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Author name code: soltau
ADS astronomy entries on 2022-09-14
author:"Soltau, Dirk" 

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Title: Adaptive optics upgrades for laser communications to the ESA
    optical ground station
Authors: Fischer, E.; Kudielka, K.; Berkefeld, T.; Soltau, D.;
   Perdigués-Armengol, J.; Sodnik, Z.
2021SPIE11852E..2AF    Altcode:
  Over the past years, Synopta have successfully applied adaptive
  optics (AO) in optical ground stations to enhance the capabilities
  in satellite-to-ground laser communication links. In this paper, we
  present the outcome of an upgrade activity to the ESA Optical Ground
  Station (ESA OGS). The activities comprise the design, fabrication
  and site acceptance test results of the Cassegrain Adaptive Receiver
  Optics ("CARO") add-on instrument to the 1 m telescope of the ESA
  OGS. Additionally, we present a baseline design concept for the future
  use of a bi-directional adaptive optics system in the Coudé path
  of the ESA OGS, expected performance characteristics for a selected
  uplink application.

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Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
   A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
   Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
   Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
   Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
   Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
   Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
   D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
   Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
   Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
   Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
   Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
   Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
   Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
   Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
   B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
   Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
   Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
   J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
   J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
   Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
   A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
   E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
   Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
   J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
   A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
   Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
   H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
2020A&A...642A..11S    Altcode: 2019arXiv190311061S
  <BR /> Aims: This paper describes the Polarimetric and Helioseismic
  Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
  helioseismology instrument to observe the Sun from outside the Sun-Earth
  line. It is the key instrument meant to address the top-level science
  question: How does the solar dynamo work and drive connections between
  the Sun and the heliosphere? SO/PHI will also play an important role
  in answering the other top-level science questions of Solar Orbiter,
  while hosting the potential of a rich return in further science. <BR
  /> Methods: SO/PHI measures the Zeeman effect and the Doppler shift
  in the Fe I 617.3 nm spectral line. To this end, the instrument
  carries out narrow-band imaging spectro-polarimetry using a tunable
  LiNbO<SUB>3</SUB> Fabry-Perot etalon, while the polarisation modulation
  is done with liquid crystal variable retarders. The line and the nearby
  continuum are sampled at six wavelength points and the data are recorded
  by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
  are reduced on board, including being inverted under the assumption of
  a Milne-Eddington atmosphere, although simpler reduction methods are
  also available on board. SO/PHI is composed of two telescopes; one,
  the Full Disc Telescope, covers the full solar disc at all phases of
  the orbit, while the other, the High Resolution Telescope, can resolve
  structures as small as 200 km on the Sun at closest perihelion. The high
  heat load generated through proximity to the Sun is greatly reduced by
  the multilayer-coated entrance windows to the two telescopes that allow
  less than 4% of the total sunlight to enter the instrument, most of
  it in a narrow wavelength band around the chosen spectral line. <BR />
  Results: SO/PHI was designed and built by a consortium having partners
  in Germany, Spain, and France. The flight model was delivered to
  Airbus Defence and Space, Stevenage, and successfully integrated into
  the Solar Orbiter spacecraft. A number of innovations were introduced
  compared with earlier space-based spectropolarimeters, thus allowing
  SO/PHI to fit into the tight mass, volume, power and telemetry budgets
  provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
  challenges posed by the mission's highly elliptical orbit.

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Title: Subpixel real-time jitter detection algorithm and
    implementation for polarimetric and helioseismic imager
Authors: Roma, David; Carmona, Manuel; Bosch, Jose; Casas, Albert;
   Herms, Atila; Lopez, Manel; Ruiz, Oscar; Sabater, Josep; Berkefeld,
   Thomas; Maue, Thorsten; Nakai, Eiji; Schmidt, Wolfgang; Soltau, Dirk;
   Volkmer, Reiner; Gomez, Jose M.
2019JATIS...5c9003R    Altcode:
  The polarimetric and helioseismic imager instrument for the Solar
  Orbiter mission from the European Space Agency requires a high
  stability while capturing images, specially for the polarimetric
  ones. For this reason, an image stabilization system has been included
  in the instrument. It uses global motion estimation techniques to
  estimate the jitter in real time with subpixel resolution. Due to
  instrument requirements, the algorithm has to be implemented in a Xilinx
  Virtex-4QV field programmable gate array. The algorithm includes a 2-D
  paraboloid interpolation algorithm based on 2-D bisection. We describe
  the algorithm implementation and the tests that have been made to
  verify its performance. The jitter estimation has a mean error of 125
  pixel of the correlation tracking camera. The paraboloid interpolation
  algorithm provides also better results in terms of resources and time
  required for the calculation (at least a 20% improvement in both cases)
  than those based on direct calculation.

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Title: Spectropolarimetric Observations of an Arch Filament System
    with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
   Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
   Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
   D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
   D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
2019ASPC..526..217B    Altcode: 2018arXiv180401789B
  We observed an arch filament system (AFS) in a sunspot group with the
  GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
  AFS was located between the leading sunspot of negative polarity and
  several pores of positive polarity forming the following part of the
  sunspot group. We recorded five spectro-polarimetric scans of this
  region. The spectral range included the spectral lines Si I 1082.7
  nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
  on the silicon line which is formed in the upper photosphere. The
  line profiles are inverted with the code 'Stokes Inversion based
  on Response functions' to obtain the magnetic field vector. The
  line-of-sight velocities are determined independently with a Fourier
  phase method. Maximum velocities are found close to the ends of AFS
  fibrils. These maximum values amount to 2.4 km s<SUP>-1</SUP> next
  to the pores and to 4 km s<SUP>-1</SUP> at the sunspot side. Between
  the following pores, we encounter an area of negative polarity that
  is decreasing during the five scans. We interpret this by new emerging
  positive flux in this area canceling out the negative flux. In summary,
  our findings confirm the scenario that rising magnetic flux tubes
  cause the AFS.

