line observations. A better chance is given by multi-spectral line spectro-polarimetric observations, especially with lines having very different properties. In the present study, we use simultaneous high-precision Stokes-meter measurements of the quiet solar magnetic fields in 15 lines in the vicinity of Fe I 525.0 nm. These measurements cover the whole range of heliocentric distances. Magnetic field strength ratios of different spectral lines with respect to Fe I 525.0 nm vary between 1.07 and 2.12. This ratio depends also on the heliocentric position, moving closer to the limb it decreases and approaches values of about unity in most cases. To interpret the observations, different model approaches are compared. SIR-inversions (Stokes Inversion based on Response functions) with a two-component atmospheric model approach reproduce the basic observables much better than with one-component atmospheres. Our best fits are connected with field strengths of 1 - 2 kG and filling factors of less than five percent. To check the justification for the recent re-calibration of the data from the Michelson Doppler Imager (MDI) onboard SOHO, we carried out a numerical experiment, and we confirm our former conclusion that there is no need for such a re-calibration. Title: Horizontal flow fields observed in Hinode G-band images. II. Flow fields in the final stages of sunspot decay Authors: Verma, M.; Balthasar, H.; Deng, N.; Liu, C.; Shimizu, T.; Wang, H.; Denker, C. Bibcode: 2012A&A...538A.109V Altcode: 2011arXiv1112.1589V Context. Generation and dissipation of magnetic fields is a fundamental physical process on the Sun. In comparison to flux emergence and the initial stages of sunspot formation, the demise of sunspots still lacks a comprehensive description.
Aims: The evolution of sunspots is most commonly discussed in terms of their intensity and magnetic field. Here, we present additional information about the three-dimensional flow field in the vicinity of sunspots towards the end of their existence.
Methods: We present a subset of multi-wavelengths observations obtained with the Japanese Hinode mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the time period 2010 November 18-23. Horizontal proper motions were derived from G-band and Ca ii H images, whereas line-of-sight velocities were extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm spectral data of the Hinode/Spectro-Polarimeter, which also provided three-dimensional magnetic field information. The Helioseismic and Magnetic Imager on board SDO provided continuum images and line-of-sight magnetograms, in addition to the high-resolution observations for the entire disk passage of the active region.
Results: We perform a quantitative study of photospheric and chromospheric flow fields in and around decaying sunspots. In one of the trailing sunspots of active region NOAA 11126, we observe moat flow and moving magnetic features (MMFs), even after its penumbra had decayed. We also detect a superpenumbral structure around this pore. We find that MMFs follow well-defined, radial paths from the spot all the way to the border of a supergranular cell surrounding the spot. In contrast, flux emergence near the other sunspot prevents the establishment of similar well ordered flow patterns, which could be discerned around a tiny pore of merely 2 Mm diameter. After the disappearance of the sunspots/pores, a coherent patch of abnormal granulation remained at their location, which was characterized by more uniform horizontal proper motions, low divergence values, and smaller photospheric Doppler velocities. This region, thus, differs significantly from granulation and other areas covered by G-band bright points. We conclude that this peculiar flow pattern is a signature of sunspot decay and the dispersal of magnetic flux. Title: Polarimetry with GREGOR Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.; Soltau, D.; Volkmer, R. Bibcode: 2011ASPC..437..351B Altcode: A brief description of the new 1.5-meter solar telescope GREGOR located at the Observatorio del Teide in Tenerife will be given. GREGOR will provide a spatial resolution of about 75 km on the Sun, and with its light collecting capability we will be able to study the development of small magnetic features with high cadence. From the beginning, it will be equipped with the GREGOR Fabry-Pérot Interferometer (GFPI) for the visible spectral range and with a GRating Infrared Spectrograph (GRIS). Both postfocus instruments can be combined with a polarimeter, and in both cases the light is modulated by two ferro-electric liquid crystals. A calibration unit can be inserted to determine the instrumental polarization. Because of the altazimuthal mount, time-dependent rotation of the polarimetric reference plane is introduced, and we have to develop a polarization model of the telescope. Measurements to verify this model are in preparation. Title: On the Diagnostics of the Quiet Sun Magnetic Fields: Multi-Line Spectro-Polarimetric Observations and Inversion Results Authors: Demidov, M. L.; Balthasar, H. Bibcode: 2011ASPC..437..189D Altcode: Sophisticated diagnostics of the quiet Sun magnetic fields are a very important issue of modern solar physics because of the existence of their deep genetic connections with active regions. For this aim, we use high-precision spectro-polarimetric observations in about twenty spectral lines in an almost 3 nm wide spectral domain around the line Fe I 525.02 nm. These observations cover the whole solar disk. A detailed statistical analysis of magnetic strength ratios in different combinations of spectral lines is performed. For seven sufficiently strong Fe I lines observed at disk center, we applied the SIR code (Stokes Inversion based on Response functions). It was impossible to reproduce the Stokes I and V profiles of these selected lines simultaneously in the framework of models with only one atmospheric component. But a very good agreement between observations and inversion results was obtained for a model with two atmospheric components, one with magnetic field and the other without. Reliable values were found for the magnetic field strength and the filling factor. Title: On the diagnostics of the quiet Sun's magnetic fields: application of the SIR inversion to the full-disk Stokes-meter observations in 15 spectral lines Authors: Demidov, M. L.; Balthasar, H. Bibcode: 2011ASInC...2..169D Altcode: Although quiet solar magnetic fields are weak and they are difficult to measure, they cover most of the solar disk, even the whole one during epochs of minimal activity. They are basically responsible for the formation of the open flux from the Sun, and, consequently, reliable diagnostics of them are very important. In this study, we use a raster scan covering the whole solar disk of high precision Stokes-meter measurements of the quiet solar magnetic fields in 15 simultaneously recorded lines in the vicinity of Fe I 525.02 nm. A two-component model atmosphere and the SIR (Stokes Inversion based on Response functions) approach were used for theoretical modeling. Two types of inversion results were obtained for magnetic component: one with kG magnetic field strength, high temperature and small filling factor, and the other one with relatively weak magnetic field (no more then 200 G), low temperature and big filling factor. A possible explanation of such result is briefly discussed. An application of the obtained results for the urgent issue to calibrate SOHO/MDI magnetograms is presented. 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: The GREGOR Fabry-Perot interferometer: a new instrument for high-resolution solar observations Authors: Denker, Carsten; Balthasar, Horst; Hofmann, Axel; Bello González, Nazaret; Volkmer, Reiner Bibcode: 2010SPIE.7735E..6MD Altcode: 2010SPIE.7735E.217D The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of the first-light instruments of the 1.5-meter GREGOR solar telescope currently being commissioned at Observatorio del Teide (OT), Tenerife, Spain. A spectral resolution of R ~ 250, 000 over the wavelength range from 530-860 nm can be achieved using a tunable dual etalon system. A high spectral resolving power is needed to extract physical parameters (e.g., temperature, plasma velocity and the magnetic field vector) from inversions of photospheric and chromospheric spectral lines. The GFPI is outfitted with a polarimeter, which accurately measures the full Stokes vector. Precision polarimetry is facilitated by a calibration unit in the immediate vicinity of GREGOR's secondary focus. The GFPI operates close to the diffraction limit of GREGOR, thus providing access to fine structures as small as 60 km on the solar surface. The field-of-view (FOV) of 52" × 40" is sufficiently large to cover significant portions of active regions. Large-format, high-cadence CCD detectors are an integral part of the instrument to ensure that scans of spectral lines can be obtained in time spans corresponding to the evolution time scale of solar phenomena such as granulation, evolving magnetic fields or dynamic chromospheric features. Besides describing the technical features of the GFPI and providing a status report on commissioning the instrument, we will use two-dimensional spectropolarimetric data obtained with the Vacuum Tower Telescope (VTT) at OT to illustrate GFPI's science capabilities. 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: Magnetic loop emergence within a granule Authors: Gömöry, P.; Beck, C.; Balthasar, H.; Rybák, J.; Kučera, A.; Koza, J.; Wöhl, H. Bibcode: 2010A&A...511A..14G Altcode: 2009arXiv0910.4449G
Aims: We investigate the temporal evolution of magnetic flux emerging within a granule in the quiet-Sun internetwork at disk center.
Methods: We combined IR spectropolarimetry of high angular resolution performed in two Fe i lines at 1565 nm with speckle-reconstructed G-band imaging. We determined the magnetic field parameters by a LTE inversion of the full Stokes vector using the SIR code, and followed their evolution in time. To interpret the observations, we created a geometrical model of a rising loop in 3D. The relevant parameters of the loop were matched to the observations where possible. We then synthesized spectra from the 3D model for a comparison to the observations.
Results: We found signatures of magnetic flux emergence within a growing granule. In the early phases, a horizontal magnetic field with a distinct linear polarization signal dominated the emerging flux. Later on, two patches of opposite circular polarization signal appeared symmetrically on either side of the linear polarization patch, indicating a small loop-like structure. The mean magnetic flux density of this loop was roughly 450 G, with a total magnetic flux of around 3 × 1017 Mx. During the ~12 min episode of loop occurrence, the spatial extent of the loop increased from about 1 to 2 arcsec. The middle part of the appearing feature was blueshifted during its occurrence, supporting the scenario of an emerging loop. There is also clear evidence for the interaction of one loop footpoint with a preexisting magnetic structure of opposite polarity. The temporal evolution of the observed spectra is reproduced to first order by the spectra derived from the geometrical model. During the phase of clearest visibility of the loop in the observations, the observed and synthetic spectra match quantitatively.
Conclusions: The observed event can be explained as a case of flux emergence in the shape of a small-scale loop. The fast disappearance of the loop at the end could possibly be due to magnetic reconnection. Title: The three-dimensional structure of sunspots. II. The moat flow at two different heights Authors: Balthasar, H.; Muglach, K. Bibcode: 2010A&A...511A..67B Altcode: 2009arXiv0912.3661B
Aims: Many sunspots are surrounded by a radial outflow called the moat flow. We investigate the moat flow at two different heights of the solar atmosphere for a sunspot whose magnetic properties were reported in the first paper of this series.
Methods: We use two simultaneous time series taken with the Transition Region And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The field-of-view is centered on the small sunspot NOAA 10886 located near disk center. Horizontal velocities are derived by applying two different local correlation tracking techniques.
Results: Outflows are found everywhere in the moat. In the inner moat, the velocities from the UV series are larger than those from white light, whereas in the outer part of the moat we find the converse result.
