Author name code: kneer ADS astronomy entries on 2022-09-14 author:"Kneer, Franz J." ------------------------------------------------------------------------ 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: 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: 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: 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: On the structure and dynamics of Ellerman bombs. Detailed study of three events and modelling of Hα Authors: Bello González, N.; Danilovic, S.; Kneer, F. Bibcode: 2013A&A...557A.102B Altcode:
Aims: We study the structure and dynamics of three Ellerman bombs (EBs) observed in an evolving active region.
Methods: The active region NOAA 11271 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife on August 18, 2011. We used the two-dimensional Triple Etalon SOlar Spectrometer (TESOS) to obtain time sequences of the active region and of EBs in Hα at a cadence of 15 s. Simultaneously, we obtained full Stokes profiles with the Tenerife Infrared Polarimeter (TIP II) in the two magnetically sensitive Fe i infrared lines (IR) at 1.56 μ, scanning spatial sections of the area with cadences of 28-46 s. The Hα data were reconstructed with speckle methods to study the evolution of the atmospheric stratification. Two methods were used to extract magnetic field information from the IR Stokes profiles: 1) fitting of the (Q,U,V) profiles by Gaussians; and 2) applying the Milne-Eddington approximation, assuming two separate magnetic structures in the resolution element and fitting by trial and error some profiles from the EB areas. Data from SDO-HMI and -AIA were also used. We performed two-dimensional (2D) non-LTE radiative transfer calculations of Hα in parameterised models of EBs.
Results: The three EBs studied in detail occurred in a complex active region near sunspots. They were very bright with a factor of 1.5-2.8 brighter than the nearby area. They lived for 1/2 h and longer. They were related to broadband faculae, but the latter were not the brightest features in the field of view. The EBs occurred in magnetic field configurations with opposite polarity close together. One EB was located at the outskirts of a penumbra of a complex sunspot and showed repeated "flaring" in SDO-AIA data. Another was close to a strong field patch and moved into this during the end of its lifetime. The third EB showed clear changes of field structure during the time it was observed. We obtained from the 2D modelling that heating and increase in Hα opacity are likely to occur at heights of 300-800 km. Line shifts and asymmetries can well be reproduced by velocities at these heights and also at much larger heights.
Conclusions: The three EBs occurred at sites with magnetic fields of opposite polarity, which were likely the cause of the Hα brightening upon reconnection. Title: The GREGOR Solar Telescope on Tenerife Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G. Bibcode: 2012ASPC..463..365S Altcode: 2012arXiv1202.4289S 2011 was a successful year for the GREGOR project. The telescope was finally completed in May with the installation of the 1.5-meter primary mirror. The installation of the first-light focal plane instruments was completed by the end of the year. At the same time, the preparations for the installation of the high-order adaptive optics were finished, its integration to the telescope is scheduled for early 2012. This paper describes the telescope and its instrumentation in their present first-light configuration, and provides a brief overview of the science goals of GREGOR. Title: The GREGOR Solar Telescope Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F. Bibcode: 2012IAUSS...6E.203D Altcode: The 1.5-meter GREGOR solar telescope is a new facility for high-resolution observations of the Sun. The telescope is located at the Spanish Observatorio del Teide on Tenerife. The telescope incorporates advanced designs for a foldable-tent dome, an open steel-truss telescope structure, and active and passive means to minimize telescope and mirror seeing. Solar fine structure can be observed with a dedicated suite of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot Interferometer", and the "Grating Infrared Spectrograph". All post-focus instruments benefit from a high-order (multi-conjugate) adaptive optics system, which enables observations close to the diffraction limit of the telescope. The inclusion of a spectrograph for stellar activity studies and the search for solar twins expands the scientific usage of the GREGOR to the nighttime domain. We report on the successful commissioning of the telescope until the end of 2011 and the first steps towards science verification in 2012. Title: 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: Hopes and expectations with GREGOR Authors: Kneer, F. Bibcode: 2012AN....333..790K Altcode: This contribution to the series of GREGOR inauguration articles addresses the history of the GREGOR telescope. It was obvious since a long time that the study of the atmospheric dynamics on the Sun needs telescopes with a large aperture. So the first plans to replace the 40 years old Gregory-Coudé Telescope, with its 45 cm primary mirror, by a large, 1.5-meter telescope date back to 1997. After a positive review of the project by the Deutsche Forschungsgemeinschaft in 2000, the large financial support started in 2000. Unfortunately, the new technology of the Cesic mirrors was not yet ripe to produce the large primary mirror with this light-weight material. So, the project was much delayed. After recollecting for the reader several dates, I also go through some properties of GREGOR. I recall the aims of the project and discuss difficulties and ways to realise the intentions. Title: The 1.5 meter solar telescope GREGOR Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Waldmann , T. A. Bibcode: 2012AN....333..796S Altcode: The 1.5 m telescope GREGOR opens a new window to the understanding of solar small-scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro-polarimeter for the visible wavelength range, the GRating Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR is equipped with a high-order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro-polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness. Title: The GREGOR Fabry-Pérot Interferometer Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.; Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados, M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.; Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer, R.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..880P Altcode: 2012arXiv1210.2921P The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution of R ≈ 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. Title: Shear and vortex motions in a forming sunspot . Twist relaxation in magnetic flux ropes Authors: Bello González, N.; Kneer, F.; Schlichenmaier, R. Bibcode: 2012A&A...538A..62B Altcode:
Aims: We measure proper motions of fine structures in a forming sunspot to infer information about the dynamics of flux emergence at the sub-photospheric level.
Methods: The active region NOAA 11024 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife over several days in July 2009. Here, we concentrate on a two-hour sequence taken on July 4, when the leading spot was at an early stage of its evolution. Speckle reconstructions from Ca ii K images and polarimetric data in Fe i λ6173 allow us to study proper motions of umbral fine structures.
Results: We detect three prominent features: (1) A light bridge, divided by a dark lane along its axis, shows proper motions in opposing directions on its sides, with velocities of ~100-500 m s-1. The flows are seen in both the Ca ii K and the broadband time sequences. (2) Umbral dots in one umbral region outline a vortex with speeds of up to 550 m s-1. The direction of the motion of the umbral dots is different from that in the light bridge. (3) At one rim of the umbra, the fine structure of the magnetic field moves horizontally with typical velocities of 250-300 m s-1, prior to the formation of the penumbra.
Conclusions: We report on shear and vortex motions in a forming sunspot and interpret them as tracers of twist relaxation in magnetic flux ropes. We suggest that the forming sunspot contains detached magnetic flux ropes that emerge at the surface with different amounts of twist. As they merge to form a sunspot, they untwist giving rise to the observed shear and vortex motions. Title: On acoustic and gravity waves in the solar photosphere and their energy transport Authors: Kneer, F.; Bello González, N. Bibcode: 2011A&A...532A.111K Altcode:
Aims: We study acoustic and atmospheric gravity waves in the quiet Sun to estimate their energy transport to the chromosphere.
Methods: A two-dimensional time sequence from quiet Sun disc centre was analysed with simultaneous spectroscopic observations in Fe i 5576 Å and Fe i 5434 Å (both with Landé factor g = 0). We calculated response functions of the velocities for the line minimum shifts and atmospheric transmissions of waves for the two lines. For this, NLTE line formation in granular and intergranular model atmospheres from numerical simulations were performed. For the interpretation of the observed waves and for the estimates of energy fluxes, we assumed adiabatic propagation of plane waves in an isothermal model atmosphere. Fourier analyses of intensity and velocity fluctuations were carried out. They yield power, phase, and coherence as functions of frequency ν (from temporal Fourier transforms) and in the kh - ν plane (from three-dimensional transforms). The power spectra, together with the mass densities at velocity formation heights, give then the energy fluxes.
Results: The rms velocities found here in the acoustic and gravity wave domains are lower by a factor ~1.5 as in earlier work. We therefore admit a factor of 2 for an upward correction of the estimated fluxes. For acoustic waves we find: 1) upward propagating waves are present on the Sun with frequencies up to 14-15 mHz (periods U ≈ 70 s); 2) the approximation of plane adiabatic waves in an isothermal atmosphere appears adequate for estimating the energy fluxes; 3) the acoustic energy fluxes are in the same range as found in our earlier work from ground-based, two-dimensional spectroscopy, 1500-3100 W m-2 at an atmospheric height of ~380 km and 1300-2700 W m-2 at 570 km. The energy flux carried by gravity waves is difficult to determine. We find: 1) phase and coherence spectra between continuum and velocity fluctuations show that convective overshoot and gravity waves are superimposed. We account for the convective flows using these coherence spectra. 2) At low frequencies, the vertical wavelength Λz can be short (≪300 km), yielding large corrections for atmospheric transmissions (factors > 100). We thus exclude from the flux estimates waves with |kz| > 20 Mm-1 and with vertical group velocities υgr,z < 0.3 km s-1. They are likely to be strongly reduced in amplitude by radiative damping. 3) With these caveats, the energy fluxes carried by gravity waves are found in the range of 4000 - 8200 W m-2 at 380 km and 700-1400 W m-2 at 570 km. Gravity waves thus also contribute to the energy transport into the chromosphere. Title: Acoustic waves in the solar atmosphere at high spatial resolution. II. Measurement in the Fe I 5434 Å line Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O.; Shchukina, N. Bibcode: 2010A&A...522A..31B Altcode:
Aims: We investigate the energy supply of the solar chromosphere by acoustic waves.
Methods: A time sequence with high spatial and temporal resolution from the quiet Sun disc centre in Fe i 5434 Å (Landé factor g = 0) is analysed. We used models from a numerical simulation of granular convection and apply NLTE spectral line transfer to determine the height of formation. For estimates of acoustic energy flux, we adopted wave propagation with inclinations of the wave vector with respect to the vertical of 0°, 30°, and 45°. For a granular and an intergranular model, the transmissions of the atmosphere to high-frequency waves were determined for the three inclination angles. Wavelet and Fourier analyses were performed and the resulting power spectra were corrected for atmospheric transmission.
Results: We find waves with periods down to ~40 s. They occur intermittently in space and time. The velocity signal is formed at a height of 500 km in the granular model and at 620 km in the intergranule. At periods shorter than the acoustic cutoff (~190 s), ~40% of the waves occur above granules and ~60% above intergranules. By adopting vertical propagation, we estimate total fluxes above granules of 2750-3360 W m-2, and of 910-1 000 W m-2 above intergranules. The weighted average is 1730-2 060 W m-2. The estimates of the total fluxes increase by 15% when inclined wave propagation of 45° is assumed. Title: GREGOR telescope: start of commissioning Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. Bibcode: 2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the first time, that the entire light path has seen sunlight. The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system. This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with a multi-conjugate adaptive optics system that is presently under development at KIS. Title: GREGOR solar telescope: Design and status Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G. Bibcode: 2010AN....331..624V Altcode: The integration and verification phase of the GREGOR telescope reached an important milestone with the installation of the interim 1 m SolarLite primary mirror. This was the first time that the entire light path had seen sunlight. Since then extensive testing of the telescope and its subsystems has been carried out. The integration and verification phase will culminate with the delivery and installation of the final 1.5 m Zerodur primary mirror in the summer of 2010. Observatory level tests and science verification will commence in the second half of 2010 and in 2011. This phase includes testing of the main optics, adaptive optics, cooling and pointing systems. In addition, assuming the viewpoint of a typical user, various observational modes of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared Spectrograph (GRIS), and high-speed camera systems will be tested to evaluate if they match the expectations and science requirements. This ensures that GREGOR will provide high-quality observations with its combination of (multi-conjugate) adaptive optics and advanced post-focus instruments. Routine observations are expected for 2012. Title: On the energy flux in acoustic waves in the solar atmosphere . Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O. Bibcode: 2010MmSAI..81..757B Altcode: The energy supply for the radiative losses of the quiet solar chromosphere is studied. Time sequences from quiet Sun disc centre were obtained with the ``Göttingen'' Fabry-Pérot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the non-magnetic Fe I 5576 Å line. The data were reconstructed with speckle methods. The velocities as measured at the line minimum were subjected to Fourier and wavelet analysis. The energy fluxes were corrected for the transmission of the solar atmosphere. We find an energy flux of ∼ 3 000 W m-2 at a height of h=250 km. Approximately 2/3 of it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20 mHz band. The waves occur predominantly above inter-granular areas. We speculate that the acoustic flux in waves with periods shorter than the acoustic cutoff period (U≈190 s) can contribute to the basal heating of the solar chromosphere, in addition to atmospheric gravity waves. Title: Chromosphere of active regions on the Sun . Authors: Kneer, F. Bibcode: 2010MmSAI..81..604K Altcode: The first part of this contribution deals with the chromosphere of sunspots. The models of umbrae give strongly self-reversed Ca H and K line cores. Much `macro-turbulent' broadening is needed to fit the modeled line profiles to the observations. Thus, observed dynamics in sunspot chromospheres are discussed. In the second part, the chromsphere of plages is treated. We start with the relation of K emission vs. average magnetic field strength and continue with chromospheric models. Since chromospheres are most easily observed in Halpha , various simplifications for the interpretation of this line, including the cloud model, are discussed and results are given. Dynamic phenomena in plages, such as moustaches and magneto-atmospheric waves along fibrils, will be shown. Ideas about heating mechanisms of active chromspheres will be mentioned. Title: Faculae at the poles of the Sun revisited: infrared observations Authors: Blanco Rodríguez, J.; Kneer, F. Bibcode: 2010A&A...509A..92B Altcode:
Aims: This study extends earlier investigations on faculae and their small-scale magnetic fields near the solar poles (polar faculae - PFe) to measurements of the magnetically sensitive infrared (IR) Fe I lines at 1.5 μm, which provide more accurate information about the magnetic field than lines in the visible spectral range.
Methods: PFe were observed with the Tenerife Infrared Polarimeter (TIP II) mounted at the Vacuum Tower Telescope/Observatorio del Teide/Tenerife. Several areas at various heliocentric angles were scanned. Faculae near the solar equator (equatorial faculae - EFe) were also observed for comparison with PFe. The full Stokes vector of the Fe I line pair at 1.5 μm was measured. The magnetic field properties were determined (1) from the centre of gravity (COG); (2) with the weak field approximation (WFA); (3) assuming the strong field regime (SFR); and (4) with inversions under the hypothesis of Milne-Eddington (ME) atmospheres. Line-of-sight (LOS) velocities were determined from the COG of I profiles and from the zero-crossing of the V profiles.
Results: The main findings of this work can be divided in five parts: (1) the detected PFe do not harbour sufficient magnetic flux to account for the global flux observed with other methods. (2) Near the solar limb, the apparent, measured transversal field components are most times stronger than the longitudinal components by factors of up to 10 for both PFe and EFe, as found from observations with HINODE SOT. (3) Many PFe indeed harbour kilo-G magnetic fields. Of those, more than 85% possess the same magnetic polarity as the global field. The inclinations γ of the strong fields, \vert B\vert≥ 900 G in the SFR, are compatible with their vertical emergence from the solar surface. (4) The results for weaker fields, \vert B\vert≤ 600 G from ME inversions, indicate a random magnetic field orientation. (5) The velocities from I profiles and V zero-crossings are in average 0.3 km s-1 towards observer, for both PFe and EFe. The zero-crossings of V exhibit a large velocity dispersion, of up to 3 km s-1. Title: Acoustic waves in the solar atmosphere at high spatial resolution Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O. Bibcode: 2009A&A...508..941B Altcode: Aims. The energy supply for the radiative losses of the quiet solar chromosphere is studied. On the basis of high spatial resolution data, we investigate the amount of energy flux carried by acoustic waves in the solar photosphere.
Methods: Time sequences from quiet Sun disc centre were obtained with the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the non-magnetic Fe i 5576 Å line. The data were reconstructed with speckle methods. The velocity and intensity fluctuations at line minimum were subjected to Fourier and wavelet analyses. The energy fluxes at frequencies higher than the acoustic cutoff frequency (period U ≈ 190 s) were corrected for the transmission of the solar atmosphere, which reduces the signal from short-period waves.
Results: Both Fourier and wavelet analysis give an amount of energy flux of ~3000 W m-2 at a height h = 250 km. Approximately 2/3 of it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20 mHz band. Extrapolation of the flux spectra gives an energy flux of 230-400 W m-2 at frequencies ν > 20 mHz. We find that the waves occur predominantly above inter-granular areas.
Conclusions: We conclude that the acoustic flux in waves with periods shorter than the acoustic cutoff period can contribute to the basal heating of the solar chromosphere, in addition to the atmospheric gravity waves found recently. Title: Full-Stokes Polarimetry with Speckle Techniques Authors: Bello González, N.; Kneer, F.; Okunev, O. Bibcode: 2009ASPC..405..407B Altcode: The new full-Stokes polarimeter implemented in the 2D `Göttingen' Fabry-Perot spectrometer, based on ferroelectric liquid crystals, yields magnetograms with minimised seeing induced crosstalk. A spatial resolution of 0."30--0."35 is achieved after applying speckle methods. The detection limit for the magnetic field strength is 16 G (≡ 3σ), yielding a polarimetric sensitivity of 7--8×1015 Mx. Examples of intensity maps, Dopplergrams and magnetograms from quiet Sun are discussed. Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot interferometer Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker, C.; Hofmann, A.; Kneer, F.; Puschmann, K. G. Bibcode: 2009IAUS..259..665B Altcode: One of the first post-focus instruments of the new solar telescope GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope (VTT) on Tenerife. This spectrometer is equipped with a full-Stokes polarimeter. The modulation is performed with two ferroelectric liquid crystals, one acting nominally as quarter-wave plate, and the other as half-wave plate. A modified Savart plate serves as polarimetric beam splitter. With the present liquid crystals, the optimum wavelength range of this polarimeter is between 580 and 660 nm. The spectro-polarimeter will benefit from the capabilities of the new telescope GREGOR which will provide a spatial resolution of about 0″.1 (75 km on the solar surface). Thus we will be able to investigate small magnetic features, and we will study their development with high cadence. Title: Dynamics of small-scale magnetic fields on the Sun: observations and numerical simulations Authors: Bello González, N.; Yelles Chaouche, L.; Okunev, O.; Kneer, F. Bibcode: 2009A&A...494.1091B Altcode: Context: Small-scale magnetic fields play an important role in the structure and the dynamics of the solar atmosphere.
Aims: This study aims at revealing the evolution of magnetic fields, together with granular convection in the quiet Sun by means of observations with high spatial, spectral, and temporal resolution and of numerical MHD simulations.
Methods: Time sequences from quiet Sun disc centre were obtained with the upgraded “Göttingen” Fabry-Perot spectropolarimeter at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the Fe I 6173 Å line. The data were reconstructed with speckle methods. For comparison with the observations, numerical simulations of granular magnetoconvection were carried out with the MURaM code. The intensities and Stokes vectors emerging from the simulation box were degraded in wavelength, spatial co-ordinates, and noise to the quality of the observations.
Results: The noise in the observed magnetograms from the centre-of-gravity method is σ_B≈2 G, yielding a polarimetric sensitivity of 3 × 1015 Mx, at a cadence of 23 s with 0.33 arcsec spatial resolution in a field of view of ∼33 arcsec× 25 arcsec. Many of the observed V profiles in network and internetwork (IN) areas exhibit strong asymmetries that indicate strong magnetoconvection. The temporal evolutions of IN structures and of a bright point (BP), as seen in broadband and line-minimum images, in Dopplergrams, and in magnetograms, are presented. The magnetic field structure in the numerical MHD simulations is even more complex than seen in the observations. Correspondingly, the emergent Stokes profiles are often very abnormal. The degradation yields a reduction of the intrinsic field strength to the “observed” one by a factor 4-5. The spectral resolution of the spectrometer is adequate, yet the limitation in spatial resolution and by noise filtering swamps the details seen in the non-degraded simulations. A BP was not found in the simulations, presumably because BP's are not so common and the simulated box is quiet small: only 6 Mm wide in both horizontal directions.