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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
    Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
   C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
   González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
   Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
   A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
   R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V    Altcode: 2018arXiv180507752V
  The solar magnetic field is responsible for all aspects of solar
  activity. Sunspots are the main manifestation of the ensuing solar
  activity. Combining high-resolution and synoptic observations has
  the ambition to provide a comprehensive description of the sunspot
  growth and decay processes. Active region NOAA 12396 emerged on 2015
  August 3 and was observed three days later with the 1.5-meter GREGOR
  solar telescope on 2015 August 6. High-resolution spectropolarimetric
  data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
  photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
  with the chromospheric He I λ1083.0 nm triplet. These near-infrared
  spectropolarimetric observations were complemented by synoptic
  line-of-sight magnetograms and continuum images of the Helioseismic
  and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

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Title: Flows along arch filaments observed in the GRIS `very fast
    spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
   Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
   Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
   R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
   W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
   J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G    Altcode: 2017arXiv170102206G
  A new generation of solar instruments provides improved spectral,
  spatial, and temporal resolution, thus facilitating a better
  understanding of dynamic processes on the Sun. High-resolution
  observations often reveal multiple-component spectral line profiles,
  e.g., in the near-infrared He i 10830 Å triplet, which provides
  information about the chromospheric velocity and magnetic fine
  structure. We observed an emerging flux region, including two small
  pores and an arch filament system, on 2015 April 17 with the `very
  fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
  situated at the 1.5-meter GREGOR solar telescope at Observatorio del
  Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
  per minute) spectral scans of the solar surface and its potential to
  follow dynamic processes on the Sun. We demonstrate the performance
  of the `very fast spectroscopic mode' by tracking chromospheric
  high-velocity features in the arch filament system.

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Title: Use of adaptive optics in ground stations for high data rate
    satellite-to-ground links
Authors: Fischer, E.; Berkefeld, Th.; Feriencik, Mikael; Feriencik,
   Marco; Kaltenbach, V.; Soltau, D.; Adolph, P.; Czichy, R.; Kunde,
   J.; Heine, F.; Saucke, K.; Meyer, R.; Richter, I.; Sodnik, Z.
2017SPIE10562E..3LF    Altcode:
  Over the past years we have successfully applied adaptive optics (AO)
  in some optical ground stations (OGS) to improve the signal-to-noise
  ratio of satellite to ground laser communications.

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Title: Slipping reconnection in a solar flare observed in high
    resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
   J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
   Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
   Volkmer, R.; Waldmann, T.
2016A&A...596A...1S    Altcode: 2016arXiv160500464S
  A small flare ribbon above a sunspot umbra in active region 12205 was
  observed on November 7, 2014, at 12:00 UT in the blue imaging channel
  of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
  filter. Context observations from the Atmospheric Imaging Assembly
  (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
  Telescope (SOT) onboard Hinode, and the Interface Region Imaging
  Spectrograph (IRIS) show that this ribbon is part of a larger one
  that extends through the neighboring positive polarities and also
  participates in several other flares within the active region. We
  reconstructed a time series of 140 s of Ca II H images by means of the
  multiframe blind deconvolution method, which resulted in spatial and
  temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
  velocities of small-scale bright knots in the observed flare ribbon
  were measured. Some knots are stationary, but three move along the
  ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
  opposite direction and exhibit highly correlated intensity changes,
  which provides evidence of a slipping reconnection at small spatial
  scales. <P />Movies associated to Figs. 1 and 2 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>

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Title: Deep probing of the photospheric sunspot penumbra: no evidence
    of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
   Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
   Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
   O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
   Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
   Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B    Altcode: 2016arXiv160708165B
  Context. Some models for the topology of the magnetic field in
  sunspot penumbrae predict regions free of magnetic fields or with
  only dynamically weak fields in the deep photosphere. <BR /> Aims:
  We aim to confirm or refute the existence of weak-field regions in
  the deepest photospheric layers of the penumbra. <BR /> Methods:
  We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
  by inverting spectropolarimetric data of two different sunspots
  located very close to disk center with a spatial resolution of
  approximately 0.4-0.45”. The data have been recorded using the GRIS
  instrument attached to the 1.5-m solar telescope GREGOR at the El
  Teide observatory. The data include three Fe I lines around 1565 nm,
  whose sensitivity to the magnetic field peaks half a pressure scale
  height deeper than the sensitivity of the widely used Fe I spectral
  line pair at 630 nm. Before the inversion, the data were corrected
  for the effects of scattered light using a deconvolution method with
  several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
  = 0 we find no evidence of regions with dynamically weak (B&lt;
  500 Gauss) magnetic fields in sunspot penumbrae. This result is much
  more reliable than previous investigations made on Fe I lines at 630
  nm. Moreover, the result is independent of the number of nodes employed
  in the inversion, is independent of the point spread function used to
  deconvolve the data, and does not depend on the amount of stray light
  (I.e., wide-angle scattered light) considered.