Conclusions: The results imply that the white light velocities represent a general outflow of the quiet sun plasma in the moat, while UV velocities are dominated by small bright points that move faster than the general plasma flow. Title: Spectro-Polarimetric Observations of Solar Magnetic Fields and the SOHO/MDI Calibration Issue Authors: Demidov, M. L.; Balthasar, H. Bibcode: 2009SoPh..260..261D Altcode: 2009arXiv0908.2731D Comparisons of solar magnetic-field measurements made in different spectral lines are very important, especially in those lines in which observations have a long history or (and) specific diagnostic significance. The spectral lines Fe I 523.3 nm and Fe I 525.0 nm belong to this class. Therefore, this study is devoted to a comprehensive analysis using new high-precision Stokes-meter full-disk observations. The disk-averaged magnetic-field strength ratio R=B(523.3)/B(525.0) equals 1.97±0.02. The center-to-limb variation (CLV) is R=1.74−2.43μ+3.43μ2, where μ is the cosine of the center-to-limb angle. For the disk center, we find R=2.74, and for near-limb areas with μ=0.3, R equals 1.32. There is only a small dependence of R on the spatial resolution. Our results are rather close to those published three decades ago, but differ significantly from recent magnetographic observations. An application of our results to the important SOHO/MDI magnetic data calibration issue is discussed. We conclude that the revision of the SOHO/MDI data, based only on the comparison of magnetic-field measurements in the line pair Fe I 523.3 nm and Fe I 525.0 nm (increasing by a factor of 1.7 or 1.6 on average according to recent publications) is not obvious and new investigations are urgently needed. Title: An Extended Line-Ratio Method Application: Comparison of Large-Scale Solar Magnetic Field Observations in Different Spectral Lines and Observatories Authors: Demidov, M. L.; Golubeva, E. M.; Veretsky, R. M.; Balthasar, H. Bibcode: 2009ASPC..405..241D Altcode: We explore the distribution of the magnetic strength ratios (MSR) across the solar disk in different combinations of spectral lines and observatories. It was found that along with expected center-to-limb variations (CLV) of MSRs, there are significant polar-equatorial asymmetries of CLVs in some cases. The results of comparing the experimental MSR CLVs with 3D multi-ray theoretical simulations in the framework of two-component flux tubes models are presented. Title: The Height Dependence of the Magnetic Vector Field in Sunspots Authors: Balthasar, H.; Bommier, V. Bibcode: 2009ASPC..405..229B Altcode: A complex active region was observed simultaneously with the solar telescopes VTT and THEMIS on Tenrife in May 2005. Spatial scans across the sunspot group were performed at both telescopes. The full Stokes-vector was recorded in several photospheric spectral lines, i.~e. at the VTT in a group of iron and silicon lines in the near infrared and at THEMIS in iron and chromium lines in the visible. Inversions were carried out independently for the different lines in order to derive the magnetic field strength, its inclination and azimuth together with the temperature stratification. Thus we obtained the three-dimensional structure of the magnetic field. Selected locations in the penumbra and in light bridges were considered in detail. We find a general tendency that the magnetic field is weaker and less inclined in higher layers. Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot interferometer Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker, C.; Hofmann, A.; Kneer, F.; Puschmann, K. G. Bibcode: 2009IAUS..259..665B Altcode: One of the first post-focus instruments of the new solar telescope GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope (VTT) on Tenerife. This spectrometer is equipped with a full-Stokes polarimeter. The modulation is performed with two ferroelectric liquid crystals, one acting nominally as quarter-wave plate, and the other as half-wave plate. A modified Savart plate serves as polarimetric beam splitter. With the present liquid crystals, the optimum wavelength range of this polarimeter is between 580 and 660 nm. The spectro-polarimeter will benefit from the capabilities of the new telescope GREGOR which will provide a spatial resolution of about 0″.1 (75 km on the solar surface). Thus we will be able to investigate small magnetic features, and we will study their development with high cadence. Title: The three-dimensional structure of the magnetic field of a sunspot Authors: Balthasar, Horst; Gömöry, Peter Bibcode: 2009IAUS..259..225B Altcode: Spectro-polarimetric observations in several spectral lines allow to determine the height variation of the magnetic field of a small sunspot throughout the solar photosphere. The full Stokes-vector is measured with high spatial resolution. From these data we derive the magnetic field vector. The magnetic field strength decreases with height everywhere in the spot, even in the outer penumbra where some other authors have reported the opposite. The precise value of this decrease depends on the exact position in the spot. Values vary between 0.5 and 2.2 G km-1 when they are determined from an iron and a silicon line in the near infrared. The magnetic field is less inclined in the higher layers where the silicon line is formed. Once the magnetic vector field is known, it is straight forward to determine current densities and helicities. Current densities exhibit a radial structure in the penumbra, although it is still difficult to correlate this with the structure seen in the intensity continuum. In spite of this, current densities have a potential to serve as diagnostic tools to understand the penumbra, at least with the spatial resolution of the upcoming telescopes. The mean infered helicity is negative, as expected for a spot in the northern hemisphere. Nevertheless, there are locations inside the spot with positive helicity. Title: The Moat Flow in Two Different Heights Authors: Balthasar, H.; Muglach, K. Bibcode: 2008ESPM...12.2.26B Altcode: We investigate time series obtained with the Transition Region And Coronal Explorer (TRACE) simultaneously in two wavelength ranges, in whitelight (WL) and in the ultraviolet at 170 nm (UV). In the quiet sun, the UV is most sensitive to layers just below the temperature minimum. The field-of-view was centered on a small sunspot passing the central meridian. Horizontal velocities are determined by local correlation techniques (LCT), and we compare two different LCT-methods. We find an extended outflow in the moat. We detect the outflow up to four times the radius of the spot. For both wavelength ranges the outer boundary of the flow is located at the same distance from the center of the spot. In the inner moat velocities are higher in the UV, indicating higher velocities in the upper layers. In the outer moat higher velocities are detected in WL. Title: GREGOR - The Calibration Unit Authors: Hofmann, A.; Rendtel, J.; Arlt, K.; Balthasar, H. Bibcode: 2008ESPM...12..6.9H Altcode: In 2010 we expect "first light" for GREGOR - a new solar telescope with large aperture and modern scientific instruments. It is designed to observe small-scale dynamic magnetic structures below a size of 70 km on the Sun with high spectral resolution and polarimetric accuracy. For this purpose, the polarimetric concept of GREGOR is based on a combination of post-focus polarimeters with pre-focus equipment for high precision calibration. The Astrophysical Institute Potsdam developed the GREGOR calibration unit which is an integral part of the telescope. We give an overview on function and design of the calibration unit and present the results of extensive testing series in the Solar Observatory "Einsteinturm". Title: The three-dimensional structure of sunspots. I. The height dependence of the magnetic field Authors: Balthasar, H.; Gömöry, P. Bibcode: 2008A&A...488.1085B Altcode: Aims: We investigate the height dependence of the magnetic field of a sunspot, which has been until now a controversial issue.
Methods: Full-Stokes profiles of a sunspot, derived from infrared spectro-polarimetric measurements, were investigated. The magnetic field strength, inclination and azimuth were obtained using an inversion code. The results from two different spectral lines deliver the height dependence of the magnetic vector field. Vertical current densities and helicities as well as the vertical derivative of the vertical component of the magnetic field strength are calculated using Maxwell's equations.
Results: Inside the spot, the total magnetic field strength decreases with height, even in the outer penumbra, where the opposite trend was reported by other investigators. Outside the spot, the field strength increases with height apart from at a few small locations. This result is interpreted in terms of magnetic canopies. Magnetic field lines are less inclined in higher layers everywhere in the field of view. In the umbra, the vertical component of the magnetic field decreases by values in the range 0.5-2.2 G km-1, depending on the applied method. Mean values in the inner penumbra are smaller than in the umbra. In the outer penumbra, the vertical magnetic component increases independently of the local intensity distribution. A pore close to the spot exhibits a more rapid decrease with height than the spot itself. The electric current densities and helicities depend on the fine structure of the sunspots. Typical values of the current densities vary in the range ±40 mA m-2. The mean values are -11 mA m-1 for the umbra and -2 mA m-1 for the penumbra, respectively, but the propagated errors are of the same order as the mean values. There are indications that the radial structure of the penumbra is related to enhanced current densities, but at the present resolution we are unable to establish a correlation with local intensity fluctuations.
Conclusions: If the spatial resolution is sufficiently high, electric current densities and helicities could be applied as reliable diagnostic tools for understanding penumbral fine structure. Title: First-Light Science Cases for the GREGOR Fabry-Perot Interferometer Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados, M.; Kneer, H. F. Nicklas; Puschmann, K. G. Bibcode: 2008ESPM...12..6.8D Altcode: The light-gathering capacity and resolving power of the 1.5-meter aperture GREGOR telescope will provide solar observations of the full Stokes vector with high temporal, spectral and spatial resolution. As one of the first-light instruments, the GREGOR Fabry-Perot Interferometer (GFPI) is well suited for observations with adaptive optics (AO) correction. Post-facto image correction (speckle masking imaging and deconvolution) will further enhance the data quality to approach the diffraction-limited resolution of the telescope. We will describe the GFPI optical design and its basic operating procedures. Instruments characteristics such as field-of-view, cadence, spectral resolution, and spectroscopic/polarimetric observing modes will result in boundary conditions, which have to be carefully considered in optimizing the scientific outcome of the first-light observations. We will present two science cases for quiet Sun and active region studies to illustrate the capabilities of this imaging spectro-polarimeter. Title: Comparison of Solar Magnetic Fields Measured at Different Observatories: Peculiar Strength Ratio Distributions Across the Disk Authors: Demidov, M. L.; Golubeva, E. M.; Balthasar, H.; Staude, J.; Grigoryev, V. M. Bibcode: 2008SoPh..250..279D Altcode: 2008SoPh..tmp..125D In this paper we analyze the distribution of magnetic strength ratios (MSR) across the solar disk using magnetograms in different spectral lines from the same observatory (Mount Wilson Observatory (MWO) and Sayan Observatory (SO)), magnetograms in the same line from different observatories (MWO, SO, Wilcox Solar Observatory (WSO)), and in different spectral lines from different observatories (the three observatories mentioned above, the National Solar Observatory/Kitt Peak (KP) and Michelson Doppler Imager (MDI) on board Solar and Heliospheric Observatory (SoHO)). We find peculiarities in some combinations of data sets. Besides the expected MSR center-to-limb variations, there is an equator-to-pole asymmetry, especially in the near-limb areas. Therefore, it is generally necessary to use 2D matrices of correction coefficients to reduce one kind of observation into another one. Title: Two-dimensional spectroscopy of sunspots. II. Search for propagating waves and drifting velocity filaments in photospheric layers Authors: Balthasar, H.; Schleicher, H. Bibcode: 2008A&A...481..811B Altcode: Aims: Running penumbral waves are often reported from observations in chromospheric lines or lines formed in the upper photosphere. In this work we investigate whether they can be detected in a line formed in the mid to lower photosphere.
Methods: We used time series of two-dimensional spectra of an iron line that is insensitive to the magnetic field and that is formed in the lower to mid photosphere.
Results: No running penumbral waves are detected in this line formed in the lower and mid photosphere. In the moat, outward moving velocity features are detected. They are slightly faster than the plasma motions but much slower than running penumbral waves.
Conclusions: Running penumbral waves are a phenomenon occurring in higher layers, i.e. the lower chromosphere and the upper photosphere, but not in the mid photosphere or below. In the moat, we found long-living filamentary velocity features drifting outwards. Title: Propagating features in photospheric layers of sunspots Authors: Schleicher, Helmold; Balthasar, Horst Bibcode: 2007AN....328..717S Altcode: No abstract at ADS Title: Rotational periodicities in sunspot relative numbers Authors: Balthasar, H. Bibcode: 2007A&A...471..281B Altcode: Context: The search for active longitudes on the Sun has a long history, and many controversial results have been published. Recently the question became more important when active longitudes were found on other stars.
Aims: The aim of this paper is to investigate an integral measure of solar activity available for a long time interval and which allows enough frequency resolution for the investigation of active longitudes. Such a measure is given by the daily sunspot relative numbers.