Conclusions: The combination of high-resolution observations with numerical simulation is a highly valuable means for studying small-scale magnetic fields on the Sun. Two-dimensional, low-noise data with spectral resolution as good as achieved here and with spatial resolution of 0.1 arcsec and better are needed to better understand this important part of the solar magnetism.

A movie is only available in electronic form at http://www.aanda.org Title: Small-scale magnetic field dynamics on the Sun at high spatial and temporal resolution Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2008A&A...490L..23B Altcode: Aims: We present examples of the time evolution of phenomena occurring in the quiet Sun photosphere as seen from observations of high spatial and spectral resolution and with a time cadence of 23 s.
Methods: A time sequence of about 5 min has been taken with the Göttingen Fabry-Perot spectropolarimeter at the VTT in the Fe I 6173 Å line. The data were reconstructed with speckle methods.
Results: With a polarimetric sensitivity of 2 × 10-3~Ic (σ_B=2 G), the formation of a bright point as seen from broadband and line-minimum intensities, as well as in magnetograms and Dopplergrams can be traced in detail. Other events, like a stable mixed-polarity configuration in the intergranules and the appearance of magnetic signature above granules in both dark and bright areas are presented. Title: Evolution of Small-scale Magnetodynamics on the Sun with High Spatial and Temporal Resolution Authors: Bello González, N.; Kneer, F. Bibcode: 2008ESPM...12..2.6B Altcode: For the detection and study of small-scale magnetic fields on the Sun, observations with both high spatial resolution and high polarimetric sensitivity are required. The combination formed by the upgraded Göttingen FPI spectrometer (spectral resolution of 25mÅ, at 617.3nm), full Stokes polarimeter, Adaptive Optics (KAOS) and speckle reconstruction techniques, provide broadband images of 0.25 arcsec spatial resolution and magnetograms of 0.33 arcsec, with minimised seeing induced signals yielding a polarimetric sensitivity of ~0.002 Ic. A description of the optical system as well as results from the analysis of intensity maps, Dopplergrams and magnetograms from quiet and active regions on the Sun will be presented. The data were taken in the FeI 6173Å. We select few examples from the huge variety of magnetodynamic processes seen in the observations, e.g. the fast evolution of a bright point in broadband and line minimum intensity, in magnetograms, and in Dopplergrams is shown. Further examples indicate convective collapse, magnetic field advection, and magnetic field diffusion. Title: High-resolution Spectropolarimetry with the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife: History and Success of the Göttingen Programme Authors: Kneer, F.; Bello Gonzalez, N. Bibcode: 2008ESPM...12.2.30K Altcode: The efforts of the Göttingen solar physics group on high spatial resolution and 2D spectroscopy started in 1986. First results were obtained with speckle broadband imaging (de Boer 1992) and with 2D spectroscopy by means of one Fabry-Perot etalon (FPI) and a Universal Birefringent Filter (UBF). 2D Stokes V polarimetry followed soon. The UBF was replaced by a 2nd FPI which allowed short exposures also in the narrow-band channel of the spectrometer. Thus 2D spectropolari- metry could be combined with speckle reconstruction. The ``Göttingen FPI'' has been upgraded in 2005 for high efficiency and in 2007 for full Stokes polarimetry and good spectral resolution. It has become a fast and versatile instrument that has been, and will be, operated sucessfully for many scientific programmes on the atmospheric dynamics of the Sun. Title: Fast events and waves in an active region of the Sun observed in Hα with high spatial resolution Authors: Sánchez-Andrade Nuño, B.; Bello González, N.; Blanco Rodríguez, J.; Kneer, F.; Puschmann, K. G. Bibcode: 2008A&A...486..577S Altcode: Context: We study the chromosphere of an active region of the Sun in the Hα line.
Aims: The development of new instrumentation and new methods of data analysis allows to scrutinize the dynamics of the solar chromosphere with high spatial, spectral, and temporal resolution. The observations we present shed light on some magneto-dynamic processes occurring above an active region in the chromosphere.
Methods: We took a time series of 55 min in Hα from AR 10875 at θ≈36°. We used the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, to obtain two-dimensional spectrograms in Hα. Adaptive optics and image reconstruction yielded a spatial resolution better than 0.5 arcsec throughout the time sequence. From the wealth of structures, we selected areas of interest to study further, in detail, some ongoing processes.
Results: A small straight surge developed aside of a pore with upward phase speed of 100 km s-1 and line-of-sight (LOS) velocity of 15 km s-1. The surge retreated rapidly with LOS velocity of 45 km s-1 at its mouth. It underwent a rebound and fell back again. Two sympathetic mini-flares were observed that lasted only approximately 40 s, but showed strong Hα emission. We found magnetoacoustic waves in long fibrils as mainly short wave trains, short packets or pulses, i.e., solitary waves consisting of small (1´´-2´´) blobs. They start at either end of the fibrils and travel with phase speeds of 12-14 km s-1, i.e., close to the tube speed and approximately the sound velocity for sufficiently large magnetic field strengths. Some waves speed up to reach velocities of the order of 30 km s-1. This is much lower than the expected Alfvén velocity of ≥200 km s-1 for reasonable magnetic field strengths and mass densities. We suggest that slow waves are not purely longitudinal, but possess gas velocities perpendicular to the direction of propagation of few km s-1. Also, fast waves travel along sinuous lines suggesting entangled magnetic fields. They spread out along the direction of propagation in the course of their evolution and often vanish. We discuss the implications. Title: Narrow-band full Stokes polarimetry of small structures on the Sun with speckle methods Authors: Bello González, N.; Kneer, F. Bibcode: 2008A&A...480..265B Altcode: Aims:For the detection and the study of small-scale magnetic fields on the Sun, it is important to obtain observations with both high spatial resolution and high polarimetric sensitivity.
Methods: A second narrow-band etalon and a full Stokes polarimeter, based on ferroelectric liquid crystals, were implemented in the two-dimensional “Göttingen” Fabry-Perot spectrometer/polarimeter at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife. First observations with the Fe I 6173 Å line and their data analysis with speckle methods are described.
Results: The new polarimeter yields magnetograms of a field of view of 31 arcsec×52 arcsec with minimised seeing induced signals and without spurious signals as from the use of beam-splitting calcites. The achieved spatial and temporal resolution are 0.30-0.35 arcsec and 36 s, respectively. With a detection limit for the field strength of 16 G (\cor3σ), a polarimetric sensitivity of 7-8×1015 Mx is obtained. Examples of intensity maps, Dopplergrams, and magnetograms from quiet and active regions on the Sun are discussed. Some of the results on solar magnetism are on 1) a pore with small-scale structure where we find a region with very low temperature gradient, 2) polar faculae with strong magnetic field signals and weaker signals in other areas surrounding them, and 3) small-scale inter-network magnetic fields with area fillings in the resolution elements of the order of 0.15. Title: On the properties of faculae at the poles of the Sun Authors: Blanco Rodríguez, J.; Okunev, O. V.; Puschmann, K. G.; Kneer, F.; Sánchez-Andrade Nuño, B. Bibcode: 2007A&A...474..251B Altcode: Context: Faculae at the poles of the Sun, or polar faculae (PFe), take part in the solar magnetic cycle. Their occurrence maximum is shifted by 5-6 years with respect to the sunspot cycle. PFe are stable phenomena, with lifetimes of several hours to days, and harbour magnetic fields of kilo-Gauss strength. Yet their role for the global magnetic field at the solar poles is unknown.
Aims: To contribute to the knowledge of the physical properties of PFe and to the understanding of their role in the global magnetism of the Sun.
Methods: PFe were observed on 21-24 August 2005 with the Vacuum Tower Telescope at the Observatorio del Teide. The “Göttingen” Fabry-Perot spectrometer was used with a Stokes V polarimeter to scan the Fe i 6173 Å line (Landé factor g = 2.5) and the Hα line in two-dimensional fields of view (FOVs). A large observational coverage of the polar caps was obtained. The data were analysed with speckle methods. Magnetic field strengths were determined with the weak field approximation, with the approximation of the strong field regime, and with the centre of gravity (COG) method. Velocities were measured with the COG method and from the zero-crossing of the Stokes V profiles.
Results: PFe show a decrease of the continuum and broadband intensity contrast towards the disc centre and no decrease of contrast towards the limb, similar to as faculae in active regions near the equator. Extrapolating from the observed FOVs to the total areas of PF occurrence around the solar poles, we find 4 120 PFe in the northern polar cap and, asymmetrically to this number, 1 250 PFe near the south pole. The total area coverages by PFe are ~7.6×108 km2 and ~3.4×108 km2 near the solar north and south poles, respectively. Some of the PFe exhibit magnetic polarities opposite to the global polarity at the time of observation. The resulting total magnetic fluxes in PFe fall short by an order of magnitude from those found in the literature for the fluxes at the polar caps. This also holds if we include magnetic structures which are not related to brightenings. We conclude that with the present spatial resolution of 0.4 arcsec-0.5 arcsec (FWHM), PFe represent the “large-scale” end of a distribution of unipolar strands near the solar poles. The velocities in PFe show amplitudes of 2 km s-1, with systematic up-flows in the Stokes I profile, but no average velocity measured in the V zero-crossings. Title: Spicule emission profiles observed in He i 10 830 Å Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.; Trujillo Bueno, J.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2007A&A...472L..51S Altcode: 2007arXiv0707.4421S Aims:Off-the-limb observations with high spatial and spectral resolution will help us understand the physical properties of spicules in the solar chromosphere.
Methods: Spectropolarimetric observations of spicules in the He i 10 830 Å multiplet were obtained with the Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife, Spain). The analysis shows the variation of the off-limb emission profiles as a function of the distance to the visible solar limb. The ratio between the intensities of the blue and the red components of this triplet (R=I_blue/I_red) is an observational signature of the optical thickness along the light path, which is related to the intensity of the coronal irradiation.
Results: We present observations of the intensity profiles of spicules above a quiet Sun region. The observable R as a function of the distance to the visible limb is also given. We have compared our observational results to the intensity ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere assuming spherical geometry. The agreement is purely qualitative. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here. Title: Modern Solar Facilities - Advanced Solar Science Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D. Bibcode: 2007msfa.conf.....K Altcode: An international workshop entitled: Modern Solar Facilities - Advanced Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop, which was attended by 88 participants from 24 different countries, gave a broad overview of the current state of solar research, with emphasis on telescopes and instrumentation, high-resolution and high-precision observations, and theory and interpretation. The book collects written versions of 71 papers presented at the conference. 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: Temporal evolution of intensity, velocity and magnetic field of sunspots at high spatial resolution Authors: Bello González, N.; Kneer, F.; Puschmann, K. G. Bibcode: 2007msfa.conf..217B Altcode: We present results of sunspot observations obtained in April 2006 with the new "Göttingen" Fabry-Perot spectrometer. Thanks to the large field of view (77"x58") of the new optical setup it has been possible to perform 2D-spectropolarimetric observations of a small sunspot and ist surroundings at a heliocentric angle [Theta] ~ 40Å. A long time series of about one hour has been taken scanning along the magnetic Fe I 6173 Å and the non-magnetic Fe I 5576 Å spectral lines quasi-simultaneously. Hence, with the help of image reconstruction techniques, the temporal evolution of the sunspot fine-structure in intensity as well as in velocity and magnetic field is analysed at high spatial resolution. Title: Off-limb spectroscopy of the He I 10830 Å multiplet: observations vs. modelling Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.; Trujillo Bueno, J.; Kneer, F. Bibcode: 2007msfa.conf..177S Altcode: Spectropolarimetric observations of spicules were carried out with the new optical setup of the Tenerife Infrared Polarimeter (TIP 2) at the VTT, showing the variation of the He I 10830Å multiplet off-limb emission profiles with increasing distance to the solar visible limb. The ratio between the intensities of the blue and the red components of this triplet (R = Iblue/Ired) is an observational signature of the optical thickness along the light path, which, at the same time, is proportional to the population of the lower (metastable) level that takes part in these transitions. Our observational results show a variation of R as a function of the distance to the limb. In agreement with recent theoretical results we conclude that R could be used as a diagnostic tool for downward UV coronal irradiance, which is believed to be responsible for the population of the metastable level of the He I 10830 Å triplet. We have compared our observational results with the ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere (assuming spherical geometry) finding a fairly poor agreement. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here. Title: From the "Göttingen" Fabry-Perot Interferometer to the GREGOR FPI Authors: Puschmann, K. G.; Kneer, F.; Nicklas, H.; Wittmann, A. D. Bibcode: 2007msfa.conf...45P Altcode: Fabry-Perot Interferometers (FPIs) have advantages over slit spectrographs, allowing fast two-dimensional, narrowband imaging and post factum image reconstruction of the spectropolarimetric data obtained. The resulting intensity, velocity and magnetic field maps are a fundamental base for the understanding of the dynamics of the solar atmosphere and its magnetic fields at smallest spatial scales. Efforts are undertaken to provide, with the Göttingen Fabry-Perot interferometer, an up-todate post-focus instrument for the German 1.5 m GREGOR solar telescope. Therefore a renewal of the spectrometer has been achieved during the first half of 2005. First observations at the German Vacuum Tower Telescope (VTT) reveal new scientific aspects and a very promising outlook for the future at GREGOR. In this contribution a general description of the upgraded spectrometer is given. Its final optical design at GREGOR is described and an optical analysis of the GREGOR FPI is outlined. Latest results with the new instrument obtained at the VTT are presented. 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: Modern solar facilities - advanced solar science Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D. Bibcode: 2007msfa.conf....0K Altcode: An international workshop entitled: Modern Solar Facilities - Advanced Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop, which was attended by 88 participants from 24 different countries, gave a broad overview of the current state of solar research, with emphasis on telescopes and instrumentation, high-resolution and high-precision observations, and theory and interpretation. The book collects written versions of 71 papers presented at the conference. Title: Methods in high-resolution solar spectroscopy Authors: Kneer, F. Bibcode: 2007msfa.conf...67K Altcode: After few historical remarks, the needs in high-resolution spectroscopy are outlined. They are concerned with temporal, spatial, and wavelength resolution for a reasonable field of view of supergranulation cell or larger. At 0."1 spatial resolution ([about] 72.5 km on the Sun) the measurement for a snapshot should be finished within the transit time ttr [about] 10 s (size of resolution element/sound speed). Finally, the performances of grating spectrometers and Fabry-Perot interferometers are compared. The latter are far superior to grating spectrographs due to their high resolution-luminosity product. Title: Observations of a flaring active region in H[alpha] Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2007msfa.conf..273S Altcode: A 40 min time series of the active region NOAA AR10875 was obtained on April 26th, 2006 under very good seeing conditions using the new "Göttingen" - Fabry-Perot interferometer at the German Vacuum Tower Telescope, Observatorio del Teide, Tenerife. The Hα line was scanned giving two-dimensional images at 21 different wavelength positions with a cadence of ~ 20 s per scan. After speckle reconstruction the spatial resolution achieved was better than 0".35. The data provide a unique possibility to study the temporal evolution of a pre-flaring, flaring and post-flaring solar active region in Hα. From the analysis of the present spectrometric data set we expect important advances in the understanding of Alfén waves, dynamics of fibrils and filaments and the physical nature of the sigmoid structure seen in the core of Hα. Here we present first results from this data set. Title: Dynamics of the quiet photosphere and its magnetic field under high spatial resolution Authors: Puschmann, K. G.; Kneer, F.; Domínguez Cerdeña, I. Bibcode: 2007msfa.conf..151P Altcode: An excellent 1 h 10 min time series of a quiet solar region near disk centre was acquired on 4th of May 2006 at the German Vacuum Tower Telescope. Using the new "Göttingen" Fabry-Perot interferometer together with the Kiepenheuer Adaptive Optics system spectropolarimetric images were obtained, scanning the Fe I 5247Å and Fe I 5250Å lines with a temporal cadence of 17 s each. Thanks to speckle reconstruction methods the achieved spatial resolution of the obtained intensity, velocity and magnetic field maps is ~ 0."3. First results on the dynamics of the quiet photosphere and magnetic fields reveal strengthening and weakening of the polarisation signal in interaction to granular convection processes indicating advection and diffusion of magnetic flux at smallest scales. Field structures, very elongated along intergranular lanes, show high dynamics, combine and split, and leave strong fingerprints at high photospheric layers where related temperatures fluctuate. Recent numerical MHD simulations come close to our findings. Possible indications of magnetic flux annihilation, flux tube evacuation or signs of upward-propagating shock fronts are illustrated. Title: Study of polar faculae with north pole coverage of the Sun Authors: Blanco Rodríguez, J.; Okunev, O.; Puschmann, K. G.; Kneer, F. Bibcode: 2007msfa.conf..181B Altcode: We present here a description of the main characteristics of faculae at the poles of the Sun (polar faculae PFe) observed in a series of observations covering the north solar pole. Statistics of a group of these PFe are used to estimate the contrast behaviour from [mμ] = 0.6 towards the limb as well as their magnetic field. Hα is also observed to analyse the behaviour of PFe in the chromosphere. Title: Magnetic Fields of the Quiet Sun: Distribution of Field Strengths Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ASPC..358...48D Altcode: The quiet Sun photospheric plasma has a variety of magnetic field strengths going from zero to 1800 G. The empirical characterization of these field strengths requires a probability density function (PDF), i.e., a function P(B) describing the fraction of quiet Sun occupied by each field strength B. We present a method to combine magnetic field strength measurements based on the Zeeman effect and the Hanle effect in order to estimate the true P(B). The application of the method to real observations renders a set of possible PDFs, which outline the general characteristics of the quiet Sun magnetic fields. Their most probable field strength differs from zero. The magnetic energy density is a significant fraction of the kinetic energy of the granular motions at the base of the photosphere (larger than 15 or larger than 2×103 erg cm-3). The unsigned flux density (or mean magnetic field strength) has to be between 130 G and 190 G. A significant part of the unsigned flux (between 10% and 40%) and of the magnetic energy (between 40% and 80%) are provided by the field strengths larger than 1 kG which, however, occupy only a small fraction of the surface (between 1% and 4%).