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Title: Spectropolarimetric observations of an arch filament system
    with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
   Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
   Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
   A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
   Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
   M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B    Altcode: 2016arXiv160901514B
  Arch filament systems occur in active sunspot groups, where a fibril
  structure connects areas of opposite magnetic polarity, in contrast to
  active region filaments that follow the polarity inversion line. We
  used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
  Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
  nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
  to investigate the photospheric magnetic field and velocities, and
  use the line core intensities and velocities of the helium line to
  study the chromospheric plasma. The individual fibrils of the arch
  filament system connect the sunspot with patches of magnetic polarity
  opposite to that of the spot. These patches do not necessarily coincide
  with pores, where the magnetic field is strongest. Instead, areas are
  preferred not far from the polarity inversion line. These areas exhibit
  photospheric downflows of moderate velocity, but significantly higher
  downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
  line. Our findings can be explained with new emerging flux where the
  matter flows downward along the field lines of rising flux tubes,
  in agreement with earlier results.

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Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
   Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
   T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
   Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
   A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F    Altcode: 2016arXiv160800513F
  Context. A significant part of the penumbral magnetic field returns
  below the surface in the very deep photosphere. For lines in the
  visible, a large portion of this return field can only be detected
  indirectly by studying its imprints on strongly asymmetric and
  three-lobed Stokes V profiles. Infrared lines probe a narrow layer
  in the very deep photosphere, providing the possibility of directly
  measuring the orientation of magnetic fields close to the solar
  surface. <BR /> Aims: We study the topology of the penumbral magnetic
  field in the lower photosphere, focusing on regions where it returns
  below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
  datasets from Hinode and from the GREGOR infrared spectrograph. We
  inferred the quality and polarimetric accuracy of the infrared data
  after applying several reduction steps. Techniques of spectral
  inversion and forward synthesis were used to test the detection
  algorithm. We compared the morphology and the fractional penumbral
  area covered by reversed-polarity and three-lobed Stokes V profiles for
  sunspots at disk center. We determined the amount of reversed-polarity
  and three-lobed Stokes V profiles in visible and infrared data of
  sunspots at various heliocentric angles. From the results, we computed
  center-to-limb variation curves, which were interpreted in the context
  of existing penumbral models. <BR /> Results: Observations in visible
  and near-infrared spectral lines yield a significant difference in the
  penumbral area covered by magnetic fields of opposite polarity. In
  the infrared, the number of reversed-polarity Stokes V profiles is
  smaller by a factor of two than in the visible. For three-lobed Stokes
  V profiles the numbers differ by up to an order of magnitude.

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Title: Horizontal flow fields in and around a small active region. The
    transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
   Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
   A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
   Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
   M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V    Altcode: 2016arXiv160507462V
  Context. The solar magnetic field is responsible for all aspects
  of solar activity. Thus, emergence of magnetic flux at the surface
  is the first manifestation of the ensuing solar activity. <BR />
  Aims: Combining high-resolution and synoptic observations aims to
  provide a comprehensive description of flux emergence at photospheric
  level and of the growth process that eventually leads to a mature
  active region. <BR /> Methods: The small active region NOAA 12118
  emerged on 2014 July 17 and was observed one day later with the 1.5-m
  GREGOR solar telescope on 2014 July 18. High-resolution time-series
  of blue continuum and G-band images acquired in the blue imaging
  channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
  complemented by synoptic line-of-sight magnetograms and continuum
  images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
  the Solar Dynamics Observatory (SDO). Horizontal proper motions and
  horizontal plasma velocities were computed with local correlation
  tracking (LCT) and the differential affine velocity estimator (DAVE),
  respectively. Morphological image processing was employed to measure
  the photometric and magnetic area, magnetic flux, and the separation
  profile of the emerging flux region during its evolution. <BR />
  Results: The computed growth rates for photometric area, magnetic
  area, and magnetic flux are about twice as high as the respective
  decay rates. The space-time diagram using HMI magnetograms of five days
  provides a comprehensive view of growth and decay. It traces a leaf-like
  structure, which is determined by the initial separation of the two
  polarities, a rapid expansion phase, a time when the spread stalls,
  and a period when the region slowly shrinks again. The separation
  rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
  it decreases when the separation comes to a halt. Horizontal plasma
  velocities computed at four evolutionary stages indicate a changing
  pattern of inflows. In LCT maps we find persistent flow patterns such
  as outward motions in the outer part of the two major pores, a diverging
  feature near the trailing pore marking the site of upwelling plasma and
  flux emergence, and low velocities in the interior of dark pores. We
  detected many elongated rapidly expanding granules between the two
  major polarities, with dimensions twice as large as the normal granules.

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Title: Upper chromospheric magnetic field of a sunspot penumbra:
    observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
   M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
   H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
   Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
   O.; Waldmann, T.
2016A&A...596A...8J    Altcode: 2016arXiv160801988J
  <BR /> Aims: The fine-structure of the magnetic field in a sunspot
  penumbra in the upper chromosphere is to be explored and compared
  to that in the photosphere. <BR /> Methods: Spectropolarimetric
  observations with high spatial resolution were recorded with the 1.5-m
  GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
  observed spectral domain includes the upper chromospheric Hei triplet
  at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
  spectral lines. The upper chromospheric magnetic field is obtained
  by inverting the Hei triplet assuming a Milne-Eddington-type model
  atmosphere. A height-dependent inversion was applied to the Sii 10
  827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
  field. <BR /> Results: We find that the inclination of the magnetic
  field varies in the azimuthal direction in the photosphere and in the
  upper chromosphere. The chromospheric variations coincide remarkably
  well with the variations in the inclination of the photospheric field
  and resemble the well-known spine and interspine structure in the
  photospheric layers of penumbrae. The typical peak-to-peak variations
  in the inclination of the magnetic field in the upper chromosphere
  are found to be 10°-15°, which is roughly half the variation in
  the photosphere. In contrast, the magnetic field strength of the
  observed penumbra does not vary on small spatial scales in the upper
  chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
  of the observations that is possible with the GREGOR telescope at 1.08
  microns, we find that the prominent small-scale fluctuations in the
  magnetic field inclination, which are a salient part of the property
  of sunspot penumbral photospheres, also persist in the chromosphere,
  although at somewhat reduced amplitudes. Such a complex magnetic
  configuration may facilitate penumbral chromospheric dynamic phenomena,
  such as penumbral micro-jets or transient bright dots.