Methods: A search for periodicities is performed with a classical Fast Fourier Transform (FFT), with a wavelet analysis and with the tool of superimposed epochs.
Results: The FFT yields a hump of power peaks near the synodic rotation period of 27 days, but only a very weak and insignificant enhancement around 13.5 days, indicating that the mean rotational variation of the sunspot numbers typically has one maximum and one minimum (overlaid by minor fluctuations). The wavelet analysis shows that spectral power for single periods varies for certain time intervals. A systematic drift during the solar activity cycle is not detected. Similar results are obtained from the superimposed epochs. Periodic “flip-flops” with time scales of a few years as for some stars are not found for the Sun in this investigation.
Conclusions: Sunspots are not distributed equally over the longitudes; there is a more active and a less active hemisphere. The rotation period derived from the pattern varies over long time scales. The results found in this work are not in favor of an explanation of the variations due to a differential rotation law. The rotation of the sunspot distribution pattern might reflect the internal rotation of the Sun, but it better fits the range of highest rotation rates in the upper convection zone than the rotation near the tachocline.

Figure [see full text] is only available in electronic form at http://www.aanda.org 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: Simultaneous polarimetric observations with VTT and THEMIS Authors: Balthasar, H.; Bommier, V. Bibcode: 2007msfa.conf..229B Altcode: Spectro-polarimetric observations of sunspot groups have been performed simultaneously with the VTT and with THEMIS. At the VTT we observed a group of iron and silicon lines at 1078 nm with the Tenerife Infrared Polarimeter, and at THEMIS we observed in five spectral channels (MTRmode): Fe 630 nm, Na D, Hα, Fe 557.6 nm and alternatively Cr 578 nm or Fe 525 nm. The inversion of the Stokes-profiles was done with the SIR-code for the infrared lines and for Fe 630 nm, for the other spectral ranges the inversion is still pending. So far we derived that the magnetic field strength decreases with height at most locations inside the spots, in contrast to some recently published results of other investigations. 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: Magnetic vector field above a sunspot Authors: Gömöry, P.; Balthasar, H. Bibcode: 2007msfa.conf..221G Altcode: We present an analysis of the spectro-polarimetricmeasurements of the active region NOAA 10886 taken with the Tenerife Infrared Polarimeter in the Fe I 10783 Å spectral line. The magnetic field strength and the magnetic inclination and azimuth were inferred from the data using the inversion code SIR. The vertical current densities and the vertical derivative of the vertical component of the magnetic field were then calculated for the leading spot of the AR 10886. We revealed that typical values of the vertical current densities vary in the range ± 40mAm-2 inside the spot. Moreover, we found an extended area of enhanced vertical current densities in the umbra (values up to -80mAm-2). Our analysis also showed that the vertical component of the magnetic field strength decreases by 0.6 - 1.6Gkm-1 and 0.5 - 0.8Gkm-1 in the umbra and inner penumbra; on the other hand we found an increase of the vertical component of the magnetic field in the outer penumbra (typical values varying between 0.1 - 0.5Gkm-1). 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: Vertical current densities and magnetic gradients in sunspots Authors: Balthasar, H. Bibcode: 2006A&A...449.1169B Altcode: Aims.The vertical component of electric current densities and the height dependence of the vertical component of the magnetic field in sunspots were determined.Methods. Full-Stokes magnetograms of eight sunspots obtained from infrared spectro-polarimetric measurements were investigated. The magnetic field strength and the magnetic inclination and azimuth were obtained from an inversion code. Vertical current densities and the vertical derivative of the vertical component of the magnetic field strength resulted from Maxwell equations.Results. It is found that electric current densities and magnetic gradients depend on the finestructure of the sunspots. Typical values for current densities vary in the range ±40 mA m-2, but their errors are of the same order. Disturbances in the radial structure of the penumbra are related to enhanced current densities up to 149 mA m-2, and a maximum value of 166 mA m-2 was found in a light bridge. There are indications that the radial structure of the penumbra is related to current densities, but no correlation to the local intensity fluctuations was found in the outer penumbra. The vertical component of the magnetic field decreases by 0.5-1.5 G km-1 in the umbra. Mean values in the inner penumbra are somewhat smaller than in the umbra, and locally dark structures exhibit a faster decrease with height than bright ones. In the outer penumbra the vertical magnetic component increases, independent of the local intensity distribution. Conclusions. Electric current densities could be a diagnostic tool for understanding the penumbral finestructure, although the presently available spatial resolution is probably not good enough to avoid artifacts. Magnetic extrapolations might depend crucially on this problem. Title: The Vertical Component of Electric Current Densities in Sunspots Authors: Balthasar, H. Bibcode: 2005ESASP.600E..55B Altcode: 2005dysu.confE..55B; 2005ESPM...11...55B No abstract at ADS Title: Influence of Instrumental Effects on High Frequency Oscillations Observed with Trace Authors: Muglach, K.; Balthasar, H. Bibcode: 2005ESASP.596E..76M Altcode: 2005ccmf.confE..76M No abstract at ADS Title: The Vertical Component of Electric Current Densities in Sunspots Authors: Balthasar, H. Bibcode: 2005ESASP.596E...8B Altcode: 2005ccmf.confE...8B No abstract at ADS 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: Some properties of an isolated sunspot Authors: Balthasar, H.; Collados, M. Bibcode: 2005A&A...429..705B Altcode: We present an investigation of a single sunspot observed in the neutral Fe line at 1089.6 nm with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope on Tenerife. Using the SIR code, we obtain maps of the magnetic field strength, inclination and azimuth, and Doppler velocities. The magnetic field strength drops from 2800 G in the umbra to about 700 G at the outer penumbral boundary, where we encounter an average magnetic inclination of 72o. Comparing the magnetic flux passing through different areas, we conclude that the inner penumbra must be deep, while the outer penumbra could be shallow. Assuming that the magnetic field strength encountered at the outer penumbral boundary forms a smooth surface through which the total flux of the spot passes, it would be approximately an ellipsoidal cap with a top height of 5250 km. This scenario leads to an average vertical magnetic gradient of 0.4 G km-1. Evershed Doppler velocities are about 2 km s-1. Two penumbral locations related to dark intensity features exhibit a steeper and slightly stronger magnetic field than elsewhere in the penumbra, and one of them is connected to an interruption of the Evershed effect. Title: Two magnetic components in sunspot penumbrae Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M. Bibcode: 2004A&A...427..319B Altcode: The magnetic and kinematic configuration of sunspot penumbrae is investigated by performing an inversion of the Stokes profiles of three infrared lines at 1565 nm. We use a two-component model atmosphere to describe, at least to first order, the unresolved structure of the penumbra. The observed Stokes profiles are successfully fitted, including those exhibiting abnormal shapes. The results of the inversion are consistent with the idea that the penumbra is formed by almost horizontal flux tubes embedded in a more vertical background magnetic field, as proposed by Solanki & Montavon (\cite{Sol93}). The tubes possess weaker fields than the background except in the very outer penumbra, and carry most of the Evershed flow. We characterize the radial variation of the magnetic field vector and the velocity vector in these atmospheric components. In the middle penumbra and beyond, the magnetic field and the flow in the tubes are seen to return to the solar surface. Everywhere in the penumbra, there is a perfect alignment of the magnetic field vector and the velocity vector in the component describing the penumbral flux tubes. We find that the Evershed flow is supercritical in many places of the outer penumbra, and supersonic at some locations near the outer sunspot boundary. Based on these inversions, we suggest that the azimuthal fluctuations in the average magnetic field inclination and strength inferred from simple one-component models are caused by fluctuations in the filling factor (i.e., the fractional area of the resolution element occupied by flux tubes), not by changes in the intrinsic magnetic and kinematic properties of the background or the flux-tube atmospheres. Also, we confirm the jump of magnetic field azimuth proposed by Müller et al. (\cite{Mul02}) to explain the observed net circular polarization of infrared lines. 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: Oscillations in Sunspots observed in the Near Infrared Authors: Balthasar, H. Bibcode: 2003SoPh..218...85B Altcode: Spectropolarimetric time series of two sunspots are investigated to search for magnetic field oscillations. While the existence of velocity oscillations in the five-minute band is clearly confirmed, periodic variations of the magnetic field strength or the magnetic angles inclination and azimuth are small and restricted to very narrow areas. They occur in single frequency bins, but different for magnetic field strength and angles. Small dark structures embedded in one penumbra or in the near surroundings of the other spot exhibit enhanced power for the magnetic variations at all frequencies. Phase differences are rather unsure. The obtained values are in agreement with intrinsic magnetic field variations produced by slow magnetoacoustic modes as well as with an opacity mechanism connected with fast modes. Title: Velocity Field of a Complex Sunspot with Light Bridges Authors: Schleicher, H.; Balthasar, H.; Wöhl, H. Bibcode: 2003SoPh..215..261S Altcode: For the leading part of sunspot group NOAA 8323, which rapidly changed its complex structure, a time series of the line-of-sight (LOS) component of the velocity field was obtained. With a two-dimensional Fabry-Pérot spectrometer, the magnetically insensitive line Fe i 557.6 nm was scanned. The inclination of the LOS (heliographic angle) to the vertical was θ=28.5°. The umbra of the observed spot was divided by a system of light bridges into several parts. The spatial and temporal velocity field also exhibits a considerable complexity: in one extended umbral area there is a downward flow of 1 km s−1 relative to other dark sub-umbrae. At the center-side penumbra, with a line-of-sight Evershed outflow of 1.5 km s−1, a persistent patch, somewhat darker than the average penumbra, has a LOS velocity of 1.3 km s−1 in opposite direction, probably a downflow. At the limb-side penumbra, a photosphere-like area is interspersed, interrupting the Evershed flow which resumes with typical strength beyond this feature towards the outer penumbral boundary. Most interesting is the behavior of the light bridges, which have a slight blue shift, interrupted by short events of strong blue or red shifts which - within the time resolution of 35 s - instantly affect a considerable part of a light bridge. Title: Mercury Transit Observed with TESOS at the VTT on Tenerife Authors: Schleicher, Helmold; Wöhl, Hubertus; Balthasar, Horst Bibcode: 2003ANS...324..114S Altcode: 2003ANS...324..P21S No abstract at ADS Title: Properties of a Simple Sunspot Observed in the Near Infrared Authors: Balthasar, Horst Bibcode: 2003ANS...324...30B Altcode: 2003ANS...324..D05B No abstract at ADS Title: Field-aligned Evershed flows in the photosphere of a sunspot penumbra Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.; Schlichenmaier, R. Bibcode: 2003A&A...403L..47B Altcode: We determine the inclinations of the vector magnetic field and flow velocity in a sunspot penumbra by interpreting full Stokes profiles of three infrared lines observed with the Tenerife Infrared Polarimeter. It is shown that analyses based on