The quiet Sun photosphere has far more unsigned magnetic flux and magnetic energy than the active regions and the network together. Title: Quiet-Sun Magnetic Fields: Simultaneous Inversion of Visible and IR Spectro-Polarimetric Observations Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ASPC..358...88D Altcode: We studied the quiet-Sun magnetic fields interpreting spectro-polarimetric observations of infrared and visible spectral lines. Magnetic field strengths and filling factors were inferred by the simultaneous inversion of Stokes profiles of the Fe I lines at 6301.5, 6302.5, 15648, and 15653 Å under the MISMA hypothesis. They cover a solar intra-network region at disk center. We analyzed Stokes profiles with signals above noise in both spectral ranges, which correspond to 40% of the field of view. Most of these 2280 profiles could only be inverted with a model including 3 magnetic components with very different field strengths, which indicates the co-existence of kG and sub-kG fields. We measured a total unsigned magnetic flux density of 9.6 G over the whole field of view. For half of the pixels the magnetic field has opposite polarities within the resolution element. We computed the probability density function of finding each magnetic field strength. It has an important contribution of kG field strengths, which concentrates most of the magnetic flux and energy. This kG contribution has a preferred magnetic polarity while the weak fields are balanced. Title: Quiet Sun Magnetic Fields from Simultaneous Inversions of Visible and Infrared Spectropolarimetric Observations Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ApJ...646.1421D Altcode: 2006astro.ph..4381D We study the quiet Sun magnetic fields using spectropolarimetric observations of the infrared and visible Fe I lines at 6301.5, 6302.5, 15648, and 15653 Å. Magnetic field strengths and filling factors are inferred by the simultaneous fit of the observed Stokes profiles under the MISMA hypothesis. The observations cover an intranetwork region at the solar disk center. We analyze 2280 Stokes profiles whose polarization signals are above noise in the two spectral ranges, which correspond to 40% of the field of view. Most of these profiles can be reproduced only with a model atmosphere including three magnetic components with very different field strengths, which indicates the coexistence of kG and sub-kG fields in our 1.5" resolution elements. We measure an unsigned magnetic flux density of 9.6 G considering the full field of view. Half of the pixels present magnetic fields with mixed polarities in the resolution element. The fraction of mixed polarities increases as the polarization weakens. We compute the probability density function of finding each magnetic field strength. It has a significant contribution of kG field strengths, which concentrates most of the observed magnetic flux and energy. This kG contribution has a preferred magnetic polarity, while the polarity of the weak fields is balanced. Title: The new 1.5m solar telescope GREGOR: first light and start of commissioning Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens; Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners. Title: The new Göttingen Fabry-Pérot spectrometer for two-dimensional observations of the Sun Authors: Puschmann, K. G.; Kneer, F.; Seelemann, T.; Wittmann, A. D. Bibcode: 2006A&A...451.1151P Altcode: Studies of small-scale dynamics and magnetic fields in the solar atmosphere require spectroscopy and polarimetry with high spatial resolution. For this purpose, spectrometers based on Fabry-Pérot interferometers (FPIs) have advantages over slit spectrographs. They possess a high throughput and allow fast two-dimensional, narrow-band imaging and image reconstruction of the data. In the present contribution we describe an upgrade, essentially renewal, of the Göttingen FPI spectrometer achieved during the first half of 2005. A new etalon from IC Optical Systems Ltd. (formerly Queensgate), England, with 70 mm free aperture for high spectral resolution has been mounted. New CCD detectors from LaVision GmbH (Göttingen) with powerful computer hard- and software were implemented. We consider the product of signal-to-noise ratio, frame rate, and field of view as a measure of the efficiency. At low light levels, e.g. in narrow-band speckle applications, this product has increased by a factor ~60 compared to the old system. In addition, several spectral regions can now be scanned quasi-simultaneously. We present first results obtained with the upgraded spectrometer. The efforts are undertaken to provide an up-to-date post-focus instrument for the new German 1.5 m GREGOR solar telescope presently under construction at the Observatorio del Teide on Tenerife. Title: The Distribution of Quiet Sun Magnetic Field Strengths from 0 to 1800 G Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ApJ...636..496D Altcode: 2005astro.ph..9243D; 2006ApJ...636..496C The quiet-Sun photospheric plasma has a variety of magnetic field strengths going from zero to 1800 G. The empirical characterization of these field strengths requires a probability density function (PDF), i.e., a function P(B) describing the fraction of quiet Sun occupied by each field strength B. We show how to combine magnetic field strength measurements based on the Zeeman effect and the Hanle effect to estimate an unbiased P(B). The application of the method to real observations renders a set of possible PDFs, which outline the general characteristics of the quiet-Sun magnetic fields. Their most probable field strength differs from zero. The magnetic energy density is a significant fraction of the kinetic energy of the granular motions at the base of the photosphere (larger than 15% or larger than 2×103 ergs cm-3). The unsigned flux density (or mean magnetic field strength) has to be between 130 and 190 G. A significant part of the unsigned flux (between 10% and 50%) and of the magnetic energy (between 45% and 85%) are provided by the field strengths larger than 500 G, which, however, occupy only a small fraction of the surface (between 1% and 10%). The fraction of kG fields in the quiet Sun is even smaller, but they are important for a number of reasons. The kG fields still trace a significant fraction of the total magnetic energy, they reach the high photosphere, and they appear in unpolarized light images. The quiet-Sun photosphere has far more unsigned magnetic flux and magnetic energy than the active regions and the network combined. Title: Chromospheric Dynamics of a Solar Active Region Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez Cuberes, M.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2005ESASP.600E..70S Altcode: 2005dysu.confE..70S; 2005ESPM...11...70S No abstract at ADS Title: Study of Polar Faculae Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2005ESASP.600E..59B Altcode: 2005dysu.confE..59B; 2005ESPM...11...59B No abstract at ADS Title: Synthesis of Stokes Profiles from a Two Component Penumbral Model Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ESASP.600E..56B Altcode: 2005ESPM...11...56B; 2005dysu.confE..56B No abstract at ADS Title: Analysis of a Wide Chromospheric Active Region Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez Cuberes, M.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2005ESASP.596E..62S Altcode: 2005ccmf.confE..62S No abstract at ADS Title: Magnetic Structures on the Sun: Osbervations with the New "GÖTTINGEN" Two-Dimensional Spectrometer on Tenerife Authors: Kneer, F.; Puschmann, K. G.; Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Wittmann, A. D. Bibcode: 2005ESASP.596E..71K Altcode: 2005ccmf.confE..71K No abstract at ADS Title: Study of Polar Faculae Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2005ESASP.596E..52B Altcode: 2005ccmf.confE..52B No abstract at ADS Title: Analysis of Polarimetric Sunspot Data from Tesos/vtt/tenerife Authors: Valdivielso Casas, L.; Bello González, N.; Puschmann, K. G.; Sánchez-Andrade Nuño, B.; Kneer, F. Bibcode: 2005ESASP.596E..67V Altcode: 2005ccmf.confE..67V No abstract at ADS Title: Study of Asymmetries of Stokes Profiles from High Spatial Resolution Spectropolarimetry Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ESASP.596E..50B Altcode: 2005ccmf.confE..50B No abstract at ADS Title: Numerical modeling of solar faculae close to the limb Authors: Okunev, O. V.; Kneer, F. Bibcode: 2005A&A...439..323O Altcode: A numerical simulation was performed to interpret high-resolution spectropolarimetric observations of polar faculae on the Sun. A semi-empirical three-dimensional model of facula structures, controlled by several free parameters, was constructed. It consists of two components, the atmosphere within small-scale magnetic flux tubes and the exterior atmosphere. Multi-ray 1.5D radiative transfer calculations were performed along oblique rays passing through a highly inhomogeneous atmosphere of the simulation box. By the comparison of the properties of the calculated Stokes profiles from the synthetic faculae with the observed properties, a set of free parameters of the model (such as: size, number density of flux tubes, internal temperature stratification and magnetic field strength) was deduced, which satisfies the observational constraints. The hypothesis about solar faculae as a conglomerate of small-scale magnetic flux tubes is verified. The model reproduces all observed properties: the continuum contrast and its center-to-limb variation, the Stokes I and V profiles of Fe I and Fe II lines, the apparent magnetic field strengths, and the displacement towards the limb of the continuum intensity against the line-of-sight magnetograms. 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: On super-resolution in astronomical imaging Authors: Puschmann, K. G.; Kneer, F. Bibcode: 2005A&A...436..373P Altcode: Our work is an attempt to fulfil one of the aims of astronomical imaging, that is, to obtain information at high angular resolution. Stars as point sources can be represented by Dirac δ-functions whose Fourier transforms contain information about the position and the (integrated) intensity at all angular frequencies. Thus, we can deconvolve unresolved images of star fields even at angular distances smaller than the diffraction limit of the telescope with which the observations are performed. We give an example of reconstruction of the image of two stars with an angular separation of a factor 2.5 less than α_Ra=1.22×λ/D. However, we find that super-resolution is feasible only for point sources. For extended objects the information about intensity fluctuations at angular frequencies u>u_max=D/λ=1/α_min is irretrievably lost. We discuss the impossibility of super-resolution for the Sun using a numerically simulated image of solar granulation. However, one can enhance the contrast of solar images, though without increasing angular resolution beyond the diffraction limit. Title: Polarimetry of sunspot penumbrae with high spatial resolution Authors: Bello González, N.; Okunev, O. V.; Domínguez Cerdeña, I.; Kneer, F.; Puschmann, K. G. Bibcode: 2005A&A...434..317B Altcode: We present two-dimensional high-spatial-resolution spectropolarimetric observations of sunspot penumbrae. They were obtained in April 2002 and May 2003 with the "Göttingen" Fabry-Pérot spectrometer at the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife). Speckle methods were applied for image reconstruction which resulted in a spatial resolution of 0.5 arcsec in the magnetograms of the penumbrae. We analysed Stokes I and V profiles of the Fe II 6149 Å line, which exhibits no instrumental Stokes Q/U→ V crosstalk, and of the Fe I line pair at 6302 Å. The main results are the following: 1) on scales larger than 0.5 arcsec, the intensity pattern of penumbrae stays the same in the continuum and core images of the 6301.5 Å line, which stem from 0 km and 300 km (above τ_5=1), respectively. Yet at scales of 0.5 arcsec and smaller the pattern in the two spectral features is clearly different. 2) On the limb side of sunspots the Evershed flow is carried by dark filaments and on the centre side by bright features and their somewhat weakened tails. We explain this with a picture in which the velocity of hot rising gas is best seen on the centre side, while on the limb side the horizontal outward and possibly downward flows are seen when the gas has cooled down. 3) The un-combed structure of the magnetic field is confirmed. On the limb side, the more horizontal fields coincide with dark fibrils or with diffuse intensity structures. Generally, the more horizontal fields are located at the positions of strong outflows. 4) Strong line-of-sight components of the magnetic fields are not found in bright filaments but in dark structures, somewhat displaced from the darkest parts. Their positions do not coincide with those of the strongest velocity fields. In general, our results are compatible with the picture of low lying flow channels coincident with the horizontal magnetic field, or possibly emerging and diving down into sub-photospheric layers, like a "sea serpent". Some further dynamic phenomena are discussed, which demonstrate the richness of processes in penumbrae, and reveal unexpected properties. Title: Quiet sun magnetic fields vs. polar faculae - local vs. global dynamo? Authors: Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2005AN....326..205O Altcode: Quiet Sun magnetic fields in the internetwork are almost ubiquitous. Simultaneous observations in infra-red and visible lines and high spatial resolution (< 0.5'') data in visible lines show that their field strengths range from below few hundred Gauss to kilo-Gauss. Most of the flux is contained in small-scale, strong-field features located mainly in intergranular lanes. The average unsigned flux density exceeds 20 Gauss. The new detections are confirmed by recent quiet Sun observations in the G band. The generation of the strong fields in the internetwork, which may be due to a local dynamo, poses a challenging problem. - Polar faculae (PFe) are small-scale magnetic features at the polar caps of the Sun. They take part in the solar cycle and are thus likely to be rooted deeply in the solar interior. They are the result of the global dynamo at the solar poles. PFe also possess kilo-Gauss magnetic fields which have the same polarity as the global magnetic field. The rôle of quiet Sun magnetic field structures and of PFe for the dynamics of the corona and for the solar wind are addressed. Title: Spectropolarimetry in a Sunspot Penumbra at High Spatial Resolution Authors: Gonzalez, N. Bello; Ounev, O.; Kneer, F. Bibcode: 2005ASSL..320..183G Altcode: No abstract at ADS Title: Spectropolarimetry in a sunspot penumbra at high spatial resolution Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ASSL..320..183B Altcode: 2005smp..conf..183B We present results from polarimetric data on sunspot penumbrae obtained with the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, using the `Göttingen' Fabry-Pérot Interferometer. Speckle image reconstruction has been performed giving us a spatial resolution of 0.6''. The observations were taken in the Fe II 6149.2 Å line which, given its particular Zeeman splitting, has no instrumental (Q,U) to V crosstalk and provides us measurements of I and V Stokes profiles to analyse velocities and magnetic fields in penumbrae. Title: Simultaneous Visible and IR spectropolarimetry of the quiet Sun Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2005ASSL..320..175D Altcode: 2005ASSL..320..175C; 2005smp..conf..175D This work presents the first quiet Sun spectropolarimetric observations carried out in the visible and the infrared (IR) simultaneously. The Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed co-spatially, and at the same time (with a time lag of only 1 minute), with high sensitive spectropolarimeters operated in two different telescopes (VTT and THEMIS at the Observatorio del Teide). We find Stokes V profiles above noise in 30% of the observed area, showing intrinsic magnetic fields of kG (traced by visible lines) co-existing with sub-kG fields (traced by infrared lines). We also found V profiles with opposite polarity in the visible and the IR in 25% of the pixels under study (8% of the area). Title: On the structure of polar faculae on the Sun Authors: Okunev, O. V.; Kneer, F. Bibcode: 2004A&A...425..321O Altcode: Faculae on the polar caps of the Sun, in short polar faculae (PFe), are investigated. They take part in the magnetic solar cycle. Here, we study the fine structures of PFe, their magnetic fields and their dynamics on short time scales. The observations stem from several periods in 2001 and 2002. They consist of spectropolarimetric data (Stokes I and V) taken in the Fe I 6301.5 and 6302.5 Å and Fe II 6149.3 Å lines with the Gregory-Coudé Telescope (GCT) and the Vacuum Tower Telescope (VTT) at the Observatorio del Teide on Tenerife. At the VTT, the ``Göttingen'' two-dimensional Fabry-Perot spectrometer was used. It allows image reconstruction with speckle methods resulting in spatial resolution of approximately 0.25 arcsec for broadband images and 0.5 arcsec for magnetograms. The application of singular value decomposition yielded a polarimetric detection limit of | V|≈2 × 10-3Ic. We find that PFe, of size of 1 arcsec or larger, possess substantial fine structure of both brightness and magnetic fields. The brightness and the location of polar facular points change noticeably within 50 s. The facular points have strong, kilo-Gauss magnetic fields, they are unipolar with the same polarity as the global, poloidal magnetic field. The ambient areas, however, exhibit weak flux features of both polarities, as in the quiet Sun near disk center. Strong upflows of 1 km s-1 are detected in the intensity profiles of PFe. The zero-crossings of the Stokes V profiles yield an average velocity of the magnetized plasma of vFT≈-0.4 km s-1 (towards the observer). 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: Dynamics of an enhanced network region observed in Hα Authors: Al, N.; Bendlin, C.; Hirzberger, J.; Kneer, F.; Trujillo Bueno, J. Bibcode: 2004A&A...418.1131A Altcode: This investigation is based on Hα observations of high spatial resolution. They stem from an enhanced network region near disk centre of the sun and consist of broad-band and narrow-band images taken with the two-dimensional ``Göttingen'' Fabry-Perot spectrometer mounted in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The ``lambdameter method'' was applied to derive intensity and velocity maps over the two-dimensional field of view reflecting the behaviour of these parameters in the solar chromosphere. The determination of the source function, the line-of-sight (LOS) velocity, the Doppler width and the optical depth was based on Beckers' cloud model (Beckers \cite{beckers}). From the LOS velocity distribution along the Hα structures we conclude that ballistic motions are unlikely to prevail. Especially the bright Hα features cannot be explained by the cloud model. It is shown how, instead, two-dimensional non-LTE radiative transfer calculations of embedded chromospheric structures lead to reasonable agreement with the observed line profiles from these bright features. It is found that many of the bright fibril-like structures near dark fibrils can be explained by radiation which is blocked by absorbing material at large heights and escapes through less opaque regions. We estimate the number densities and the temperature. With these and with the measured velocities, the kinetic energy flux and the enthalpy flux related to the motions of the fine structures can be calculated. Both fall short by at least an order of magnitude of covering energy losses by radiation of active chromospheric regions. Title: Polarimetry in sunspot penumbrae at high spatial resolution. Authors: Bello Gonzalez, N.; Okunev, O.; Dominguez Cerdena, I.; Kneer, F. Bibcode: 2004ANS...325...79B Altcode: 2004ANS...325..P03B; 2004ANS...325a..79B No abstract at ADS Title: Short period waves in the solar atmosphere. Authors: Andic, A.; Kneer, F. Bibcode: 2004ANS...325...96A Altcode: 2004ANS...325a..96A; 2004ANS...325..P26A No abstract at ADS Title: Analysis of simultaneous visible and infrared spectropolarimetric observations of quiet Sun. Authors: Dominguez Cerdena, I.; Sanchez Almeida, J.; Kneer, F. Bibcode: 2004ANS...325...94D Altcode: 2004ANS...325a..94D; 2004ANS...325..P23D No abstract at ADS Title: Adaptive optics transfer function estimation for solar observations. Authors: Sailer, M.; von der Luehe, O.; Kneer, F. Bibcode: 2004ANS...325..130S Altcode: 2004ANS...325..P65S; 2004ANS...325a.130S No abstract at ADS Title: Structure and short-time evolution of polar faculae on the sun. Authors: Okunev, O. V.; Kneer, F. Bibcode: 2004ANS...325...80O Altcode: 2004ANS...325..P04O; 2004ANS...325a..80O No abstract at ADS Title: Simultaneous Visible and Infrared Spectropolarimetry of a Solar Internetwork Region Authors: Sánchez Almeida, J.; Domínguez Cerdeña, I.; Kneer, F. Bibcode: 2003ApJ...597L.177S Altcode: 2003astro.ph..9727A; 2003astro.ph..9727S We present the first simultaneous infrared (IR) and visible spectropolarimetric observations of a solar internetwork region. The Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed, with a lag of only 1 minute, using highly sensitive spectropolarimeters operated in two different telescopes (Vacuum Tower Telescope and THEMIS at the Observatorio del Teide). Some 30% of the observed region shows IR and visible Stokes V signals above noise. These polarization signals indicate the presence of kilogauss (kG) magnetic field strengths (traced by the