Author name code: staude ADS astronomy entries on 2022-09-14 author:"Staude, Juergen" ------------------------------------------------------------------------ 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: 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: Slipping reconnection in a solar flare observed in high resolution with the GREGOR solar telescope Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák, J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann, A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.; Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T. Bibcode: 2016A&A...596A...1S Altcode: 2016arXiv160500464S A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference filter. Context observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. We reconstructed a time series of 140 s of Ca II H images by means of the multiframe blind deconvolution method, which resulted in spatial and temporal resolutions of 0.1″ and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary, but three move along the ribbon with speeds of 7-11 km s-1. Two of them move in the opposite direction and exhibit highly correlated intensity changes, which provides evidence of a slipping reconnection at small spatial scales.

Movies associated to Figs. 1 and 2 are available at http://www.aanda.org Title: Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.; Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.; Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe, O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.; Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H. Bibcode: 2016A&A...596A...2B Altcode: 2016arXiv160708165B Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere.
Aims: We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra.
Methods: We investigated the magnetic field at log τ5 = 0 is by inverting spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45''. The data have been recorded using the GRIS instrument attached to the 1.5-m solar telescope GREGOR at the El Teide observatory. The data include three Fe I lines around 1565 nm, whose sensitivity to the magnetic field peaks half a pressure scale height deeper than the sensitivity of the widely used Fe I spectral line pair at 630 nm. Before the inversion, the data were corrected for the effects of scattered light using a deconvolution method with several point spread functions.
Results: At log τ5 = 0 we find no evidence of regions with dynamically weak (B< 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations made on Fe I lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, is independent of the point spread function used to deconvolve the data, and does not depend on the amount of stray light (I.e., wide-angle scattered light) considered. Title: Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.; Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.; Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1050B Altcode: 2016arXiv160901514B Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0 nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km s-1 in the chromospheric helium line. Our findings can be explained with new emerging flux where the matter flows downward along the field lines of rising flux tubes, in agreement with earlier results. Title: Magnetic fields of opposite polarity in sunspot penumbrae Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.; Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld, T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.; Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar, A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier, K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M. Bibcode: 2016A&A...596A...4F Altcode: 2016arXiv160800513F Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface.
Aims: We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface.
Methods: We analyzed 71 spectropolarimetric datasets from Hinode and from the GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy of the infrared data after applying several reduction steps. Techniques of spectral inversion and forward synthesis were used to test the detection algorithm. We compared the morphology and the fractional penumbral area covered by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk center. We determined the amount of reversed-polarity and three-lobed Stokes V profiles in visible and infrared data of sunspots at various heliocentric angles. From the results, we computed center-to-limb variation curves, which were interpreted in the context of existing penumbral models.
Results: Observations in visible and near-infrared spectral lines yield a significant difference in the penumbral area covered by magnetic fields of opposite polarity. In the infrared, the number of reversed-polarity Stokes V profiles is smaller by a factor of two than in the visible. For three-lobed Stokes V profiles the numbers differ by up to an order of magnitude. Title: Horizontal flow fields in and around a small active region. The transition period between flux emergence and decay Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke, A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert, M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...3V Altcode: 2016arXiv160507462V Context. The solar magnetic field is responsible for all aspects of solar activity. Thus, emergence of magnetic flux at the surface is the first manifestation of the ensuing solar activity.
Aims: Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region.
Methods: The small active region NOAA 12118 emerged on 2014 July 17 and was observed one day later with the 1.5-m GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were complemented by synoptic line-of-sight magnetograms and continuum images obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator (DAVE), respectively. Morphological image processing was employed to measure the photometric and magnetic area, magnetic flux, and the separation profile of the emerging flux region during its evolution.
Results: The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days provides a comprehensive view of growth and decay. It traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km s-1 is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of dark pores. We detected many elongated rapidly expanding granules between the two major polarities, with dimensions twice as large as the normal granules. Title: Solar physics at the Einstein Tower Authors: Denker, C.; Heibel, C.; Rendtel, J.; Arlt, K.; Balthasar, Juergen H.; Diercke, A.; González Manrique, S. J.; Hofmann, A.; Kuckein, C.; Önel, H.; Senthamizh Pavai, V.; Staude, J.; Verman, M. Bibcode: 2016AN....337.1105D Altcode: 2016arXiv160906949D The solar observatory Einstein Tower ({Einsteinturm}) at the Telegrafenberg in Potsdam is both a landmark of modern architecture and an important place for solar physics. Originally built for high-resolution spectroscopy and measuring the gravitational redshift, research shifted over the years to understanding the active Sun and its magnetic field. Nowadays, telescope and spectrographs are used for research and development, i.e., testing instruments and in particular polarization optics for advanced instrumentation deployed at major European and international astronomical and solar telescopes. In addition, the Einstein Tower is used for educating and training of the next generation astrophysicists as well as for education and public outreach activities directed at the general public. This article comments on the observatory's unique architecture and the challenges of maintaining and conserving the building. It describes in detail the characteristics of telescope, spectrographs, and imagers; it portrays some of the research and development activities. Title: Upper chromospheric magnetic field of a sunspot penumbra: observations of fine structure Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados, M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar, H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.; Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...8J Altcode: 2016arXiv160801988J
Aims: The fine-structure of the magnetic field in a sunspot penumbra in the upper chromosphere is to be explored and compared to that in the photosphere.
Methods: Spectropolarimetric observations with high spatial resolution were recorded with the 1.5-m GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The observed spectral domain includes the upper chromospheric Hei triplet at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å spectral lines. The upper chromospheric magnetic field is obtained by inverting the Hei triplet assuming a Milne-Eddington-type model atmosphere. A height-dependent inversion was applied to the Sii 10 827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic field.
Results: We find that the inclination of the magnetic field varies in the azimuthal direction in the photosphere and in the upper chromosphere. The chromospheric variations coincide remarkably well with the variations in the inclination of the photospheric field and resemble the well-known spine and interspine structure in the photospheric layers of penumbrae. The typical peak-to-peak variations in the inclination of the magnetic field in the upper chromosphere are found to be 10°-15°, which is roughly half the variation in the photosphere. In contrast, the magnetic field strength of the observed penumbra does not vary on small spatial scales in the upper chromosphere.
Conclusions: Thanks to the high spatial resolution of the observations that is possible with the GREGOR telescope at 1.08 microns, we find that the prominent small-scale fluctuations in the magnetic field inclination, which are a salient part of the property of sunspot penumbral photospheres, also persist in the chromosphere, although at somewhat reduced amplitudes. Such a complex magnetic configuration may facilitate penumbral chromospheric dynamic phenomena, such as penumbral micro-jets or transient bright dots. Title: Active region fine structure observed at 0.08 arcsec resolution Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.; Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.; Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.; Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann, T.; Kneer, F.; Nicklas, H.; Sobotka, M. Bibcode: 2016A&A...596A...7S Altcode: 2016arXiv160707094S Context. The various mechanisms of magneto-convective energy transport determine the structure of sunspots and active regions.
Aims: We characterise the appearance of light bridges and other fine-structure details and elaborate on their magneto-convective nature.
Methods: We present speckle-reconstructed images taken with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the 486 nm and 589 nm bands. We estimate the spatial resolution from the noise characteristics of the image bursts and obtain 0.08″ at 589 nm. We describe structure details in individual best images as well as the temporal evolution of selected features.
Results: We find branched dark lanes extending along thin (≈1″) light bridges in sunspots at various heliocentric angles. In thick (≳ 2″) light bridges the branches are disconnected from the central lane and have a Y shape with a bright grain toward the umbra. The images reveal that light bridges exist on varying intensity levels and that their small-scale features evolve on timescales of minutes. Faint light bridges show dark lanes outlined by the surrounding bright features. Dark lanes are very common and are also found in the boundary of pores. They have a characteristic width of 0.1″ or smaller. Intergranular dark lanes of that width are seen in active region granulation.
Conclusions: We interpret our images in the context of magneto-convective simulations and findings: while central dark lanes in thin light bridges are elevated and associated with a density increase above upflows, the dark lane branches correspond to locations of downflows and are depressed relative to the adjacent bright plasma. Thick light bridges with central dark lanes show no projection effect. They have a flat elevated plateau that falls off steeply at the umbral boundary. There, Y-shaped filaments form as they do in the inner penumbra. This indicates the presence of inclined magnetic fields, meaning that the umbral magnetic field is wrapped around the convective light bridge. Title: Probing deep photospheric layers of the quiet Sun with high magnetic sensitivity Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González, M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.; Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.; Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.; Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier, K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.; Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.; Schmidt, D.; Kiess, C.; Nicklas, H. Bibcode: 2016A&A...596A...6L Altcode: 2016arXiv160506324L Context. Investigations of the magnetism of the quiet Sun are hindered by extremely weak polarization signals in Fraunhofer spectral lines. Photon noise, straylight, and the systematically different sensitivity of the Zeeman effect to longitudinal and transversal magnetic fields result in controversial results in terms of the strength and angular distribution of the magnetic field vector.
Aims: The information content of Stokes measurements close to the diffraction limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of spatial straylight and photon noise into account.
Methods: Highly sensitive full Stokes measurements of a quiet-Sun region at disk center in the deep photospheric Fe I lines in the 1.56 μm region were obtained with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise statistics and Stokes V asymmetries were analyzed and compared to a similar data set of the Hinode spectropolarimeter (SOT/SP). Simple diagnostics based directly on the shape and strength of the profiles were applied to the GRIS data. We made use of the magnetic line ratio technique, which was tested against realistic magneto-hydrodynamic simulations (MURaM).
Results: About 80% of the GRIS spectra of a very quiet solar region show polarimetric signals above a 3σ level. Area and amplitude asymmetries agree well with small-scale surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss range with some concentrations of kilo-Gauss fields.
Conclusions: The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4 are so far unique in the combination of high spatial resolution scans and high magnetic field sensitivity. Nevertheless, the unavoidable effect of spatial straylight and the resulting dilution of the weak Stokes profiles means that inversion techniques still bear a high risk of misinterpretating the data. Title: Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396 Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer, C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados, M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1090V Altcode: Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multi-instrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the GREGOR solar telescope (imaging and near-infrared spectroscopy) and the space missions Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). The observations focused on the trailing part of active region NOAA 12396 with complex polarity inversion lines and strong intrusions of opposite polarity flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV spectral profiles in the photospheric Si I λ1082.7 nm line, the chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I λ1083.9 nm line. Carefully calibrated GRIS scans of the active region provided maps of Doppler velocity and magnetic field at different atmospheric heights. We compare quick-look maps with those obtained with the ``Stokes Inversions based on Response functions'' (SIR) code, which furnishes deeper insight into the magnetic properties of the region. We find supporting evidence that newly emerging flux and intruding opposite polarity flux are hampering the formation of penumbrae, i.e., a penumbra fully surrounding a sunspot is only expected after cessation of flux emergence in proximity to the sunspots. Title: Three-dimensional structure of a sunspot light bridge Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.; Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A..59F Altcode: 2016arXiv161104803F Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay.
Methods: We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.
Results: The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-β), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.

Movies associated to Figs. 2 and 13 are available at http://www.aanda.org Title: Inference of magnetic fields in the very quiet Sun Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.; Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.; González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.; Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman, T.; Volkmer, R. Bibcode: 2016A&A...596A...5M Altcode: 2018arXiv180410089M Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution.
Aims: We present high-precision spectro-polarimetric data with high spatial resolution (0.4'') of the very quiet Sun at 1.56 μm obtained with the GREGOR telescope to shed some light on this complex magnetism.
Methods: We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component.
Results: Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak ( 150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area 50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised. Title: Fitting peculiar spectral profiles in He I 10830Å absorption features Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.; Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1057G Altcode: 2016arXiv160300679G The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He I 10830 Å triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub- and supersonic downflow velocities of up to 32 km s-1 for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. Title: 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: 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: Wave Instabilities of a Collisionless Plasma in Fluid Approximation Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, Jürgen Bibcode: 2011CoPP...51..621D Altcode: 2009arXiv0911.2912D Wave properties and instabilities in a magnetized, anisotropic, collisionless, rarefied hot plasma in fluid approximation are studied, using the 16-moments set of the transport equations obtained from the Vlasov equations. These equations differ from the CGL-MHD fluid model (single fluid equations by Chew, Goldberger, and Low, 1956) by including two anisotropic heat flux evolution equations, where the fluxes invalidate the double polytropic CGL laws. We derived the general dispersion relation for linear compressible wave modes. Besides the classic incompressible fire hose modes there appear four types of compressible wave modes: two fast and slow mirror modes - strongly modified compared to the CGL model - and two thermal modes. In the presence of initial heat fluxes along the magnetic field the wave properties become different for the waves running forward and backward with respect to the magnetic field. The well known discrepancies between the results of the CGL-MHD fluid model and the kinetic theory are now removed: i) The mirror slow mode instability criterion is now the same as that in the kinetic theory. ii) Similarly, in kinetic studies there appear two kinds of fire hose instabilities - incompressible and compressible ones. These two instabilities can arise for the same plasma parameters, and the instability of the new compressible oblique fire hose modes can become dominant. The compressible fire hose instability is the result of the resonance coupling of three retrograde modes - two thermal modes and a fast mirror mode. The results can be applied to the theory of solar and stellar coronal and wind models. Title: The Haus der Astronomie in Heidelberg-A New Center for Education and Outreach Authors: Staude, J. Bibcode: 2011ASPC..441..471S Altcode: Since October 2009, a unique facility is being erected on the grounds of the Max Planck Institute for Astronomy on top of the Königstuhl Mountain above Heidelberg, in the immediate vicinity of the State Observatory. It will be dedicated to the communication between scientists, to the development of educational material for junior and high school students, to the training of teachers and student teachers in physics, astronomy and natural sciences, and to the information of the media and the general public about new developments and results in astronomical research. The building will be donated by the Klaus Tschira Foundation, while the Max Planck Society, the University and the City of Heidelberg, and the State Departments of Research and of Education will share the running costs of the new institution. Title: Observational evidences for multi-component magnetic field structure in solar flares Authors: Lozitsky, V. G.; Staude, J. Bibcode: 2009JApA...29..387L Altcode: No abstract at ADS Title: Wave instabilities in an anisotropic magnetized space plasma Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J. Bibcode: 2008A&A...489..769D Altcode: 2008arXiv0805.2405D Aims: We study wave instability in an collisionless, rarefied hot plasma (e.g. solar wind or corona). We consider the anisotropy produced by the magnetic field, when the thermal gas pressures across and along the field become unequal.