one-component atmospheres deliver flow velocities which are more horizontal than the average magnetic field by up to 10 deg. This apparent violation of the concept of frozen-in magnetic fields is solved as soon as two magnetic atmospheres are allowed to coexist in the resolution element. The magnetic field and velocity in the atmospheric component carrying the Evershed flow are found to be aligned to within +/- 2 deg all the way from the inner to the outer penumbra. This is the first observational confirmation of magnetic fields being frozen into the plasma in sunspots. Our results indicate that sunspot penumbrae can be understood in terms of inclined flux tubes embedded in a more vertical background field. The flux tubes carry most of the Evershed flows and return to the solar surface in the middle penumbra and beyond. The background atmosphere is essentially at rest in the inner penumbra, and harbors small flows in the outer penumbra. Title: The structure of the penumbra Authors: Balthasar, H.; Bellot Rubio, L.; Collados, M. Bibcode: 2003AN....324..390B Altcode: No abstract at ADS Title: IR-Observations of the Magnetic Field in Sunspots-Oscillations in a Sunspot Authors: Balthasar, H. Bibcode: 2003ASPC..307..364B Altcode: No abstract at ADS Title: Two-dimensional distribution of oscillations in a quiescent solar prominence Authors: Terradas, J.; Molowny-Horas, R.; Wiehr, E.; Balthasar, H.; Oliver, R.; Ballester, J. L. Bibcode: 2002A&A...393..637T Altcode: Using time series of two-dimensional Dopplergrams, a temporal and spatial analysis of oscillations in a quiescent prominence has been performed. The presence of an outstanding oscillatory signal in the acquired data has allowed us to study the two-dimensional distribution of wave motions and, in particular, to detect the location of wave generation and the anisotropic propagation of perturbations from that place. Moreover, a strong damping of oscillations has been observed, with damping times between two and three times the wave period. The direction of propagation, wavelength and phase speed, together with the damping time and wave period, have been quantified and their spatial arrangement has been analysed. Thanks to the goodness of the observational data, the image alignment procedure applied during the data reduction stage and the analysis tools employed, it has been possible to carry out a novel and far-reaching observational study of prominence oscillations. The five movies are available at http://www.edpsciences.org Title: Penumbral finestructure: need for larger telescopes Authors: Balthasar, H.; Sütterlin, P.; Collados, M. Bibcode: 2001AN....322..367B Altcode: We obtained at the same time G-band images at the Dutch Open Telescope (DOT) on La Palma and spectropolarimetric data in the near infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The spectropolarimetric data show interesting correlations. Bright filaments have a smaller magnetic field s trength, and higher Evershed velocities occur in dark structures. This result is in agreement with some previous observations, but also in contradiction to others. However, we suffer from the fact that the resolution limit of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial power spectra derived from the DOT data indicate a typical width of 250 km for penumbral filaments. Obviously a solar telescope with an aperture of at least 1.5~m is needed to obtain sophisticated results for penumbral structures. Title: Penumbral Finestructure: Need for Larger Telescopes Authors: Balthasar, H.; Sütterlin, P.; Collados, M. Bibcode: 2001AGM....18S1003B Altcode: We obtained at the same time G-band images at the Dutch Open Telescope (DOT) on La Palma and spectropolarimetric data in the near infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The spectropolarimetric data show interesting correlations. Bright filaments have a smaller magnetic field strength, and higher Evershed velocities occur in dark structures. This result is in agreement with some previous observations, but also in contradiction to others. However, we suffer from the fact that the resolution limit of the VTT at a wavelength of 1.565 μm corresponding to 400 km. Spatial power spectra derived from the DOT data indicate a typical width of 250 km for the penumbral filaments. Obviously a solar telescope with an aperture of at least 1.5 m is needed to obtain sophisticated results for penumbral structures. Title: Magnetic field oscillations in sunspots and active regions Authors: Balthasar, Horst; Collados, Manuel; Muglach, Karin Bibcode: 2001ESASP.464..163B Altcode: 2001soho...10..163B In order to investigate the oscillatory behaviour of the magnetic field in sunspots and pores, full Stokes measurements of 1.56 μm iron lines have been performed using the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope on Tenerife. As expected, velocity oscillations have power peaks at five minutes. First results for temporal variations of the magnetic field show that they occur in locally restricted areas in sunspots. Periods in the five minute range are preferred. In addition, we investigate magnetograms taken with the Michelson Doppler Imager (MDI) on SOHO. Intensity images in white light and around 160 nm were obtained with TRACE as well. Intensity power is strongly with TRACE as well. Intensity power is strongly suppressed in the sunspot area, although we find powerpeaks in the five and three minute ranges. Title: Inversion of Stokes Profiles with Artificial Neural Networks Authors: Carroll, T. A.; Balthasar, H.; Muglach, K.; Nickelt, I. Bibcode: 2001ASPC..236..511C Altcode: 2001aspt.conf..511C No abstract at ADS Title: Wave modulation and wave sources in the solar convection zone Authors: Kiefer, M.; Stix, M.; Balthasar, H. Bibcode: 2000A&A...359.1175K Altcode: We investigate the behavior of upward running sound waves in the lower photosphere by means of a 2-hour time series of FPI-filtergrams and a corresponding series of white-light images. From the FPI-filtergrams we obtain velocities in two heights in the solar photosphere. Using specific filters in the k_h-nu -space, we extract running sound waves from the velocity time series and the granulation from the white-light series. The relation between granular structure and wave amplitude is examined. To this end the granulation images are subdivided into intensity classes. The amplitudes of the waves are extracted on the pixel maps corresponding to these classes. We find hints for wave modulation due to the inhomogeneities in the solar convection zone: The behavior of the wave amplitudes meets theoretical predictions with respect to frequency- and height-dependence. The dependence on the horizontal wave number meets the predictions too, but due to low wave coherence at high wave numbers no definitive statement is possible. Further the darkest locations in the granulation are preferred by waves of increased amplitudes. There also seems to be a preference for the brightest granular regions. In both cases the behavior of the waves can be well described by subsurface sound sources. This is confirmed by comparison of the data with a simple model of a subsurface sound source. Title: Multi-mode oscillations of sunspots Authors: Zhugzhda, Y. D.; Balthasar, H.; Staude, J. Bibcode: 2000A&A...355..347Z Altcode: Oscillations of the magnetic field in the sunspot photosphere have been detected by recent high-resolution, two-dimensional observations. Their power is concentrated in isolated small flux bundles (pores) outside of larger umbrae and at the boundary between umbra and penumbra of larger spots. The slow body mode provides an explanation of the appearance of magnetic oscillations in small sunspots if the azimuth number m=0, but also of the small features piling up in rings in large sunspots. In the latter model the magnetic oscillations are the signature of the slow body mode with m>> 1, which bears a resemblance to the well-known whispering gallery mode in acoustics. The slow surface modes and fast body modes are also discussed. Title: Oscillations in a solar pore Authors: Balthasar, H.; Collados, M.; Muglach, K. Bibcode: 2000AN....321..121B Altcode: Temporal variations of a solar pore were observed at the ground based Vacuum Tower Telescope (VTT) on Tenerife and with the satellite TRACE. At the VTT Stokes I and V of the iron line at 1.56 mu m, originating in the deep photosphere, was measured. TRACE delivered UV images at 170 nm which show chromospheric continuum. In a part of the pore we find oscillations of the magnetic field in the 5 minute range. Velocities derived from shifts of the Stokes V profiles show 5 minutes everywhere in the pore, but the coherence of magnetic field and velocities is low. The intensity at 170 nm varies with 3 minutes, and for a part of the whole time series additionally with 4 minutes. Title: Multi-mode Magnetic Oscillations in Sunspots Authors: Zhugzhda, Y.; Balthasar, H.; Staude, J. Bibcode: 1999ESASP.448..417Z Altcode: 1999mfsp.conf..417Z; 1999ESPM....9..417Z No abstract at ADS Title: Oscillations in Sunspots: Observations and Modelling Authors: Staude, J.; Rendtel, J.; Balthasar, H.; Zhugzhda, Y. Bibcode: 1999ESASP.448..373S Altcode: 1999ESPM....9..373S; 1999mfsp.conf..373S No abstract at ADS Title: New Results of 2D-Spectroscopy of Sunspots - Temporal Variations of the Magnetic Field Authors: Balthasar, H. Bibcode: 1999ASPC..184..141B Altcode: Two-dimensional spectra of a sunspot were obtained at the German Vacuum Tower Telescope (VTT) on Tenerife using the 2D-spectrometer of the Göttingen observatory. The magnetic field strength is derived from the I-profiles of the Fe I line at 684.3 nm. Temporal variations of the magnetic field occur at the umbra-penumbra transition of larger spots and in the central part of some small spots and pores. A clear coherence between the variations of the magnetic field and those of intensities or Doppler shifts is not detected. Title: Temporal fluctuations of the magnetic field in sunspots Authors: Balthasar, H. Bibcode: 1999SoPh..187..389B Altcode: The magnetic field strength in sunspots was derived from time series of two-dimensional spectra taken with the Göttingen 2D-spectrometer at the Vacuum Tower Telescope on Tenerife in August 1997. For the present measurements the magnetically sensitive line Fe i 684.3 nm was selected. The main spot of the investigated sunspot group has a maximum magnetic field strength of 2270 G. Enhanced power of the magnetic field variations was found at the boundary between umbra and penumbra for all frequency ranges. These fluctuations are not well correlated with those of intensity variations or line shifts. Other spatial power peaks occur in a dark patch inside the centreside penumbra and at the centres of some accompanying small spots. Since no clear peaks at certain frequencies are found, the variations are not harmonic oscillations. A possible relation to Hα flares is investigated. There are several cases of published observations of magnetic field variations where flares occurred soon after the measurements, but very little before. Therefore it is not very probable that flares act as exciters of magnetic field variations. Title: On the Relation Between Solar Oscillations and Granulation Authors: Kiefer, M.; Balthasar, H. Bibcode: 1999ASPC..183..465K Altcode: 1999hrsp.conf..465K No abstract at ADS Title: New Results of 2D-Spectroscopy of Sunspots Authors: Balthasar, H. Bibcode: 1999ASPC..183..100B Altcode: 1999hrsp.conf..100B No abstract at ADS Title: Magnetic field oscillations in sunspots - - a `whispering gallery' mode? Authors: Staude, J.; Balthasar, H.; Zhugzhda, Y. D. Bibcode: 1999AGAb...15....9S Altcode: 1999AGM....15..A08S Oscillations of the magnetic field in the sunspot photosphere have been detected by recent high-resolution, two-dimensional, spectro-poarimetric observations at Tenerife and aboard the SOHO satellite. Their power is concentrated in isolated small flux bundles (pores) outside of larger umbrae and in patches at the boundary between umbra and penumbra of larger spots. The slow body mode of magneto-acoustic waves in an intense magnetic fluxtube provides an explanation of the strange appearance of such magnetic oscillations. This applies to small sunspots if the azimuth number m=0, but also to the small features piling up in rings at the border of the umbrae of larger sunspots. In the latter model the magnetic oscillations are the signature of the slow body mode with m >> 1, which bears a resemblance to the well-known whispering gallery mode in acoustics. The slow surface