visible lines) coexisting with sub-kG fields (traced by the infrared lines). In addition, one-quarter of the pixels with signal have visible and IR Stokes V profiles with opposite polarity. We estimate the probability density function of finding each longitudinal magnetic field strength in the region. It has a tail of kG field strengths that accounts for most of the (unsigned) magnetic flux of the region. Title: On the fractal dimension of small-scale magnetic structures in the Sun Authors: Janßen, K.; Vögler, A.; Kneer, F. Bibcode: 2003A&A...409.1127J Altcode: We compare, by means of fractal analyses, the shapes of observed small-scale magnetic structures on the Sun with those of magnetic features resulting from numerical simulations of magnetoconvection. The observations were obtained with the ``Göttingen'' Fabry-Perot spectrometer at the Vacuum Tower Telescope at the Observatorio del Teide on Tenerife. Magnetograms with 0\farcs4-0\farcs5 spatial resolution were obtained from two-dimensional Stokes V polarimetry in the Fe I 6302.5 Å line and by image reconstruction with speckle methods. The simulations of magnetoconvection was performed with the MURAM code. It solves the time-dependent MHD equations for a compressible, partly ionized plasma including radiative transfer in LTE. To determine the fractal dimensions the perimeter-area relation is used. We discuss the influence of seeing and noise in the fractal dimension D of the observed magnetograms. A dependence of D on the distance from disk center could not be found. The observations give D=1.21+/-0.05 for a pixel size corresponding to 0\farcs105, while for the numerical simulations D=1.38+/-0.07 for a pixel size of 20.83 km. If we use a yardstick adapted to the spatial resolution the observations give the dimension D=1.41+/-0.05 in close agreement with the simulations. This agreement is remarkable since the pixel sizes and spatial resolutions of the simulations and of the observations differ by a factor of 15. The finding supports the view of self-similarity of solar magnetic structures over a large range of scales. In addition, it demonstrates the realism of the simulations and suggests that all important physical processes are included. We discuss our results in comparison with other investigations. Title: Inter-network magnetic fields observed with sub-arcsec resolution Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2003A&A...407..741D Altcode: 2003astro.ph..6329C; 2003astro.ph..6329D We analyze a time sequence of Inter-Network (IN) magnetograms observed at the solar disk center. Speckle reconstruction techniques provide a good spatial resolution (0\farcs5 cutoff frequency) yet maintaining a fair sensitivity (some 20 G). Patches with signal above noise cover 60% of the observed area, most of which corresponds to intergranular lanes. The large surface covered by signal renders a mean unsigned magnetic flux density between 17 G and 21 G (1 G equiv 1 Mx cm-2). The difference depends on the spectral line used to generate the magnetograms (łinetwo or łineone ). Such systematic difference can be understood if the magnetic structures producing the polarization have intrinsic field strengths exceeding 1 kG, and consequently, occupying only a very small fraction of the surface (some 2%). We observe both, magnetic signals changing in time scales smaller than 1 min, and a persistent pattern lasting longer than the duration of the sequence (17 min). The pattern resembles a network with a spatial scale between 5 and 10 arcsec, which we identify as the mesogranulation. The strong dependence of the polarization signals on spatial resolution and sensitivity suggests that much quiet Sun magnetic flux still remains undetected. 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: Transfer Function Calibration for Speckle Reconstruction Authors: Sailer, Markus; von der Lühe, Oskar; Kneer, Franz Bibcode: 2003ANS...324...23S Altcode: 2003ANS...324..C04S No abstract at ADS Title: Velocity and Magnetic Fields in Sunspot Penumbrae at Hight Spatial and Spectral Resolution Authors: Bello González, Nazaret; Kneer, Franz Bibcode: 2003ANS...324...28B Altcode: 2003ANS...324..D03B No abstract at ADS Title: Hausdorff-Dimension of Magnetic Structures Authors: Janssen, Katja; Vögler, Alexander; Kneer, Franz Bibcode: 2003ANS...324...30J Altcode: 2003ANS...324..D06J No abstract at ADS Title: Dynamics of Solar Chromospheric Finestructures in H-alpha observed with High Spatial Resolution Authors: Al, Nurol; Kneer, Franz; Hirzberger, Johann Bibcode: 2003ANS...324..111A Altcode: 2003ANS...324..P17A 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: Quiet-Sun Magnetic Fields at High Spatial Resolution Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003ApJ...582L..55D Altcode: 2002astro.ph.11454C; 2002astro.ph.11454D We present spectropolarimetric observations of internetwork magnetic fields at the solar disk center. A Fabry-Pérot spectrometer was used to scan the two Fe I lines at 6301.5 and 6302.5 Å. High spatial resolution (0.5") magnetograms were obtained after speckle reconstruction. The patches with magnetic fields above noise cover approximately 45% of the observed area. Such large coverage renders a mean unsigned magnetic flux density of some 20 G (or 20 Mx cm-2), which exceeds all previous measurements. Magnetic signals occur predominantly in intergranular spaces. The systematic difference between the flux densities measured in the two iron lines leads to the conclusion that, typically, we detect structures with intrinsic field strengths larger than 1 kG occupying only 2% of the surface. Title: High Resolution 2D Spectro-polarimetric Observations of Polar Faculae and Quiet Sun in Two Iron Lines Authors: Domínguez Cerdeña, I.; Okunev, O.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003ASPC..307..370D Altcode: No abstract at ADS Title: Two-dimensional speckle spectroscopy of Hα features Authors: Al, N.; Hirzberger, J.; Kneer, F. Bibcode: 2003AN....324..364A Altcode: In May 2002, the solar chromosphere was observed with a two-dimensional spectrometer which is mounted in the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife. The aim of this observation was to investigate the fine structure of the solar chromosphere seen in Hα . We took narrow-band filtergrams (Delta lambda ~ 72 mÅ) by scanning through this line. Broad-band images taken strictly simultaneously with the narrow-band filtergrams were restored by speckle methods. The instantaneous optical transfer function from this restoration procedure was used for the reconstruction of the narrow-band images. Some results of this high spatial resolution observation are presented below. Title: From the Gregory-Coudé Telescope to GREGOR: a development from past to future. Summary of workshop held in Göttingen, July 24-26, 2002 Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D. Bibcode: 2003AN....324..283K Altcode: No abstract at ADS Title: Study of polar faculae by means of spectro-polarimetric observations and radiative transfer calculations Authors: Okunev, O.; Kneer, F. Bibcode: 2003AN....324..330O Altcode: Polar faculae are of special interest for solar physics because of their close relationship to the global magnetic field of the Sun and to solar activity, and because of the recently found kilogauss magnetic fields, which are very unusual for the structures outside active regions at high latitudes of the Sun. The idea is that polar faculae can be represented by bundles of unresolved small-scale magnetic flux tubes, which are characterized by sizes of about 100 km and strong magnetic fields. High resolution spectro-polarimetric observations of the considered structures were performed and complemented by the radiation transfer calculations with oblique rays passing through an inhomogeneous magnetic medium. The recent results of observations and numerical calculations are presented. Title: Speckle spectro-polarimetry of magnetic structures Authors: Janssen, K.; Kneer, F. Bibcode: 2003AN....324..328J Altcode: Two-dimensional spectrograms were obtained with the Vacuum Tower Telescope, Tenerife, in order to study small-scale structures and faculae on the Sun. Using the speckle reconstruction method, we obtain high-resolution images and wavelength scans. Magnetic fields can be studied from Stokes V profiles, and velocity maps are gained by the Doppler shift of the center of gravity of Stokes I. Here some results about small-scale structures and their magnetic fields are shown. Title: High resolution 2D spectro-polarimetric observations of the quiet Sun in two iron lines Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003AN....324..327D Altcode: No abstract at ADS Title: A Fabry-Perot spectrometer for high-resolution observation of the Sun Authors: Kneer, F.; Al, N.; Hirzberger, J.; Nicklas, H.; Puschmann, K. G. Bibcode: 2003AN....324..302K Altcode: No abstract at ADS Title: Short-period waves in the solar atmosphere Authors: Wunnenberg, M.; Andjić, A.; Kneer, F. Bibcode: 2003AN....324..356W Altcode: No abstract at ADS Title: Evidence for short-period acoustic waves in the solar atmosphere Authors: Wunnenberg, M.; Kneer, F.; Hirzberger, J. Bibcode: 2002A&A...395L..51W Altcode: Short-period acoustic waves are thought to supply the energy for the radiative losses of the non-magnetic chromosphere of the Sun and, in general, of late-type stars. Here, we present evidence for the existence of waves in the solar atmosphere with periods in the range of 50 s <P< 100 s. Two-dimensional time sequences with a cadence of 25 s were obtained from quiet Sun disk center in Fe I 5434 Å. The observations were performed with the ``Göttingen'' Fabry-Perot spectrometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. They are subjected to speckle reconstruction and to a wavelet analysis. The atmospheric ranges forming the velocity signals are narrowed by linear combinations of Doppler maps from wavelengths near line center. The power in the short-period range is concentrated above intergranular spaces. We estimate an acoustic flux into the chromosphere of approximately 3*E6 erg cm-2 s-1, as needed for the chromospheric radiative losses. Title: Formation of granular intensity fluctuations on the Sun Authors: Pérez Rodríguez, E.; Kneer, F. Bibcode: 2002A&A...395..279P Altcode: We deal with granular intensity fluctuations in the Sun and how they are caused by temperature fluctuations. We calculate temperature response functions RFT(lambda ,z) in the solar photosphere. We apply the Diagonal Element Lambda Operator (DELO) method to calculate the response functions for the continuum (lambda lambda = 380 nm-2.5 mu ). LTE is assumed throughout. It is demonstrated that, within the framework of the linear approximation, the H- continuum absorption plays an important role for the formation of the fluctuations in continuum images. It counteracts substantially the intensity fluctuations caused by variations of the Planck function. The temperature response functions are used to calculate, for three models of temperature fluctuations, the continuum intensity contrasts and their formation height for the above wavelength range. 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: Weak magnetic flux features on the Sun Authors: Hartj, B.; Kneer, F. Bibcode: 2002A&A...385..264H Altcode: We observed weak magnetic flux in enhanced Ca K network and in its surroundings at various positions on the solar disc (cos theta =1.0dots0 .1). The Gregory Coudé Telescope at the Observatorio del Teide on Tenerife was used together with an image scanner and a Stokes V polarimeter. 1/2(Ilambda +/- Vlambda ) spectrograms in the 6302 Å region were taken. A second order flat fielding and smoothing brought the polarimetric sensitivity to a detection limit of 0.001 Ic (with Ic = continuum intensity) for exposure times of 300 ms in pixels corresponding to 0.5''x0.19'' (widehat = slit width x pixel size of detector). We present correlations between continuum intensity, line center intensity, and magnetic flux and discuss Stokes V profiles. The V amplitude asymmetry from areas with strong flux decreases towards the limb, a change of sign is not identified. The magnetic fields are ordered around strong flux centers with decreasing mean field strength outwards from the centers. In the range of 1x 1016 Mx to 5x 1016 Mx (in one pixel of 5x 1014 cm2) the probability distribution of the magnetic flux is ~ |Phi |-q with q~3, different from a Gaussian distribution. From this we derive tentativily a radial dependence from the flux centers of the form Phi (r) ~ 1/r. For the probability distributions a significant center-to-limb variation is not detected. Together with the center-to-limb behaviour of the asymmetries, we interpret this tentatively as an isotropic orientation of the weak magnetic flux elements and of the gas flows. A vertical orientation of the magnetic fields is also compatible with the measurements, though. Title: Dynamics of small features in the solar chromosphere Authors: Al, N.; Bendlin, C.; Kneer, F. Bibcode: 2002A&A...383..283A Altcode: A spatially highly resolved time series of a quiet region at disk centre taken in the Na D_2 line with the ``Göttingen'' spectrometer in the Vacuum Tower Telescope/Tenerife was used to study the dynamic behaviour of different chromospheric features. Two CCDs were employed for simultaneous exposures of narrow-band and ``white-light'' images forming 128 repetitive ``scans'' of 30 images each in nearly two hours. The data set yielded line profiles over the two-dimensional field of view which served to create various maps indicating, e.g., vertical velocities or minimum line intensities. The analysis of the features of interest was further based on maps displaying the horizontal velocity field derived from white-light images. The occurrence of various bright points was monitored, showing quite different properties. Some persistent intra-network bright points follow the horizontal flows of the underlying photosphere. During the time series, a ``K grain'' is seen to occur several times at the same location. The power spectrum of the fluctuation of the minimum intensity of its corresponding Na D_2 mean line profile exhibits a pronounced absolute maximum for a period of about 24 min. The behaviour of several peculiar intra-network bright points still lacks an unequivocal interpretation. Possibly, the signature of gravity waves has been detected. Further investigation revealed that the power spectra of the fluctuation of Doppler shift and minimum intensity calculated for one of these bright points both show an absolute maximum for a period of 4.3 min. In the course of these fluctuations, time spans of regular oscillations were noticed for all such points lasting from about 15 to 25 min. Power spectra calculated only over these times exhibit pronounced absolute maxima in a rather narrow frequency range. 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: Speckle spectro-polarimetry of magnetic structures Authors: Janssen, K.; Kneer, F. Bibcode: 2001AN....322..383J Altcode: High spatial resolution images with spectral and polarimetric information were obtained with the Vacuum Tower Telescope (VTT), Tenerife, in order to study dynamic small scale structures on the Sun. With the Göttingen Fabry-Perot interferometer (FPI) we observed faculae at different ( cos , theta ) positions on the Sun. Simultaneously with these narrow-band images, 150 broad-band images were taken from which high resolution images are calculated with the spectral ratio and the speckle masking methods. With the aid of the transfer functions, gained with the speckle recontruction, the narrow-band FPI images can be reconstructed as well. Here our first results are presented. 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: A Fabry-Perot spectrometer for high-resolution observation of the Sun Authors: Kneer, F.; Hirzberger, H. Bibcode: 2001AN....322..375K Altcode: Fabry-Perot interferometers (FPIs) are powerful instruments for spectro-polarimetry of the Sun with high spatial resolution. They allow easy image reconstruction of two-dimensional fields of view. Some examples of high quality results obtained with the ``Göttingen'' FPI spectrometer, mounted in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife, are presented in a poster to this workshop. We thus concentrate on the design of a new instrument for the 1.5 m GREGOR solar telescope. We discuss the pros and cons of telecentric and collimated mounting and describe the expected performance, especially the spectral resolution, of our design. Title: 2D-spectroscopy of the Evershed flow in sunspots Authors: Hirzberger, J.; Kneer, F. Bibcode: 2001A&A...378.1078H Altcode: The radial variation of the Evershed flow in two small sunspots (NOAA 8737 and NOAA 9145) is studied by means of two-dimensional spectrograms of high spatial resolution. We find a systematic decrease of the flow velocity with photospheric height and a shift of the velocity maximum towards larger penumbral radii in higher layers but no clear correlation between flow velocity and continuum intensity. At the outer penumbral boundaries the Evershed flow ceases abruptly and even downward directed flow velocities in the deepest probed photospheric layers were found. Furthermore, granules adjacent to the penumbral boundary show a systematic redshift of their spot-side parts which is attributed to fast, eventually supersonic, downflows between them and the penumbral boundary. 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: High resolution 2D-spectroscopy of granular dynamics Authors: Hirzberger, J.; Koschinsky, M.; Kneer, F.; Ritter, C. Bibcode: 2001A&A...367.1011H Altcode: Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun. The observations were obtained with the ``Göttingen'' two-dimensional (2D) Fabry-Perot interferometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Time sequences of spectral scans across the non-magnetic Fe I 5576 Å line were taken from disc center. The 2D spectroscopic images were reconstructed with speckle methods, from which a spatial resolution of 0\farcs4-0\farcs5 was achieved. A power and coherence analysis of intensity and velocity maps from different photospheric heights has been carried out. The coherence between intensity and velocity fluctuations stays high for structural scales >0\farcs5, which underlines the high spatial resolution of the data. Furthermore, the vertical flow field and its time evolution within exploding granules have been analyzed. We find fast downflows in the dark centers of exploding granules with velocities up to 1.2 km s-1. Additionally, we estimated the flow velocities of so-called ``dark dots''. We discuss indications that these structures represent a new type of downflow within the centers of bright granules. Title: A Fabry-Perot Spectrometer for High-Resolution Observation of the Sun Authors: Kneer, F.; Hirzberger, J. Bibcode: 2001AGM....18S1005K Altcode: Fabry-Perot interferometers (FPIs) are powerful instruments for spectro-polarimetry of the Sun with high spatial resolution. They allow easy image reconstruction of two-dimensional narrow-band fields of view. Some examples of high quality results obtained with the ``Göttingen'' FPI spectrometer, mounted in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife, are presented in a poster to this workshop. We thus concentrate on the design of a new instrument for the 1.5 m GREGOR solar telescope. We discuss the pros and cons of telecentric and collimated mounting and describe the expected performance, especially the spectral resolution, of our design. Title: Speckle Spectro-Polarimetry of Small-Scale Magnetic Structures Authors: Janßen, K.; Koschinsky, M.; Kneer, F. Bibcode: 2001ASPC..236..407J Altcode: 2001aspt.conf..407J 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.; 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: Speckle spectro-polarimetry of solar magnetic structures Authors: Koschinsky, M.; Kneer, F.; Hirzberger, J. Bibcode: 2001A&A...365..588K Altcode: We present speckle observations of small-scale magnetic structures on the Sun. They were obtained with the ``Göttingen'' Fabry-Perot interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, from quiet and active regions close to disc center. A Stokes V polarimeter was added to the FPI to measure V profiles in the Fe I 6302.5 Å line. The setup allows image reconstruction with speckle methods. The achieved spatial resolution in the magnetograms is 0farcs4 -0farcs5 . We describe the observational technique and the data reduction. The results from small-scale magnetic flux elements in a very quiet region, in an active region with pores and abnormal granulation, and in a sunspot with its surroundings are discussed. In the quiet Sun, granular dynamics dominate the time evolution of the magnetic elements. Flux occurs in both bright intergranular points and in dark intergranular spaces. Likewise, with the present spatial resolution, no preference of magnetic flux in abnormal granulation in an active region can be found. Flux occurs in both bright (abnormal) small-scale granules and in the darker spaces in between them. The small sunspot studied has very little magnetic flux in its ambient quiet regions, especially no strong, conspicuous concentrations of returned flux, i.e. of flux with polarity opposite to that in the sunspot. Title: Speckle Spectro-Polarimetry of Magnetic Structures Authors: Janßen, K.; Kneer, F. Bibcode: 2001AGM....18.P222J Altcode: High spatial resolution images with spectral and polarimetric information were obtained with the Vacuum Tower Telescope (VTT), Tenerife, in order to study dynamic small scale structures on the Sun. With the