Methods: We apply the 16-moment transport equations (obtained from the Boltzmann-Vlasov kinetic equation) including the anisotropic thermal fluxes. The general dispersion relation for the incompressible wave modes is derived.
Results: It is shown that a new, more complex wave spectrum with stable and unstable behavior is possible, in contrast to the classic fire-hose modes obtained in terms of the 13-moment integrated equations. Title: Instability of entropy waves in cosmic plasma Authors: Somov, B. V.; Dzhalilov, N. S.; Staude, J. Bibcode: 2008CosRe..46..392S Altcode: A dispersion equation is derived for small disturbances of the magnetohydrodynamic type in optically transparent plasma with cosmic abundance of elements. The electron heat conductivity along the magnetic field and proton heat conductivity across the field are taken into account. It is shown that entropy waves increase exponentially in wide ranges of temperatures and densities of the cosmic plasma. Manifestations of instability of the entropy waves in the cosmic plasma are discussed. 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: Magneto-Hydro-Dynamic Waves In The Collisionless Space Plasma Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J. Bibcode: 2007SunGe...2...65D Altcode: The instability of magneto-hydro-dynamic (MHD) waves in an anisotropic, collisionless, rarefied hot plasma is studied. Anisotropy properties of such a plasma are caused by a strong magnetic field, when the thermal gas pressures across and along the field become unequal. Moreover, there appears an anisotropy of the thermal fluxes. The study of the anisotropy features of the plasma are motivated by observed solar coronal data. The 16 moments equations derived from the Boltzmann-Vlasov kinetic equation are used. These equations strongly differ from the usual isotropic MHD case. For linear disturbances the wave equations in homogenous anisotropic plasma are deduced. The general dispersion relation for the incompressible wave modes is derived, solved and analyzed. It is shown that a wide wave spectrum with stable and unstable behavior is possible, in contrast to the usual isotropic MHD case. The dependence of the instability on magnetic field, pressure anisotropy, and heat fluxes is investigated. The general instability condition is obtained. The results can be applied to the theory of solar and stellar coronal heating, to wind models and in other modeling, where the collisionless approximation is valid. 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: Peculiarities of entropy and magnetosonic waves in optically thin cosmic plasma Authors: Somov, B. V.; Dzhalilov, N. S.; Staude, J. Bibcode: 2007AstL...33..309S Altcode: 2007PAZh...33..352S The stability problem for small magnetohydrodynamic (MHD) perturbations in an optically thin, perfectly conducting uniform plasma with a cosmic abundance of elements is solved in the linear approximation. The electron heat conduction along the magnetic field and the proton heat conduction across the field are taken into account. We have shown for the first time that the entropy waves can grow exponentially, while the magnetosonic waves are damped in a wide range of physical conditions closest to the conditions in stellar coronae with the proper allowance for radiative losses. Slow magnetosonic waves are damped particularly rapidly. For the solar corona, the calculated damping decrement of slow magnetosonic waves agrees well with the averaged one in 11 quasi-periodic events observed from the TRACE satellite in extreme ultraviolet radiation. Other possible astrophysical applications of the results obtained are briefly discussed. Title: The Characteristic Length Scale of the Magnetic Fluctuation in a Sunspot Penumbra: A Stochastic Polarized Radiative Transfer Approach Authors: Carroll, T. A.; Staude, J. Bibcode: 2007astro.ph..3327C Altcode: The characteristic size of penumbral structures are still below the current resolution limit of modern solar telescopes. Though we have seen a significant progress in theoretical work over the last decades no tight constraints can be placed on the size of penumbral structures in order to favor models with relatively large and thick magnetic flux elements, just at or below the current resolution limit, or on the other hand, clusters of optically thin micro-structures. Based on a macroscopic 2-component inversion and the approach of polarized radiative transfer in stochastic media, we have estimated the characteristic length scale of the magnetic fluctuation in a sunspot penumbra from observed Stokes spectra. The results yield a coherent picture for the entire magnetic neutral line of the penumbra and indicate that the magnetic fluctuations have a typical length scale between 30 km and 70 km. Title: New high resolution solar telescope GREGOR Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier, K.; Wittmann, A. D. Bibcode: 2007msfa.conf...39V Altcode: The 1.5m solar telescope GREGOR is being constructed at Tenerife, Spain. Its purpose is to observe with high spatial and spectral resolution small-scale dynamic magnetic features on the Sun. The telescope is completely open with retractable dome and actively cooled primary mirror made of silicon carbide to minimize thermal effects on the image quality. After completion it will be one of the most powerful solar telescopes. This paper presents a general overview of the telescope characteristics and the current status. Title: The Characteristic Length Scale of the Magnetic Fluctuation in a Sunspot Penumbra: A Stochastic Polarized Radiative Transfer Approach Authors: Carroll, T. A.; Staude, J. Bibcode: 2006ASPC..358..137C Altcode: The characteristic size of penumbral structures are still below the current resolution limit of modern solar telescopes. Though we have seen a significant progress in theoretical work over the last decades no tight constraints can be placed on the size of penumbral structures in order to favor models with relatively large and thick magnetic flux elements, just at or below the current resolution limit, or on the other hand, clusters of optically thin micro-structures.

Based on a macroscopic 2-component inversion and the approach of polarized radiative transfer in stochastic media, we have estimated the characteristic length scale of the magnetic fluctuation in a sunspot penumbra from observed Stokes spectra. The results yield a coherent picture for the entire magnetic neutral line of the penumbra and indicate that the magnetic fluctuations have a typical length scale between 30 km and 70 km. 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: Line Formation in Inhomogeneous Atmospheres and the Magnetic Structure of the Internetwork Authors: Carroll, T. A.; Staude, J. Bibcode: 2005ESASP.596E...9C Altcode: 2005ccmf.confE...9C 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: Dynamics of solar active regions. II. Oscillations observed with MDI and their relation to the magnetic field topology Authors: Muglach, K.; Hofmann, A.; Staude, J. Bibcode: 2005A&A...437.1055M Altcode: We present new results of an international joint observing campaign, which was carried out in September 2000 to study the oscillatory behaviour of solar active regions. We concentrate on oscillations in the lower layers of the solar atmosphere as observed with the Michelson Doppler Imager (MDI, Scherrer et al. 1995, Sol. Phys., 162, 129). The resulting photospheric oscillation power maps are compared with chromospheric maps from simultaneous UV continuum data (taken with the TRACE instrument). From a magnetic field extrapolation of the MDI magnetograms we infer that the reduction in chromospheric high frequency power and enhancement of photospheric high frequency power may be explained by the interaction of acoustic waves with the magnetic canopy. Title: Active Region Oscillations and Their Relation to the Magnetic Field Topology Authors: Muglach, K.; Hofmann, A.; Staude, J. Bibcode: 2005AGUSMSH13C..03M Altcode: In this contribution we present an analysis of time sequences of MDI intensity and Doppler velocity together with simultaneous filtergrams taken by TRACE at 1700A in an active region. The high frequency halos found in MDI velocity and the deficiency of high frequency power sampled at the height of the TRACE UV filter around the active region can be explained by an interaction of the acoustic wave field with the magnetic field of the active region. From a magnetic field extrapolation we calculate the plasma β for the complete TRACE FOV up to the base of the corona. The contours giving the location of β approximately 1 where h=500 km agree very well with the decrease in 1700A high frequency power. Title: Line formation in turbulent magnetic atmospheres Authors: Carroll, T. A.; Staude, J. Bibcode: 2005AN....326..296C Altcode: We present a stochastic formulation of the polarized radiative transfer in an atmosphere permeated by a random magnetic field. On the basis of a Markov process we describe the line formation as a stochastic process which allows us to account for a finite correlation length of the fluctuating structures. The resulting stochastic master equation describes the evolution of the expectation value of the Stokes vector (the macroscopic observable) through the atmosphere. As the correlation length (mean structural length scale of the fluctuating or turbulent elements) appears explicitly in the stochastic transport equation it can be used as a diagnostic parameter from which an estimation of the underlying structural length scale is possible. Title: The Helioseismological CORONAS-F DIFOS Experiment Authors: Lebedev, N. I.; Kuznetsov, V. D.; Oraevskii, V. N.; Staude, J.; Kostyk, R. I. Bibcode: 2004ARep...48..871L Altcode: The CORONAS-F DIFOS experiment continues the CORONAS-I studies started in 1994, devoted to investigations of solar global oscillations. CORONAS-F was launched July 31, 2001. Variations in the intensity of the solar radiation are measured in the six spectral intervals of the multi-channel photometer: 350, 500, 650, 850, 1100, and 1500 nm, with the bandwidths being about 10% of the central wavelength of each interval. The scientific goals of the experiment, a brief description of the instrument, and observational conditions are presented, as well as the data processing techniques. The first observations of the low-order p eigenmodes of the solar oscillations are presented for various wavelength ranges. A decrease in the relative amplitudes with observing wavelength is indicated. The amplitude ratios for various spectral ranges agree well with those detected earlier in ground-and space-based experiments. 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: Eigenoscillations of the differentially rotating Sun. II. Generalization of the Laplace tidal equation Authors: Dzhalilov, N. S.; Staude, J. Bibcode: 2004A&A...421..305D Altcode: 2002astro.ph..1170D The general partial differential equation governing linear adiabatic nonradial oscillations in a spherical, differentially and slowly rotating non-magnetic star is derived. This equation describes mainly low-frequency and high-degree g-modes, convective g-modes, rotational Rossby-like vorticity modes, and their mutual interaction for arbitrarily given radial and latitudinal gradients of the rotation rate. Applying to this equation the ``traditional approximation'' of geophysics results in a separation into radial- and angular-dependent parts of the physical variables, each of which is described by an ordinary differential equation. The angular parts of the eigenfunctions are described by the Laplace tidal equation generalized here to take into account differential rotation. It is shown that there appears a critical latitude in the sphere where the frequencies of eigenmodes coincide with the frequencies of inertial modes. The resonant transformation of the modes into the inertial waves acts as a resonant damping mechanism of the modes. Physically this mechanism is akin to the Alfvén resonance damping mechanism for MHD waves. It applies even if the rotation is rigid. The exact solutions of the Laplace equation for low frequencies and rigid rotation are obtained. The eigenfunctions are expressed by Jacobi polynomials which are polynomials of higher order than the Legendre polynomials for spherical harmonics. In this ideal case there exists only a retrograde wave spectrum. The modes are subdivided into two branches: fast and slow modes. The long fast waves carry energy opposite to the rotation direction, while the shorter slow-mode group velocity is in the azimuthal plane along the direction of rotation. It is shown that the slow modes are concentrated around the equator, while the fast modes are concentrated around the poles. The band of latitude where the mode energy is concentrated is narrow, and the spatial location of these band depends on the wave numbers (l, m). Title: Observations of oscillations in the transition region above sunspots Authors: Rendtel, J.; Staude, J.; Curdt, W. Bibcode: 2003A&A...410..315R Altcode: Observations during two campaigns of the SUMER spectrograph and the EIT imager onboard SoHO were used to analyse oscillations in bright sunspot plumes. We report variations of both intensity and velocity seen in EUV emission lines originating in the sunspot upper chromosphere and the transition region. The wavelet analysis reveals rapidly changing conditions in the emitting volumes. Generally, oscillations in the 5 min range dominate in the chromosphere, while the transition region lines show oscillations at shorter periods (2 to 3 min). A drift of the oscillation period of the Doppler velocity from 5 min to 2.5 min within about 30 min can be explained by a strongly non-stationary behaviour of the upper chromosphere and transition region, probably related to downstream of material within the plume region. Synchronous EIT observations of the lower corona show no intensity oscillations. This hints either at a strong damping or a downward reflection in the upper transition region or lower corona. Title: Current Status of the 1.5m Solar Telescope GREGOR Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkfeld, Thomas; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittman, Axel; Hofmann, Axel; Sobotka, Michal; Klvana, Miroslav Bibcode: 2003ANS...324..112V Altcode: 2003ANS...324..P19V No abstract at ADS Title: GREGOR: the new 1.5m solar telescope on Tenerife Authors: Volkmer, Reiner; von der Luehe, Oskar; Kneer, Franz; Staude, Juergen; Hofmann, Axel; Schmidt, Wolfgang; Sobotka, Michal; Soltau, Dirk; Wiehr, Eberhardt; Wittmann, Axel; Berkefeld, Thomas Bibcode: 2003SPIE.4853..360V Altcode: The new 1.5 m high resolution telescope will be build up on the reused solar tower of the German 45 cm Gregory Coudé Telescope at the Teide Observatory, Izaña, Tenerife. The