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Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
   Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
   Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
   Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
   T.; Kneer, F.; Nicklas, H.; Sobotka, M.
2016A&A...596A...7S    Altcode: 2016arXiv160707094S
  Context. The various mechanisms of magneto-convective energy transport
  determine the structure of sunspots and active regions. <BR />
  Aims: We characterise the appearance of light bridges and other
  fine-structure details and elaborate on their magneto-convective
  nature. <BR /> Methods: We present speckle-reconstructed images taken
  with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
  486 nm and 589 nm bands. We estimate the spatial resolution from the
  noise characteristics of the image bursts and obtain 0.08″ at 589
  nm. We describe structure details in individual best images as well
  as the temporal evolution of selected features. <BR /> Results: We
  find branched dark lanes extending along thin (≈1″) light bridges
  in sunspots at various heliocentric angles. In thick (≳ 2″) light
  bridges the branches are disconnected from the central lane and have a Y
  shape with a bright grain toward the umbra. The images reveal that light
  bridges exist on varying intensity levels and that their small-scale
  features evolve on timescales of minutes. Faint light bridges show
  dark lanes outlined by the surrounding bright features. Dark lanes are
  very common and are also found in the boundary of pores. They have a
  characteristic width of 0.1″ or smaller. Intergranular dark lanes of
  that width are seen in active region granulation. <BR /> Conclusions: We
  interpret our images in the context of magneto-convective simulations
  and findings: while central dark lanes in thin light bridges are
  elevated and associated with a density increase above upflows, the dark
  lane branches correspond to locations of downflows and are depressed
  relative to the adjacent bright plasma. Thick light bridges with central
  dark lanes show no projection effect. They have a flat elevated plateau
  that falls off steeply at the umbral boundary. There, Y-shaped filaments
  form as they do in the inner penumbra. This indicates the presence of
  inclined magnetic fields, meaning that the umbral magnetic field is
  wrapped around the convective light bridge.

---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
    magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
   M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
   Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
   Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
   Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
   Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
   Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L    Altcode: 2016arXiv160506324L
  Context. Investigations of the magnetism of the quiet Sun are hindered
  by extremely weak polarization signals in Fraunhofer spectral
  lines. Photon noise, straylight, and the systematically different
  sensitivity of the Zeeman effect to longitudinal and transversal
  magnetic fields result in controversial results in terms of the strength
  and angular distribution of the magnetic field vector. <BR /> Aims:
  The information content of Stokes measurements close to the diffraction
  limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
  spatial straylight and photon noise into account. <BR /> Methods: Highly
  sensitive full Stokes measurements of a quiet-Sun region at disk center
  in the deep photospheric Fe I lines in the 1.56 μm region were obtained
  with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
  statistics and Stokes V asymmetries were analyzed and compared to a
  similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
  diagnostics based directly on the shape and strength of the profiles
  were applied to the GRIS data. We made use of the magnetic line ratio
  technique, which was tested against realistic magneto-hydrodynamic
  simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
  of a very quiet solar region show polarimetric signals above a 3σ
  level. Area and amplitude asymmetries agree well with small-scale
  surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
  analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
  range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
  The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
  are so far unique in the combination of high spatial resolution scans
  and high magnetic field sensitivity. Nevertheless, the unavoidable
  effect of spatial straylight and the resulting dilution of the weak
  Stokes profiles means that inversion techniques still bear a high risk
  of misinterpretating the data.

---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
    of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
   C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
   M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
   Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
   R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
   Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V    Altcode:
  Improved measurements of the photospheric and chromospheric
  three-dimensional magnetic and flow fields are crucial for a precise
  determination of the origin and evolution of active regions. We present
  an illustrative sample of multi-instrument data acquired during a
  two-week coordinated observing campaign in August 2015 involving,
  among others, the GREGOR solar telescope (imaging and near-infrared
  spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
  and Interface Region Imaging Spectrograph (IRIS). The observations
  focused on the trailing part of active region NOAA 12396 with complex
  polarity inversion lines and strong intrusions of opposite polarity
  flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
  spectral profiles in the photospheric Si I λ1082.7 nm line, the
  chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
  λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
  provided maps of Doppler velocity and magnetic field at different
  atmospheric heights. We compare quick-look maps with those obtained
  with the “Stokes Inversions based on Response functions” (SIR)
  code, which furnishes deeper insight into the magnetic properties
  of the region. We find supporting evidence that newly emerging flux
  and intruding opposite polarity flux are hampering the formation
  of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
  expected after cessation of flux emergence in proximity to the sunspots.