Göttingen Fabry-Perot interferometers (FPIs) we observed faculae at different cos θ positions on the Sun. Simultaneously with these narrow-band images, 150 broad-band images were taken from which high resolution images can be calculated with the Spectral Ratio and the Speckle Masking methods. Once these high resolution images are completed, the narrow-band FPI images can be reconstructed as well. Here we present our first results. Title: Granular velocities of the Sun from speckle interferometry Authors: Krieg, J.; Kneer, F.; Koschinsky, M.; Ritter, C. Bibcode: 2000A&A...360.1157K Altcode: We present observations of granular velocities and their relation to the granular intensity pattern from the disc center of the Sun. They were obtained in June 1997 with the Vacuum Tower Telescope at the Observatorio del Teide on Tenerife. High spatial resolution, 0''4-0''5 for the velocities, was achieved with speckle methods applied to two-dimensional narrow- band images in Na D2 from the "Göttingen" Fabry- Perot interferometer. The velocity observations refer to a geometric height of 50-200 km (above τ5 = 1). Velocity amplitudes of ±2.2 km s-1 are seen. The high velocity regions are small-scale and the upflows coincide frequently with the bright borders of granules or with small-scale brightenings. A statistical analysis reveals only a rough consistency to the -5/3 or -17/3 law of log(power) vs. log(wavenumber) expected for isotropic turbulence (cf. Espagnet et al. 1993). We consider an agreement with such power laws as accidental since the intensity and velocity power spectra found here decrease smoothly from flat ones at low wavenumbers to steep ones at high wavenumbers. The coherence of velocity and intensity fluctuation stays above 0.5 up to horizontal wavenumbers kh ≍ 11 Mm-1 0.8 " and the phase difference between intensity and velocity stays stable down to structures of 0''5. While the intensity pattern exhibits a clearly non-Gaussian distribution, the velocity distribution can be represented by a Gaussian with a "macroturbulent" velocity of 0.825 km s-1. Title: Die Rotation der Sonne Authors: Janßen, Katja; Kneer, Franz Bibcode: 2000A&R....58...40J Altcode: Sonnenspektren hoher spektraler Auflösung sind vielfach begehrt. Sie werden im Unterricht, in Arbeitsgemeinschaften und in Vorlesungen verwendet. Anhand solcher Spektren lässt sich vieles aus dem wichtigen Gebiet der astronomischen Spektroskopie erklären und lernen. Title: On weak magnetic flux structures of the Sun Authors: Stolpe, F.; Kneer, F. Bibcode: 2000A&A...353.1094S Altcode: The micro-image-scanner of the Gregory Coudé Telescope at the Observatorio del Teide/Tenerife is used for observations of structures with weak magnetic flux in the solar atmosphere. The methods for the data reduction are chosen carefully to achieve the highest possible performance, also with respect to the needs of handling large amounts of data. A lower detection limit of magnetic flux on the Sun of 2 108 Wb on an area of 0\farcs67x0\farcs67 was achieved. Magnetic structures of weak magnetic flux are observed using different spectral lines in network and intra-network regions at disk center of the Sun. The present study deals mainly with a high spatial resolution observation in the magnetically sensitive Fe I 630.25 nm line. We find that weak flux may appear almost everywhere in the granular pattern, with a 65 %\ preference for intergranular spaces. Some elements have diameters of 2\arcsec-3\arcsec with substructure and distorted shape. Many elements are very small, <1\arcsec. From the ubiquitous appearance of weak magnetic flux structures in the granular pattern, in regions of both upward and downward flow, and in regions of line weakening and line enhancement, we argue that their magnetic pressure may not exceed the granular flow pressure. This gives an upper limit of the amplitude of the magnetic flux density of |B|=5.5 10-2 T in agreement with the result by Keller et al. (1994)

1 Wb = 1 V s = 108 Mx

1 T = 1 V s m-2 = 104 Gauss. Title: Universitäts-Sternwarte. Jahresbericht für 1999. Authors: Kneer, F. Bibcode: 2000MitAG..83..339K 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: High Resolution 2D-Spectroscopy of the Sun Authors: Hirzberger, J.; Kneer, F. Bibcode: 2000HvaOB..24...89H Altcode: With the "Goettingen" Fabry-Perot interferometer which is installed at the Vacuum Tower Telescope in Izana, Tenerife the non-magnetic FeI 5576 A line was scanned in a field of quiet granulation at solar disk center. From the simultaneously obtained broad band images an instantaneous optical transfer function (OTF) of the Earth's atmosphere was computed with speckle interferometric methods. Restoring the narrow band data from this OTF the spatial resolution of the two-dimensional spectra was successfully enhanced by a factor of two. Title: Coordinated Observation of a Small Magnetic Region with SUMER and GCT Authors: Wilken, V.; Kneer, F.; Curdt, W. Bibcode: 1999ESASP.446..711W Altcode: 1999soho....8..711W No abstract at ADS Title: Coordinated Observation Of A Small Magnetic Region With GCT And SUMER Authors: Wilken, V.; Kneer, F.; Curdt, W. Bibcode: 1999ESASP.446..707W Altcode: 1999soho....8..707W The SUMER instrument and the Gregory-Coude-Telescope (GCT) at the Observatorio del Teide/Tenerife have been used for observations of a small magnetic region in the solar atmosphere. With the GCT 2-dimensional spectro-polarimetry was performed and later analysed by applying the "centre of gravity method" (Semel, 1967) to measure the longitudinal magnetic flux. In this way we obtained seven magnetograms of the target area during the three hours campaign, while SUMER performed every five minutes EUV-scans in two spectral lines. The magnetograms show two cells with diameters of approximately 20000 km and 26000 km. Inside the cells the measured flux within the resolution element of 0.76 arcsec*0.76 arcsec. was ~1*109 Wb (corresponding to 33 Gauss flux density) on average. On the other hand the boundary regions have fluxes up to 1*1010 Wb. SUMER's intensity images of Si II (Chromosphere) and C IV (Transition region) show strong brightenings which very well resemble the magnetic flux pattern in the Photosphere. The intensities of Ne VIII (lower Corona) correlate with the magnetic flux as well, but far less than the former two lines. During the 3h observing run the coarse magnetic structure remains essentially unchanged. However, on scales smaller than 3 arcsec., the temporal intensity fluctuations of the EUV-lines show little similarity, if any. Possibly, at small scales the different EUV-lines originate from different structures which are not excited simultaneously. Title: Sonnenspektren für den Unterricht. Authors: Janßen, K.; Kneer, F. Bibcode: 1999S&W....38..454J Altcode: No abstract at ADS Title: Height variation of the solar granulation Authors: Krieg, J.; Wunnenberg, M.; Kneer, F.; Koschinsky, M.; Ritter, C. Bibcode: 1999A&A...343..983K Altcode: We analyze spectral scans of narrow-band images across the Na D_2 line. They were obtained from disc centre of the Sun with our Fabry-Perot interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio del Teide. The FPI was set to a bandwidth of 200 mAngstroms FWHM and the spectral stepwidth was 100 mAngstroms. Our aim is to study the variation of the granulation pattern with height in the atmosphere. To achieve high spatial resolution the simultaneously taken broad-band images are restored with speckle methods. With the knowledge of these reconstructed images we were also able to restore the narrow-band images. The formation heights are found from temperature response functions RF_T. In the wings of NaD_2, the response functions for different wavelengths exhibit a substantial overlap in atmospheric heights. Therefore we use linear combinations which allow a better height discrimination. Applying the same combinations to the D_2 images we can visualize the height variation of the granular pattern. The granular intensity fluctuations are a matter of the deep photosphere alone. They disappear at heights of about 100 km (above tau_ {5000}=1). Title: Erratum: Two-dimensional spectroscopic observations of chromospheric oscillations Authors: Al, Nurol; Bendlin, Cornelia; Kneer, Franz Bibcode: 1999A&A...342..311A Altcode: For technical reasons, Figs. ref{f8} and ref{f9} were printed with incorrect colour separation. To rectify this unfortunate error, the correct Figs. ref{f8} and ref{f9} with the captions are reprinted below. Title: Solar Observation with High Spatial and Spectral Resolution Authors: Krieg, J.; Wunnenberg, M.; Kneer, F.; Koschinsky, M.; Ritter, C.; von der Lühe, O. Bibcode: 1999AGAb...15...88K Altcode: 1999AGM....15..P03K The solar atmosphere is, like stellar atmospheres in general, highly dynamic on small scales. To understand, e.g., the generation of turbulent motion and waves or chromospheric and coronal heating processes, observations with high resolution are needed. We achieve both high spatial and spectral resolution with a double Fabry-Perot interferometer which allows image restoration with speckle methods. Our new results include the height variation of the granular intensity pattern and velocity maps of unprecedented spatial resolution. Title: Universitäts-Sternwarte. Jahresbericht für 1998. Authors: Kneer, F. Bibcode: 1999MitAG..82..329K Altcode: No abstract at ADS Title: Spectral and Spatial High Resolution Observations of the Sun with Image Reconstruction and Deconvolution Methods Authors: Koschinsky, M.; Krieg, J.; Kneer, F.; Ritter, C.; Wunnenberg, M. Bibcode: 1999ASPC..183..349K Altcode: 1999hrsp.conf..349K No abstract at ADS 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: Granular Intensities and Velocities with High Spatial Resolution Authors: Ritter, C.; Krieg, J.; Wunnenberg, M.; Kneer, F.; Koschinsky, M. Bibcode: 1999AGAb...15....7R Altcode: 1999AGM....15..A04R We present results obtained with our two-dimensional spectrometer in the solar Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The spectrometer is based on Fabry-Perot interferometers which scan in wavelength across spectral lines. The observations were taken in the Na D_2 line from a quiet region at the disc centre of the Sun. The data analysis uses speckle methods for image restoration. We find the heights in the solar atmosphere where the measured intensity and velocity fluctuations originate from Response Functions. The granular intensity pattern disappears at 100 - 150 km (above tau_5 = 1). The granular velocities are high with amplitudes of 2.5 km s^{-1}, while the rms velocity is 0.6 km s^{-1}. Thus, the velocity field is highly intermittent. Title: Coordinated Observation of a Small Magnetic Region with SUMER and GCT Authors: Wilken, V.; Kneer, F.; Curdt, W. Bibcode: 1999AGAb...15...91W Altcode: 1999AGM....15..P08W The SUMER instrument and the Gregory-Coudé-Telescope (GCT) at the Observatorio del Teide/Tenerife have been used for observations of a small magnetic region in the solar atmosphere. The GCT measured the longitudinal magnetic flux, while SUMER performed EUV-scans. The magnetograms show two cells with diameters of approximately 23 000 km. Inside the cells the flux within the resolution element of 0.''76 x 0.''76 was 1 ṡ 10^9 Wb (corresponding to 33 Gauss flux density). The boundary regions have fluxes up to 1 ṡ 1010 Wb. SUMER's intensity images of Si II (Chromosphere) and C IV (Transition Region) show strong brightenings which very well resemble the magnetic flux pattern in the Photosphere. The intensities of Ne VIII (lower Corona) correlate with the magnetic flux far less than the former two lines. On small scales the temporal intensity fluctuations of the EUV lines show only little similarity among each other. Possibly, at small scales the different EUV lines originate from different structures which are not excited simultaneously. Title: Solar Observation with high spectral resolution and image restoration. Authors: Koschinsky, M.; Kneer, F.; Wunnenberg, M.; Krieg, J.; Ritter, C. Bibcode: 1999AGAb...15....6K Altcode: 1999AGM....15..A02K Observations of the Sun with both, high spectral and high spatial resolution are needed for an understanding of the structure, the dynamics and the temporal evolution of small scale features in the solar photosphere. To achieve this, high technical requirements on the optical setup have to be satisfied, and also extensive methods of data reduction and image restoration are needed. We present our approach to obtain high resolution observational data by using a double Fabry-Perot interferometer at the Vacuum Tower Telescope (VTT) on Tenerife. The spectral resolution is about 30 mÅ. Different methods of image reconstruction to remove distortions by seeing and telescopic aberrations to a high extent are presented as well. Title: Fine structure of polar faculae. Authors: Makarov, V. I.; Okunev, O. V.; Pravdjuk, L. M.; Kneer, F. Bibcode: 1999joso.proc..151M Altcode: Using photoheliograms with high spatial resolution (SSSO) it was found that polar faculae consists of a few fine structure elements with the sizes ranging from 200 km to 400 km (the telescopic resolution limit is about 180 km). Presumably, polar faculae are caused by magnetic flux concentrations and their shape reminds of the set of flux tubes. Title: Some remarkable bright points seen in the Na D2 line. Authors: Al, N.; Bendlin, C.; Kneer, F. Bibcode: 1999joso.proc..133A Altcode: A spatially highly resolved time series of the solar chromosphere was taken with a two-dimensional spectrometer mounted in the German Vacuum Tower Telescope (VTT) on Tenerife. The authors obtained narrow-band filtergrams (Δλ = 30 mÅ) and white-light images strictly simultaneously with two CCDs. Repetitive tuning of a Fabry-Perot interferometer allowed to scan through the Na D2 line (5890 Å) in short intervals. In this contribution, the authors focus on bright points in the intra-network using different diagnostic tools to study their temporal and oscillatory behaviour. Title: Diagnostics and Dynamics of the Solar Chromosphere Authors: Kneer, F.; von Uexküll, M. Bibcode: 1999ASSL..239...99K Altcode: 1999msa..proc...99K Research of the chromosphere of the Sun is exciting, as it has been over more than a century. The present contribution can only give glimpses into the wealth of chromospheric structures and dynamics. Likewise, in view of the limited space, it is not possible to present in due balance the published work on the solar chromosphere. The reader is referred to the monographs by Bray and Loughhead (1974, with a historical account and many references to early work) and by Athay (1976) for the state of knowledge two decades ago. Among the conferences dealing meanwhile with the chromosphere we mention the proceedings edited by Bonnet and Delache (1976) and by Ulmschneider et al. (1991). Withbroe and Noyes (1977) treated the mass and energy flow in the chromosphere and corona; a throughout account of the Ca II K2v cell grains is given by Rutten and Uitenbroek (1991); the review by Narain and Ulmschneider (1996) deals with chromospheric and coronal heating mechanisms. Last but not least, the book ``Le Soleil'' by Secchi (1877) is historically precious and full of still viable ideas. Title: Two-dimensional spectroscopic observations of chromospheric oscillations Authors: Al, Nurol; Bendlin, Cornelia; Kneer, Franz Bibcode: 1998A&A...336..743A Altcode: The oscillatory behaviour of the solar chromosphere was studied from observations of a quiet region at disk centre using various diagnostic tools. The two-dimensional spectrometer in the Vacuum Tower Telescope/Tenerife (Spain) served to obtain a spatially highly resolved time series of ``white-light'' images and narrow-band filtergrams in the Na D_2 line. With a tunable Fabry-Perot interferometer, this line was scanned taking 30 images (i.e. a ``scan'') around the line core with wavelength steps of 30 m Angstroms and a spectral resolution of about 200 000. From these images, line profiles were derived for every pixel in the field of view. With each such narrow-band scan, a scan of ``white-light'' images was taken strictly simultaneously. The whole time series comprises (2x) 128 scans. Every 56 s, a new pair of scans was started with two CCDs, thus the observation covers nearly two hours. Finally, after correlation and other reduction procedures, a field size of 69\farcs4 x 50\farcs4 remained with 0\farcs2/pixel on the CCD-chips. In the data reduction, new images were created representing the minimum intensity (I) of each line profile in the field of view, and also velocity (V) maps (derived from the Doppler shifts of the line profiles) for all 128 scans. >From these images, power spectra and diagnostic diagrams were computed. In the subsequent analysis, a distinction between network and intra-network regions was made where this seemed appropriate. One- and two-dimensional (V-I) phase and coherence spectra were analysed with regard to oscillations and to the nature of the waves leaving their marks in these diagrams. Several noteworthy results also raised the question of the actual line formation height of Na D_2, among them being the non-detection of a chromospheric eigenmode. While an explanation for a conspicuous 70(deg) plateau in a small region of the phase spectra already exists, the suspected reason behind the decreasing phase difference from about -60(deg) for the f-mode down to ~ -120(deg) for higher modes is still subject to some speculation. Moreover, the data gave evidence of gravity waves, probably discovered for the first time in a V-I phase spectrum of Na D_2. Title: MISC, an instrument for multi-dimensional spectroscopy Authors: Stolpe, F.; Kneer, F. Bibcode: 1998A&AS..131..181S Altcode: A new instrument for multi-dimensional spectroscopy at the Gregory CoudeTelescope (GCT) at the Observatorio del Teide/Tenerife is presented. The system, consisting of a scanning device, a Stokes-V polarimeter and a suitable CCD system, performs fast spatial scanning. It preserves the good polarization properties of the telescope by using a Bowen compensator. We describe the instrument, the different modes of operation, and how it is controlled and give some performance data. Title: Oscillations of the Sun's chromosphere. VIII. Horizontal motions of CA II K bright points Authors: Wellstein, S.; Kneer, F.; von Uexkuell, M. Bibcode: 1998A&A...335..323W Altcode: We present a re-analysis of a time series of solar disc centre Ca ii K2v filtergrams taken with the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. We concentrate on the measurements of proper motions of K grains in the internetwork regions and of bright points in the chromospheric network. For the K grains we find horizontal velocities of 2-15 km s(-1) , values much lower than those deduced by Steffens et al. (1996) from a smaller sample, analyzed differently. In accord with our earlier conclusion from k-omega diagrams (Kneer & von Uexkuell 1993) and with numerical simulations by Carlsson & Stein (1997) high-frequency (pseudo-) p-modes can viably explain the K grains. Yet, the rareness of the K grains may indicate a connection to magnetic fields. The proper motions of the network bright points are non-periodic, very impulsive, with velocities of 7-10 km s(-1) . Estimating the energy flux if these motions are magnetic kink waves (cf. Choudhuri et al. 1993, Muller et al. 1994), we find it sufficient to heat the solar corona, but too small to cover the radiative losses of the chromospheric network. Title: Spectral line radiation from solar small-scale flux tubes. II Authors: Hasan, S. S.; Kneer, F.; Kalkofen, W. Bibcode: 1998A&A...332.1064H Altcode: We examine spectral line radiation from small-scale magnetic flux tubes in the solar atmosphere. This is a continuation of work by Kneer et al. (1996). The main difference with the previous investigation is in the choice of the external atmosphere. Earlier we adopted an atmosphere resembling the empirical quiet Sun model for the ambient medium. In the present study, we iteratively adjust the temperature structure of the external atmosphere to fit the Stokes I and V profiles and the average continuum intensities with those obtained from observations. Our models are hotter in the uppermost photospheric layers and cooler in the deeper layers than the quiet Sun model and agree well with semi-empirical flux tube models. Title: Ground-based Observation with High Spatial and Spectral Resolution Authors: Krieg, J.; Kneer, F.; Koschinsky, M.; Ritter, C.; Starck, J. -L. Bibcode: 1998ESASP.417..317K Altcode: 1998cesh.conf..317K No abstract at ADS Title: Dynamics of Solar Fine Structure: Observation with High Spatial Resolution Authors: Al, N.; Bendlin, C.; de Boer, C. R.; Denker, C.; Kneer, F.; Schmitt, D.; Volkmer, R.; Wilken, V. Bibcode: 1998ASPC..154..553A Altcode: 1998csss...10..553A The Sun is an ideal object for studying non-magnetic and magnetic processes in cool stars. Here, we focus on fine structures of a few 100 km in the solar atmosphere. Granular overshoot, motions and waves of magnetic elements in the quiet Sun and in plages, etc., all affect the atmospheric structure from the bottom of the photosphere up to the corona and the solar wind. Observations with high spatial resolution are required to reveal the dynamic behaviour and to understand the underlying physical processes. During the past five years, speckle methods have become an excellent tool to obtain images of solar fine structure with diffraction-limited resolution. We demonstrate by some examples how one can gain new insights from speckle interferometry. Likewise, spectroscopy of solar fine structure is also making rapid progress towards high spatial