new telescope is a Gregory type with open telescope structure, alt-azimuth mount, complete retractable dome, and a pool of well established and new developed post focus instruments. An adaptive optics system provides the capability for diffraction limited observations at visible wavelengths and the polarimetry device in the secondary focus reduces the perturbation due to instrumental polarization in an efficient way. We describe the main optical characteristics and the focal plane instrumentation with respect to the latest status of the project. Title: Oscillations of velocity and magnetic fields in sunspot umbrae Authors: Staude, J. Bibcode: 2003AN....324..391S Altcode: No abstract at ADS Title: Diagnostics of Magnetic Field Mesostructuring Authors: Carroll, T. A.; Staude, J. Bibcode: 2003ASPC..307..125C Altcode: No abstract at ADS Title: Meso-structured magnetic atmospheres: Stochastic polarized radiative transfer and Stokes profile inversion Authors: Carroll, T. A.; Staude, J. Bibcode: 2003AN....324..392C Altcode: No abstract at ADS Title: Multi-Component Magnetic Field Structure in Solar Flares Authors: Lozitsky, V. G.; Staude, J. Bibcode: 2003ASPC..307..378L Altcode: No abstract at ADS Title: GREGOR, a 1.5 m Gregory-type telescope for solar observation Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Soltau, W. Schmidt D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2002NCimC..25..689K Altcode: No abstract at ADS Title: Signature of differential rotation in solar disk-integrated chromospheric line emission Authors: Hasler, K. -H.; Rüdiger, G.; Staude, J. Bibcode: 2002AN....323..123H Altcode: UARS SOLSTICE data have been subjected to Fourier and wavelet analyses in order to search for the signature of the solar rotation law in the disk-integrated irradiance of UV lines. Lyman-alpha, Mg II, and Ca II data show a different behaviour. In the SOLSTICE data there are significant temporal variations of the rotation rate of the UV tracers over 5 - 6 years. Often several distinct rotation periods appear almost simultaneously. Beside the basic period around 27 days there are signals at 32 - 35 days corresponding to the rotation rate at very high latitudes. For more than 5 years during another period of the solar cycle the rotational behaviour is quite different; there is an indication of differential rotation of active regions in these Ca II ground-based data. The data contain a wealth of information about the solar differential rotation, but it proves difficult to disentangle the effects of the different emitting sources. Title: Magnetic field oscillations of sunspots? Authors: Staude, J. Bibcode: 2002AN....323..317S Altcode: For 3 decades it is known that sunspots show oscillations of velocity and intensity, that is of thermodynamic quantities. Oscillatory power is concentrated at periods around 2 \ldots 3 min, 5 min, and ga 20 min. Attempts to measure related magnetic field oscillations were contradictory. Now there are hints of significant magnetic signals in 2-D spectro-polarimetric data with power mainly in pores and at the boundary between the umbra and the penumbra of larger spots. We discuss these data and possibilities of their interpretation which are still a matter of debate. The magnetic oscillations could be the signature of a `whispering gallery' like mode of slow body waves in a thick magnetic flux-tube. However, other interpretations such as opacity oscillations or a crosstalk from velocity or compressive waves cannot be ruled out as long as better observed data, measurements of phase shifts in particular, and more realistic models are still missing. Title: On nonadiabatic waves in the photospheres of cool stars Authors: Pregla, A. V.; Zhugzhda, Y. D.; Staude, J. Bibcode: 2002AN....323..465P Altcode: The coupled set of equations of hydrodynamics and radiative transfer is derived for small disturbances in a plane, grey atmosphere. Only radiative transfer is taken into account in the energy equation; dynamical effects of radiation are ignored. A mean stationary radiative flux through the photosphere is taken into account. The radiative transfer equation is used by assuming the Eddington approximation, moreover, an exponential height profile of the temperature and an analytical opacity formula are supposed. For this model we obtained an asymptotic solution for plane nonadiabatic acoustic waves and radiation waves. The approach provides a detailed discussion of the interaction of nonadiabatic p-modes and radiation waves in a realistic model of the photosphere of a solar-like star. Title: Long-period eigenoscillations of the solar interior: 1-3 yr, 20-40 yr, and 1500-20000 year modes Authors: Staude, Jürgen; Dzhalilov, Namig S. Bibcode: 2002ESASP.477..167S Altcode: 2002scsw.conf..167S Waves with periods much larger than the rotation period become trapped in the solar radiative interior. The modelling considers compressible, nonadiabatic, Rossby- like modes (ɛ-mechanism and radiative losses are taken into account) for a very small latitudinal gradient of rotation, without an arbitrary choice of other free parameters. We found global vorticity modes in 3 separate period ranges of ≍1-3 yr, 20-40 yr, and 1500-20000 yr which are maximum unstable. The discovered resonant cavity modes (called R-modes) are different from the known r-modes. We discuss some prospects to develop the theory of R-modes as a driver of the dynamics in the convective zone which could explain e.g., observed short-term fluctuations of rotation, a control of the solar magnetic cycle, and abrupt changes of terrestrial climate in the past (Dansgaard-Oeschger events). Title: Eigenoscillations of the differentially rotating Sun. I. 22-year, 4000-year, and quasi-biennial modes Authors: Dzhalilov, N. S.; Staude, J.; Oraevsky, V. N. Bibcode: 2002A&A...384..282D Altcode: 2002astro.ph..1120D Retrograde waves with frequencies much lower than the rotation frequency become trapped in the solar radiative interior. The eigenfunctions of the compressible, nonadiabatic (epsilon -mechanism and radiative losses taken into account) Rossby-like modes are obtained by an asymptotic method assuming a very small latitudinal gradient of the rotation rate. An integral dispersion relation for the complex eigenfrequencies is derived as a solution of the boundary value problem. The discovered resonant cavity modes (called R-modes) are fundamentally different from the known r-modes: their frequencies are functions of the solar interior structure, and the reason for their existence is not related to geometrical effects. The most unstable R-modes are those with periods of ~1-3 yr, 18-30 yr, and 1500-20 000 yr; these three separate period ranges are known from solar and geophysical data. The growing times of those modes which are unstable with respect to the epsilon -mechanism are ~102, 103, and 105 years, respectively. The amplitudes of the R-modes are growing towards the center of the Sun. We discuss some prospects to develop the theory of R-modes as a driver of the dynamics in the convective zone which could explain, e.g., observed short-term fluctuations of rotation, a control of the solar magnetic cycle, and abrupt changes of terrestrial climate in the past. Title: Global Oscillations of the Sun in a Wide Optical Spectral Range: DIFOS Experiment Onboard CORONAS-F Authors: Oraevsky, V.; Lebedev, N.; Kuznetsov, V.; Staude, J.; Kostyk, R. Bibcode: 2002cosp...34E.345O Altcode: 2002cosp.meetE.345O The DIFOS experiment onboard the CORONAS-F spacecraft continues the investigation of solar global oscillations, which was started in 1994 during the CORONAS-I mission. The satellite was launched on July 31, 2001. It uses a multi-channel photometer to observe irradiance fluctuations. The photometer measures fluctuations of the solar flux in six optical spectral ranges: near 350, 500, 650, 850, 1100, and 1500 nm with a bandwidth of about 10% of the central wavelength for each. After a short description of the instrumentation and data analyses, we present results of observations of low-degree p-modes of global oscillations for different observational optical ranges. The oscillation amplitudes were found to decrease with the growth of the wavelength. The amplitude ratios for different wavelength are in a good agreement with earlier observations and theoretical predictions. Title: GREGOR: a 1.5 m telescope for solar research Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Berkefeld, Th.; Kneer, F.; Staude, J. Bibcode: 2001AN....322..353V Altcode: GREGOR will be a new 1.5 meter solar telescope at the Teide Observatory, Izaña, Tenerife. It will provide observations with high polarimetric precision at visible and infra-red wavelengths from Earth in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR replaces the 45 cm Gregory Coudé telescope. Title: Introduction to Volume 322 (5/6) Proceedings of the Joint-Discussion #1 and the Mini-Symposia #9 and #10 at the Joint European and National Astronomical Meeting (JENAM) for 2001 Authors: Strassmeier, K. G.; Staude, J.; Dreizler, S. Bibcode: 2001AN....322..271S Altcode: This volume of AN contains the proceedings of the Joint Discussion #1 (JD-1) ``Astronomy with Robotic Telescopes: Present and Future Projects'' and of the Mini Symposia #9 (MS-9) ``Hot subdwarfs, white dwarfs, and low-mass star evolution'', and #10 (MS-10) ``Large Telescopes for Solar Physics''. The meetings were held as part of the JENAM 2001 conference ``Five Days of Creation. Astronomy with Large Telescopes from Ground and Space'' in Munich, Germany, from September 10 through 15, 2001. Title: Post-focus instrumentation for GREGOR Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.; Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2001AN....322..361K Altcode: GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR. Title: The inversion of Stokes profiles with artificial neural networks Authors: Carroll, T. A.; Staude, J. Bibcode: 2001A&A...378..316C Altcode: We investigate the application of artificial neural networks (ANNs) for the interpretation of Stokes profiles. We have employed ANNs to approximate the nonlinear inverse mapping between the Stokes profiles and some of the underlying atmospheric parameters. This approximate model is used in the following to carry out a fast non-iterative inversion of synthetic Stokes profiles. We have used synthetic Stokes profiles of the photospheric infrared line Fe I lambda 15648 to demonstrate that the ANNs are capable to yield accurate single valued estimates of the complete magnetic field vector, line-of-sight (LOS) velocity, microturbulence, macroturbulence and the filling factor with exceptional speed. For a stratified atmosphere we also demonstrate that these single valued parameters do represent very good averaged values of the input stratification. To retrieve some of the temperature information encoded in the Stokes profiles we modeled a neural network classifier on the basis of several semi-empirical model atmospheres (i.e. temperature and pressure stratification). With this classifier we are able to determine the probability that a given Stokes profile has its origin from a particular temperature stratification of a semi-empirical model. Title: GREGOR: high resolution solar observations from 1 AU Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.; Staude, J.; Pailer, N. Bibcode: 2001ESASP.493..417V Altcode: 2001sefs.work..417V No abstract at ADS Title: Waves in Sunspots: Resonant Transmission and the Adiabatic Coefficient Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D. Bibcode: 2001SoPh..202..281S Altcode: We investigate linear acoustic-gravity waves in three different semi-empirical model atmospheres of large sunspot umbrae. The sunspot filter theory is applied, that is, the resonant transmission of vertically propagating waves is modelled. The results are compared with observed linear sunspot oscillations. For three umbral models we present the transmission coefficients and the energy density of the oscillations with the maxima of transmission. The height dependence of the adiabatic coefficient (the ratio of specific heats) γ strongly influences the calculated resonance frequencies. The variable γ can explain the observed closely spaced resonance period peaks. The first resonance in the 3 min range is interpreted as a resonance of the upper chromosphere only, while the higher order peaks are resonances of the whole chromosphere. Title: Observations of oscillations above sunspots Authors: Rendtel, Jürgen; Staude, Jürgen Bibcode: 2001ESASP.493..337R Altcode: 2001sefs.work..337R No abstract at ADS Title: Analysis and interpretation of Stokes profiles with artificial neural networks Authors: Carroll, T. A.; Staude, J. Bibcode: 2001ESASP.493..183C Altcode: 2001sefs.work..183C No abstract at ADS Title: Shifts of p-mode frequencies by wave tunneling through the solar atmosphere Authors: Dzhalilov, Namig S.; Staude, Jürgen Bibcode: 2001ESASP.464..625D Altcode: 2001soho...10..625D Global adiabatic p-modes are modelled by an asymptotic theory, taking into account the influence of the solar atmosphere on the formation of the eigenoscillations: waves of the whole frequency range 2-10 mHz are now reaching the chromosphere-corona transition region (CCTR) by the tunneling of acoustic waves through the atmospheric barriers. The main acoustic cavity inside the Sun becomes considerably extended in this way, leading to a change of frequencies: low frequencies are increased, while high frequencies are decreased. The transition from low p-mode frequencies to high peak frequencies >6mHz is smooth. The imaginary parts of the frequencies indicate a decay of the amplitudes, resulting from considerable energy losses by tunneling from the main cavity. A penetration of linear p-modes to the corona is impossible. The behavior of the CCTR is that of a free surface: the p-modes may drive forced surface gravity waves of this free surface. Title: Problems in the interpretation of sunspot oscillation measurements Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D. Bibcode: 2001ESASP.464..247S Altcode: 2001soho...10..247S Sunspot oscillations are observed in spectral lines formed at different depths in the sunspot atmosphere. The interpretation of measurements in chromospheric lines is problematic as the lines are formed in NLTE. So the measured power spectra do not originate from one specific depth in the atmosphere but are smoothed out over a larger region. This will also influence the phase shifts of the waves measured in different spectral lines and might cause some misinterpretation. These complications are illustrated by our model calculations: Modelling the transmission of magneto-atmospheric waves through the sunspot atmosphere by means of the sunspot filter approach, we show the "real" power spectra at different atmospheric depths. These results are compared with Ca II-H/K power spectra gained from the NLTE calculations of the Ca II-H/K lines in an atmosphere perturbed by our waves. All results are preliminary. Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.; Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2001AGM....18.P223K Altcode: GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar atmosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the Observatorio del Teide on Tenerife. We describe the optical design and the focal plane instrumentation. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying processes. GREGOR will also serve as a test bed for next generation solar telescopes. Title: Sunspot transition region oscillations Authors: Rendtel, J.; Staude, J.; Wilhelm, K.; Gurman, J. P. Bibcode: 2001ESASP.464..235R Altcode: 2001soho...10..235R Intensity and velocity oscillations have been observed over a period of 4.3 hours in lines of Ne VIII and C IV with the SUMER spectrograph aboard SOHO. These lines are formed in the EUV plume above a sunspot. Applying a wavelet analysis, we find oscillations mainly close to 3 mHz. The temporal behaviour is strongly intermittent, particularly for the velocity oscillations. This non-stationary behaviour may be related with occurrence of blinkers in the umbral transition region. Title: Resonant Transmission of Magneto-atmospheric Waves in Sunspot Umbrae Authors: Staude, J.; Rendtel, J.; Settele, A. Bibcode: 2001IAUS..203..320S Altcode: Oscillations of velocity and intensity, of the magnetic field in the photosphere as well, have been observed at all height levels of the atmosphere above sunspots from the photosphere up to the lower corona. We discuss the nonstationary behavior of intensity and velocity oscillations; they have been observed by SOHO in transition region lines formed in the EUV plume of a sunspot during a continuous time series of 4.3 hours. Applying a wavelet analysis, we find periods around 3 mHz with different periods in the observed EUV lines. Moreover, we discuss the observed oscillations within the frame of model calculations for the resonant transmission of magneto-atmospheric waves through realistic models of the sunspot subphotosphere and atmosphere. Title: Long-period Eigenoscillations of the Solar Interior: 22-year, 4500-year, and Quasi-biennial Modes Authors: Staude, J.; Dzhalilov, N. S. Bibcode: 2001AGM....18..P04S Altcode: Waves with periods much larger than the rotation period become trapped in the solar radiative interior. Our modelling considers compressible, nonadiabatic, Rossby-like modes (ɛ-mechanism and radiative losses are taken into account) for a very small latitudinal gradient of rotation, without an arbitrary choice of further free parameters. These `R-modes' are fundamentally different from the known `r-modes': their frequencies are functions of the solar interior structure, and the reason for their existence is not related to geometrical effects. The amplitudes of the R-modes are growing towards the center of the Sun. We found global vorticity modes in 3 separate period ranges around 1.3-2.0, 22, and 4500 years (with an onset at 1500 years) which are maximum unstable. They could possibly control the solar activity cycle, cause the 1.3 year period variation of solar rotation which was recently found in the deeper convective zone and produce the quasi-biennial oscillations in solar activity and geophysical data. Moreover, they could be related to the abrupt changes of terrestrial climate in the past (Dansgaard-Oeschger events). Title: Low-Frequency Eigenoscillations of the Differentially Rotating Solar Interior Authors: Dzhalilov, N. S.; Staude, J. Bibcode: 2001ASPC..248..173D Altcode: 2001mfah.conf..173D No abstract at ADS Title: Influence of the solar atmosphere on the p-mode eigenoscillations Authors: Dzhalilov, N. S.; Staude, J.; Arlt, K. Bibcode: 2000A&A...361.1127D Altcode: An asymptotic theory of global adiabatic p-modes is developed, taking into account the influence of the solar atmosphere. It is shown that waves of the whole frequency range nu ~ 2-10 mHz may reach the chromosphere-corona transition region (CCTR) by means of a tunneling through the atmospheric barriers. The primary acoustic cavity inside the Sun becomes considerably extended by this way, leading to a change of frequencies: low frequencies are increased, while high frequencies are decreased. The transition from low p-mode frequencies to high peak frequencies (nu >~ 6;mHz) is smooth. The locations of the turning points are determined from the wave equation for {div}*/rightarrow{v}. It is shown that the internal turning point of the acoustic cavity is strongly shifted toward the center of the Sun, while the upper turning point is shifted from the surface to CCTR. That means, the turning points cannot be located in the convective zone. A new complex integral dispersion relation for the eigenfrequencies is derived. The imaginary parts of the frequencies indicate a decay of the amplitudes, resulting from considerable energy losses by tunneling from the main cavity. It is shown that waves with a decaying amplitude (complex frequency) may exist in a limited area only, penetration of linear p-modes to the corona is impossible. The CCTR acts as a free surface. We conclude that the p-modes may drive forced surface gravity waves at this surface. 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: Helioseismologie - ein neues Fenster der Sonnenforschung. Authors: Staude, J. Bibcode: 2000A&R....37....4S Altcode: No abstract at ADS Title: Friedrich Wilhelm Jäger (1914 - 14. Februar 2000). Authors: Staude, J. Bibcode: 2000MitAG..83...13S Altcode: No abstract at ADS Title: Sonnenphysik in Potsdam Title: Sonnenphysik in Potsdam Title: Solar physics in Potsdam. Authors: Staude, Jürgen Bibcode: 2000AcHA...11...81S Altcode: Solar research initiated the establishment of the Astrophysical Observatory Potsdam (AOP) in 1874. The present contribution outlines the development of solar physics in Potsdam from the early history of the AOP to this day. The main topics are the work of Karl Schwarzschild, the investigations related to the general theory of relativity, the foundation of the Einstein tower, Walter Grotrian's founding of modern coronal physics, and the investigations of sunspot magnetic fields. Title: Sonnenforschung in Potsdam - Streiflichter aus der Geschichte Title: Sonnenforschung in Potsdam - Streiflichter aus der Geschichte Title: Solar research in Potsdam - sidelights on its history. Authors: Staude, Jürgen; Hofmann, Axel Bibcode: 2000AcHA....8..107S Altcode: No abstract at ADS Title: GREGOR: A 1.5m Telescope for Solar Research Authors: von der Lühe, O.; Schmidt, Wolfgang; Soltau, Dirk; Kneer, Franz; Staude, Jurgen Bibcode: 2000ESASP.463..629V Altcode: 2000sctc.proc..629V No abstract at ADS 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: The Influence of the Adiabatic Coefficient and the Magnetic Field on Sunspot Oscillations Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1999ESASP.448..367S Altcode: 1999ESPM....9..367S; 1999mfsp.conf..367S 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: Determination of the Velocity Vector Field in an Asymmetric Sunspot Based on Vector Magnetograph Measurements Authors: Krivtsov, A. M.; Hofmann, A.; Staude, J.; Klvaña, M.; Bumba, V. Bibcode: 1999ASPC..184..108K Altcode: A new method to determine the distribution of the full velocity vector in an asymmetric sunspot is presented. Measurements of the Doppler velocity and of the vector of the magnetic field are used as initial data for these calculations. The determination is subdivided into two stages: in a first step we obtain the distribution of the velocity projection onto the solar surface, and in the second step the orthogonal component of the velocity field is calculated. The resulting vector velocity field is in good agreement with the basic features of the siphon flow model of penumbral flux tubes. Title: SUMER Observations of Intensity Oscillations in the Transition Region of a Sunspot Authors: Rendtel, J.; Staude, J.; Innes, D. E.; Wilhelm, K. Bibcode: 1999ASPC..184..271R Altcode: UV spectroscopic data obtained with the SUMER spectrograph aboard SOHO have been analysed to detect oscillations in the chromosphere-corona transition region (TR) above sunspots. We observed the active region NOAA 7986 in the wavelength bands around the Ne VIII line at 770.4 Å and the C IV line at 1548.1 Å on August 29, 1996, between 09:08 UT and 13:31 UT. Simultaneous observations with the Normal Incidence Spectrometer of CDS aboard SOHO have shown, that the spot had a bright EUV plume at TR temperatures. A preliminary data analysis indicates intensity oscillations in the 2-minute range (7.3...7.9 mHz) in both spectral lines. The temporal variation of oscillatory power in the two spectral lines is generally in opposite directions, i.e. during an increase of oscillatory power in the Ne VIII line we find a decrease in the C IV line. A similar but smaller tendency is observed in the average intensity of the line profiles. This hints at a non-adiabatic behaviour of the oscillations and a slow cooling of the emitting sunspot plume region. Title: Sunspot Oscillations Authors: Staude, J. Bibcode: 1999ASPC..184..113S Altcode: Sunspots show oscillations of velocity, of intensity, and probably of the magnetic field; the oscillations are observed at different periods (2-3 min, 5 min, <= 20 min), at all height levels of the sunspot atmosphere, and with different spatial distributions and characteristic phase relations. In the present paper a short review on the various phenomena is given, with focusing on oscillations of the magnetic field at photospheric levels and on oscillations in the transition region to the corona above sunspots, derived from recent 2-D observations with high spatial resolution. The observed data are compared with the predictions from theory and modelling. 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: Third Advances in Solar Physics Euroconference: Magnetic Fields and Oscillations Authors: Schmieder, B.; Hofmann, A.; Staude, J. Bibcode: 1999ASPC..184.....S Altcode: The third Advances in Solar Physics Euroconference (ASPE) "Magnetic Fields and Oscillations"concluded a series of three Euroconferences sponsored by the European Union. The meeting took place in Caputh near Potsdam, Germany, on September 22-25, 1998, followed by the JOSO (Joint Organization for Solar Observations) 30th Annual Board Meeting on September 26, 1998. The ASPE formula is attractive and compares well with other meetings with "show-and-tell" character. This meeting had 122 participants coming from 26 countries; 36 participants came from countries formerly behind the Iron Curtain; a "politically incorrect" estimate says that 48 participants were below 35 years of age, with an unusually large female-to-male ratio. This characteristic of youngness is the more striking since solar physics is a perhaps overly established field exhibiting an overly senior age profile. It was a good opportunity to train this young generation in Solar Physics. The conference topic "Magnetic Fields and Oscillations" obviously was wide enough to cater to many an interest. These proceedings are organized according to the structure of the meeting. They include the topics 'High resolution spectropolarimetry and magnetometry', 'Flux-tube dynamics', 'Modelling of the 3-D magnetic field structure', 'Mass motions and magnetic fields in sunspot penumbral structures', 'Sunspot oscillations', 'Oscillations in active regions - diagnostics and seismology', 'Network and intranetwork structure and dynamics', and 'Waves in magnetic structures'. These topics covered the first 2.5 days of the conference. The reviews, oral contributions, and poster presentations were by no means all of the meeting. The ASPE formula also adds extensive plenary sessions of JOSO Working groups on topics that involve planning of Europe-wide collaboration. At this meeting these concerned solar observing techniques, solar data bases, coordination between SOHO and ground-based observing, and preparations for August 11, 1999 when more Europeans will be eclipsed than ever before. The contributions to these sessions have been included into the present volume as well. The participants of the EU-TMR Research Network 'Solar Magnetometry Network' came together to discuss in a special working group session questions of their future collaboration. Title: An attempt to estimate nonideal effects on the electron partial pressure in the solar interior up to density order 5/2 Authors: Meister, C. -V.; Staude, J.; Pregla, A. V. Bibcode: 1999AN....320...43M Altcode: Helioseismology is probing the equation of state of the solar interior with ever increasing precision. Recently, even nonideal pressure modifications below 1 % are being considered, mainly due to the use of different partition functions. In the present paper only the electron partial pressure has been studied, and thus no partition function was taken into account. Instead, the pressure was calculated beyond the usually applied Debye-Huckel theory, and quantum-mechanical electron exchange was taken into account very carefully. If the total electron pressure at distances from the solar centre larger than 0.83 solar radii could be described by equilibrium thermodynamics, it proved smaller than the value for an ideal gas due to the dominating Debye-Huckel screening. On the contrary, at distances smaller than 0.83 solar radii electron exchange increases the total pressure up to values above the ideal pressure. Pressure modifications up to one per cent are caused by the higher-order interactions beyond the Debye-Huckel screening. Title: Measurements of magnetic field strength on T Tauri stars Authors: Guenther, Eike W.; Lehmann, Holger; Emerson, James P.; Staude, Jürgen Bibcode: 1999A&A...341..768G Altcode: We have investigated the magnetic field strength of one weak-line and four classical T Tauri stars. The magnetic field strength is derived from the differential change of the equivalent width of photospheric Fe I lines in the presence of a magnetic field, calculated using a full radiative transfer code. The method was successfully tested by applying it to a non-magnetic solar-type star, and to VY Ari which is believed to have a strong magnetic field. For two of the classical T Tauri stars, we find a product of magnetic field strength and filling factor B * f = (2.35+/- 0.15) kG for T Tau, and B * f = (1.1+/- 0.2) kG for LkCa 15. For the classical T Tauri star UX Tau A and the weak-line T Tauri star LkCa 16 the detection is only marginal, indicating magnetic field strengths of the order of 1 kG and possibly of more than 2 kG, respectively. No field could be detected for the classical T Tauri star GW Ori. For the two classical T Tauri stars for which we have detected a field, we find the filling factors to be larger than ~ 0.5, which indicates that the magnetic field covers most of the photosphere. We also show that ignoring a magnetic field can, depending on the lines used, result in errors in effective temperature and underestimates of veiling. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio de los Roque de los Muchachos of the Instituto de Astrofisica de Canarias Title: GREGOR, a 1.5 M Solar Telescope Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.; Staude, J. Bibcode: 1999AGAb...15....5V Altcode: 1999AGM....15..A01V We present the design of a new large solar telescope which is going to be installed at the Observatorio del Teide, in the tower that presently houses the 45cm Gregory-Coudé-Telescope. The new telescope has an aperture of 1.5 meters and its optical design is basically a Gregorian configuration. It will be an open telescope in an azimuthal mount. An adaptive optics system is incorporated in the optical design as well as a polarimetry package. The feasibility of lightweight optics for the primary mirror has been investigated in an industrial pre-study. The focal plane instrumentation will include a high resolution filter spectrometer similar to the existing TESOS instrument at the VTT and a new spectro-polarimeter for the visible and the near UV. The latter instrument is presently being developed jointly by the KIS and the High Altitude Observatory in Boulder, USA. Budget permitting, detailed (Phase-B) planning will start in 2000, and the telescope will be developed and built in 2002 and 2003 with first light in spring of 2004. Title: Max-Planck-Institut für Astronomie, Heidelberg-Königstuhl. Jahresbericht 1997. Authors: Staude, J.; Appenzeller, I.; Bührke, T. Bibcode: 1999mfah.bookQ....S Altcode: No abstract at ADS Title: A new method to calculate the resonant response of a sunspot model atmosphere to magneto-atmospheric waves Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1999AN....320..147S Altcode: In order to understand the observed oscillations in sunspots we present a new method for calculating the resonant response of a realistic semi-empirical model of the sunspot umbral atmosphere and subphotosphere to magneto-atmospheric waves in a vertical magnetic field. The depth dependence of both the adiabatic coefficient and the turbulent pressure is taken into account. This requires an extension of the wave equations by Ferraro & Plumpton (1958). We compare the coefficients of wave transmission, reflection, and conversion between fast mode and slow mode waves for different assumptions, compare the results with those from earlier modelling efforts, and point out possible sources of mistakes. The depth dependence of the adiabatic coefficient strongly influences the resulting spectrum of resonance frequencies. The condition of a conservation of wave flux is violated if the depth dependence of the turbulent pressure is not properly considered. Title: High resolution spectro-polarimetric observations of sunspot penumbrae. Authors: Maleki, D.; Staude, J. Bibcode: 1999joso.proc...85M Altcode: Spectro-polarimetric observations with high spatial resolution have been obtained in sunspot penumbrae and used to derive the magnetic field structure in different filamentary fine structures. Some results from a preliminary data analysis are listed. Title: Magnetic fields and oscillations. 3rd Euroconference ASPE98 (Advances in Solar Physics Euroconference 1998), Potsdam/Caputh (Germany), 22 - 25 Sep 1998. Poster contributions. Authors: Schmieder, B.; Staude, J. Bibcode: 1999joso.proc...74S Altcode: All of the oral presentations of ASPE98 will be published in a separate volume of the ASP Conference Series, while this volume contains the poster presentations. 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: Max-Planck-Institut für Astronomie, Heidelberg-Königstuhl. Jahresbericht 1998. Authors: Staude, J.; Appenzeller, I.; Bührke, T. Bibcode: 1999mfah.bookR....S Altcode: No abstract at ADS Title: Determination of the full velocity vector based on vector magnetograph measurements in an asymmetric sunspot Authors: Krivtsov, A. M.; Hofmann, A.; Staude, J.; Klvana, M.; Bumba, V. Bibcode: 1998A&A...335.1077K Altcode: A new method to determine the distribution of the full velocity vector in an asymmetric sunspot is presented. Measurements of the Doppler velocity and of the vector of the magnetic field are used as initial data for these calculations. The determination is subdivided into two stages: in a first step we obtain the distribution of the velocity projection onto the solar surface, and in the second step the orthogonal component of the velocity field is calculated. The method has been applied to a sunspot observed from two observatories over 7 days, that is at different positions on the solar disk and in different phases of its development. The resulting vector velocity field is in good agreement with the basic features of the siphon flow model of penumbral flux tubes. The velocities are directed outwards from the sunspot, and they have small values in the umbra and maximum values in the central part of the penumbra, while in the outer penumbra the velocities decrease rapidly. The vertical velocities are mainly localized at the umbral boundary (upflows) and at the outer parts of the penumbra (downflows). Title: German-Russian Cooperation in Helioseismology Authors: Horn, T.; Hasler, K. -H.; Arlt, K.; Staude, J.; Oraevsky, V. N.; Zhugzhda, Y. D. Bibcode: 1998ESASP.417..243H Altcode: 1998cesh.conf..243H No abstract at ADS Title: Sunspot Oscillations from SUMER Spectra Authors: Rendtel, J.; Staude, J.; Innes, D.; Wilhelm, K.; Gurman, J. B. Bibcode: 1998ESASP.417..277R Altcode: 1998cesh.conf..277R No abstract at ADS Title: Oscillations in a Sunspot Transition Region Observed with SOHO Authors: Staude, J.; Rendtel, J.; Innes, D.; Wilhelm, K.; Gurman, J. B. Bibcode: 1998ESASP.418..651S Altcode: 1998soho....6..651S Measurements of oscillations in the chromosphere-corona transition region (TR) above sunspots are of fundamental importance for investigating sunspot structure and dynamics; for instance, resonator models of magneto-atmospheric waves and their non-adiabatic behavior can be tested in this way (Staude et al., 1985). UV spectroscopic data obtained with the SUMER spectrograph aboard SOHO have been analyzed to detect such oscillations. The longest time series was obtained on August 29, 1996, between 09:08 UT and 13:31 UT. During this period, scans were made over the active region NOAA 7986 in the wavelength bands around 770.4 AA (Ne VIII line, formed at T ~6 times 105 K) and 1548.1 AA (C IV line, T ~7 times 104 dots 1.3 times 105 K). The large dominating sunspot of this active region was close to the disk centre. Simultaneous observations with the Normal Incidence Spectrometer of CDS aboard SOHO have shown, that the spot had a bright EUV plume at TR temperatures (Maltby et al., 1998). For compensating possible instrumental and exposure effects, we extract background information from each image. A preliminary data analysis indicates intensity oscillations in the 2-minute range (at 7.4 dots 7.7 mHz) in both spectral lines and a slow temporal decrease of oscillatory power in the Ne VIII line, but an increase in the C IV line. These results hint at a non-adiabatic behavior of the oscillations and a slow cooling of the emitting sunspot plume region. Further supplementary observations of the active region NOAA 7986 are from EIT aboard SOHO (in the Fe IX/X lines at 171 AA --- T ~1.3 times 106 K --- a time series of 2 hours has been obtained simultaneous to the first part of the SUMER series, moreover, single high-resolution pictures in 4 UV lines exist) as well as from the magnetograph of the Einsteinturm observatory at Potsdam showing a rather complex polarity distribution. It is planned to extend the study towards velocity variations and to correlations between the oscillations in the two SUMER lines. Furthermore, correlations will be investigated towards the EIT time series. Title: Oscillations of the magnetic field in an active region Authors: Horn, T.; Staude, J. Bibcode: 1998IAUS..185..449H Altcode: In 1994 we performed observations at the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife) using a polarimeter in front of a two-dimensional imaging spectrometer with a tunable narrow-band Fabry-Perot interferometer. We observed the main sunspot of the active region NOAA 7577 and measured the Doppler line shift and the Zeeman splitting of the line Fe I 6173 AA. The data show significant power of velocity and magnetic field oscillations in period bands at 3 min and 5 min, a strong coherence of the velocity and magnetic field oscillations, and a clear dependence of the phase difference on the period and on the position, pointing out a longitudinal character of the oscillations. Title: Oscillation of the magnetic field in an active region. Authors: Horn, T.; Staude, J. Bibcode: 1998joso.proc...79H Altcode: The solar vacuum telescope VTT at Tenerife has been used to obtain high-resolution two-dimensional spectro-polarimetric observations of oscillations in the photospheric layers of sunspots. The spectra of velocity oscillations show the known features of closely packed power peaks in bands of periods around 3 min (strengthened) and 5 min (weakened with respect to the quiet Sun). In the same frequency bands the VTT data show significant oscillations of the magnetic field strength as well, which could not be attributed to disturbing influences. Maximum power of both velocity and magnetic oscillations and a strong correlation between them, in the 3-min band in particular, is found to occur in those parts of the umbra where the magnetic lines of force are parallel to the line-of-sight. The oscillations are characterized by a marked spatial fine structure and a non-stationary behaviour. Title: Two-dimensional measurements of sunspot oscillations Authors: Staude, J.; Horn, T. Bibcode: 1997ASSL..225..235S Altcode: 1997scor.proc..235S High-resolution two-dimensional spectro-polarimetric observations of oscillations in the photospheric layers of a sunspot have been obtained using the Vacuum Tower Telescope at Tenerife. A Fabry-Perot interferometer has been applied to get narrow-band filtergrams directly and to scan through the line profile. The spectra show significant power of oscillations of velocity $v$ and of the magnetic field strength as well. Both are concentrated in bands of peaks at periods around 3 min ($v$ strengthened) and 5 min ($v$ weakened with respect to the quiet Sun), with maxima occuring in those parts of the umbra where the magnetic lines of force are parallel to the line-of-sight. Coherence and the phase difference between both types of oscillations show a clear dependence on the magnetic field direction as well. Title: Observations of Sunspot Umbral Oscillations Authors: Horn, T.; Staude, J.; Landgraf, V. Bibcode: 1997SoPh..172...69H Altcode: 1997ESPM....8...69H The solar vacuum telescopes VTT and GCT at Tenerife have been used to obtain high-resolution two-dimensional spectro-polarimetric observations of oscillations in the photospheric layers of sunspots. At the GCT the area of the sunspot has been scanned by shifting the spectrograph slit; at the VTT a Fabry-Pérot interferometer has been applied to get narrow-band filtergrams directly and to scan through the line profile. Title: Contribution Functions for Polarized Radiative Transfer Authors: Staude, J. Bibcode: 1996SoPh..164..183S Altcode: The concepts of contribution functions (CF) and of mean depths of line formation of unpolarized light as well as of Stokes profiles will be critically discussed. After having outlined the historical development arguments are given in favour of the use of directly observable quantities such as the emergent line intensity or the polarized components seen through polarization optics only. The arguments are provided by a probability interpretation of the CF; the ambiguities of line depression CF as well as some physically strange features in Stokes profiles are avoided if the rules based on this interpretation are observed. Some problems of the interpretation of measurements in chromospheric lines will be discussed as well. Title: Two-dimensional measurements of sunspot oscillations. Authors: Staude, J.; Horn, T.; Landgraf, V. Bibcode: 1996AGAb...12...91S Altcode: No abstract at ADS Title: Spectral darkening functions of solar p-modes - an effective tool for helioseismology. Authors: Zhugzhda, Y. D.; Staude, J.; Bartling, G. Bibcode: 1996A&A...305L..33Z Altcode: Darkening functions (contrasts) of intensity fluctuations due to waves in a nongrey LTE model of the solar atmosphere are calculated for different wavelengths λ in the optical continuum spectrum. Adiabatic and isothermal acoustic waves as well as temperature waves are considered. A change of the sign of the darkening function for certain ranges of λ is revealed for adiabatic waves. This effect makes it possible to observe modes with l>=3 even in stars. Observations of the darkening function of p-modes at different λ are proposed as a new tool, making it possible to check numerical models of p-modes, to impose restraints to the choice of the boundary conditions, to reduce the arbitrariness in the calculation of nonadiabatic corrections to eigenfrequencies, and to improve the accuracy of solar interior sounding in this way. Title: On the possibility of detection of p-modes with L> 3 in the sun-like stars Authors: Staude, J.; Zhugzhda, Y. D. Bibcode: 1996ASPC..109..161S Altcode: 1996csss....9..161S No abstract at ADS Title: An analytic theory of adiabatic p-modes in the atmospheres of the Sun and Sun-like stars. Authors: Dzhalilov, N. S.; Staude, J. Bibcode: 1995A&A...303..561D Altcode: The height profile of temperature T of the solar or a stellar model, extending from the subphotosphere through the atmosphere up to the corona, has been piecewise approximated by various nonlinear and linear functions for the different regions. Solving the basic equations of adiabatic, nonvertical oscillations for these regions in the Cowling approximation we obtained the eigenfunctions for the p-modes in analytic form. Using these exact solutions it has been demonstrated, that the mechanism of resonant transmission of acoustic waves through the considered layers is sufficient to explain the main features of the observed frequency spectrum of the solar p-modes, including the 5-min oscillations and the peaks in the high-frequency tail. It has been shown that the upper turning point of the resonator for low frequencies ν<~4mHz does not coincide with the boundary of the acoustic potential barrier, the latter extending from the steep gradient of T at the upper subphotosphere up to that above the minimum of T. The wakes of the waves penetrate deep into the barrier (up to a height of 500km in the solar atmosphere) and are reflected from there. High frequencies are reflected from the chromosphere-corona transition region. For not any frequency there exists a total reflection; with increasing frequency there is an increasing leakage of wave energy into the corona. It has been shown that all observable characteristics of oscillations depend directly on the phase shift {DELTA}φ between upward and downward running waves. The resonance peaks in the spectrum arise at {DELTA}φ=0, where {DELTA}φ has been defined in the limits [-π, +π]. The dependence of the power spectrum on the height, on the frequency, and on the degree l has been demonstrated. The first resonant frequencies always correspond to the 5-min oscillations. Title: Solar Irradiance Oscillations: Preliminary Results of the Coronas-Difos Experiment Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev, I. M.; Kostyk, R. I.; Pflug, K.; Rüdiger, G.; Staude, J.; Bettac, H. -D. Bibcode: 1995ESASP.376b.353L Altcode: 1995soho....2..353L; 1995help.confP.353L No abstract at ADS Title: An Analytical Model of Adiabatic P-Modes Resonant Transmission Through the Solar Atmosphere Authors: Dzhalilov, N. S.; Staude, J. Bibcode: 1995ESASP.376b.441D Altcode: 1995soho....2..441D; 1995help.confP.441D No abstract at ADS Title: First results of the CORONAS-DIFOS experiment. Space observations of solar irradiance oscillations. Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev, I. M.; Kostyk, R. I.; Pflug, K.; Ruediger, G.; Staude, J.; Bettac, H. -D. Bibcode: 1995A&A...296L..25L Altcode: The DIFOS experiment aboard the satellite CORONAS has been designed to observe irradiance fluctuations due to global solar oscillations. The satellite was launched on March 2, 1994. It uses a photometer measuring fluctuations of the solar flux in three channels: near 550nm, 750nm, and from 400nm through 1.1μm. After a short description of the instrumentation and the data analysis we present first, preliminary results of observations of low-degree p-modes including their variation in time. Title: Book-Review - Robotic Telescopes in the 1990S Authors: Filippenko, A. V.; Staude, J. Bibcode: 1995AN....316..154F Altcode: No abstract at ADS Title: Visibility Functions of Solar and Stellar Irradiance Variations Authors: Staude, J.; Bartling, G.; Zhugzhda, Y. D.; Dzhalilov, N. S. Bibcode: 1995ASPC...83..451S Altcode: 1995IAUCo.155..451S; 1995aasp.conf..451S No abstract at ADS Title: An Analytic Theory of Adiabatic p-modes in the Atmospheres of the Sun and Sun-like Stars Authors: Dzhalilov, N. S.; Staude, J. Bibcode: 1995ASPC...83..449D Altcode: 1995IAUCo.155..449D; 1995aasp.conf..449D No abstract at ADS Title: Sonnenforschung am Sonnenobservatorium Einsteinturm des Astrophysikalischen Instituts Potsdam. Authors: Staude, J. Bibcode: 1995epaa.book...98S Altcode: No abstract at ADS Title: Sonnenforschung am Einsteinturm. Authors: Staude, J. Bibcode: 1995Stern..71..142S Altcode: No abstract at ADS Title: Radiation-Hydrodynamic Waves and Solar P Modes: Visibility Functions Authors: Staude, J.; Zhugzhda, Y. D.; Dzhalilov, N. S. Bibcode: 1995ASPC...76..338S Altcode: 1995gong.conf..338S No abstract at ADS Title: Radiation-hydrodynamic waves in an optically grey atmosphere. II. Analysis of wave properties and effects of thermal conductivity in a homogeneous model. Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1994A&A...291.1001D Altcode: The properties of radiation-hydrodynamic waves in a radiative, thermally conducting, uniform atmosphere are investigated, avoiding the Eddington approximation and considering a temporal as well as a spatial analysis. The analysis of the dispersion equation shows the existence of acoustic, radiation, and thermal wave modes and a relaxation mode as well. The generalized Spiegel formula is discussed and the accuracy of the Eddington approximation for the radiation-hydrodynamic waves is considered. The amplitudes and phases of disturbances of gas and radiation pressure, intensity, and temperature are obtained for standing and travelling waves and for the relaxation mode too. The polar angle dependence of the phase shift between velocity and intensity is investigated. The predictions for full-disk intensity observations and the deficiencies of earlier, less complete approaches are discussed. Title: Radiation Hydrodynamic Waves and Global Solar Oscillations Authors: Staude, J.; Dzhalilov, N. S.; Zhugzhda, Y. D. Bibcode: 1994SoPh..152..227S Altcode: 1994IAUCo.143..227S; 1994svs..coll..227S We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating, thermally conducting, homogeneous atmosphere in LTE with a finite mean free path of photons. Avoiding the Eddington approximation the remaining simplifications in the basic equations are discussed, the generalized dispersion relation is analysed, and some wave properties in a grey model are studied. The properties of waves in a stratified atmosphere are analysed as well. In connection with the predicted properties of the nonadiabatic waves we discuss observations ofp-modes by measuring brightness fluctuations. Title: Sunspot umbral oscillations Authors: Staude, J. Bibcode: 1994smf..conf..248S Altcode: No abstract at ADS Title: Interpretation of sunspot oscillations Authors: Staude, J. Bibcode: 1994ASIC..433..189S Altcode: No abstract at ADS Title: Visibility functions of solar and stellar luminosity oscillations. Authors: Staude, J.; Bartling, G.; Dzhalilov, N. S.; Zhugzhda, Y. D. Bibcode: 1994AGAb...10..116S Altcode: No abstract at ADS Title: Sonnenforschung in Potsdam - Das Sonnenobservatorium Einsteinturm des Astrophysikalischen Instituts Potsdam. Authors: Staude, J. Bibcode: 1994ABLD....5.....S Altcode: Contents: 1. Das Astrophysikalische Observatorium Potsdam. 2. Die Relativitätstheorie. 3. Instrumentarium des Einsteinturms. 4. Forschungsprogramm. 5. Das Astrophysikalische Institut Potsdam. Title: Radiation-Hydrodynamic Waves in the Solar Atmoshere Authors: Zhugzhda, Y. D.; Staude, J.; Dzhalilov, N. S. Bibcode: 1994emsp.conf....9Z Altcode: No abstract at ADS Title: Radiation-hydrodynamic waves in an optically non-grey atmosphere Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.; Staude, J. Bibcode: 1993A&A...278L...9Z Altcode: We derive the dispersion equation of radiation-hydrodynamic waves for a nongrey atmosphere in Local Thermodynamic Equilibrium (LTE) avoiding the Eddington approximation. It is shown that the Rosseland mean opacity doesn't describe the relaxation processes in the atmosphere except the opaque limit. For the transparent limit the relaxation time depends on the so-called Newton mean opacity. The grey and nongrey approximations are compared for a model of the solar photosphere. Title: Planeten - Wanderer im All Authors: Lang, Kenneth R.; Whitney, Charles A.; Staude, J.; Bührke, T. Bibcode: 1993pwia.book.....L Altcode: In allgemeinverständlicher Form und ohne fachliche Vorkenntnisse beim Leser vorauszusetzen stellen die Autoren unser Planetensystem vor. Der klar geschriebene Text wird durch eine Fülle z.T. bisher unveröffentlichter Fotos aufgelockert, und die Ergebnisse von Raumsonden- und Satellitenmissionen bis 1992 sind berücksichtigt. "...besticht durch exzellentes Bildmaterial und Stilsicherheit in der Formulierung. Die Autoren erklären astronomische Sachverhalte umfassend und leichtverständlich. Der Leser erlebt einen faszinierenden Raumflug durch unser Sonnensystem...Mit sinnvoll eingeschobenen Zusammenfassungen und Kurzinformationen, umfassendem Anhang, Register und Bilbliographie. Ein ideales Buch für interessierte Laien und angehende Astronomen." (Westdeutsche Zeitung) Title: Book-Review - the Sun - a Laboratory for Astrophysics Authors: Schmelz, J. T.; Brown, J. C.; Staude, J. Bibcode: 1992AN....313..348S Altcode: No abstract at ADS Title: Book-Review - the Sun and Cool Stars - Activity Magnetism Dynamos - I.A.U.COLL - Helsinki 1990JUL17-20 Authors: Tuominen, I.; Moss, D.; Rudiger, G.; Staude, J. Bibcode: 1992AN....313..318T Altcode: No abstract at ADS Title: Book-Review - Solar Observations - Techniques and Interpretation - First Canary Islands Winter School of Astrophysics Authors: Sanchez, F.; Collados, M.; Vazquez, M.; Staude, J. Bibcode: 1992AN....313Q.302S Altcode: No abstract at ADS Title: Radiation-hydrodynamic waves in an optically gray atmosphere. I - Homogeneous model Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1992A&A...257..359D Altcode: We consider the coupled set of equations of hydrodynamics and radiative transfer. Only radiative transfer is taken into account in the energy equation, while other mechanisms of heat transfer are ignored. Disturbances of the tensor of radiative pressure are included in the linearized momentum equation. This term proves to be of great importance for radiation-acoustic waves. LTE as well as a gray approximation and homogeneity of the atmosphere are assumed. The hydrodynamic equations are solved by using an exact solution of the radiative transfer equation (no Eddington approximation is made). The dispersion equation for the nonadiabatic oscillations is derived. This equation is valid for arbitrary optical thickness and generalizes all hitherto known results. Title: Oscillations &Seismological Diagnostics of Sunspots (Invited) Authors: Staude, J. Bibcode: 1992LNP...397..181S Altcode: 1992sils.conf..181S Comparisons between recent observations of umbrae and detailed numerical model calculations have achieved a substantial agreement. This implies that the hitherto developed models for the structure and dynamics of sunspot umbrae seem to reflect essential features of the nature of sunspots, notwithstanding the various simplifying assumptions. Recent analytic calculations for simplified umbral models also confirmed our model of a system of umbral resonators (Campos, 1989; Evans and Roberts, 1990); Campos (1989) only argued in favour of an additional resonator for pure Alfvén waves. The model provides an important tool for sounding subphotospheric and atmospheric layers of sunspots and possibly of other magnetized stellar atmospheres. Further observations of oscillations should try to improve the spatial resolution on the sun and the coverage of the data in space and time. Model calculations should abandon the restrictive assumptions by considering nonlinear and nonadiabatic processes such as radiative dissipations of waves and, moreover, self-consistent calculations of wave propagation and non-LTE line formation are needed to improve the diagnostics. Title: Das Sonnenobservatorium Einsteinturm in Potsdam. Erforschung solarer Magnetfelder und der Physik von Sonnenflecken. Authors: Staude, J. Bibcode: 1991S&W....30..505S Altcode: No abstract at ADS Title: Book-Review - Dynamics of Quiescent Prominences - I.A.U. COLL.117 - Hvar - Croatia Authors: Ruzdjak, V.; Tandberg-Hanssen, E.; Staude, J. Bibcode: 1991AN....312..326R Altcode: No abstract at ADS Title: The Potsdam vector magnetograph: methodical experiences and results. Authors: Staude, J.; Hofmann, A.; Bachmann, G. Bibcode: 1991sopo.work...49S Altcode: After a short historical introduction the instrumentation of the double line vector magnetograph is described as it is working in connection with the tower telescope of the Solar Observatory "Einsteinturm" at Potsdam. Subsequently the authors outline the calibration of the instrumental response to incident polarised light. The theoretical calibration of deriving the magnetic field components from the observed Stokes profiles is the next step. Finally the authors give a few examples of vector magnetograms and outline some of their methods for deriving further information from the magnetograms. Title: Solar Research at Potsdam: Papers on the Structure and Dynamics of Sunspots. Authors: Staude, J. Bibcode: 1991RvMA....4...69S Altcode: No abstract at ADS Title: Book-Review - Energetic Phenomena on the Sun Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.; Staude, J. Bibcode: 1990AN....311..416K Altcode: No abstract at ADS Title: Book-Review - Asymptotics of High Order Differential Equations Authors: Paris, R. B.; Wood, A. D.; Staude, J. Bibcode: 1990AN....311..425P Altcode: No abstract at ADS Title: Book-Review - the Physics of Solar Flares Authors: Tandberg-Hanssen, E.; Emslie, A. G.; Staude, J. Bibcode: 1990AN....311..106T Altcode: No abstract at ADS Title: Seismological diagnostics of sunspot umbral structure. Authors: Staude, J. Bibcode: 1990PDHO....7..302S Altcode: No abstract at ADS Title: Book-Review - Advances in - and Asteroseismology - I.A.U. SYMP.123 Authors: Christensen-Dalsgaard, J.; Frandsen, S.; Staude, J. Bibcode: 1989AN....310..280C Altcode: No abstract at ADS Title: Probing of Sunspot Umbral Structure by Oscillations Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V. Bibcode: 1989ASIC..263..601Z Altcode: 1989ssg..conf..601Z No abstract at ADS Title: Book-Review - Solar and Stellar Physics - 5TH European Solar Meeting - Titisee / Schwarzwald - Germany - 1987APR27-30 Authors: Schroter, E. H.; Schussler, M.; Staude, J. Bibcode: 1989AN....310...66S Altcode: No abstract at ADS Title: Possibilities and Problems of the Interpretation of Solar Magnetograph Measurements and Applications to Flare-Active Regions Authors: Staude, J.; Hofmann, A. Bibcode: 1989ESASP.285..123S Altcode: 1989rsp..conf..123S The basic uncertainties encountered in the interpretation of magnetograph data, and possibilities for deriving more reliable information are reviewed. The problems are illustrated by describing the data handling of a vector magnetograph. Examples of observed flare-active regions demonstrate the state of information which can be obtained. Title: Oscillations and the temperature minimum in sunspot umbrae Authors: Locans, V.; Skerse, D.; Staude, J.; Zhugzhda, Iu. D. Bibcode: 1988A&A...204..263L Altcode: Observed umbral oscillation with periods of 2 - 3 min can be explained by slow-mode longitudinal magnetoatmospheric waves which are partly trapped in the umbral photosphere and chromosphere. Detailed numerical calculations for such a resonator in semi-empirical model atmospheres predict details of umbral oscillations which, after comparison with observed data, provide new information on the atmospheric structure. The results support arguments in favour of a low value of the temperature minimum (≤3000K) in the dark parts of umbrae, while the oscillations are deteriorated in bright umbral structures such as dots or light bridges. Title: A two-component working model for the atmosphere of a large sunspot umbra Authors: Obridko, V. N.; Staude, J. Bibcode: 1988A&A...189..232O Altcode: A two-component working model for the atmosphere of the umbra of a typical large sunspot is proposed which represents an improvement over the earlier Wroclaw-Ondrejov