---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
   Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
   Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
   R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
   S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
   von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F    Altcode: 2016arXiv161104803F
  Context. Active regions are the most prominent manifestations of solar
  magnetic fields; their generation and dissipation are fundamental
  problems in solar physics. Light bridges are commonly present during
  sunspot decay, but a comprehensive picture of their role in the
  removal of the photospheric magnetic field is still lacking. <BR />
  Aims: We study the three-dimensional configuration of a sunspot,
  and in particular, its light bridge, during one of the last stages of
  its decay. <BR /> Methods: We present the magnetic and thermodynamical
  stratification inferred from full Stokes inversions of the photospheric
  Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
  Infrared Spectrograph of the GREGOR telescope at the Observatorio del
  Teide, Tenerife, Spain. The analysis is complemented by a study of
  continuum images covering the disk passage of the active region, which
  are provided by the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
  with penumbral continuum intensity that separates the central umbra from
  a smaller umbra. We find that in this region the magnetic field lines
  form a canopy with lower magnetic field strength in the inner part. The
  photospheric light bridge is dominated by gas pressure (high-β),
  as opposed to the surrounding umbra, where the magnetic pressure
  is higher. A convective flow is observed in the light bridge. This
  flow is able to bend the magnetic field lines and to produce field
  reversals. The field lines merge above the light bridge and become
  as vertical and strong as in the surrounding umbra. We conclude that
  this occurs because two highly magnetized regions approach each other
  during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
  are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
   Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
   Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
   González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
   Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
   Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
   T.; Volkmer, R.
2016A&A...596A...5M    Altcode: 2018arXiv180410089M
  Context. Over the past 20 yr, the quietest areas of the solar surface
  have revealed a weak but extremely dynamic magnetism occurring
  at small scales (&lt;500 km), which may provide an important
  contribution to the dynamics and energetics of the outer layers of
  the atmosphere. Understanding this magnetism requires the inference
  of physical quantities from high-sensitivity spectro-polarimetric
  data with high spatio-temporal resolution. <BR /> Aims: We present
  high-precision spectro-polarimetric data with high spatial resolution
  (0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
  telescope to shed some light on this complex magnetism. <BR /> Methods:
  We used inversion techniques in two main approaches. First, we assumed
  that the observed profiles can be reproduced with a constant magnetic
  field atmosphere embedded in a field-free medium. Second, we assumed
  that the resolution element has a substructure with either two constant
  magnetic atmospheres or a single magnetic atmosphere with gradients of
  the physical quantities along the optical depth, both coexisting with
  a global stray-light component. <BR /> Results: Half of our observed
  quiet-Sun region is better explained by magnetic substructure within
  the resolution element. However, we cannot distinguish whether this
  substructure comes from gradients of the physical parameters along the
  line of sight or from horizontal gradients (across the surface). In
  these pixels, a model with two magnetic components is preferred, and
  we find two distinct magnetic field populations. The population with
  the larger filling factor has very weak ( 150 G) horizontal fields
  similar to those obtained in previous works. We demonstrate that the
  field vector of this population is not constrained by the observations,
  given the spatial resolution and polarimetric accuracy of our data. The
  topology of the other component with the smaller filling factor is
  constrained by the observations for field strengths above 250 G:
  we infer hG fields with inclinations and azimuth values compatible
  with an isotropic distribution. The filling factors are typically
  below 30%. We also find that the flux of the two polarities is not
  balanced. From the other half of the observed quiet-Sun area 50% are
  two-lobed Stokes V profiles, meaning that 23% of the field of view
  can be adequately explained with a single constant magnetic field
  embedded in a non-magnetic atmosphere. The magnetic field vector and
  filling factor are reliable inferred in only 50% based on the regular
  profiles. Therefore, 12% of the field of view harbour hG fields with
  filling factors typically below 30%. At our present spatial resolution,
  70% of the pixels apparently are non-magnetised.

---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
    features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
   Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
   Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
   Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
   M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G    Altcode: 2016arXiv160300679G
  The new generation of solar instruments provides better
  spectral, spatial, and temporal resolution for a better
  understanding of the physical processes that take place on the
  Sun. Multiple-component profiles are more commonly observed with these
  instruments. Particularly, the He I 10830 Å triplet presents such
  peculiar spectral profiles, which give information on the velocity
  and magnetic fine structure of the upper chromosphere. The purpose
  of this investigation is to describe a technique to efficiently fit
  the two blended components of the He I 10830 Å triplet, which are
  commonly observed when two atmospheric components are located within
  the same resolution element. The observations used in this study were
  taken on 2015 April 17 with the very fast spectroscopic mode of the
  GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
  telescope, located at the Observatorio del Teide, Tenerife, Spain. We
  apply a double-Lorentzian fitting technique using Levenberg-Marquardt
  least-squares minimization. This technique is very simple and much
  faster than inversion codes. Line-of-sight Doppler velocities can
  be inferred for a whole map of pixels within just a few minutes. Our
  results show sub- and supersonic downflow velocities of up to 32 km
  s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
  filamentary structures. The slow component presents velocities close
  to rest.

---------------------------------------------------------
Title: The adaptive optics system of the 1.5m GREGOR solar telescope:
    four years of operation
Authors: Berkefeld, Thomas; Schmidt, Dirk; Soltau, Dirk; Heidecke,
   Frank; Fischer, Andreas
2016SPIE.9909E..24B    Altcode:
  We present the properties of the adaptive optics (AO) system of
  the German 1.5m solar telescope GREGOR, located on the island
  of Tenerife, Spain. The conventional AO system uses a correlating
  Shack-Hartmann-Sensor with a 92mm subaperture size and a 256-actuator
  stacked-piezo deformable mirror (DM). AO performance results and
  practical experience based on the last four years of operation
  are presented. A recently installed second wavefront sensor with
  exchangeable lenslets / subaperture sizes in combination with an
  EM-CCD camera is used for low light observations such as polarimetric
  measurements of the solar system planets. Further developments include
  algorithmic improvements, the use of the night-time sensor for solar
  (off-limb) observations and solar MCAO.