resolution. Our two-dimensional, narrow-band spectrometer (Delta\lambda = 20-30 mAA ), working with a scanning Fabry-Perot interferometer, proves very powerful in several aspects. We present some results obtained in Na D_2 from the quiet solar chromosphere. Using suitable observing techniques together with image restoration, we aim at achieving diffraction-limited resolution also for narrow-band spectroscopy. Title: Universitäts-Sternwarte. Jahresbericht für 1997. Authors: Kneer, F. Bibcode: 1998MitAG..81..287K Altcode: No abstract at ADS Title: Spectro-Polarimetry of Polar Faculae Authors: Homann, T.; Kneer, F.; Makarov, V. I. Bibcode: 1997SoPh..175...81H Altcode: This contribution deals with the properties of small-scale magnetic elements at the polar caps of the Sun. Spectro-polarimetric observations, obtained with high spatial resolution with the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife, were analysed. We find, though with limited data sets, that polar faculae differ in two aspects from faculae of the network in non-active regions near the equator (equatorial faculae): (1) Polar faculae appear to have the same magnetic polarity as the general polar magnetic field. Presumably, the latter is rooted in the small-scale faculae. The equatorial faculae show both magnetic polarities. (2) Polar faculae, with a size of 3.5'' ± 1.3'', are larger than equatorial faculae with 2.1'' ± 0.4''. Yet as for equatorial faculae, polar faculae possess kilogauss magnetic fields. Title: Speckle measurements of the centre-to-limb variation of the solar granulation. Authors: Wilken, V.; de Boer, C. R.; Denker, C.; Kneer, F. Bibcode: 1997A&A...325..819W Altcode: The Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife was used to perform speckle observations of photospheric granulation from disc centre to limb at λ=550+/-5nm. Images were reconstructed with the spectral ratio technique (von der Luehe 1984) and the speckle masking method (Weigelt 1977, Optics Comm. 21, 55, Weigelt & Wirnitzer 1983, Optics Letters 8, 389, Lohmann et al. 1983, Applied Optics 22, 4028). The granular rms contrast relative to the local average intensity decreases monotonically from 13.5+/-1.0% at disc centre to 8-9% at cosθ=0.1. The granular images as well as the power spectra of the intensity fluctuations show a fading of the coarse granular pattern towards the limb while smaller structures become more pronounced off the disc centre. We identify these as the bright worm-like structures appearing sometimes at the granular borders (de Boer et al. 1992A&A...257L...4D). This finding supports the result from simulations of granular dynamics by Steffen et al. (1994, Shocks in the solar photosphere and their spectroscopic signature. In: Schuessler M., Schmidt W. (eds.) Solar Magnetic Fields, Cambridge Univ. Press, p. 298). There the bright structures are locations of low pressure between the centres of granules and intergranular spaces with penetration of hot gas into the lower photosphere. Title: Flare Multi-Line 2D-SPECTROSCOPY Authors: Mein, P.; Mein, N.; Malherbe, J. -M.; Heinzel, P.; Kneer, F.; von Uexkull, M.; Staiger, J. Bibcode: 1997SoPh..172..161M Altcode: 1997ESPM....8..161M A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are: Title: High spatial-resolution spectropolarimetry of small-scale solar magnetic fields. Authors: Stolpe, F.; Kneer, F. Bibcode: 1997A&A...317..942S Altcode: We present a study of the structure and the dynamics of small-scale magnetic elements within solar plage regions. Spectropolarimetric observations with high spatial and spectral resolutions have been obtained for three iron lines with different sensitivities to magnetic field strength and temperature with the Gregory Coud e Telescope at the Observatorio del Teide/Tenerife. The main results are: (o) With the present spatial resolution of 0.6-1.0", the continuum intensity from magnetic areas is close to the average intensity of the quiet Sun (+/-5%). There is a slight tendency of decreasing intensity with increasing magnetic flux within the resolution elements. (o) Macroscopic velocities with rms values of 1.5-2.0km/s as used to explain the widths of the Stokes V profiles are not seen with the spatial resolution obtained here. (o) The large observed fluctuations in the wavelength separation of the red and blue Stokes V maxima suggest that there may be a considerable variation in the properties of the flux tubes. This should give constraints for modeling small-scale flux tubes. Title: Universitäts-Sternwarte. Jahresbericht für 1996. Authors: Kneer, F. Bibcode: 1997MitAG..80..257K Altcode: No abstract at ADS Title: 2d-Spectroscopy with the Image Scanner of the Gregory-Coude-Telescope on Tenerife Authors: Stolpe, F.; Koschinsky, M.; Kneer, F. Bibcode: 1997ExA.....7..301S Altcode: No abstract at ADS Title: Methods of Two-Dimensional Spectroscopy Authors: Kneer, F. Bibcode: 1997ASPC..118..329K Altcode: 1997fasp.conf..329K One of the main fields of solar research is the study of dynamic processes of small-scale structures. For this purpose, time sequences of spectroscopic and polarimetric information in two spatial dimensions with best achievable quality are needed. The present contribution deals with the ways to obtain images in small wavelength bands. Among these are image scanners and the MSDP (Multi-Channel Subtractive Double Pass Spectrograph). Further potential instruments are scanning Fabry-Perot interferometers (FPI). The principles of such instruments are discussed. The results obtained hitherto from the FPI in the Vacuum Tower Telescope at the Observatorio del Teide are promising. Small-band, two-dimensional spectroscopy with spatial resolution close to the telescopic diffraction limit seems possible in the near future. Title: Small-scale magnetic fields on the Sun. Authors: Kneer, F. Bibcode: 1996NAWG.1996..181K Altcode: Spectro-polarimetric observations with high spatial resolution of small-scale magnetic fields are presented. They were taken from plages near disc centre of the Sun with the Gregory Coudé Telescope at the Observatorio del Teide/Tenerife. Stokes I and V profiles calculated from static flux tubes are compared with the observations. The small-scale magnetic elements have substructure and are dynamic. They possess varying gas velocities and temporarily strong magnetic fields. Title: On the use of Bowen compensators for polarimetry. Authors: Koschinsky, M.; Kneer, F. Bibcode: 1996A&AS..119..171K Altcode: For high precision polarimetry it is very desirable to observe with a telescope that is free of instrumental polarization. Yet it is often inevitable to introduce optical devices which generate crosstalk between the Stokes Q,U components and the V component due to phase retardations upon reflection at mirror surfaces. We show that Bowen compensators are well suited to compensate for these phase changes. They consist of 2 rotatable λ/8 phase retarder plates, and it can be shown that they act on polarized light either by a rotation of the axes of the polarization ellipse followed by a prescribed, desired phase change or by a phase change followed by rotation of the ellipse. We present applications of Bowen compensators in the Gregory Coude Telescope at the Observatorio del Teide/Tenerife. Title: High Resolution Observations of Small-Scale Magnetic Elements and Interpretation Authors: Kneer, F.; Stolpe, F. Bibcode: 1996SoPh..164..303K Altcode: This contribution deals with the properties of small-scale magnetic elements in plages. Spectro-polarimetric observations, obtained with the highest possible spatial resolution with the German solar telescopes at the Observatorio del Teide on Tenerife, were analysed. We conclude from the spread of line parameters measured in the Stokes I and V profiles of Fe I and Fe II lines that a wide range of magnetic properties is realised in the solar atmosphere. The flow velocities in small-scale magnetic flux tubes, deduced from the zero-crossing of the V profiles at high spatial resolution, show a fluctuation of vDoppler = 580 m s-1. This is substantially smaller than the "turbulent" broadening velocities of vDoppler = 2 - 3 km s−1 commonly derived by fitting V profiles from flux tube models to low spatial resolution data, e.g. from a Fourier Transform Spectrometer. Attempts to explain the high resolution I and V profiles by models of hydrostatic flux tubes are discussed. It appears impossible to accomplish agreement between the modeled and observed radiation of lines with strong and weak magnetic sensitivity at the same time. We suggest a scenario in which small-scale magnetic elements possess substructure and are dynamic, with gas flows and magnetic field strengths varying in space and time. Title: Spectral line radiation from solar small-scale magnetic flux tubes. Authors: Kneer, F.; Hasan, S. S.; Kalkofen, W. Bibcode: 1996A&A...305..660K Altcode: We consider spectral line radiation from small-scale magnetic model flux tubes in the solar atmosphere. The structure of the tube is determined from the magnetostatic equations in the thin flux tube approximation. We assume that the tube is in energy equilibrium and pressure balance with the ambient medium. For the latter, we construct a quiet sun model with an artificial heating term in order to reproduce the VAL C model, treating the medium as a plane-parallel atmosphere. The flux tube models are parameterized by the plasma β_0_ (the ratio of gas the pressure to the magnetic pressure), the convective efficiency parameter α, and the radius R_0_ at height z=0 (τ_5000_=1) in the quiet sun. The Stokes I and V profiles emerging from the models and averaged over areas that include the neighbourhood of the flux tube are calculated for various spectral lines with different sensitivity for magnetic field strength and temperature. The profiles are compared with high spatial resolution observations of plages near disc centre that have been obtained with the Gregory Coude Telescope at the Observatorio del Teide/Tenerife. The information contained in both I and V profiles is found to be very useful in constraining the theoretical models. The best match of models with observations is achieved for values of β_0_ between 0.3 and 0.5. For a sufficiently wide separation of the V extrema of the strongly split lines, a broadening mechanism is required. Pure velocity (microturbulent) broadening compatible with observations of strongly split lines gives too much broadening for weakly split lines. A broadening that is proportional to the Lande factor, i.e., magnetic broadening, appears to be more appropriate. This suggests dynamic models with temporary enhancement of the magnetic field strength. The continuum intensity of our models is higher and the absorption and V amplitude in the FeII 6149A line are stronger than observed. An improvement in the match between model predictions and observations is likely to come from models in which the ambient gas has a lower temperature as well as a lower temperature gradient than are found in the quiet, field-free sun. Such models are currently under development for cylindrical flux tubes. Title: Short-period waves in small-scale magnetic flux tubes on the Sun. Authors: Volkmer, R.; Kneer, F.; Bendlin, C. Bibcode: 1995A&A...304L...1V Altcode: We present a time sequence of spectro-polarimetric measurements of high spatial and spectral resolution. It was obtained in the Fe I 6302A line from a moderately active region near disc centre of the Sun. The observation was performed with a two-dimensional spectrometer which uses a Fabry-Perot interferometer for wavelength scanning and to which a Stokes-V polarimeter was added. This allows us to follow horizontal motions of structures, here of small-scale magnetic elements, to study structural changes, and to measure vertical velocities of the magnetized plasma. In an isolated magnetic feature we find quasi-periodic horizontal motions with 2km/s amplitude and, with high statistical significance, vertical oscillations of 280m/s rms velocity and with periods near 100s. The energy flux in these short-period waves is estimated at 1.6-2.3x10^7^ergxcm-2/s, yet only for this isolated small feature. So the energy supply appears sufficient for chromospheric heating in bright structures of the Ca network, but it falls much below the needs to balance the radiative loss in larger plage areas. Title: A proposal for a low instrumental polarization coude telescope. II. The German Gregory-Coude Telescope at the Observatorio del Teide. Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Kneer, F. Bibcode: 1995A&AS..113..359S Altcode: We have put into practice the technique to minimize the instrumental polarization (IP) of coude telescopes proposed by Martinez Pillet & Sanchez Almeida (1991): a λ/2-plate inserted into the optical path, with the proper orientation, cancels the IP. The compensation of the Gregory-Coude Telescope at the Observatorio del Teide turns out to fulfil theoretical expectations. Empirical tests at 630nm demonstrate that its IP decreases by a factor ~4. We show that the residual IP is not intrinsic to the method but it is due to the limited precision of the retarder presently used. In addition, observations indicate that the insertion of the λ/2-plate does not noticeably deteriorate the optical quality of the whole telescope. In short, this work proves the practical soundness of the λ/2-plate technique to reduce IP. Title: Speckle masking imaging of the moustache phenomenon. Authors: Denker, C.; de Boer, C. R.; Volkmer, R.; Kneer, F. Bibcode: 1995A&A...296..567D Altcode: We present high spatial resolution observations of a sunspot near the solar disc centre obtained with the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife). Our investigation aims at a better comprehension of umbral and penumbral fine structures. The speckle masking image reconstruction technique was applied to narrow-band filtergrams taken in the red wing of Hα. The reconstructed images reveal small-scale structures close to the telescopic diffraction limit of 0.19". Especially, the moustache phenomenon - the intensity enhancement in the inner wings of strong chromospheric absorbtion lines - is clearly discernible. The moustaches are concentrated at the outer border of the penumbra and in its neighbourhood. There, they appear at locations coinciding with the intergranular lanes. The moustaches are not circular in shape. Instead they show sharp intensity peaks surrounded by bright areas with frayed borders. Due to the high spatial resolution achieved in the restored filtergrams and the correction for the speckle transfer function, we find much higher intensities than in previous investigations concerning the moustache phenomenon. The peak intensities are sometimes larger than 1.7 times the intensity of the granular background, i.e. the line profiles in the inner wing of Hα exhibit emission features. Attempts to restore narrow-band filtergrams with speckle interferometry are relatively new. In this paper it is shown that the speckle masking technique is capable to reconstruct images with a low signal-to-noise ratio taken within a passband of 0.05nm. Title: Oscillations of the Sun's chromosphere. VII. K grains revisited. Authors: von Uexkuell, M.; Kneer, F. Bibcode: 1995A&A...294..252V Altcode: We analyse time sequences of high spatial resolution filtergrams obtained simultaneously in Mg b_2_ and Ca K_2v_ from quiet Sun disc centre with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Special attention is paid to the temporal evolution of the bright points, or K grains, in the interior of the chromospheric network. These represent the intensity maxima of brightness oscillations in K_2v_ with large amplitude. The oscillations last 1 to 5 periods of 150-240s duration and are strongly non-sinusoidal. They do not appear to be excited by pulses from below and then to decay. They rather exhibit the beat phenomenon of a horizontally extended wave field. The high amplitude oscillations occur only rarely, during 5-10% of the time, if we pose the limit that high amplitude means that the maximum intensity is a factor 1.5 larger than the average intensity. The power spectrum does not show any signature of a chromospheric "3 min" mode nor of a mode at the acoustic cutoff frequency (period 3.5min), nor do we find a power ridge at constant frequency. Instead, as in our earlier finding, the chromospheric oscillations are ordered in modes in continuation of the 5min modes. Modeling will thus need to adopt that the waves propagate in a three-dimensional medium with, at least partially, reflecting boundaries. The bright points of the chromospheric network behave very differently, more chaotic, like noise. They show most power at low frequencies which we interpret as the consequence of the stochastic intensity fluctuations. Title: Speckle-masking imaging of bright points (moustaches) Authors: Denker, C.; Deboer, C. R.; Kneer, F. Bibcode: 1995IAUS..176P..51D Altcode: No abstract at ADS Title: Wellen in der Sonnenchromosphäre. Authors: Kneer, F.; von Uexküll, M. Bibcode: 1994S&W....33..871K Altcode: No abstract at ADS Title: On the fluctuation of wing strengths as diagnostics of the solar atmosphere Authors: Kneer, F.; Nolte, U. Bibcode: 1994A&A...286..309K Altcode: We investigate the feasibility to obtain information on pressure fluctuations in the solar atmosphere from the collisionally dominated damping wings of strong Fraunhofer lines. One expects that the depression in the wings of lines from neutral atoms of predominantly ionised species, as Na, Fe, Mg, is proportional to the pressure. Thus we measured the fluctuations of continuum intensity and wing strength of Na D_2_ and Mg b_2_ from high spatial resolution observations obtained with the Gregory Coude Telescope at the Observatorio del Teide/Tenerife. Strong fluctuations of the wing strengths are indeed seen on granular scales. They are uncorrelated with the continuum brightness. Modelling of atmospheric temperature and pressure fluctuations, including response functions for intensity and wing strength, shows that temperature fluctuations have larger effects, by factors 5-6, than pressure perturbations upon both continuum brightness and wing strength. With precise measurements of temperature fluctuations and analysing the wing strengths of several lines which differ in their pressure dependence the detection of pressure fluctuations will become possible. Title: Speckle observations of solar granulation Authors: de Boer, C. R.; Kneer, F. Bibcode: 1994IAUS..158..398D Altcode: No abstract at ADS Title: Spectro-polarimetry of magnetic elements with high spatial resolution Authors: Kneer, F.; Amer, M. A. Bibcode: 1994smf..conf..319K Altcode: No abstract at ADS Title: Oscillations of the Sun's chromosphere. VI. K grains, resonances, and gravity waves. Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1993A&A...274..584K Altcode: We present observations of simultaneous filtergram time sequences in Mg b2, Ca K and Hα obtained from quiet Sun disc centre with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Fourier analyses are performed to obtain power, coherence and phase spectra in the k-ω plane. There, the dominant features are the wellknown ridges of the 5 min resonant modes. Yet in the chromosphere the ridges extend to high wavenumbers (wavelengths ≍ 1.3 Mm) and to high frequencies (periods ≍ 105 s). Neither the famous chromospheric "3 min" oscillations nor an oscillation at the acoustic cutoff frequency (period 210 s) appear exceptionally pronounced. The signature of gravity waves is indicated from phase relations.

We distinguish between the behaviour in the interior of the chromospheric network and on the boundary. The network boundary behaves less oscillatory than the interior. In snapshots of chromospheric intensities the K grains (Beckers 1964), or, synonymously the bright cell points, appear in the cell interior. They represent the phases of high temperature of a wave field with partly resonant and coherent properties. (We take intensity fluctuations as proxies for temperature fluctuations.) The waves are only partly upward propagating p-modes with a multitude of eigenvalues in frequency and wavenumber, like the subphotospheric p-modes. We suggest that an excitation mechanism acts within the chromosphere itself to drive the waves. This could explain the phase relations between intensity and velocity oscillations. Title: High spatial resolution spectro-polarimetry of small-scale magnetic elements on the Sun Authors: Amer, M. A.; Kneer, F. Bibcode: 1993A&A...273..304A Altcode: Spectro-polarimetric observations from plage regions on the Sun, obtained with the Gregory Coudé Telescope at Observatorio del Teide/Tenerife, were analysed. They consist of high spatial resolution data recorded with a Stokes V polarimeter and a CCD detector from the magnetically sensitive lines Fe II 6149 (geff = 1.33) and Fe I 6151 (geff = 1.83) simultaneously with the non-magnetic Fe I 5576 line and from Fe I 6173 (geff = 2.5) also simultaneously with Fe I 5576.

The average asymmetries of the V profiles are in agreement with previous measurements obtained with low spatial resolution, and the average wavelength positions of the zero crossings of the V profiles are consistent with the picture of zero average velocity within magnetic fluxtubes. Within the magnetic features and from one feature to the next, there exist strong fluctuations of the asymmetries of the emergent V profiles and of the velocities. The latter can be as large as 1 km s-1. Yet neither a correlation nor an anticorrelation between asymmetry and flow can be found. Siphon flows may occur across the borders of regions with opposite polarity.