sunspot model. The main component is assumed to consist of cold matter at photospheric levels, a thin chromosphere, a shallow transition region, and a deep-set corona. The secondary component in the model has a volume filling factor of 5-10 percent at all heights and is suggested to consist of thin fine-structure elements which are elongated parallel to the magnetic field. The present model is able to account for the basic features of sunspot observations at frequencies from X-rays up to microwaves. Title: Oscillations and waves in sunspots. Authors: Staude, J.; Zhugzhda, Iu. D.; Locans, V. Bibcode: 1987PAICz..66..161S Altcode: 1987eram....1..161S The authors review the basic features of oscillations observed at different height levels in the sunspot atmosphere, moreover, various possibilities for a theoretical interpretation are discussed. Title: The interpretation of oscillations in sunspot umbrae Authors: Zhugzhda, Iu. D.; Locans, V.; Staude, J. Bibcode: 1987AN....308..257Z Altcode: Possibilities for an interpretation of oscillations observed in several period bands (3 min, 5 min, 20 min) and at different heights in sunspot umbrae are reviewed. At subphotospheric depths two independent resonators are acting: a resonator for slow, quasi-transverse waves which can explain the lifetimes of bright umbral dots (greater than or equal to 20 sec), and a resonator for fast (acoustic), quasi-longitudinal waves which could result in the 5-min oscillations. The acoustic resonator strongly couples with the slow-mode longitudinal resonator at photospheric and chromospheric heights, the latter producing the resonance peaks in the 3-min period band. The whole scheme of resonance levels generalizes and corroborates a chromospheric resonator model earlier proposed by the present authors. Comparisons with alternative models and recent measurements show that the present model most naturally explains the majority of observed data. Title: Electric current density in the sunspot photosphere derived from vector magnetograms. Authors: Hofmann, A.; Staude, J. Bibcode: 1987PAICz..66..105H Altcode: 1987eram....1..105H The authors present observational results from which they determine azimuthal currents flowing across the magnetic field. Title: Models of the solar atmosphere above sunspots Authors: Staude, J. Bibcode: 1986CoSka..15..299S Altcode: The "Wroclaw-Ondřejov sunspot model", together with its recent improvements, provides a unified working model based on self-consistent physical assumptions for a large of heights from the deepest photospheric levels up to the lower corona. Using the WOSM together with emission models developed for various wavelength regions, the theoretically predicted emissions have been beautifully checked by comparison with new observed data. Title: Spektroskopische Untersuchungen am Einsteinturm: Zur Physik der Korona und der Sonnenflecken. Authors: Staude, J. Bibcode: 1986Stern..62..109S Altcode: No abstract at ADS Title: Investigation of the large preceding spot of AR 2779 from SMM data Authors: Siarkowski, M.; Jakimiec, J.; Staude, J. Bibcode: 1986CoSka..15..111S Altcode: Complex data from the SMM spacecraft (UVSP and XRP/FCS) have been used to investigate the structure and dynamics of the large p spot of the active region NOAA 2779 from November 1980. The spot shows an inhomogeneous structure characterized by a light bridge. In comparison with the darkest photospheric umbral cores the light bridge is bright in the photosphere and the transition region, but darker in the chromosphere. In the transition region the authors found upward motions above the umbra, but downward motions in the light bridge. Compared to the spot's surroundings the Ly-α emission is stronger above the umbra up to a factor of 3, but its spatial distribution is more inhomogeneous than the photospheric emission. Title: Oscillations in the chromosphere and transition region above sunspot umbrae - A photospheric or a chromospheric resonator? Authors: Zhugzhda, Ia. D.; Locans, V.; Staude, J. Bibcode: 1985A&A...143..201Z Altcode: A model for a chromospheric resonator for slow waves is proposed, and its basic features are compared with those of the model for a photospheric resonator for fast waves, proposed by Thomas and Scheuer (1982), (TS). Moreover, the model predictions are tested for agreement with recent observations of umbral oscillations. The observations in the umbral chromosphere and transition region are in agreement with the model presented but are difficult to reconcile with the TS model. This conclusion does not exclude the possibility that a TS-type photospheric resonator is excited as well. Finally, necessary improvements in the existing simplified theories are outlined. Title: On the inhomogeneous structure of the chromosphere-corona transition region above sunspot umbrae Authors: Staude, J. Bibcode: 1985AN....306..197S Altcode: Recent multiple wavelength observations of sunspot umbrae are explained within the framework of an inhomogeneous, two-component model of the structure of the umbral transition region, the Wroclaw-Ondrejov model. Simple analytical expressions for the atmospheric structure in each component, and in the lower corona, are derived and the free parameters were fitted to observations of EUV emission line intensities. It is shown that the main component of the umbral transition has a shallow transition region and a deep set corona. The second 'active' component displayed a large transition region embedded in the main coronal component.The spatial filling factor of the active component was about 5-10 percent in sunspots having bright EUV plumes. For sunspots without bright EUV plumes, the spatial filling factor was more than ten times smaller. The EUV emission line intensities are compared to temperature measurements in both quiet and active sunspot regions and the results are discussed in detail. Title: Interpretation of Oscillations in Ultraviolet Lines Observed above Sunspot Umbrae Authors: Staude, J.; Zhugzhda, Iu. D.; Locans, V. Bibcode: 1985SoPh...95...37S Altcode: Our theory of a resonator for slow magneto-atmospheric waves in the chromosphere of a sunspot umbra has been used to check different models of the structure of the chromosphere and transition region. Oscillations of velocity and intensity in CIV, SiIV, and OIV lines observed by Gurman et al. (1982) on the SMM spacecraft have been compared with the calculated oscillations. The observed spectrum of resonant peaks could well be explained by a gradient model of the umbral chromosphere. Different assumptions concerning the structure of the transition region do not influence the calculated resonance periods, but the amplitudes and phases of oscillations are modified. There is strong evidence for a concentration of the observed oscillations in cold fine structure elements of the transition region, even if the filling factor of such elements is very small (some few percent). Isothermal rather than adiabatic oscillations in the cold elements should be assumed in order to explain the observed fluctuations of line intensity; the relative amplitudes of pressure oscillations in the hot main component with a steep gradient of temperature are too small to explain the observed intensity fluctuations. Title: The Atmosphere of a Sunspot Based on Observations in the X-Ray Extreme Ultraviolet Optical and Radio Ranges Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger, A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.; Sylwester, J. Bibcode: 1984SvA....28..557S Altcode: No abstract at ADS Title: The atmosphere of a sunspot based on observations in the X-ray, extreme ultraviolet, optical, and radio ranges Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger, A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.; Sylwester, J. Bibcode: 1984AZh....61..956S Altcode: A model of the solar atmosphere above a sunspot umbra is developed on the basis of published X-ray, EUV, optical, and radio observations, summarizing the findings of working conferences held at Wroclaw in November-December 1979 (Bromboszcz et al. 1981) and at Ondrejov in September-October 1981 (Bromboszcz et al., 1982). A lower-chromosphere model like that of Teplitskaya et al. (1977 and 1978) is extended upward by applying a strong temperature gradient, with T = 40,000 K and n(e) = 4 x 10 to the 10th/cu cm at z = 2000 km above the umbral chromosphere. At z = 3000-5000 km, cool loops with T = (1-100) x 10 to the 4th k are surrounded by hot (1.8 x 10 to the 6th K) coronal matter with a narrow transition layer and n(e) = 5 x 10 to the 8th/cu cm which occupies 0.8-0.9 of the total volume. Title: A Model of the Oscillations in the Chromosphere and Transition Region above Sunspot Umbrae Authors: Zhugzhda, Iu. D.; Staude, J.; Locans, V. Bibcode: 1984SoPh...91..219Z Altcode: In an earlier paper (Solar Phys.82, 369) the present authors proposed a model for the interpretation of velocity and intensity oscillations with periods between 2 and 3 minutes observed above umbrae. The model explains the oscillations by the resonant transmission of slow-mode magnetic-acoustic waves which are semi-trapped in a chromospheric cavity. In this way we get an independent method of checking semi-empirical models of umbral atmospheres. Title: A Model of the Oscillations in the Chromosphere and Transition Region above Sunspot Umbrae Authors: Zugzda, Y. D.; Staude, J.; Locans, V. Bibcode: 1984AN....305..236Z Altcode: No abstract at ADS Title: Ein Modell der Oszillationen der Chromosphäre und Übergangsregioh über Sonnenfleckenumbrae Authors: Žugžda, Y. D.; Staude, J.; Locans, V. Bibcode: 1984AN....305Q.236Z Altcode: No abstract at ADS Title: A Model of the Oscillations in the Chromosphere and Authors: Žugžda, Y. D.; Staude, J.; Locans, V. Bibcode: 1984AN....305R.236Z Altcode: No abstract at ADS Title: A working model of sunspot structure in photosphere, chromosphere and corona, derived from X-ray, EUV, optical and radio observations Authors: Staude, J.; Hildebrandt, J.; Fuerstenberg, F.; Krueger, A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.; Sylwester, J. Bibcode: 1983AcA....33..441S Altcode: The presented sunspot model consists of several parts which have been consistently put together: the umbral model describing the spatial distribution of thermodynamic quantities up to the transition region as derived from EUV and optical observations, the magnetic field model, the model of X-ray emission, and the S-component emission model. The model assumptions have been tested and corroborated by recently published observations with high spatial resolution obtained in the X-ray and EUV spectral range from Skylab, HRTS, and SMM, at centimeter wavelengths from RATAN, VLA, and WSRT, and by ground-based magnetograms. Title: A Model of the Oscillations in the Chromosphere and Transition Region Above Sunspot Umbrae Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V. Bibcode: 1983PDHO....5..451Z Altcode: 1984PDHO....5..451Z In an earlier paper the authors proposed a model for the interpretation of velocity and intensity oscillations with periods between 2 and 3 minutes observed above umbrae. The oscillations are explained by the resonant transmission of slow mode magneto-acoustic waves which are semi-trapped in a chromospheric cavity. The model has now been improved by more detailed calculations and corroborated by recently published observations: The calculations are in good agreement with (1) the height dependence of the observed phase difference between velocity and intensity oscillations, and with (2) the frequency spectrum of oscillations in the transition region above sunspots observed on the SMM spacecraft during the SMY. Title: Results of vector magnetographic measurements in the active region SD 228/229 on 15 July 1982. Authors: Bachmann, G.; Hofmann, A.; Staude, J. Bibcode: 1983PDHO....5..369B Altcode: 1984PDHO....5..369B The authors present measurements of vector magnetic fields in an active region of 15 July 1982 obtained with the new code-impulse magnetograph working in the wing of Fe I 5250 line. Linear polarization down to 0.004 corresponding to transverse magnetic fields of about 150 G has been taken into account. The direction of the transverse magnetic fields is compared with dark chromospheric structure elements in Hα filtergrams and with the contours of sunspots obtained by means of a heliogram. For long-lived stable structures, such as the central part of the zero-line filament or systems of fibrils and threads, the correspondence is good, in contrast to short-lived. In regions with weak magnetic fields no correspondence is found. Title: Seismology of Sunspot Atmospheres Authors: Zhugzhda, Iu. D.; Locans, V.; Staude, J. Bibcode: 1983SoPh...82..369Z Altcode: 1983IAUCo..66..369Z The present work deals with the theory of oscillations with periods of about 3 min observed in the chromosphere above sunspot umbrae. The model of these oscillations (slow mode magneto-acoustic waves trapped in a chromospheric resonant cavity) provides an independent method of checking empirical models of the chromosphere above sunspots. Title: Beobachtungen an neuen bipolaren Nebeln Authors: Staude, J.; Neckel, Th. Bibcode: 1983MitAG..60..322S Altcode: No abstract at ADS Title: A unified working model for the atmospheric structure of large sunspot umbrae Authors: Staude, J. Bibcode: 1981A&A...100..284S Altcode: Horizontally averaged working models are derived for both the umbra of a large stable sunspot and the mean undisturbed environment for reference. It is noted that these models extend on a common geometrical height scale from subphotospheric layers to the base of the transition layer between chromosphere and corona; they are based on uniform and self-consistent physical assumptions for all layers and are able to explain the basic features of many observations at different wavelengths, including recent data from space. The present sunspot model furnishes the lower boundary condition for an attempt to model the transition layer and lower corona above large umbrae. Title: Evidence for an X-Type Neutral Sheet Producing Chromospheric Activity Authors: Seehafer, N.; Staude, J. Bibcode: 1980SoPh...67..121S Altcode: Force-free magnetic field extrapolation for region McMath 12417 on 4 July 1973 corroborates a suggestion by Roy and Michalitsanos (1974): A large moving magnetic feature presses together opposite fluxes to form an X-type neutral sheet; the supposed geometry of the field as derived from chromospheric activity (subflares, ejections) is confirmed by the calculated lines of force. Title: Problems concerning the calibration and interpretation of magnetograph observations in the solar photosphere and chromosphere Authors: Staude, J. Bibcode: 1980tpmb.meet...58S Altcode: The paper presents procedures for the calibration of solar