---------------------------------------------------------
Title: Flows in and around Active Region NOAA12118 Observed with
    the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
   Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
   A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
   Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
   M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V    Altcode: 2016arXiv160301109V
  Accurate measurements of magnetic and velocity fields in and around
  solar active regions are key to unlocking the mysteries of the
  formation and the decay of sunspots. High spatial resolution images
  and spectral sequences with a high cadence obtained with the GREGOR
  solar telescope give us an opportunity to scrutinize 3-D flow fields
  with local correlation tracking and imaging spectroscopy. We present
  GREGOR early science data acquired in 2014 July - August with the GREGOR
  Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
  of blue continuum (λ 450.6 nm) images of the small active region
  NOAA 12118 were restored with the speckle masking technique to derive
  horizontal proper motions and to track the evolution of morphological
  changes. In addition, high-resolution observations are discussed in
  the context of synoptic data from the Solar Dynamics Observatory.

---------------------------------------------------------
Title: GREGOR MCAO looking at the Sun
Authors: Schmidt, Dirk; Berkefeld, Thomas; Heidecke, Frank; Fischer,
   Andreas; von der Lühe, Oskar; Soltau, Dirk
2014SPIE.9148E..1TS    Altcode:
  A multi-conjugate adaptive optics systems has been deployed at the
  1.5-meter solar telescope GREGOR for on-sun experiments of MCAO in
  November 2013. GREGOR MCAO incorporates three deformable mirrors (DMs)
  conjugate to 0, 8, and 25 km line of sight distance. Two correlating
  Shack-Hartmann wavefront sensor units are deployed: a high-order on-axis
  wavefront sensor (OA-WFS) with 10-cm subapertures and 10 arcsec field
  of view, and a low-order multi-direction wavefront sensor (MD-WFS)
  with 50-cm subapertures that sample the wavefront in 19 guide regions
  distributed over one arcminute. The MCAO loop was closed repeatedly in
  November '13, as well as in January and May '14. However, in particular
  strong static aberrations that were not removed well by the system,
  derogated the image in the MCAO compensated focal plane. GREGOR MCAO
  is now permanently installed and available for experiments that shall
  advance the development of solar MCAO.

---------------------------------------------------------
Title: Recent results and future DMs for astronomy and for space
    applications at CILAS
Authors: Sinquin, Jean-Christophe; Bastard, Arnaud; Beaufort, Emmanuel;
   Berkefeld, Thomas; Cadiergues, Laurent; Costes, Vincent; Cousty,
   Raphaël.; Dekhtiar, Charles; Di Gesu, Frédéric; Gilbert, Xavier;
   Grèzes-Besset, Catherine; Groeninck, Denis; Hartung, Markus; Krol,
   Hélène; Moreau, Aurélien; Morin, Pierre; Pagès, Hubert; Palomo,
   Richard; Scharmer, Göran; Soltau, Dirk; Véran, Jean-Pierre
2014SPIE.9148E..0GS    Altcode:
  We present recent experimental results obtained with CILAS deformable
  mirrors (DMs) or demonstration prototypes in solar and night-time
  astronomy (with ground-based telescopes) as well as observation
  of the Earth (with space telescopes). These important results have
  been reached thanks to CILAS technology range composed of monomorph
  and piezostack deformable mirrors, drivers and optical coatings. For
  instance, the monomorph technology, due to a simple architecture can
  offer a very good reliability for space applications. It can be used
  for closed or open loop correction of the primary mirror deformation
  (thermal and polishing aberrations, absence of gravity). It can also
  allow a real-time correction of wavefront aberrations introduced by
  the atmosphere up to relatively high spatial and temporal frequencies
  for ground-based telescopes. The piezostack technology is useful for
  very high order correction at high frequency and under relatively low
  operational temperature (down to -30°C), which is required for future
  Extremely Large Telescopes (ELTs). This wide range of applications
  is exposed through recent examples of DMs performances in operation
  and results obtained with breadboards, allowing promising DMs for
  future needs.

---------------------------------------------------------
Title: First successful deployment of the ZIMPOL-3 system at the
    GREGOR telescope
Authors: Ramelli, Renzo; Gisler, Daniel; Bianda, Michele; Bello
   González, Nazaret; Berdyugina, Svetlana; Soltau, Dirk
2014SPIE.9147E..3GR    Altcode:
  Since several years the Zurich Imaging polarimeter (ZIMPOL)
  system is successfully used as a high sensitivity polarimeter. The
  polarimeter system, which is mainly based on a fast modulator and a
  special demodulating camera with a masked CCD, has been continuously
  improved. The third version of the system (ZIMPOL-3) is routinely used
  at IRSOL, Locarno. The fast modulation allows to "freeze" intensity
  variations due to seeing, and to achieve a polarimetric sensitivity
  below 10<SUP>-5</SUP> if the photon statistics is large enough. In
  October 2013 the ZIMPOL system has been brought and installed for the
  first time at the GREGOR telescope in Tenerife for a spectropolarimetric
  observing campaign. There, the system configuration took advantage
  from the calibration unit installed at the primary focus of the GREGOR
  telescope, while the analyzer was inserted in the optical path just
  before the spectrograph slit after several folding mirrors. This
  setup has been tested successfully by the authors for the first time
  in this occasion.