On some locations with high V signal we see very strong line weakenings and suggest that there the area filling factor of the magnetic elements amounts to 30 - 50 %. At a height of about 200 km the tubes merge and loose their identity. The magnetic field strengths can be derived from the separation of the extrema of the V profiles of Fe I 6173. They are large, about 2500 gauss (at τ5 = 1 in the tube). The V profiles observed with high spatial resolution do not seem to require high non-thermal, micro- or macroturbulent broadening. Title: On the photospheric temperature in small-scale magnetic flux concentrations Authors: Fabiani Bendicho, P.; Kneer, F.; Trujillo Bueno, J. Bibcode: 1992A&A...264..229F Altcode: Results are presented of 2D radiative transfer calculations performed for geometric configurations that simulate partly evacuated small-scale magnetic flux sheets embedded in the ambient solar atmosphere. Temperature distributions in (gray) radiative equilibrium at low optical depths where radiation transfer dominates the energy budget are obtained. Two-dimensional radiative equilibrium flux sheet models are calculated using a novel method which shows that the temperature enhancement of the upper layers of photospheric magnetic flux concentrations is due to the radiation channeling effect, i.e., that horizontal radiative transfer tends to channel emerging radiation into the lower opacity regions. The walls of the flux sheets are found to radiate energy from subphotospheric surrounding layers, giving rise to a strong heating of the atmosphere of the flux sheets. Radiative energy migrates horizontally from the heated flux sheets towards the ambient medium and there it heats the atmosphere at low optical depths. Title: Speckle observations of abnormal solar granulation Authors: de Boer, C. R.; Kneer, F. Bibcode: 1992A&A...264L..24D Altcode: We present observations of solar granulation obtained with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Speckle methods were applied to restore images of abnormal granulation in the vicinity of a sunspot near disk center. These reconstructions show nests and chains of bright 'points', whose diameters and spatial distances are close to the diffraction limit of the telescope (about 0.2 arcsec). The 'points' are not always circular in shape but also elongated. If these features are identified with the footpoints of small-scale magnetic fluxtubes, their fast temporal evolution within one or two minutes and their horizontal motion with velocities up to 2 - 3 km/sec will influence the understanding of fluxtube dynamics. Title: Stokes V asymmetry due to stationary siphon flows Authors: Degenhardt, D.; Kneer, F. Bibcode: 1992A&A...260..411D Altcode: Results are presented of an investigation of theoretically derived Stokes I and V profiles emerging from an atmosphere which contains magnetic flux tubes harboring stationary siphon flows. The Stokes I and V profiles are calculated for three magnetically sensitive lines. The relative area and amplitude asymmetries of the Stokes V, as well as the zero-crossing wavelength of the V profile, are calculated for the upstream part of the flux tube arch as well as for the downstream part of the arch. It is shown that a wide range of physically realistic parameters of the simulations yield positive relative area and amplitude asymmetries with values comparable to the observations. Title: High resolution observations of the Evershed flow Authors: Boerner, P.; Kneer, F. Bibcode: 1992A&A...259..307B Altcode: Observations with high spatial resolution of the Evershed effect in a sunspot near the limb are presented. They were obtained with the Gregory Coude Telescope at Observatorio del Teide, Tenerife, and consist of photographic spectrograms in the wavelength region 5160-5180A and corresponding slit-jaw images in white light at various positions of the sunspot image on the slit of the spectrograph. The measurement of the velocity field covers a height range of approximately 100 km to 700 km in the Mg b2 line. The Evershed flow is inhomogeneous at all heights, though decreasing in amplitude with increasing height. We find maximum velocities of 4 km/s at the lowest layer. The flow goes clearly beyond the outer penumbra border. In Mg b2 the Evershed effect is inverse, on average, while at the 500 km level it is not. We suggest that in one fortunate case, with slit orientation parallel to a flow tube, we see siphon flows outward, reaching to the height of the Mg b2 layer and ending in photospheric faculae. The stationarity of the flow on small scales is questioned. Title: A new instrument for high resolution, two-dimensional solar spectroscopy. Authors: Bendlin, C.; Volkmer, R.; Kneer, F. Bibcode: 1992A&A...257..817B Altcode: A two-dimensional spectrometer suitable for solar observations of high spatial, spectral, and temporal resolution was built and successfully tested with the German Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Using a universal birefringent filter and a Fabry-Perot interferometer (FPI), narrow-band (⪉30 mÅ) filtergrams can be obtained. With this instrument, it is possible to scan through a Fraunhofer line at an appropriate number of wavelength settings within a few seconds. Here, fast scanning is accomplished by tuning only the FPI. The images are taken by two CCDs. One of them is coupled with an image intensifier to achieve short integration times. Due to the instrument's design, the adequate field of view has a diameter of about 20-40 arsec. The spectrometer can be tuned to virtually any wavelength in the visible spectrum. Title: Speckle observations of solar granulation. Authors: de Boer, C. R.; Kneer, F.; Nesis, A. Bibcode: 1992A&A...257L...4D Altcode: We present observations of solar granulation in a plage region near disc center obtained with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Speckle methods were employed for data acquisition and data reduction. The images show small-scale structures of the size near the telescopic diffraction limit of 0.2 arcsec. We call attention to bright lanes at the borders between granules and intergranular areas. Conceivably, they are the intensity signature of strong upflows at the border of granules or of shocks in supersonic convection which are predicted by computer simulations of the granular phenomenon. Title: Small-scale waves and motions in photosphere and chromosphere of the Sun. Authors: Kneer, F. Bibcode: 1992AnGeo..10...47K Altcode: This is a review on motions and waves in the solar atmosphere. The discussion is limited to non-active phenomena in the solar atmosphere. Firstly, the gross structure - the average temperature profile in the photosphere, chromosphere, transition region and corona - is outlined and the energetic needs to maintain this structure are addressed. Then the various small-scale phenomena and processes in the photosphere and chromosphere are described. Secondary motions such as gravity waves and acoustic waves as well as waves involving the magnetic field, are excited by the granulation and may carry energy upward. The chromosphere shows several distinct features and dynamical processes. Within the cell interior of the chromospheric network, grains with quasi-periodic brightening are observed. At the cell boundaries, where magnetic fields are concentrated, less oscillatory motions but more stochastic variations than those seen in the cell interior are observed. For the boundaries as well as for the spicules, the magnetic field dominates the dynamics and may provide the means of chromospheric heating. Title: Universitäts-Sternwarte. Jahresbericht für 1991. Authors: Kneer, F. Bibcode: 1992MitAG..75..165K Altcode: No abstract at ADS Title: Sonnenbeobachtung bei hoher Auflösung. Authors: Kneer, F. Bibcode: 1992GGMit..29....5K Altcode: No abstract at ADS Title: Fluctuation of wing strengths as diagnostic tool for the structure of granulation. Authors: Nolte, U.; Kneer, F.; Wiehr, E. Bibcode: 1992AGAb....7..150N Altcode: No abstract at ADS Title: On the structure of spectral line gap regions Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1991A&A...247..556K Altcode: The analysis of a photographic spectrogram of the plage region near the disk center of the sun is undertaken to study small-scale magnetic features with special attention given to the structure of fluxtubes, and a related model is developed. Line-gap regions are identified in the Fe-I line which are characterized by redshifts and fluctuation velocity as well as an asymmetric profile indicative of a direct relationship between increasing downflow and increasing depth. The observations are compared to calculated line profiles in which a magnetic tube under certain conditions is present. The pressure and density are calculated for the tube under the assumption of hydrostatic equilibrium, and the observed intensity profiles can be reproduced when the correct parameters are used. The calculations demonstrate that a strong kilogauss magnetic field can be introduced to explain the line gap in the Fe-II 6149-A line. Title: Universitäts-Sternwarte. Jahresbericht für 1990. Authors: Kneer, F. Bibcode: 1991MitAG..74..163K Altcode: No abstract at ADS Title: MgH as a diagnostic tool for fluctuations in the solar photosphere Authors: Kulaczewski, J.; Degenhardt, D.; Kneer, F. Bibcode: 1990A&A...234..530K Altcode: A linear perturbation method is used to calculate the behavior of an MgH spectral line at 5175 A as a function of temperature and pressure fluctuations. Particular attention is given to the MgH spectral lines of the A2Pi-X2Sigma(+) (0,0)-system in solar active and quiet regions. It is found that Mgh 5175 A is sensitive to temperature perturbations in the height range of 0 to 300 km with a peak in the response function near 100 km. Title: Stability of cool flux tubes in the solar chromosphere. II - Non-linear dynamical behaviour Authors: Hassan, S. S.; Kneer, F. Bibcode: 1990A&A...232..536H Altcode: A single vertical cool flux tube in the solar chromosphere is focused upon for stability studies. The analysis of a previous study by Hasan and Kneer (1986) is extended to the nonlinear regime with a view to examining the consequences of having self-exciting mechanisms of oscillations above the photosphere. In particular, the possibility of whether the motions driven by the convective instability caused by the presence of CO could extract sufficient energy from the radiation field near the Tmin region of empirical models and deposit it in higher layers to produce chromospheric heating is investigated. The time evolution of this instability is followed by solving the MHD equations in the thin flux tube approximation. The analysis includes energy exchange with the radiation field. The simulations of a flux tube with a transmitting upper boundary show that the average energy flux in the oscillations is inadequate for chromospheric heating. Title: Multidimensional radiative transfer in stratified atmospheres. VI - Radiative instabilities Authors: Trujillo Bueno, J.; Kneer, F. Bibcode: 1990A&A...232..135T Altcode: The possibility that radiative instabilities in stellar atmospheres are driven by transfer of energy processes between stellar gas and the radiation field is considered. Harmonic temperature fluctuations in gray radiative equilibrium atmospheres are introduced, and the linear response of the radiation field to the ensuing Planck-function and opacity fluctuations is investigated. Analytical and numerical calculations are performed, emphasizing the influence of the multidimensional radiative transfer (MRT) effects of opacity fluctuations on the radiative relaxation time as a function of the wavenumber of the perturbations. Quantitative examples are given for stellar atmospheres with solarlike T(eff) and gravitational stratification. It is concluded that, while the MRT effects of B fluctuations generally tend to be stabilizing, the MRT effects of chi fluctuations are optically important for driving radiative instabilities. Title: Universitäts-Sternwarte. Jahresbericht für 1989. Authors: Kneer, F. Bibcode: 1990MitAG..73...97K Altcode: No abstract at ADS Title: Waves in active regions: observations. Authors: Kneer, F. Bibcode: 1990PDHO....7..277K Altcode: This review deals with oscillations in prominences, with the 5 min p modes in active regions, and with waves in sunspots. Title: Observations of Magnetic Features with the German Solar Telescopes at the Observatorio-Del / Tenerife Authors: Kneer, F.; Soltau, D.; Wiehr, E. Bibcode: 1990IAUS..142..113K Altcode: No abstract at ADS Title: Oscillations of the sun's chromosphere. V - Importance of network dynamics for chromospheric heating Authors: von Uexkuell, M.; Kneer, F.; Malherbe, J. M.; Mein, P. Bibcode: 1989A&A...208..290V Altcode: A 64-min time sequence of disk center H-alpha spectrograms taken with the MSDP spectrograph at the Observatoire du Pic du Midi is analyzed. This type of spectrograph allows spectroscopy of a two-dimensional field of view. From the H-alpha line profiles at each pixel, line-shift and minimum intensity fluctuation are determined as functions of spatial and temporal coordinates. A frequency analysis with standard Fourier techniques is performed. It is confirmed that in the interior of the chromospheric network cells the oscillatory behavior dominates, whereas at the boundaries one generally finds random motions on scales of 2-10 arcsec. The random behavior of the H-alpha structures outlines the permanent rearrangement of the magnetic field lines pushed around by the subphotospheric granular flow. Title: The Gregory-Coudé- Telescope at the Observatorio Del Teide Tenerife Authors: Kneer, F.; Wiehr, E. Bibcode: 1989ASIC..263...13K Altcode: 1989ssg..conf...13K No abstract at ADS Title: Universitäts-Sternwarte. Jahresbericht für 1988. Authors: Kneer, F. Bibcode: 1989MitAG..72..107K Altcode: No abstract at ADS Title: Spatially Resolved Spectra of Solar Granules Authors: Holweger, H.; Kneer, F. Bibcode: 1989ASIC..263..173H Altcode: 1989ssg..conf..173H No abstract at ADS Title: On the Influence of Opacity Fluctuations on the Energy Transfer by Radiation Authors: Trujillo-Bueno, J.; Kneer, F. Bibcode: 1989ASIC..263..441T Altcode: 1989ssg..conf..441T No abstract at ADS Title: Spectroscopy of the solar photosphere with high spatial resolution Authors: Wiehr, E.; Kneer, F. Bibcode: 1988A&A...195..310W Altcode: A high-resolution spectrogram from the solar photosphere obtained with the recently installed Gregory-Coude telescope at the Canary Islands is analyzed. Continuum intensity fluctuations are seen at scales down to 0.53 arcsec, which demonstrates the high spatial resolution. Peak velocities reach 1.5 km/s, while rms velocities range from 350 to 490 m/s. It is found that, for deeply-formed spectral lines, shifts are well correlated with continuum intensity fluctuations at scales between 1.5 and 6 arcsec. Title: Two-dimensional spectroscopy of the Sun in Hα. Authors: von Uexküll, M.; Kneer, F.; Mein, P. Bibcode: 1988AGAb....1...11V Altcode: No abstract at ADS Title: The Gregory-Coudé-Telescope in the Observatorio del Teide, Izaña. Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D. Bibcode: 1988AGAb....1...46K Altcode: No abstract at ADS Title: Multidimensional radiative transfer in stratified atmospheres Authors: Kneer, F.; Trujillo-Bueno, J. Bibcode: 1987A&A...183...91K Altcode: Energy transport by radiation is an important contribution to the energy budget in stellar atmospheric structures. In this paper, radiative relaxation of small-scale structures is investigated. The authors show in a linear analysis: (1) Already at structural lengths of 10 opacity scale heights, horizontal photon exchange is important for the energy budget. (2) In atmospheric layers near continuum optical depth τc = 1 and below, the continuum absorption and emission processes dominate the radiative relaxation. (3) Weak spectral lines or lines with σlɛ ≤ 1 have little influence on the energy exchange. (4) At large heights, transport in few spectral lines with σlɛ very large 1 can compete with continuum processes. Title: Multidimensional radiative transfer in stratified atmospheres. IV - Radiative cooling by LTE and non-LTE spectral lines Authors: Trujillo-Bueno, J.; Kneer, F. Bibcode: 1987A&A...174..183T Altcode: The question of efficiency of radiative energy losses in spectral lines is addressed. In a semi-infinite atmosphere with constant temperature, the total radiative energy loss (integrated over all depths) in a spectral line without continuum is infinite, in both LTE and non-LTE. Thus, only local energy balances may be considered with such models. The authors give radiative cooling functions for various non-LTE parameters and structural lengths of a two-dimensional stratified atmosphere. At the surface, cooling is less efficient in non-LTE than in LTE. At large optical depths, both become equal and are non-negligible. In these layers horizontal transfer effects become important for the energy balance. Title: Einige Aspekte der Erfordernisse und Möglichkeiten zeitlicher Auflösung in der optischen Sonnenphysik Authors: Kneer, F.; Knölker, M. Bibcode: 1987MitAG..68..167K Altcode: No abstract at ADS Title: Observations from Space vs. Ground Based Observations: Advantages and Disadvantages Authors: Kneer, F. Bibcode: 1987LNP...292..159K Altcode: 1987ssp..conf..159K A comparison of solar observations from space and from the ground is made. Title: Radiative Relaxation in Small Scale Structures Authors: Trujillo-Bueno, J.; Kneer, F. Bibcode: 1987rfsm.conf..281T Altcode: The authors discuss the effects of multidimensional radiative transfer on the energy exchange by radiation in small-scale structures. Title: Construction of the German Solar Telescopes at Observatorio del Teide/Tenerife: The Gregory-Coude Telescope Authors: Kneer, F.; Schmidt, W.; Wiehr, E.; Wittmann, A. D. Bibcode: 1987MitAG..68..181K Altcode: No abstract at ADS Title: Stability of cool flux tubes in the solar chromosphere. Linear analysis. Authors: Hasan, S. S.; Kneer, F. Bibcode: 1986A&A...158..288H Altcode: The linear stability of cool flux tubes in the solar chromosphere which are initially in radiative equilibrium is examined. Owing to the presence of carbon monoxide, there exists a narrow region near the temperature minimum where the temperature gradient becomes steep enough to drive a convective instability. The thin flux tube equations are used and in a simple manner radiative heat exchange with the ambient medium are included. Initial states of constant beta (where beta is the ratio of gas to magnetic pressure) are considered. Results for various values of beta are presented. It is found that for beta less than 5.7 the tube is overstable with periods in the range 300-600 s. At beta = 5.7 a bifurcation occurs into two purely growing modes. Growth rates, eigenvectors of the fundamental modes are calculated and phase relationships are examined. It is suggested that overstable oscillations should invariably be associated with cool flux tubes. These oscillations transport energy and can thus change the thermodynamic structure of flux tubes. It is conjectured that the CO overstability may be responsible for spicules. Title: Energy Transport by Radiation Authors: Kneer, F. Bibcode: 1986ssmf.conf..147K Altcode: The exchange of energy by radiation is an important contribution to the energy budget of solar fine structures. The short horizontal distances necessitate a multidimensional treatment of the radiation transfer. Several aspects are discussed. (1) The equations and their properties are described in various geometries. (2) A review on earlier work is given. (3) Calculations of first order perturbations in a gravitationally stratified atmosphere are presented and compared with Spiegel's (1957) analytic result. (4) The radiative stability of a stratified atmosphere is discussed. Title: Oscillations of the sun's chromosphere. IV - Temporal evolution of H-alpha profile Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1986A&A...155..178K Altcode: H-alpha observations of the quiet solar chromosphere at disk center are presented, including a 9 min time sequence of photographic filtergrams in line center and + or - 0.5 A and a 54 min sequence of photographic spectrograms. The very different dynamical behavior of the interior and boundary of the network cells is emphasized. The dominant processes in the interior are waves in the 5 min period range and with shorter periods. The energy flux in these waves is estimated to be too small to account for the radiative losses from standard chromospheric models. In the cell boundaries, the material flows down, on time average, near the centers of rosettes. The short time fluctuations are mainly stochastic while the oscillations are reduced. This suggests that the energy balance in the cell boundaries is determined by MHD turbulence. Title: Multidimensional Radiative Transfer in Stratified Atmospheres: Radiative Cooling by LTE and non-LTE Spectral Lines Authors: Trujillo-Bueno, J.; Kneer, F. Bibcode: 1986MitAG..67..304T Altcode: A detailed paper has been submitted to Astron. Astrophys. Title: Interpretation of High Resolution Observations Authors: Kneer, F. Bibcode: 1985tphr.conf...63K Altcode: No abstract at ADS Title: Oscillations of the sun's chromosphere. III - Simultaneous H-alpha observations from two sites Authors: von Uexkuell, M.; Kneer, F.; Mattig, W.; Nesis, A.; Schmidt, W. Bibcode: 1985A&A...146..192V Altcode: The authors analyze time sequences of Hα filtergrams taken simultaneously from two distant observatories, Capri and Izaña. By means of a coherence analysis the authors discriminate between instrumental effects including seeing and truly solar intensity fluctuations. Waves with periods as short as 60 s are present in the solar chromosphere; the lower limit is set by the time resolution of the observations. Title: Oscillations of the sun's chromosphere. II - H-alpha line centre and wing filtergram time sequences Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1985A&A...144..443K Altcode: In order to investigate the dynamics of the solar chromosphere we perform a Fourier analysis of time sequences (total duration 128 min) of Hα photographic filtergrams taken simultaneously at disc centre in line centre and ±0.5 Å from the line centre. The results are: (i) At low frequencies (periods >450 s) the brightness fluctuations are caused by the temporal evolution of Hα structures at the boundaries of the chromospheric network. We observe that much of the coarse chromospheric structure survives the 128 min time span. We derive lifetimes of 2-8 min for the small-scale structure and 5-20 min for the larger structures. (ii) The modal structure of the 5 min oscillation is clearly visible in the power spectra of the three filtergram. The fundamental (f) mode can be followed to high horizontal wavenumbers kh ≍3.7 Mm-1 and follows the expected relationship ω2f = gkh, where g is the surface gravity. (iii) A chromospheric resonant mode cannot be found in the k - ω plane. (iv) The higher resonant p modes reach into the acoustic wave domain (periods T ≍ 150 s) and thus require the transition zone as the upper reflecting layer. (v) We find no evidence for internal gravity waves. (vi) From a coherence and phase analysis we conclude that the brightness fluctuations of the chromospheric structure seen in -0.5 Å lead those in +0.5 Å by 2 min at kh =2 Mm -1 and by 4 min at kh =0.5 Mm-1. (vii) From the same coherence and phase analysis we can identify acoustic waves in the solar atmosphere with periods as short as 80 s. They possess as much power as the 5 min oscillations and are seen better outside the chromospheric network than within the