photoelectric magnetographs, which relate to the practical calibration of the primarily measured state of polarization in a magneto-sensitive line and to the theoretical derivation of magnetic field parameters from the polarization measurements. Disturbing influences are discussed including external disturbances such as stray light and instrumental polarization, saturation effects, and fine structures of the solar atmosphere, of velocity and magnetic fields. Problems in line formation theory are also discussed. Title: Force-free Magnetic Field Extrapolation for the Complex Sunspot Group of August 1972 Authors: Seehafer, N.; Staude, J. Bibcode: 1979AN....300..151S Altcode: A method for theoretical extrapolation of photospheric longitudinal magnetograms to higher levels for force-free magnetic fields is presented. The method has been used to calculate the magnetic field vector and lines of force in the flare active region of August 1972. Calculated fields are compared with other observations such as structures in H-alpha. Results of August 3 show that the loop prominence systems observed during the flares of August 2 and 4 are represented by a force field with a positive value of alpha, rather than a current-free field. The extractable energy supply of this force-free field is of the order of maximum flare demand (10 to the 32nd erg); the height dependence of the magnetic field strengths agrees with that from radio and X-ray estimates. Similar results are obtained for the August 7 magnetic field structure. It is suggested that the mean magnetic field structure of the active region may be represented by a force-free field much better than by a potential field. Title: Magnetfelder der Sonne und der Sterne. I. Authors: Scholz, G.; Staude, J. Bibcode: 1979Stern..55...65S Altcode: No abstract at ADS Title: Magnetfelder der Sonne und der Sterne. II. Authors: Scholz, G.; Staude, J. Bibcode: 1979Stern..55..206S Altcode: No abstract at ADS Title: Models of Heat Flux in the Subphotospheric Layers of Sunspots and the Interpretation of Umbral Granulation Authors: Staude, J. Bibcode: 1978BAICz..29...71S Altcode: Different models of heat flux in the normal convective zone (deep and shallow reference models) and in an umbral flux tube in magnetostatic equilibrium are investigated by numerical calculations. Recent observations of umbral granulation are explained by residual cellular convection which still transfers a small fraction of energy to the subphotospheric flux tube. The models deduced from special assumptions concerning the reduced convective heat flux are also compatible with other recent observations such as superadiabatic temperature gradients in the deep umbral photosphere, and with results from nonlinear calculations considering effects of interaction between the magnetic field and turbulent convection. Some criteria for the inhibiting effect of the magnetic field on convection, derived from linear theories seem to be too strong. Title: Influence of scintillation and scattering of light on magnetographic measurements. Authors: Bachmann, G.; Staude, J. Bibcode: 1977IzKry..56..148B Altcode: No abstract at ADS Title: Influence of the instrumental polarization on magnetographic observations. Authors: Eger, F. W.; Staude, J. Bibcode: 1977IzKry..56..149E Altcode: No abstract at ADS Title: Investigations in the field of magnetographic observations at the Einstein Solar Observatory in Potsdam. Authors: Staude, J. Bibcode: 1977IzKry..56R.205S Altcode: No abstract at ADS Title: Force-free magnetic field extrapolation for the complex sunspot group of August 1972. Authors: Seehafer, N.; Staude, J. Bibcode: 1977PDHO....3..137S Altcode: No abstract at ADS Title: Light Variations of AP Stars: 10-COLOUR Photometry and its Interpretation by a Magnetic SPOT Model Authors: Schöneich, W.; Staude, J. Bibcode: 1976paps.coll..387S Altcode: 1976IAUCo..32..387S No abstract at ADS Title: Models of the Solar Convective Zone: The Influence of Free Parameters in Mixing Length Theories Authors: Staude, J. Bibcode: 1976BAICz..27..365S Altcode: Using Opik's (1950) mixing-length theory of convection, Mullan (1971) obtained extremely shallow models of the solar convection zone whose structure is incompatible with current conceptions of solar physics in general and with the deep models resulting from the Boehm-Vitense theory (1958) in particular. In the present paper, the Opik theory is generalized to take into account an anisotropy of small-scale turbulence; this version is then compared with the Boehm-Vitense theory. Neglecting a thin surface layer where radiative losses are important, a simple analytic comparison alone shows that both theories yield the same results, if the free parameters are chosen consistent with each other. To study the influence of the different parameters, a series of solar convection-zone models has been calculated numerically, assuming an empirical photospheric model as the upper boundary condition and various values of the parameters in both theories. Title: Einige Methoden und Ergebnisse der modernen Sonnenforschung. Authors: Staude, J. Bibcode: 1976AsSch..13..101S Altcode: No abstract at ADS Title: Methodical improvements of magnetographic measurements Authors: Bachmann, G.; Künzel, H.; Pflug, K.; Staude, J. Bibcode: 1976CoSka...6..395B Altcode: No abstract at ADS Title: Model calculations concerning the subphotospheric layers of stable sunspots. Authors: Staude, J. Bibcode: 1976fsp..conf...63S Altcode: No abstract at ADS Title: Methodical improvement of magnetographic measurements. Authors: Bachmann, G.; Künzel, H.; Pflug, K.; Staude, J. Bibcode: 1976str..book..395B Altcode: No abstract at ADS Title: The Anomalous Splitting of the π-component of a ZEEMAN Triplet in Sunspot Umbrae and Suggestions for its Interpretation Authors: Kuenzel, H.; Staude, J. Bibcode: 1975AN....296..171K Altcode: An investigation of the anomalous splitting of the pi-component of the line Fe I at 6302.5 A in umbrae is conducted, taking into account Zeeman spectrograms from 1200 sunspots of the maximum year 1957. Disturbing effects are examined, giving attention to blends, stray light, and instrumental polarization. The observations appear to show a preponderance of left-hand screws of the magnetic field vector H in most umbrae independent of the polarity and the solar hemisphere. Title: Mie- und Rayleigh-Streuung in der Erdatmosphäre Authors: Staude, J. Bibcode: 1974MitAG..35Q.267S Altcode: No abstract at ADS Title: Possibilities regarding the determination of the structure of solar magnetic fields outside the photosphere Authors: Staude, J. Bibcode: 1974ZMete..24..214S Altcode: Physically well founded predictions of the solar activity and associated terrestrial effects require better, i.e. more detailed, knowledge of magnetic fields in the solar atmosphere, the chromosphere in particular. A critical review on methods of observing the solar magnetic fields is followed by a discussion of approaches of how to extrapolate, theoretically, into higher layers of the solar atmosphere the magnetic fields measured rather precisely in the photosphere. The force-free magnetic fields are given particular consideration; possibilities of testing by observations the theoretically calculated fields are described. Finally, the review contains proposals for further investigations. Title: Die Frühjahrstagung in Garching. Authors: Staude, J. Bibcode: 1974S&W....13..111S Altcode: No abstract at ADS Title: On the interpretation of some peculiarities observed in zeeman-split line contours in sunspots Authors: Staude, Jürgen Bibcode: 1973SoPh...32..403S Altcode: Strong line wings and the V-reversal in umbral countours of Fe I 6302.5 Å and similar lines have been explained earlier by inhomogeneous magnetic models. It is shown that both effects may also be explained assuming a homogeneous magnetic field and homogeneous umbral model atmospheres. Title: Non-LTE Line Formation in a Magnetic Field. II: The Influence of Non-Coherent Scattering on Line Contours Authors: Domke, H.; Staude, J. Bibcode: 1973SoPh...31..291D Altcode: Theoretical line contours calculated for fixed values of the line constants and a given model atmosphere show an increase of the Stokes parameters Q, U, and V but a decrease of I if the portion of non-coherent scattering increases. These effects increase from the centre of the solar disk to the limb. The action of scattering may be approximately simulated in LTE contours by increasing the gradient of the source function and fitting in this way theoretical contours to observed ones. There remains, however, the effect of V-reversal near the line core, which is caused by anomalous dispersion and is abnormally increased by scattering. Title: Non-LTE Line Formation in a Magnetic Field. I: Non-Coherent Scattering and True Absorption Authors: Domke, H.; Staude, J. Bibcode: 1973SoPh...31..279D Altcode: The formation of a Zeeman-multiplet by noncoherent scattering and true absorption in a Milne-Eddington atmosphere is considered assuming a homogeneous magnetic field and complete depolarization of the atomic line levels. The transfer equation for the Stokes parameters is transformed into a scalar integral equation of the Wiener-Hopf type which is solved by Sobolev's method in closed form. The influence of the magnetic field on the mean scattering number in an infinite medium is discussed. Title: Flächenpolarimetrie der südlichen Milchstraße Authors: Staude, J.; Wolf, K.; Schmidt, Th. Bibcode: 1973MitAG..34...95S Altcode: No abstract at ADS Title: A Surface Polarization Survey of the Milky way and the Zodiacal Light (presented by th. Schmidt) Authors: Staude, J.; Wolf, K.; Schmidt, Th. Bibcode: 1973IAUS...52..139S Altcode: No abstract at ADS Title: About the influence of a magnetic field on the model atmosphere of a magnetic star. Authors: Staude, J. Bibcode: 1973AN....294..113S Altcode: No abstract at ADS Title: About the Influence of a Magnetic Field on the Model Atmosphere of a Magnetic Star Authors: Staude, J. Bibcode: 1972AN....294..113S Altcode: No abstract at ADS Title: Circular Polarisation Measurements of the Zodiacal Light Authors: Staude, J.; Schmidt, Th. Bibcode: 1972A&A....20..163S Altcode: Key words: circular polarisation - zodiacal light Summary. The circular polarisation component of the zodiacal light is shown to be zero within the accuracy of l 10/00 (p. p. thousands). Title: On the Mean Depth of Line Formation in a Magnetic Field Authors: Staude, Jürgen Bibcode: 1972SoPh...24..255S Altcode: Probability interpretation of radiative transfer is used to calculate the contribution of different layers of the solar atmosphere to the emergent intensity. Generally the mean depths of line formation increase with increasing intensity; this is valid also for arbitrarily polarized constituents of a line formed in a magnetic field. Title: Flächenpolarimetrie des südlichen Gesamthimmels Authors: Wolf, K.; Staude, J. Bibcode: 1972MitAG..31..167W Altcode: No abstract at ADS Title: Einige Methoden und Ergebnisse der modernen Sonnenforschung. Authors: Staude, J. Bibcode: 1972AsSch...9...90S Altcode: No abstract at ADS Title: A Generalized Analytic Solution to the Equations of Transfer in a Magnetic Field Authors: Staude, Jürgen Bibcode: 1971SoPh...18...22S Altcode: No abstract at ADS Title: Remarks on Some Recent Papers Concerning Line Formation in a Magnetic Field Authors: Staude, Jürgen Bibcode: 1971SoPh...18...24S Altcode: No abstract at ADS Title: On apparent differences in magnetic field strengths measured from Zeeman splittings of molecular lines and Fe i λ 5250.2 Å Authors: Staude, Jürgen Bibcode: 1971SoPh...17..331S Altcode: No abstract at ADS Title: Line Formation in a Magnetic Field and the Interpretation of Magnetographic Measurements. III: Calculations for Different Spot Models and Arbitrary Depth Dependence of the Magnetic Field Vector Authors: Staude, J. Bibcode: 1970SoPh...15..102S Altcode: The strong temperature dependence of the line FeIλ 5250.2 Ā has been studied by calculating line contours and magnetographic calibration curves for different spot models and the BCA. Line contours calculated for arbitrary depth dependence of the magnetic field vector show depolarization effects within the Zeeman components for transversal fields with variable direction and changes of the observed plane of polarization if anomalous dispersion is taken into account. Title: Europium and Lanthanum in Sunspot and in the Undisturbed Photosphere Authors: Bachmann, G.; Pflug, K.; Staude, J. Bibcode: 1970SoPh...15..113B Altcode: Line profiles of EUIIλ4129.7 Å and LaIIλ4086.7 Å were observed photoelectrically and photographically in the photosphere and within sunspots and after correction were compared with calculated profiles. The observed large hyperfine structure broadening and isotope shift of λ4129.7 Å confirm the Eu origin of this line and suggest a larger Eu abundance than that recently published by Grevesse and Blanquet (1969). The line profiles within the spot may be well represented by means of the spot model of Hénoux (1969), while older spot models are not able to do it. An abundance difference between spot and photosphere has not been observed. Title: Line Formation in a Magnetic Field and the Interpretation of Magnetographic Measurements. II: The Influence of Different Atmosphere Models and of a Magnetic Field Gradient Authors: Staude, J. Bibcode: 1970SoPh...12...84S Altcode: The solution of the equations of transfer for the Stokes parameters in a magnetic field given by Unno (1956) has been generalized for a non-linear source function. Model calculations have been carried out for empiric atmosphere models of the photosphere and spots both for homogeneous magnetic fields and for a field strength gradient. Their influence on line contours and magnetographic calibration curves had been studied for the line FeI λ5250.2 Å. Title: About the Influence of Inhomogeneities of Magnetic Fields on Line Contours and Magnetographic Measurements Authors: Staude, J. Bibcode: 1969SoPh....8..264S Altcode: The discrepancies between theoretical and experimental calibration curves for solar magnetographs (Severny, 1967) may be explained by horizontal inhomogeneities of the observed but not resolved magnetic field region. Using the Unno solution of the equations of transfer simple two-stream models have been constructed. For the more complicated case of a depth dependence of the magnetic field vector it is shown assuming pure absorption and permitting arbitrary variations of the magnetic field vector and the atmosphere model with depth that a solution of the equations of transfer may be found by iteration. Title: Influence of inhomogeneities of magnetic fields on line contours and magnetographic measurements. Authors: Staude, J. Bibcode: 1969VeGG...13..123S Altcode: No abstract at ADS