---------------------------------------------------------
Title: EST: the largest and most sensitive spectropolarimeter
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A. : Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2013hsa7.conf..808C    Altcode:
  Magnetic field plays a crucial role to understand most phenomena
  happening in the solar atmosphere. Sunspots, flares, prominences,
  coronal mass ejections are well known examples of its interaction
  with the solar plasma. To study the properties of this interaction,
  one needs to analyze the imprint it leaves in the radiation through
  the polarization induced in spectral lines, via the Zeeman and Hanle
  effects. Outside sunspots, the polarization degree of the emitted
  light is usually well below one part in one thousand, which requires
  sophisticated techniques to measure it accurately. To further complicate
  the situation, telescopes use mirrors and these introduce undesired
  polarization which is two or three orders of magnitude larger than
  that caused by the magnetic field of solar structures. For this reason,
  present telescopes doing polarimetry require an adequate modelling to
  correct the measured data from these spurious effects. In addition,
  most of the magnetic field interactions with the plasma take place
  at small scales. The best achievable angular resolution is mandatory
  to adequately study magnetic phenomena. The European solar Telescope
  (EST) has been defined to overcome these difficulties. Here, some
  aspects of the design are described.

---------------------------------------------------------
Title: The European Solar Telescope
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
   B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2013MmSAI..84..379C    Altcode:
  The European Solar Telescope (EST) is a project to design, build and
  operate an European Solar 4-meter class telescope to be located in the
  Canary Islands, with the participation of institutions from fifteen
  European countries gathered around the consortium EAST (European
  Association for Solar Telescopes). The project main objective up to the
  present has been the development of the conceptual design study (DS)
  of a large aperture Solar Telescope. The study has demonstrated the
  scientific, technical and financial feasibility of EST. The DS has been
  possible thanks to the co-financing allocated specifically by the EU
  and the combined efforts of all the participant institutions. Different
  existing alternatives have been analysed for all telescope systems and
  subsystems, and decisions have been taken on the ones that are most
  compatible with the scientific goals and the technical strategies. The
  present status of some subsystems is reviewed in this paper.

---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
   Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
   Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
   Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S    Altcode: 2012arXiv1202.4289S
  2011 was a successful year for the GREGOR project. The telescope was
  finally completed in May with the installation of the 1.5-meter primary
  mirror. The installation of the first-light focal plane instruments was
  completed by the end of the year. At the same time, the preparations
  for the installation of the high-order adaptive optics were finished,
  its integration to the telescope is scheduled for early 2012. This
  paper describes the telescope and its instrumentation in their present
  first-light configuration, and provides a brief overview of the science
  goals of GREGOR.

---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
   W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
   der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
   Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D    Altcode:
  The 1.5-meter GREGOR solar telescope is a new facility for
  high-resolution observations of the Sun. The telescope is located at the
  Spanish Observatorio del Teide on Tenerife. The telescope incorporates
  advanced designs for a foldable-tent dome, an open steel-truss telescope
  structure, and active and passive means to minimize telescope and mirror
  seeing. Solar fine structure can be observed with a dedicated suite
  of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
  Interferometer", and the "Grating Infrared Spectrograph". All post-focus
  instruments benefit from a high-order (multi-conjugate) adaptive optics
  system, which enables observations close to the diffraction limit of
  the telescope. The inclusion of a spectrograph for stellar activity
  studies and the search for solar twins expands the scientific usage
  of the GREGOR to the nighttime domain. We report on the successful
  commissioning of the telescope until the end of 2011 and the first
  steps towards science verification in 2012.

---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
    literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
   Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
   Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
   M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
   T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D    Altcode: 2012arXiv1210.3167D
  In this review, we look back upon the literature, which had the
  GREGOR solar telescope project as its subject including science cases,
  telescope subsystems, and post-focus instruments. The articles date
  back to the year 2000, when the initial concepts for a new solar
  telescope on Tenerife were first presented at scientific meetings. This
  comprehensive bibliography contains literature until the year 2012,
  i.e., the final stages of commissioning and science verification. Taking
  stock of the various publications in peer-reviewed journals and
  conference proceedings also provides the “historical” context
  for the reference articles in this special issue of Astronomische
  Nachrichten/Astronomical Notes.

---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
   Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
   Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
   Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S    Altcode:
  The 1.5 m telescope GREGOR opens a new window to the understanding
  of solar small-scale magnetism. The first light instrumentation
  includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
  spectro-polarimeter for the visible wavelength range, the GRating
  Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
  excellent performance of the first two instruments has already been
  demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
  solar telescope and number 3 in the world. Its all-reflective Gregory
  design provides a large wavelength coverage from the near UV up to at
  least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
  is equipped with a high-order adaptive optics system, with a subaperture
  size of 10 cm, and a deformable mirror with 256 actuators. The science
  goals are focused on, but not limited to, solar magnetism. GREGOR
  allows us to measure the emergence and disappearance of magnetic flux
  at the solar surface at spatial scales well below 100 km. Thanks to its
  spectro-polarimetric capabilities, GREGOR will measure the interaction
  between the plasma flows, different kinds of waves, and the magnetic
  field. This will foster our understanding of the processes that heat the
  chromosphere and the outer layers of the solar atmosphere. Observations
  of the surface magnetic field at very small spatial scales will shed
  light on the variability of the solar brightness.