network. (viii) The phase difference between intensity in Hα line centre and velocity, constructed from the two Hα wing filtergrams, decreases from about 90° at low frequencies and high wavenumbers to 0° at high frequencies and low wavenumbers. Tentatively we interpret this as a change from mainly standing waves for the low order p modes to mainly upward propagating waves in the acoustic wave domain. Acoustic waves are thus candidates for the heating process of the inter-network regions. Title: Report of the working group on future observations of the sun. Authors: Dere, K.; Kneer, F.; Landman, D. Bibcode: 1985cdm..proc...14D Altcode: No abstract at ADS Title: Radiative equilibrium models and heating requirements. Authors: Kneer, F. Bibcode: 1985cdm..proc..252K Altcode: Strong cooling in the IR rotation-vibration bands of carbon monoxide makes the solar atmosphere convectively unstable near the temperature minimum of the empirical models. Some of the calculated radiative equilibrium and heated models are bistable. The author speculates that the instability due to molecule formation contributes to the production of chromospheres. Title: Waves in the chromosphere observed in Hα. Authors: Kneer, F.; von Uexküll, M. Bibcode: 1985cdm..proc..282K Altcode: The authors analyze Hα filtergram time sequences and emphasize the further development and use of filter spectroscopy for studies on the dynamics of the solar atmosphere. Title: Interpretation of high-resolution observations. Authors: Kneer, F. Bibcode: 1985MPARp.212...63K Altcode: The path on which one arrives from observation to knowledge is highly recursive. This contribution is intended to draw attention to the ways of specification of the assumptions necessarily made to solve the diagnostic problem. Both observational conditions and earlier experience enter the assumptions about the complexity, initial and boundary conditions of the process under consideration. High-resolution observations reveal a wealth of small-scale, dynamic phenomena whose properties must be taken into account when diagnosing by way of simulation and calculation of emergent intensities. Title: Chromospheric umbral oscillations. Authors: Mattig, W.; von Uexküll, M.; Kneer, F. Bibcode: 1984ESASP.220...59M Altcode: 1984ESPM....4...59M No abstract at ADS Title: Interpretation of High-Resolution Measurements, Selected Problems (Keynote) Authors: Kneer, F. Bibcode: 1984ssdp.conf..110K Altcode: This review deals with four problems bearing on small-scale dynamical processes: (1) small-scale intensity fluctuations, (2) small-scale velocities, (3) average models of the solar atmosphere, and (4) small-scale magnetic fields. Title: A possible explanation of the Wilson-Bappu relation and the chromospheric temperature rise in late-type stars. Authors: Kneer, F. Bibcode: 1983A&A...128..311K Altcode: IR vibration-rotation bands of CO are noted to cause a radiative instability due to the extreme temperature sensitivity of molecule formation, in the course of an attempt to construct stellar atmospheres which are in radiative equilibrium for the case of a T(eff) of 5800 K, which approximates the T(eff) of the sun. It is accordingly suggested that such stellar atmospheres, in principle, may not exist. CO molecule-based arguments can be extended to other molecular species which should destabilize the atmospheres of cooler stars. This implies that, for the sun, the instability occurs at the mass column density of the temperature minimum deduced from observations. For sunspot chromospheres, the predicted critical mass column density agrees with that of the onset of the chromospheric temperature rise in current sunspot models. It is further suggested that the chromospheres of late-type stars are produced inevitably, and that their seed is located at their base. Title: The chromosphere above sunspot umbrae. IV. Frequency analysis of umbral oscillations. Authors: von Uexküll, M.; Kneer, F.; Mattig, W. Bibcode: 1983A&A...123..263V Altcode: The authors analyse time sequences of photographic spectrograms in Ca II H, K, 8498 Å, and 8542 Å, in Sodium D1 and D2, in Ni I 5893 Å and Hα, obtained from two sunspots. The frequency analysis of line intensities and shifts for the umbral chromospheric oscillations in the period range 110 s-200 s is discussed. Title: The chromosphere above sunspot umbrae. IV - Frequency analysis of umbral oscillations Authors: Uexkuell, M. V.; Kneer, F.; Mattig, W. Bibcode: 1983A&A...123..263U Altcode: An analysis is made of time sequences of photographic spectrograms in Ca II H, K, 8498 A, and 8542 A, in sodium D1 and D2, and in Ni I 5893 A and H-alpha obtained from two sunspots with the Vacuum Tower Telescope at Sacramento Peak Observatory. The two sunspot chromospheres are found to behave similarly with regard to their phase relationships but somewhat differently with regard to the oscillation resonant frequencies. In one and the same umbra, oscillation modes having different frequencies may be excited. The vertical velocity of propagation of the phase in umbral chromospheres, which is 10-25 km/s, decreases with increasing frequency and is much lower than the Alfven speed. The umbral chromospheric oscillations are thus slow mode waves. The downward motion enhances the intensity by some 65 deg (H-alpha) to 85 deg (D1), indicating dissipation of mechanical energy. It is also found that the mechanical energy flux of the umbral chromospheric oscillations is not sufficient to account for the chromospheric radiative losses. Title: Brightness oscillations of the sun's chromosphere in K and H-alpha Authors: Kneer, F.; von Uexkuell, M. Bibcode: 1983A&A...119..124K Altcode: The authors have performed a power analysis of time sequences of photographic K and Hα filtergrams from disc center of the sun. The results are: In the k-ω-diagram from the Ca II K filtergrams, the modal structure of the 5-min-oscillation is clearly seen. The 5-min modes are difficult to detect in the k-ω-diagrams from the Hα sequences. In both lines, K and Hα, the authors observe ridges in the k-ω-diagrams running parallel to the kh-axis. Their periods correspond to the chromospheric 3-min-oscillation. But power appears also, in discrete ridges, at shorter periods P = 60 s...150 s, where the lower limit is given by the Nyquist frequency of the observations. After subtraction of the time averaged intensity at each position in the filtergrams, the rms fluctuations are 3.5% in K and 4.0% in Hα. Title: Zur Aufheizung der Chromosphäre später Sterne Authors: Kneer, F. Bibcode: 1983MitAG..60..301K Altcode: No abstract at ADS Title: New features of the oscillation spectrum of the sun Authors: Kneer, F.; von Uexkuell, M.; Newkirk, G., Jr. Bibcode: 1982A&A...113..129K Altcode: The results of a Fourier analysis of observations of brightness fluctuations in a sequence of CN 3883 Angstrom filtergrams are presented. From the 75 min time interval and field of view of 170 x 220 sq arcsec, a 40 sec sampling interval was examined, maintaining a spatial resolution as high as 1600 km. The data is filtered for a high wavenumber power spectrum, and an average power coefficient is calculated by examining power spectra for each of the sub-arrays. It is concluded that the 5 min velocity oscillation modal structure is easily detected in brightness fluctuations in the CN band, the surface gravity mode is the strongest single feature aside from the zero frequency ridge caused by convection, and the trapped chromospheric mode may be represented by a constant frequency ridge. Improved broad band filtergrams may be used to analyze little explored regions of the oscillation spectrum and to interpret intensity fluctuations as temperature fluctuations. Title: Zur Struktur der Chromosphäre über Sonnenflecken Authors: Kneer, F.; Mattig, W.; von Uexküll, M. Bibcode: 1982MitAG..55...65K Altcode: No abstract at ADS Title: Chromosphärische Helligkeits-oszillationen Authors: Kneer, F.; Newkirk, G.; von Uexküll, M. Bibcode: 1982MitAG..55...70K Altcode: No abstract at ADS Title: The analysis of solar limb observations. II - Geometrical smearing Authors: Durrant, C. J.; Kneer, F.; Maluck, G. Bibcode: 1981A&A...104..211D Altcode: Center-of-disk and limb observations of photospheric brightness fluctuations reveal a systematic suppression of the values at the limb. This is a geometrical effect arising from the line of sight at the limb passing through various structures across the surface. This effect is examined here in the light of recent granular temperature models using a simple model incorporating the dominant granular scale. The geometry is found to have little influence on the deep-seated granular brightness field but to strongly suppress the brightness fluctuations caused by the upper photospheric temperature field. The significance of these results for the restoration of limb observations is discussed. Title: The chromosphere above sunspot umbrae. III - Spatial and temporal variations of chromospheric lines Authors: Kneer, F.; Mattig, W.; v. Uexkuell, M. Bibcode: 1981A&A...102..147K Altcode: The lines Ca II H, K, 8542 A, Na I D(1) and D(2), Ni I 5893 A, and H-alpha, were analyzed in photographic spectrograms obtained from a sunspot. The following results are found for the umbra: (1) the H and K lines are highly correlated, with an emission cores maximum-intensities ratio of 1.2; (2) the K intensities are poorly correlated with those of 8542, D(2), and H-alpha; this behavior is attributed to atmospheric structure horizontal fluctuations having little correlations between those in high and low layers, (3) the periodic temporal fluctuations of the K emission core with umbral flashes are identified, and found to occur throughout the umbral area covered by the spectrograph slit; and (4) fluctuations in the photospheric Ni I 5893 A line cannot be matched to the chromospheric fluctuations, in accord with Giovanelli (1978). Title: OSO-8 Observations of CAII H and K MGII H and K Lyman-Alpha and Lyman-Beta above a Sunspot Authors: Kneer, F.; Scharmer, G.; Mattig, W.; Wyller, A.; Artzner, G.; Lemaire, P.; Vial, J. C. Bibcode: 1981SoPh...69..289K Altcode: Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of Lα above the umbra an electron density of 4.3 × 1010 cm-3 ≲ne* ≲2.3 × 1011 cm-3 at 20 000 K is estimated. Title: The Chromosphere above Sunspot Umbrae - Part Three - Spatial and Temporal Variations of Chromospheric Lines Authors: Kneer, F.; Mattig, W.; Uexkull, M. V. Bibcode: 1981phss.conf..318K Altcode: No abstract at ADS Title: Multidimensional radiative transfer in stratified atmospheres. III - Non-LTE line formation Authors: Kneer, F. Bibcode: 1981A&A....93..387K Altcode: Multidimensional radiative transfer under non-LTE conditions is investigated. Line formation strictly by two-level atoms is treated with both coherent scattering and complete redistribution and with non-LTE parameters ranging from epsilon 0.1 to 0.000001. Lateral transfer effects increase with increasing non-LTE conditions and may, in the solar case, compete with observational limitation of angular resolution. Calculations of line transfer in simple model structures in the solar chromosphere show that horizontal migration of photons may diminish the contrast by an order of magnitude compared to that expected in a one-dimensional treatment. Title: Sunspot chromospheres and their relation to the chromospheres of laten main sequence stars. Authors: Mattig, W.; Kneer, F. Bibcode: 1981A&A....93...20M Altcode: The sunspot umbra parameters such as spectral type, effective temperature, and chromospheric Ca II H and K line emission are related to the same parameters of luminosity class V stars of spectral type G 8 to M 2. The sunspots follow the Wilson-Bappu relation. It is concluded that the strong magnetic fields in umbrae may control the nonradiative energy supply of the sunspot chromosphere; however, the heating mechanism is not reflected in the average appearance of the H and K line cores. Title: Coherence Analysis of Granular Intensity Authors: Kneer, F. J.; Mattig, W.; Nesis, A.; Werner, W. Bibcode: 1980SoPh...68...31K Altcode: A high resolution spectrogram of the Mg b2 line from the quiet Sun disc centre is subjected to a coherence analysis. We find that the coherence between intensity fluctuations in the continuum and the wings of the line breaks down at a distance Δλ = 0.35 Å from line centre. From this and the r.m.s. intensity contrast as a function of Δλ we are led to the following simple model of temperature fluctuation δT in the solar photosphere: A lower part (below 50 km, or τ5000 > 0.25) with strongly inward increasing δT and an upper part (above 50 km) with constant δT = 75 K. The two parts are supposed to fluctuate incoherently. Title: On time-dependent ionization in stellar chromospheres Authors: Kneer, F. Bibcode: 1980A&A....87..229K Altcode: This investigation deals with the question of whether ionization equilibrium in stellar chromospheres is adjusted quickly or slowly compared with dynamical time scales. It is shown that the adjustment time for ionization of hydrogen may be of the order of 10 to the 2nd s (middle solar chromosphere) to 10 to the 3rd s (upper solar chromosphere). This has consequences on the structure of chromospheres; for instance, stationary flows - which are limited to subsonic speed in plane-parallel geometry - drastically change the electron density in comparison to the static case. Unless confirmed by consistent dynamical calculations, chromospheric models based on the assumption of statistical steady state should be taken as rough estimates of chromospheric structure. Title: Observations of Chromospheric Lines from OSO-8 Authors: Grossmann-Doerth, U.; Kneer, F.; Uexkuell, M.; Artzner, G. E.; Vial, J. C. Bibcode: 1980SoPh...66....3G Altcode: The line profiles of Lα, Ca II K and Mg IIk were measured with the spectrometer of the `Laboratoire de Physique Stellaire et Planétaire' on board of OSO-8. The results of these measurements are presented. Title: Report from the discussion group on speckle interferometry and adaptive optics Authors: Kneer, F. Bibcode: 1980fsoo.conf..298K Altcode: No abstract at ADS Title: What are the resolution limits given by the solar atmosphere itself? Authors: Kneer, F. Bibcode: 1980fsoo.conf..204K Altcode: No abstract at ADS Title: Multidimensional radiative transfer in stratified atmospheres: gray radiative equilibrium. Authors: Kneer, F.; Heasley, J. N. Bibcode: 1979A&A....79...14K Altcode: This paper tests the validity of the multidimensional Eddington, or diffusion, approximation in radiative transfer in a gray radiative-equilibrium atmosphere with opacity increasing exponentially toward the stellar interior. The diffusion approximation is unacceptable at small optical depths. The height dependence of intensity fluctuations is studied systematically by adopting the above simplified model atmosphere for the solar photosphere. Lateral radiative exchange is efficient and drastically damps the fluctuations in the uppermost layers. Title: Mehrdimensionaler Strahlungstransport im Strahlungsgleichgewicht Authors: Kneer, F. Bibcode: 1979MitAG..45...95K Altcode: No abstract at ADS Title: Report from discussion group on speckle interferometry and adaptive optics. Authors: Kneer, F. Bibcode: 1979MmArc.106..298K Altcode: No abstract at ADS Title: What are the resolution limits given by the solar atmosphere itself? Authors: Kneer, F. Bibcode: 1979MmArc.106..204K Altcode: No abstract at ADS Title: The Chromosphere above Sunspot Umbrae II. The Interpretation of the H, K and IR Lines of CA II Authors: Kneer, F.; Mattig, W. Bibcode: 1978A&A....65...17K Altcode: Summary. The chromospheres above sunspot umbrae are investigated by comparing calculated and observed profiles of the Ca ii H, K, and infra-red lines. Statistical steady state is assumed for the level populations. We test several model chromospheres in hydrostatic equilibrium. We distinguish between chromospheres which are optically thick and optically thin at the centre of the K line. In view of the observed intensity ratio 1K3/1H3 1.15 we are forced to adopt a thick model as reference chromosphere. Key words: chromosphere - sunspot umbra - Ca ii lines Title: The chromosphere above sunspot umbrae. I. Observations of the emission cores in the Ca II H- and K-lines. Authors: Mattig, W.; Kneer, F. Bibcode: 1978A&A....65...11M Altcode: Summary. Photographic spectra of the Ca ii H- and K- lines in sunspot umbrae are analysed. The emission features in the line profiles may be classified into minimum emission profiles that also lack self-reversal, and profiles which change rapidly in time and exhibit self-reversals (umbral flashes) that are most often strongly asymmetric. Average intensity profiles from the minimum emission parts of the umbra and characteristic intensities of the more active parts of the umbra are given. Key words: chromosphere - sunspot umbra - Ca ii lines Title: Chromosphärenmodell von Sonnenflecken Authors: Kneer, F.; Mattig, W. Bibcode: 1978MitAG..43..141K Altcode: No abstract at ADS Title: Report from the discussion group on speckle interferometry and adaptive optics Authors: Kneer, F. Bibcode: 1978fsoo.conf..298K Altcode: No abstract at ADS Title: What are the resolution limits given by the solar atmosphere itself? Authors: Kneer, F. Bibcode: 1978fsoo.conf..204K Altcode: No abstract at ADS Title: The effects of partial redistribution on facular K line profiles. Authors: Heasley, J. N.; Kneer, F.; Chapman, G. A. Bibcode: 1977SoPh...52..309H Altcode: We present theoretical Ca II K-line profiles and filtergram contrasts for several recent models of solar faculae. The line profiles vary greatly between models and between complete and partial frequency redistribution non-LTE calculations for any given model. The filtergram contrasts are relatively insensitive to the line formation theory which greatly simplifies the calculation for comparison with observations. All of the models considered exhibit K-line contrasts smaller than the mean value observed by Mehltretter. Title: The sun's chromospheric velocity field as inferred from the Ca II K line. Authors: Durrant, C. J.; Grossmann-Doerth, U.; Kneer, F. J. Bibcode: 1976A&A....51...95D Altcode: Theory and observation of the solar Ca II K line under high spatial resolution are briefly reviewed. It is shown that contrary to popular belief, present theory is not capable of explaining the observed features of the K line. An attempt is made to develop a schematic model of the temporal behavior of the spatially resolved K line, based on Leibacher's (1971) investigation of waves in the solar atmosphere Title: Formation of spectral lines with partial frequency redistribution. Authors: Heasley, J. N.; Kneer, F. Bibcode: 1976ApJ...203..660H Altcode: A method for treating the effects of partial frequency redistribution (PRD) in non-LTE radiative-transfer problems is presented in which the rate equations may be kept in their usual form and the PRD effects may be included by altering the form of the radiative-transfer equation. The required modifications of the transfer and statistical-equilibrium equations are outlined along with the changes these necessitate in the complete linearization method. The formulation is compared with that of Milkey et al. (1973), and sample PRD calculations are given for the solar chromospheric Ly-alpha and Ca II K line profiles. The results are found to be in excellent quantitative agreement with previous computations. Title: Radiative hydrodynamics of chromospheric transients. Authors: Kneer, F.; Nakagawa, Y. Bibcode: 1976A&A....47...65K Altcode: A self-consistent method for the numerical modeling of transient phenomena in stellar atmospheres is developed. The nonlinear equations of hydrodynamics are solved together with the equations of radiative transfer and non-LTE ionization equilibrium, and consideration is given to one-dimensional (vertical) motions in a plane-parallel atmosphere which is initially in hydrostatic and statistical equilibrium. The radiative-transfer problem is treated for a two-level-plus-continuum hydrogen atom. The coupled partial differential equations are solved through complete linearization of the corresponding difference equations. The effects of a thermal pulse introduced at the bottom of a model solar chromosphere are calculated. The temperature perturbation produces a pressure pulse which runs upwards through the atmosphere and generates complex variations of temperature, velocity, and radiation. Title: Wechselwirkung zwischen Strahlungstransport und Gasdynamik in der Sonnenchromosphäre. Authors: Kneer, F.; Nakagawa, Y. Bibcode: 1976MitAG..38..203K Altcode: No abstract at ADS Title: Comments on the redistribution function of Jefferies and White. Authors: Kneer, F. Bibcode: 1975ApJ...200..367K Altcode: The simplified form of the angle-averaged redistribution function R"(v', v) for coherent scattering in the atom's frame, suggested by Jefferies and White (1960), is neither normalized nor symmetric. It is shown how these requirements can be met by a simple change, retaining the idea that photons are completely redistributed in the Doppler core and coherently scattered in the line wings. Subject headings: functions - line formation - radiative transfer Title: Properties of the solar Ca ii K-Line at high spatial resolution Authors: Grossmann-Doerth, U.; Kneer, F.; Uexküll, M. v. Bibcode: 1974SoPh...37...85G Altcode: The analysis of three Ca II K-spectra with spatial resolution of ∼1″ is described and its results presented. The comparison of the observed single peak line profiles with model computation leads to some conclusions regarding the non-uniform large-scale velocity fields in the chromosphere. Title: On Some Characteristics of Umbral Fine Structure Authors: Kneer, F. Bibcode: 1973SoPh...28..361K Altcode: Photographic spectra of the umbra of a sunspot (1971, August 24, Rome No. 6205) around 6150 Å show fine bright threads which were identified as the spectra of a lightbridge, of the bright end of a penumbral filament and of umbral dots, respectively. It was found, in agreement with the results of other authors, that the magnetic field in bright structures is considerably weaker than in dark umbral material. Analysis of line profiles of Fe II 6149.2 Å in umbral dots indicates (a) a fieldstrength reduced by a factor ≈2 compared to the surroundings, (b) an outflow with v≈3.0 km s−1 relative to the penumbra and (c) possibly photospheric temperatures in umbral dots. Title: Profiles of Magnetically Split Lines in Sunspots Authors: Kneer, F. Bibcode: 1972A&A....18...47K Altcode: No abstract at ADS Title: Line Profiles in Sunspots Authors: Kneer, F. Bibcode: 1972A&A....18...39K Altcode: No abstract at ADS Title: Linienprofile in Sonnenflecken Authors: Kneer, F. Bibcode: 1972MitAG..31..149K Altcode: No abstract at ADS Title: Linienprofile in Sonnenflecken : ein Beitrag zur Aufstellung von Umbramodellen Title: Linienprofile in Sonnenflecken : ein Beitrag zur Aufstellung von Umbramodellen Title: Line profiles in sunspots : a contribution to the establishment of umbra models; Authors: Kneer, Franz Bibcode: 1970PhDT........99K Altcode: No abstract at ADS Title: Sunspot Intensities and their Correction for Scattered Light Authors: Kneer, F.; Mattig, W. Bibcode: 1968SoPh....5...42K Altcode: Photoelectric measurements of monochromatic spot intensities obtained with the domeless Coudé refractor in Anacapri are given. The scattered light superimposed on the spot, as deduced from measurements outside the sun's limb, amounts on the average to about 4% of the photospheric intensity. The accuracy of the derived spot intensities is better than 10%. Two of four investigated spots yielded temperatures below 3900K (ΔΘ > 0.5).