modes and fast body modes are also discussed. Title: Velocity Pulses in a Sunspot with Lightbridges Authors: Balthasar, H.; Schleicher, H.; Wöhl, H. Bibcode: 1999AGAb...15....7B Altcode: 1999AGM....15..A05B See splinter meeting SOLAR OBSERVATION WITH HIGH RESOLUTION Title: Magnetic Field Oscillations in Sunspots? Authors: Staude, Juergen; Balthasar, Horst; Zhugzhda, Yuzef Bibcode: 1999soho....9E..25S Altcode: Oscillations of velocity and intensity are known for more than 2 decades; they are observed in spectral lines formed at different height levels of the sunspot atmosphere. The interpretation of measurements of magnetic field oscillations, however, is still contradictory. We give evidence of the presence of such oscillations and describe the observed properties. The basic features of their spatial structure can be explained by slow body waves in intense magnetic flux tubes. In particular, a `whispering gallery'-like mode could be an appropriate model. Title: Prominence Doppler oscillations. Authors: Molowny-Horas, R.; Wiehr, E.; Balthasar, H.; Oliver, R.; Ballester, J. L. Bibcode: 1999joso.proc..126M Altcode: Longitudinal velocity maps have been constructed from time series of Hβ filtergrams, obtained at three positions along the emission line profile. Several examples of velocity perturbations with a periodic behaviour have been found at different spatial locations in the prominence. Periods have been determined to vary approximately between 28 and 95 minutes. The presence of damping (and in one case, of excitation) in those oscillatory motions is discussed. Title: Velocity Oscillations in Active Sunspot Groups Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H. Bibcode: 1998SoPh..182...65B Altcode: Time series of two-dimensional spectra were taken with the Göttingen 2D spectrometer at the VTT on Tenerife in 1996. They were investigated for Doppler velocities and velocity oscillations in small spots and pores of rapidly evolving sunspot groups. For the present measurements the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm were selected. Title: The role of the f-mode in the relation between solar intensity oscillations and granulation Authors: Kiefer, M.; Balthasar, H. Bibcode: 1998A&A...335L..73K Altcode: A series of white-light images is used to examine the relation of solar intensity oscillations and the granulation structure. Much of the oscillation power lies on the f-mode ridge in the diagnostic diagram. Filters are constructed to separate granulation, p-modes, and the f-mode. The filtered data are used to investigate the relation between rms-amplitudes of the oscillations and the granulation structure. Both p-modes and f-mode show a tendency to increased amplitudes in the darkest features of the granulation structure, with the f-mode showing this preference for dark regions much clearer. We emphasize that due to the different propagation characteristics of p-modes and the f-mode a separation like ours is mandatory to draw conclusions about wave excitation and diffraction. Title: Heights of formation of FeI photospheric lines Authors: Kucera, A.; Balthasar, H.; Rybak, J.; Woehl, H. Bibcode: 1998A&A...332.1069K Altcode: The determination of the location of spectral line-forming layers by means of line-depression contribution functions is checked by observational tests. The method is based on the assumption that the Doppler velocities derived from line bisectors at a given position in the profile of a spectral line are related to the actual bulk velocity at a particular height in the atmosphere. For a set of six magnetically sensitive and non-sensitive Fe I lines (543.45, 557.61, 630.15, 630.25, 649.50, 649.45 nm) the fluctuations of Doppler velocities along the slit of the spectrograph were determined at various Delta lambda from the line centers i.e. at various heights in the photosphere. Correlations of fluctuations allow us to find those parts in line profiles which are formed at identical heights in the photosphere. These experimental results are compared with theoretical estimates based on line depression contribution functions. The agreement is good and best results are found for nonmagnetic strong, but still unsaturated lines. The results support the hypothesis that it is possible to ascribe a single height point in the solar atmosphere to a given position in a spectral line profile. Title: The solar granulation in different heights. Authors: Balthasar, H. Bibcode: 1998AN....319..387B Altcode: Intensity images and Doppler-velocity maps of the quiet Sun in different heights are obtained from simultaneously recorded spectra of different lines. A relation between the intensity images is recognizable up to formation heights of 900 km above continuum, but the correlation coefficient changes sign above 400 km. The core of Hα shows a different pattern without any correlation to the continuum layer. Extreme Doppler velocities as well as the rms-velocities have minima at a height of 400 km, values of about 2 km/s occur in deep photospheric layers and 2.5 km/s in a height of 900 km. The velocities in the lower and in the upper photosphere are well correlated indicating that the pattern of the velocity field is preserved up to higher layers than the intensity pattern. Hα-velocities reach values up to 10 km/s and more, they show no correlation with the continuum intensities and almost no correlation with the line core intensities. Title: The Depth Dependence of Penumbral Absolute Velocities Authors: Balthasar, H.; Schmidt, W.; Wiehr, E. Bibcode: 1997SoPh..171..331B Altcode: Penumbral line-core shifts at different heights are determined from the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two adjacent water vapor lines for an absolute wavelength scale. The large granular blue shift of 0.6 km s-1 for the faint Fe 5435 line from deep layers yields for the centre-side penumbra absolute velocities up to 3 km s-1. This value is much larger than velocities deduced from the bisectors of the line wings of Ni 5436 and Fe 5434, thus supporting the concern against an interpretation of the line asymmetries in term of a velocity gradient with depth. Title: Velocity oscillations in active sunspot groups. Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H. Bibcode: 1997AGAb...13...12B Altcode: No abstract at ADS Title: First Observations SUMER - VTT, SI IV - CA II K Authors: Balthasar, H.; von Uexkull, M.; Innes, D.; Gigas, D.; Wilhelm, K. Bibcode: 1997ASPC..118..315B Altcode: 1997fasp.conf..315B We tried to do a comparison of Ca II K (393.3 nm) filtergrams obtained at the Vacuum Tower Telescope on Tenerife with spectra in the line Si IV 139.4 nm obtained simultaneously with the SUMER telescope on the SOHO-spacecraft. Some bright features can be well identified in both observations. We compare temporal changes of the brightness for these common features. Title: The Velocity Field in and around Sunspots. Results from 2D-Spectroscopy Authors: Balthasar, H.; Schleicher, H. Bibcode: 1997ASPC..118..111B Altcode: 1997fasp.conf..111B A sunspot was observed on June 11, 1995 with the Gottingen 2D-spectrometer at the Vacuum Tower Telescope on Tenerife using the line Fe 709 nm. The data show an radial outflow of 500 m/s outside the penumbra for about 15000 km. This flow is separated from the Evershed flow of 1.6 km/s by a sharp decrease at the boundary of the visible penumbra. The Evershed flow is associated to dark penumbral filaments, but we do not find a correlation between intensities and line asymmetries. No relation between the power distribution and the filaments is found for the 5 minute oscillations. Small spots and pores in the vicinity of the main spot show 3 minute oscillations. Title: Two-dimensional spectroscopy of sunspots. I. Intensity, velocity, and velocity power maps of a sunspot. Authors: Balthasar, H.; Schleicher, H.; Bendlin, C.; Volkmer, R. Bibcode: 1996A&A...315..603B Altcode: A time series of two-dimensional spectra of a sunspot at θ=~45° has been obtained with a spectrometer based on a Fabry-Perot interferometer. From our observations in the FeI line at 709.04nm we find that the gas plasma in the vicinity of the sunspot (the moat) has a velocity of about 500m/s directed outwards. Nevertheless, the Evershed flow shows a sharp decrease by about 1000m/s at the outer boundary of the visible penumbra. The mean white-light image averaged over 1^h^52^m^ still shows radial structures in the penumbra, indicating their long lifetime. Spatial variations of the velocities and continuum intensities have correlation coefficients of +0.66 for the centre-side penumbra and -0.57 for the limb-side one. The correlation coefficients increase to +/-0.75 for the line-centre intensities. This correlation confirms that the Evershed effect is related to the dark filaments. Outside the spot, the long-time average images of the continuum and the line-centre intensities show a chain of bright dots with a size of about one arcsec and intensities up to 4.5% higher than their surroundings. These dots are related to the outer boundary of the velocity field in the moat. In the five-minute range, velocity power spectra show a decrease in the umbra and in the penumbra, but no dependence on the radial structure. In the range between eight and twenty minutes, power is present in the centre-side penumbra; it resembles that of granular areas, but it has a radial structure. In the umbra or the limb-side penumbra, the power values are much lower. Title: A search for formation-height oscillations in umbrae. Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wiehr, E.; Woehl, H. Bibcode: 1996A&A...310..328B Altcode: The formation heights of spectral lines and continua in sunspots can be determined by measuring the apparent distance of the spot relative to the nearby solar limb. In order to confirm the existence of oscillatory variations of such limb distances and to exclude possible influences of differential image motion between the spot and the nearby limb, we have obtained time series observations of the lines Ca^+^ 8542, Mg b, and the non-magnetic line Fe 5576 simultaneously on two telescopes. No indication is found for periodic fluctuations of the spot's apparent limb distance. Only one of the seven time series shows a significant 40 min period of the line core but not of the continuum in the data from both telescopes. This variation of the line formation height, however, may be attributed to parallel guiding corrections of a spatially inhomogenous umbral chromosphere. The other time series show different periods for the two telescopes, which must be caused by unrelated guiding corrections. Title: High Resolution Polarimetric Measurements in a Sunspot Authors: Horn, T.; Hofmann, A.; Balthasar, H. Bibcode: 1996SoPh..164..321H Altcode: A Fabry-Perot interferometer is being used for two-dimensional spectropolarimetric measurements. We demonstrate the suitability of the setup for the measurement of the magnetic field and present some preliminary results from first observations. Title: Observation at 892 nm of impact "L" with the solar Vacuum Tower Telescope at Tenerife. Authors: Schleicher, H.; Balthasar, H.; Jockers, K.; Knölker, M.; Schmidt, W. Bibcode: 1995ESOC...52..171S Altcode: 1995eslj.work..171S; 1995esl9.conf..171S During the period of SL-9 impacting Jupiter, the authors observed Jupiter with the solar VTT. The impact of fragment "L" was monitored with a time series of filtergrams in the CH4-band at 892 nm. Title: Two-dimensional spectroscopy of a sunspot. Authors: Balthasar, H.; Schleicher, H.; Bendlin, C.; Volkmer, R. Bibcode: 1995AGAb...11..143B Altcode: No abstract at ADS Title: Sunspot limb distance variations measured simultaneously with two telescopes. Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E. Bibcode: 1995AGAb...11..142B Altcode: No abstract at ADS Title: Chromospheric Magnetic Field Measurements in He I 10830Å Authors: Rüedi, I.; Solanski, S. K.; Balthasar, H.; Livingston, W.; Schmidt, W. Bibcode: 1995itsa.conf..431R Altcode: No abstract at ADS Title: Sunspot Umbral Structures Observed in FE I 1027 NM Authors: Schmidt, W.; Balthasar, H. Bibcode: 1995itsa.conf..357S Altcode: No abstract at ADS Title: Impact L observed at a wavelength of 892 nm with the solar vacuum telescope on Tenerife Authors: Schleicher, H.; Balthasar, H.; Knölker, M.; Schmidt, W.; Jockers, K. Bibcode: 1995HiA....10..632S Altcode: No abstract at ADS Title: Polarimetry and spectroscopy of a simple sunspot. IV. Umbral structures observed in FeI 1027nm Authors: Balthasar, H.; Schmidt, W. Bibcode: 1994A&A...290..649B Altcode: Magnetic fields and velocities in bright umbral structures have been determined from long time sequences of high resolution Stokes-I spectra obtained with the near infrared FeI 1026.52nm line. This weak line is unblended in the umbra and has a triplet-like Zeeman pattern similar to a g_eff_=2.5 line. The umbral bright structures show velocity oscillations identical to those of the surrounding umbra. A bright structure with a size of 2 arcsec close to the center of the umbra shows a slightly lower magnetic field strength than its surroundings. This difference decreases whereas the structure becomes brighter during several hours of observations. Title: Temporal and spatial variation of physical parameters in a quiescent prominence. Authors: Balthasar, H.; Wiehr, E. Bibcode: 1994A&A...286..639B Altcode: The emission lines He 3889 A, H_8_ and Ca^+^IR_3_ are observed simultaneously in a prominence over a total of 4 hours. The time variations of the He 3889 / H_8_ emission ratio R, the thermal and the non-thermal line broadenings T_kin_ and ξ, respectively, are compared with those of the Doppler shift, v_D_, for 10 spatial locations along the slit. The time-averaged spatial variations along the slit show an increase of R, T_kin_, and ξ with height related to a decrease of the H_8_ emission, E_tot_(H_8_), in agreement with other authors. The short-time fluctuations show that quasi-oscillations, known from Doppler shifts, also exist for other physical parameters. The long-term variations over the total of 4 hours indicate a smooth increase of R, T_kin_, and ξ at the upper parts of the prominence, resembling the known spatial behaviour of these parameters at prominence edges. Also the well known anti-correlation of the emission ratio R and the E_tot_(H_8_) occurs in the long-term behaviour. We suggest that the decrease of E_tot_(H_8_) parallel with the increase of R might be related to a dissolution of the prominence yielding a smaller density of fine-structures. Title: Polarimetry and spectroscopy of a simple sunspot. 3: Velocity and magnetic field of sunspot umbral dots Authors: Schmidt, W.; Balthasar, H. Bibcode: 1994A&A...283..241S Altcode: Velocities and magnetic fields in sunspot umbrae and in umbral dots have been determined from high resolution Stokes-I spectra obtained at the Vacuum Tower Telescope (VTT) on Tenerife. Except for oscillatory motions the umbra is at rest and flow velocities in umbral dots, measured at an optical depth of about 0.01, are smaller than 25 m/s. The magnetic field strength is weakened in the dots by 10-20% for a central umbral dot and by 5-10% for a peripheral umbral dot. The line of sight decrease of magnetic field in a peripheral dot shows no difference to the surrounding umbra and amounts to 2.5-3 G/km. Title: Observations at 891 nm of the impact "L" of SL-9 on Jupiter. Authors: Balthasar, H.; Jockers, K.; Knölker, M.; Schleicher, H.; Schmidt, W. Bibcode: 1994AGAb...10..122B Altcode: No abstract at ADS Title: The Fe I 10265 Å line as an excellent tool for magnetic field measurements Authors: Schmidt, W.; Balthasar, H.; Wiehr, E. Bibcode: 1994ASIC..433...49S Altcode: No abstract at ADS Title: The Impact of Fragment ``L'' of Comet SL-9 on Jupiter Authors: Schleicher, H.; Balthasar, H.; Knolker, M.; Schmidt, W.; Jockers, K. Bibcode: 1994EM&P...66...13S Altcode: Filtergrams of high spatial and temporal resolution were obtained in the methane band centred at 892 nm during the impact of fragment L of comet Shoemaker-Levy 9 on Jupiter. The light curve shows two maxima of an emission ball observed above the limb shortly after the impact. The second maximum was the brightest and had a short life time of about 90 seconds. During it's life, the apparent height of the emission ball declined towards the surface of Jupiter; the amount of displacement is larger than the expected effect caused by Jupiter's rotation. About half an hour after the impact, a domelike feature became visible when the location of the impact rotated into the illuminated hemisphere of Jupiter. Title: On the magnetic field and the velocities in simple sunspots Authors: Balthasar, H.; Schmidt, W. Bibcode: 1994smf..conf..207B Altcode: No abstract at ADS Title: Time saeries of the penumbral Evershed effect. Authors: Schleicher, H.; Wiehr, E.; Balthasar, H.; Wöhl, H. Bibcode: 1994AGAb...10..113S Altcode: No abstract at ADS Title: Vector-Stokes polarimetry in a sunspot Authors: Hofmann, A.; Shine, R. A.; Frank, Z. A.; Schmidt, W.; Balthasar, H. Bibcode: 1994smf..conf..204H Altcode: No abstract at ADS Title: High resolution vector polarimetry of sunspot magnetic fields. Authors: Balthasar, H.; Hofmann, A.; Schmidt, W.; Shine, R. A.; Frank, Z. A. Bibcode: 1994AGAb...10..112B Altcode: No abstract at ADS Title: Polarimetry and spectroscopy of a simple sunspot. 2: On the height and temperature dependence of the magnetic field Authors: Balthasar, H.; Schmidt, W. Bibcode: 1993A&A...279..243B Altcode: We have observed a fairly regular sunspot located near disk center and have taken series of spectrograms in three different photospheric lines. The magnetic field strength across the spot has been measured in different heights of the sunspot photosphere and shows a change in slope at the umbra-penumbra boundary. The line depression contribution functions have been computed in order to obtain the height of formation of the spectral lines used in this analysis. Along the line-of-sight, we find an upward decrease of the field strength of 2.5 to 3 G/km in the penumbra and the adjacent outer part of the umbra. A relation has been deduced between the magnetic field and the brightness temperature measured across the sunspot which is strongly nonlinear and shows pronounced differences between the umbra and the penumbra. Title: Doppler oscillations in solar prominences simultaneously observed with two telescopes. Discovery of a 30 S oscillation Authors: Balthasar, H.; Wiehr, E.; Schleicher, H.; Wohl, H. Bibcode: 1993A&A...277..635B Altcode: Time series of Doppler shifts are observed simultaneously with two telescopes in order to separate actual solar velocities from influences of image motion or unperfect guiding. Several maxima of the power contours occur only in the data set from one of the two telescopes and may thus originate from non-solar sources. Considering only those power maxima which are observed with both telescopes we establish the solar origin of periods near 20 and 12 min, which may be identified with `hybrid fast modes' from model calculations. For one prominence a significant period of 30 5 is detected which theory predicts as a wave guided by the prominence fine-structures. Our prominence oscillations are restricted to spatially small areas of a few arc see diameter. Title: High Resolution Magnetic Field Measurements in the Sunspot Photosphere (Invited) Authors: Hofmann, A.; Schmidt, W.; Balthasar, H.; Tarbell, T. T.; Frank, Z. A. Bibcode: 1993ASPC...46...11H Altcode: 1993IAUCo.141...11H; 1993mvfs.conf...11H No abstract at ADS Title: Polarimetry and spectroscopy of a simple sunspot. I - On the magnetic field of a sunspot penumbra Authors: Schmidt, W.; Hofmann, A.; Balthasar, H.; Tarbell, T. D.; Frank, Z. A. Bibcode: 1992A&A...264L..27S Altcode: We investigate the magnetic field structure of a medium sized sunspot using high resolution magnetograms and spectrograms and derive a relationship between the brightness of penumbral structures and the inclination of the magnetic field. The field inclination to the spot normal is larger in the dark structures than in the bright ones. We show that the field strength does not vary between dark and bright structures. At the inner penumbral boundary the field strength is 2000 Gauss and about 1000 Gauss at the outer penumbral edge. The line-of sight component of the material flow decreases rapidly within one arcsecond at the photospheric boundary of the spot. Title: Doppler-Oszillationen unter dem Einfluss solarer Magnetfelder. Authors: Balthasar, H. Bibcode: 1992S&W....31..304B Altcode: No abstract at ADS Title: Time series of Doppler velocities in prominences. Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E. Bibcode: 1992AGAb....7..151B Altcode: No abstract at ADS Title: On the magnetic field of a sunspot penumbra. Authors: Balthasar, H.; Schmidt, W.; Hofmann, A.; Tarbell, T. D.; Frank, Z. A. Bibcode: 1992AGAb....7..153B Altcode: No abstract at ADS Title: Oscillations of Evershed velocities and asymmetries Authors: Balthasar, H.; Wiehr, E. Bibcode: 1990A&A...237..243B Altcode: Four sunspots at different heliocentric angles have been observed to study the oscillatory behavior of line asymmetries and velocities due to the Evershed effect. For two spots the power maxima of the line core velocities and of the line asymmetries are spatially anticorrelated. The central part of the penumbra as intersected by the spectrograph slit is the location of a velocity power maximum for the one spot, however, of an asymmetry power maximum for the other spot. In contrast, for two other spots several local power maxima are spatially coincident for the line asymmetry and the line core velocity. These variable spatial relations of line core velocities and line asymmetries support the idea that the Evershed effect may be a result of the superposition of penumbral fine structures affected by the underlying oscillating layers. Title: Intensity correlations in granular spectra Authors: Balthasar, H.; Grosser, H.; Schroeter, C.; Wiehr, E. Bibcode: 1990A&A...235..437B Altcode: Spectra of high spatial resolution were taken at the Gregory-Coude Telescope on Tenerife to investigate the relation between the line core intensities and the adjacent continuum for selected iron lines. Anti-correlations of these two quantities are found for the four lines with low excitation potential Fe5079, Fe5434, Fe5501, and Fe5506 which are known to show a limb effect although they have no blue shift at the disk center. An anti-correlation is also found for the line with high excitation potential, Fe5074, which shows a very small limb effect. This result is compatible with a granular intensity pattern which reverses in high layers, as suggested by numerical simulations of the granulation. Title: The Oscillatory Behaviour of Solar Faculae Authors: Balthasar, H. Bibcode: 1990SoPh..127..289B Altcode: The oscillatory behaviour of some faculae has been observed. In some cases power values in the faculae are larger than in the photosphere, but in other faculae power minima are found. Title: Die Sonnenrotation vor 100 Jahren. Authors: Balthasar, H.; Wöhl, H. Bibcode: 1990S&W....29..296B Altcode: No abstract at ADS Title: Penumbral Velocity Oscillations Authors: Balthasar, Horst Bibcode: 1990SoPh..125...31B Altcode: Doppler velocity variations of four sunspot penumbrae were observed in November 1988 at the Observatorio del Teide, Tenerife, using the spectral line Fe I 5576 Å. All of the penumbrae show local power maxima in the five-minute range, while no power is found around three minutes. This indicates that the five-minute oscillations are still present in the penumbrae, but the direction of the velocities might be tilted by the magnetic field. On the other hand, the maxima of the power and of the Evershed flow do not always occur at the same locations. Title: Doppler Velocity Oscillations in Quiescent Prominences Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1990LNP...363..255W Altcode: 1990IAUCo.117..255W; 1990doqp.coll..255W No abstract at ADS Title: Combination of a 256 x 256 pixel matrix detector and an image intensifier Authors: Balthasar, H.; Wiehr, E. Bibcode: 1989hsrs.conf..345B Altcode: No abstract at ADS Title: The solar rotation 1883 until 1893 as inferred from the Greenwich Photoheliographic Results and observations published by G. Spoerer Authors: Woehl, H.; Balthasar, H. Bibcode: 1989A&A...219..313W Altcode: The finding that the solar rotation velocity inferred from the Greenwich Photoheliographic Results (GPR) as compared to that from observations published by G. Spoerer for the years 1883 until 1893 shows a difference of the order of 0.1 deg/day is investigated in some details. An analysis of rotation velocities of stable sunspots, which are covered sufficiently by observations in both sets of data, yields no significant differences. The mean difference is nearly two orders of magnitude below the above cited value. The explanation of the difference is the presence of more short-living sunspots in the GPR, which show a more rapid rotation velocity. There are about twice as many days without any spot observations in the publications of Spoerer as compared to the GPR. Some indications are presented, that the solar behavior changed after the begining of our century. Title: The decrease of penumbral velocity and magnetic field at the outer sunspot boundary Authors: Wiehr, E.; Balthasar, H. Bibcode: 1989A&A...208..303W Altcode: Numerical simulation of atmospheric and instrumental smearing indicates that velocity and magnetic field disappear at the outer spot border within a length of maximally 1650 km and 2200 km, respectively. Accepting the (known) inclination of 84 deg, the corresponding height ranges of 165 and 220 km, respectively, are not compatible with the picture of a disappearance of both fields due to a kind of 'optical dilution' with height. Indication is given for a disappearance of the fields beyond an iso-tau discontinuity. Title: Doppler Velocity Oscillations in Quiescent Prominences Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1989HvaOB..13..131W Altcode: No abstract at ADS Title: Intensity Correlations in the Continuum and the Cores of Lines in Spectra of the Solar Granulation Authors: Schröter, C.; Balthasar, H. Bibcode: 1989AGAb....3...10S Altcode: No abstract at ADS Title: Oscillations in presence of local magnetic fields. Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1988ESASP.286..269W Altcode: 1988ssls.rept..269W Oscillatory Doppler shifts in sunspots and in small fluxtubes are observed using either the intensity profile of lines with negligible magnetic splitting or the circular Zeeman profile (Stokes-V inversion point) of lines with strong Zeeman splitting. Sunspot umbrae show local 5 min oscillations of reduced amplitude as compared to the neighbouring photosphere. Occasionally the authors find 5 min oscillations of opposite phase at both outer penumbral borders. This could be interpreted as tilting and bobbing of the spot as a whole on the oscillating solar surface. In contrast to these larger scale sunspot fluxtubes the gas in the small fluxtubes of a few hundred km diameter seems to fully participate in the photospheric oscillations without any interaction with the magnetic field. Prominence magnetic fields show sometimes a reaction to the photospheric 5 min and to the chromospheric 3 min oscillations, in addition several other periods are found. Indication is found for eigenmodes of Alfvén waves. Title: Periodic and quasiperiodic Doppler velocity variations in solar prominences along one spatial direction Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988A&A...204..286B Altcode: Temporal variations of the Doppler displacement of the Hα-emission line were measured in four quiescent prominences in autumn 1986 at the recently installed Gregory telescope on Tenerife. As detector, a 100×100 pixel diode array was used. The length of the time series was up to seven hours. The slit was oriented parallel to the solar limb in the first case and perpendicular in the others. In November 1987 another prominence was observed with a 256×256 pixel camera simultaneously in Ca+H and Hɛ over five hours. In this case, the slit was oriented parallel to the solar limb. The result for the two lines are in good agreement. The authors earlier result of periods near one hour is confirmed. Short periods near five and three minutes are found in some parts of the prominences. They might be interpreted as a reaction of the prominence on the photospheric and chromospheric oscillations. For the time series of more than five hours indications of eigenmodes of the prominences are found. Title: Comparison of the differential rotation laws and meridional motions determined from sunspot positions taken from the Greenwich Photoheliographic Results, the drawings of G. Spoerer, and the Kanzelhoehe data Authors: Balthasar, H.; Fangmeier, E. Bibcode: 1988A&A...203..381B Altcode: A comparison of the solar rotation velocities derived from the Greenwich Photoheliographic Results (GPR) and from Sporer's observations for the period 1883-1893 and from the Kanzelhohe data for 1948-1976 is presented. Although there is a good agreement of the results from Sporer's data with those from the modern GPR, it cannot be surely excluded that the decrease of the rotation velocity of the GPR during the early 20th century is of solar origin. But the comparison of the rotation velocities of recurrent groups determined from the individual positions during two passages and from the central meridian transits yield hints that systematical effects are present in the old GPR and in the Kanzelhohe data. A comparison of the meridional motions determined from Sporer's data and from the GPR yields no significant difference. Title: The center-to-limb variation of solar spectral lines Authors: Balthasar, H. Bibcode: 1988A&AS...72..473B Altcode: A listing of the center-to-limb variation of 143 solar lines from different elements measured simultaneously with the Fourier transform-spectrometer of the McMath-telescope at the Kitt Peak National Observatory is presented. The listing includes different asymmetry parameters, the limb effect, the intensity of the line core and the equivalent width. Title: Velocity variations of prominences. Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988AGAb....1R..12B Altcode: No abstract at ADS Title: Oscillations in Sunspot Umbra Penumbra and the Surrounding Photosphere Authors: Balthasar, H.; Fangmeier, E.; Kuveler, G.; Wiehr, E. Bibcode: 1988IAUS..123..183B Altcode: Doppler shifts of the nonsplit line Fe I 7090 Å have been measured simultaneously in the sunspot umbra, penumbra and the photosphere using a 100×100 diode array. The power in the range 2.5 - 4.5 mHz is found to decrease from the photosphere towards the umbra. Besides the minimum at the center of the umbra, further power minima occur at the transition region between umbra and penumbra. No significant power is found in the range 5.0 - 6.0 mHz. Title: Oscillatory motions of the Hα-emission line in quiescent prominences. Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988dssp.conf...63B Altcode: Temporal variations of the Doppler displacement of the Hα-emission were measured in 4 prominences (September 28 through October 5, 1986) at the recently installed Gregory telescope at Tenerife, using a 100×100 pixel diode array. Long periods near one hour confirm former results. The amplitude of these long periods vary with height and also in the direction parallel to the limb. Short periods near 5 minutes and near 3 minutes are found which might be interpreted as perturbations by the photospheric and chromospheric oscillations. Title: Oscillations of sunspots in the Stokes-V-inversion point. Authors: Balthasar, H.; Wiehr, E. Bibcode: 1988AGAb....1Q..12B Altcode: No abstract at ADS Title: The solar rotation elements i and Omega derived from recurrent single sunspots Authors: Balthasar, H.; Woehl, H.; Stark, D. Bibcode: 1987A&A...174..359B Altcode: Using the data of recurrent single sunspot observations obtained at Greenwich 1874 to 1976 the solar rotation elements were determined. The results confirm earlier results, where a smaller i-value and a slightly bigger Ω-value as compared to the well known Carrington rotation elements was found. No indication was found for a systematic difference between solar rotation elements determined from recurrent single sunspots as compared with results using all sunspot group positions. Title: A comparison of the oscillations in sunspot umbrae, penumbrae, and the surrounding photosphere Authors: Balthasar, H.; Wiehr, E.; Kueveler, G. Bibcode: 1987SoPh..112...37B Altcode: Time series of the nonsplit FeI 7090 Å line have been observed in several sunspots with a 100 x 100 diode array corresponding to 48 arc sec times 1.39 Å. The spatial behaviour of Doppler motions along one fixed slit position has been studied as a function of time. Former results are confirmed, that the power in the five minute range decreases from the photosphere to the umbra, where, however, values still well above the noise level are measured. Regarding the penumbra, the power tends to exhibit a maximum at locations where the line-of-sight component of a radial horizontal field should be maximal. This indicates that the direction of the oscillatory velocities might be influenced by the magnetic field or the Evershed flow. No significant power is found in the 3 min range. An exception might be seen in a small patch at the limb of the umbra of one spot. Title: Oscillatory Motions of the H Emission Line in Quiescent Prominences Authors: Balthasar, H.; Wiehr, E. Bibcode: 1987dssp.work...63B Altcode: 1987ASSL..150...63B No abstract at ADS Title: Evidence for quasi-periodic Doppler motions in solar prominences Authors: Balthasar, H.; Knoelker, M.; Wiehr, E.; Stellmacher, G. Bibcode: 1986A&A...163..343B Altcode: Observations of Doppler displacements in solar prominences have been performed using the Hα emission line. Evidence is found for the existence of quasi-periodic line-of-sight velocities in the range of 2.5 - 4.7 mHz. Former findings of long time variations near one hour are confirmed. Possible influences by misguiding and by image motion can be excluded. Scattered light from the solar aureola cannot produce the observed amplitudes. Title: The solar rotation elements i and omega derived from sunspot groups Authors: Balthasar, H.; Lustig, G.; Woehl, H.; Stark, D. Bibcode: 1986A&A...160..277B Altcode: Greenwich Photoheliographic results from 1874 to 1976 are completed to reduce the mean value errors of the i and Omega determination, and results are verified with independent data obtained between 1947 and 1984 at the Kanzelhohe observatory. The data-reduced i value of 7.137 + or - 0.017 deg is much less than the Carrington (1863) value, while the Omega(1850) vlkue of 73.75 + or - 0.15 deg is not significantly different than the Carrington Value. Title: Oszillationen in Sonnenflecken-Umbren, -penumbren und der benachbarten Photosphäre Authors: Balthasar, H.; Fangmeier, E.; Küveler, G.; Wiehr, E. Bibcode: 1986MitAG..65..155B Altcode: No abstract at ADS Title: Differential rotation of sunspot groups in the period from 1874 through 1976 and changes of the rotation velocity within the solar cycle Authors: Balthasar, H.; Vazquez, M.; Woehl, H. Bibcode: 1986A&A...155...87B Altcode: An effort is made to determine the differential rotation of the sun on the basis of the complete sample (1874-1976) of the Greenwich Photoheliographic Results. In order to improve the representation of differential rotation, a modified fit formula whose constant lies at 15 deg latitude (where sunspots nearly always occur) is introduced. Rotation is noted to strongly depend on sunspot type, with C-groups exhibiting high velocities and H- and J-spots the lowest ones. The new fit formula indicates that the highest velocity is found around the minima; at the beginning of an activity maximum, there is a secondary velocity maximum. The lowest velocities lie between the activity maximum and minimum. The braking of recurrent sunspots is confirmed. Title: Eine Jahrhundertarbeit über Sonnenfleckengruppen. Authors: Balthasar, H.; Vázquez, M.; Wöhl, H. Bibcode: 1985S&W....24..634B Altcode: No abstract at ADS Title: On the Contribution of Horizontal Granular Motions to Observed Limb-Effect Curves Authors: Balthasar, H. Bibcode: 1985SoPh...99...31B Altcode: From the comparison of 59 iron lines at the center of the solar disk with laboratory wavelenghts, the mean vertical velocity of solar granulation and its depth dependence is determined. These values are used to calculate limb-effect curves. The differences to observed curves are interpreted as mean horizontal motions. These motions yield again a depth dependence showing Doppler shifts toward the observer in deep layers and away from the observer in high layers for regions away from the disk center. Values from - 400 m s−1 through + 500 m s−1 are obtained. Title: Oscillations of the Hα Emission in Solar Prominences Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H. Bibcode: 1984SoPh...94..285W Altcode: The time dependence of Doppler shift and line-center intensity is simultaneously observed for the Hα emission of three solar prominences, each one during about two hours. Doppler oscillations with periods near one hour and amplitudes between 1 and 2 km s−1 are conspicuously visible in the recordings of all three prominences. Fourier analysis yields periods of 50, 60, and 64 min, as well as slight indications of short periods near 3 and 5 min. No oscillations are found in the line-center brightness. Title: Umbral Oscillations Measured in the Stokes-V Inversion Point Authors: Balthasar, H.; Wiehr, E. Bibcode: 1984SoPh...94...99B Altcode: The inversion point of the circular Zeeman polarization profile (V-Stokes) parameter is used to observe umbral Doppler oscillations free from disturbing influences of parasitic light. In a second step, purely umbral lines are used to avoid remaining influences from the V-profile of the (oscillating) penumbra. Among a total of nine sunspot umbrae, three exhibit oscillations within the various 1.5 to 2.5 hr samples. The periods differ significantly from 300 s, vary with time, and occur within time intervals of high tranquility thus explaining the lack of oscillations in the remaining sunspots. Title: Asymmetries and Wavelengths of Solar Spectral Lines and the Solar Rotation Determined from Fourier-Transform Spectra Authors: Balthasar, H. Bibcode: 1984SoPh...93..219B Altcode: Wavelength shifts and asymmetries of solar spectral lines and of the solar rotation are determined on the basis of 143 selected lines from Fourier-transform spectra obtained in 1980 and 1981. The asymmetries are noted to strongly depend on the formation layer of the line cores; lines with cores formed at higher layers have larger asymmetries. Wavelength shifts at the solar disk center show a depth dependence similar to that found by Keil (1980), but exhibit an exponential line. Lines with cores formed at higher layers of the solar atmosphere show wavelength shifts of approximately the gravitational redshift. Ionized element line redshifts are larger than those from neutral elements. An equatorial rotation velocity of 1.971 km/sec is found. Title: Evidence for the 22-YEAR-CYCLE in the Longitudinal Distribution of Sunspots Authors: Balthasar, Horst; Schüssler, Manfred Bibcode: 1984SoPh...93..177B Altcode: It was shown in an earlier paper that preferred hemispheres of solar activity alternate with the 22-year magnetic cycle, when analyzed in the 27.0 day Bartels rotation. Using data which cover the time between 1818 and 1983 we trace back this result to 1880 (cycle 12). Before 1880 no significant correlations are found. Title: On the Determination of Heliographic Positions and Rotation Velocities of Sunspots - Part Three - Effects Caused by Wrong Solar Image Radii and Their Corrections Authors: Balthasar, H.; Lustig, G.; Woehl, H. Bibcode: 1984SoPh...91...55B Altcode: In an earlier paper of this series it was shown how the Wilson depression influences the determination of sunspot rotation velocities. Using this finding and the fact that stable recurrent sunspots show a very constant rotation velocity it is possible to determine the effect of wrong solar image radii on the determination of sunspot rotation velocities and correct them. Title: New information about solar rotation Authors: Woehl, H.; Balthasar, H.; Koch, A.; Kueveler, G.; Roca-Cortes, T.; Schmidt, W.; Vazquez, M. Bibcode: 1984S&W....23...73W Altcode: It is pointed out that the phenomenon of solar rotation is known since the introduction of the telescope into astronomy by Galilei in 1610. Regular measurements concerning the positions of sunspots were conducted with the aid of photographic plates at the Royal Greenwich Observatory during the time from 1874 to 1976. The obtained data provide an excellent basis for statistical analysis. Information obtained as a result of such analyses is discussed. Attention is given to the determination of the Wilson depression, details regarding solar differential rotation, plans for an evaluation of data with the aid of a computer, the rotation of the solar plasma, a comparison of sunspots and plasma, the theory of differential rotation, and new information concerning solar rotation partly obtained with the aid of solar telescopes in a Spanish observatory on the island of Tenerife. Title: Asymmetrien und Wellenlängen solarer Spektrallinien aus Fourier-Transform-Spektren in Abhängigkeit von der Beobachtungsposition auf der Sonne Title: Asymmetrien und Wellenlängen solarer Spektrallinien aus Fourier-Transform-Spektren in Abhängigkeit von der Beobachtungsposition auf der Sonne Title: Asymmetries and wavelengths of solar spectral lines from Fourier transform spectra depending on the observed position on the Sun; Authors: Balthasar, Horst Bibcode: 1984PhDT.......213B Altcode: No abstract at ADS Title: An Atlas of Spectral Line Asymmetries and Their CLV From Solar FTS Spectra Authors: Balthasar, H.; Wohl, H. Bibcode: 1984ssdp.conf..317B Altcode: Preliminary informations are given on the CLV of solar spectral line asymmetries in quiet regions. The results are based on FTS spectra with high spectral resolution and a S/N of about 3000. Three main classes of the CLVs of solar spectral lines are introduced and their dependences on the excitation potentials of the lines and their heights of formation are given. In addition shifts of lines depending on their formation depths, equatorial rotation velocities and limb-effect results are given. Title: Neues über die Sonnenrotation. Authors: Balthasar, H.; Koch, A.; Küveler, G.; Roca-Cortes, T.; Schmidt, W.; Vázquez, M.; Wöhl, H. Bibcode: 1984S&W....23...73B Altcode: No abstract at ADS Title: On the Determination of Heliographic Positions and Rotation Velocities of Sunspots - Part Two - Systematic Effects Caused by the Wilson Depression Authors: Balthasar, H.; Woehl, H. Bibcode: 1983SoPh...88...71B Altcode: Using sunspot positions of small sunspots observed at Debrecen and Locarno as well as positions of recurrent sunspots taken from the Greenwich Photoheliographic Results (1940-1976) the influence of the Wilson depression on the rotation velocities was investigated. It was found that the Wilson depression can be determined by minimizing errors of the rotation velocities or minimizing the differences of rotation velocities determined from disk passages and central meridian passages. The Wilson depressions found were between 765 km and 2500 km for the first sample while they were between 0 km and several 1000 km for the second sample. The averaged Wilson depression for the second sample is between 500 km and 965 km depending on the reduction method. A dependence of the Wilson depression on the age of the spots investigated seems not to exist. Title: Preferred longitudes of sunspot groups and high-speed solar wind streams: evidence for a "solar memory". Authors: Balthasar, H.; Schuessler, M. Bibcode: 1983SoPh...87...23B Altcode: Correlation analysis of the mean longitude distribution of sunspot groups (taken from the Greenwich Photoheliographic Results) and high-speed solar wind streams (inferred from the C9 index for geomagnetic disturbances) with the Bartels rotation period P = 27.0 days shows anti-correlation for individual cycles. Title: On the Depth Dependence of the Solar Rotation Velocity Determined from Fraunhofer Lines Authors: Balthasar, H. Bibcode: 1983SoPh...84..371B Altcode: From 63 mostly unblended Fraunhofer lines measured along the solar east-west diameter the rotation velocity has been determined. The mean value is 1986 km s#X2212;1. The velocity decreases with the optical depth in the photosphere. Over a range of 700 km the difference of the velocities is 41 m s#X2212;1 for the Holweger-Müller atmosphere or 34 m s#X2212;1 for the Harvard Smithsonian reference atmosphere. Title: Erratum - Differential Rotation and Meridional Motions of Sunspots from 1874 TO 1902 Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.; Wohl, H. Bibcode: 1983A&A...117..170A Altcode: No abstract at ADS Title: Asymmetrien solarer Spektrallinien Authors: Balthasar, H. Bibcode: 1983MitAG..60..278B Altcode: No abstract at ADS Title: Oszillationen in Flecken-Umbren Authors: Soltau, D.; Balthasar, H.; Koch, A.; Küveler, G.; Wiehr, E. Bibcode: 1983MitAG..60..225S Altcode: No abstract at ADS Title: Rotationsgeschwindigkeiten von Sonnenflecken - mögliche Fehler und ihre Korrektion Authors: Balthasar, H.; Lustig, G.; Wöhl, H. Bibcode: 1983MitAG..60..236B Altcode: No abstract at ADS Title: Terrestrial O2 lines used as wavelength references - Comparison of measurements and model computations Authors: Balthasar, H.; Thiele, U.; Woehl, H. Bibcode: 1982A&A...114..357B Altcode: High precision spectral measurements of the wavelength of terrestrial O2 lines within solar spectra using the Kitt Peak 1-m Vacuum Fourier Transform Spectrometer are compared with model computations of the shifts of these lines due to wind up to 20 km. Although the wind data available existed only from radio sonde measurements about 65 km away and only from two launches per day, the shifts observed during two days could be explained well. Maximum shifts of terrestrial O2 lines of + or - 0.3 mA at about 6300 A were observed. It is shown that it may be possible to correct a general trend of the observed shifts with a precision of + or - 3 m/sec during a day. Title: Differential rotation and meridional motions of sunspots from 1874 to 1902 Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.; Woehl, H. Bibcode: 1982A&A...111..266A Altcode: Position data of sunspot groups from the period 1874-1902 are used to investigate the differential rotation of the Sun and the meridional motions of the sunspots. The equatorial velocity is higher than in the period 1940-1968 investigated by Balthasar and Wöhl (1980), while differences between the northern and southern hemispheres are less. For cycle 12 we find meridional motions towards north while in cycle 13 the motions are directed towards south like in the period 1940-1968. Our other results are comparable to those of Balthasar and Wöhl (1980) for the period 1940-1968. Title: On changes of the rotation velocities of stable, recurrent sunspots and their interpretation with a flux tube model Authors: Balthasar, H.; Schuessler, M.; Woehl, H. Bibcode: 1982SoPh...76...21B Altcode: The angular rotation velocities of stable, recurrent sunspots were investigated using data from the Greenwich Photoheliographic Results 1940 until 1968. We found constant rotation velocities during the passages on the solar disk with errors of about ±4 m s−1. During their lifetime these spots show a decreasing braking of their rotation velocities from 0.8 to 0.3 m s−1 per day. A plausible interpretation is found by assuming the spots to be coupled to a slowly rising subsurface flux tube and a rotation velocity which increases with depth. Title: Limb-Effekte und Asymmetrien solarer Spektrallinien zwischen 4800 und 6500 Angström in Fouriertransformspektren Authors: Balthasar, H.; Wöhl, H. Bibcode: 1982MitAG..55...71B Altcode: No abstract at ADS Title: Erratum - Differential Rotation and Meridional Motions of Sunspots in the Years 1940-1968 Authors: Balthasar, H.; Wohl, H. Bibcode: 1981A&A....98..422B Altcode: No abstract at ADS Title: Differentielle Rotation und meridionale Bewegungen von Sonnenflecken in den Jahren 1940 bis 1968 Authors: Balthasar, H.; Wöhl, H. Bibcode: 1981MitAG..52...26B Altcode: No abstract at ADS Title: Differential rotation and meridional motions of sunspots in the years 1940-1968 Authors: Balthasar, H.; Woehl, H. Bibcode: 1980A&A....92..111B Altcode: Using positions of sunspots from the Greenwich Photoheliographic Results from 1940 to 1968 equations for the differential rotation and meridional motions of sunspot groups are determined. The differential rotation depends on the phase in the solar cycle and on the type of the groups. The meridional motions show a general southdrift of the spots, but they are not significantly different from zero. The significance of the equatorward motion near the equator found by Ward (1965) seems to be due to an effect of selection. Changes of the meridional motions with time are not in good agreement with former publications, but they are also not significant. A dependence of the meridional motions on the local activity is not detectable. Title: Änderungen der differentiellen Rotation und meridionale Bewegungen von Sonnenflecken 1940 bis 1968. Authors: Balthasar, H.; Woehl, H. Bibcode: 1980S&W....19..385B Altcode: Various methods of measuring solar activity are discussed with emphasis given to following identifiable objects such as sunspots over a period of time. A formula describes the rotation of sunspots for the period between 1940 and 1968, and the data for each year are divided within a seven year cycle. Mathematical formulas of rotation are also presented for the northern and southern hemispheres. Latitudinal movement of sunspots is investigated and compared to the method of Ward (1965). Differences in northern and southern hemisphere movement are considered.