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Title: The GREGOR polarimetric calibration unit
Authors: Hofmann, A.; Arlt, K.; Balthasar, H.; Bauer, S. M.; Bittner,
   W.; Paschke, J.; Popow, E.; Rendtel, J.; Soltau, D.; Waldmann, T.
2012AN....333..854H    Altcode:
  The new Solar telescope GREGOR is designed to observe small-scale
  dynamic magnetic structures below a size of 70 km on the Sun
  with high spectral resolution and polarimetric accuracy. For
  this purpose, the polarimetric concept of GREGOR is based on a
  combination of post-focus polarimeters with pre-focus equipment for
  high precision calibration. The Leibniz-Institute for Astrophysics
  Potsdam developed the GREGOR calibration unit which is an integral
  part of the telescope. We give an overview of the function and design
  of the calibration unit and present the results of extensive testing
  series done in the Solar Observatory “Einsteinturm” and at GREGOR.

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Title: The GREGOR adaptive optics system
Authors: Berkefeld , Th.; Schmidt, D.; Soltau, D.; von der Lühe,
   O.; Heidecke, F.
2012AN....333..863B    Altcode:
  The new 1.5-m German solar telescope GREGOR at the Observatorio
  del Teide, Tenerife, is equipped with an integrated adaptive optics
  system. Although partly still in the commissioning phase, the system is
  already being used used for most science observations. It is designed
  to provide diffraction-limited observations in the visible-light regime
  for seeing better than 1.2 arcsec. We describe the AO system including
  the optical design, software, wavefront reconstruction, and performance.

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Title: Optical design of the new solar telescope GREGOR
Authors: Soltau, D.; Volkmer, R.; von der Lühe, O.; Berkefeld, Th.
2012AN....333..847S    Altcode:
  This article describes the considerations which led to the current
  optical design of the new 1.5 m solar telescope GREGOR. The result
  is Gregorian design with two real foci in the optical train. The
  telescope includes a relay optic with a pupil image used by a high
  order adaptive optics system (AO). The optical design is described in
  detail and performance characteristics are given. Finally we show some
  verification results which prove that - without atmospheric effects -
  the completed telescope reaches a diffraction limited performance.

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Title: Mechanical design of the solar telescope GREGOR
Authors: Volkmer, R.; Eisenträger, P.; Emde, P.; Fischer, A.; von
   der Lühe, O.; Nicklas, H.; Soltau, D.; Schmidt, W.; Weis, U.
2012AN....333..816V    Altcode:
  The mechanical structure of the GREGOR telescope was installed at the
  Observatorio del Teide, Tenerife, in 2004. New concepts for mounting
  and cooling of the 1.5-meter primary mirror were introduced. GREGOR
  is an open telescope, therefore the dome is completely open during
  observations to allow for air flushing through the open, but stiff
  telescope structure. Backside cooling system of the primary mirror
  keeps the mirror surface close to ambient temperature to prevent mirror
  seeing. The large collecting area of the primary mirror results in high
  energy density at the field stop at the prime focus of the primary
  which needs to be removed. The optical elements are supported by
  precision alignment systems and should provide a stable solar image
  at the optical lab. The coudé train can be evacuated and serves
  as a natural barrier between the outer environmental conditions and
  the air-conditioned optical laboratory with its sensitive scientific
  instrumentation. The telescope was successfully commissioned and will
  start its nominal operation during 2013.

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Title: Preparing the GREGOR solar telescope for night-time use:
    Deriving a pointing model
Authors: Granzer, T.; Halbgewachs, C.; Volkmer, R.; Soltau, D.
2012AN....333..823G    Altcode:
  We report on the results of a dedicated campaign to derive a pointing
  model for the GREGOR solar telescope which took place in December
  2011. Two main goals were in the focus of this campaign: first
  to prove the aptness of the GREGOR solar telescope for night-time,
  unattended operations and second to derive some qualitative measure of
  the amount of misalignment in the optical and mechanical parts of the
  telescope. In the final version, a root-mean-square deviation (RMSD)
  of 1.6 arcsec for the azimuth model and an RMSD of 2.3 arcsec in the
  elevation model could be achieved.

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Title: Image stabilisation system of the photospheric and helioseismic
    imager
Authors: Volkmer, R.; Bosch, J.; Feger, B.; Gomez, J. M.; Heidecke,
   F.; Schmidt, W.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.
2012SPIE.8442E..4PV    Altcode:
  The Photospheric and Helioseismic imager (PHI) on board of the ESA
  mission Solar Orbiter, to be launched in 2017, will provide measurements
  with high polarimetric accuracy of the photospheric solar magnetic
  field at high solar latitudes. The needed pointing precision requires an
  image stabilisation (ISS) to compensate for spacecraft jitter. The image
  stabilisation system works as a correlation tracker with a high-speed
  camera and a fast steerable mirror. The optomechanical and electronic
  design of the system will be presented.

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Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
   C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
   Soltau, D.; Volkmer, R.
2011ASPC..437..351B    Altcode:
  A brief description of the new 1.5-meter solar telescope GREGOR located
  at the Observatorio del Teide in Tenerife will be given. GREGOR will
  provide a spatial resolution of about 75 km on the Sun, and with its
  light collecting capability we will be able to study the development
  of small magnetic features with high cadence. From the beginning,
  it will be equipped with the GREGOR Fabry-Pérot Interferometer
  (GFPI) for the visible spectral range and with a GRating Infrared
  Spectrograph (GRIS). Both postfocus instruments can be combined
  with a polarimeter, and in both cases the light is modulated by two
  ferro-electric liquid crystals. A calibration unit can be inserted to
  determine the instrumental polarization. Because of the altazimuthal
  mount, time-dependent rotation of the polarimetric reference plane
  is introduced, and we have to develop a polarization model of the
  telescope. Measurements to verify this model are in preparation.

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Title: The Wave-Front Correction System for the Sunrise Balloon-Borne
    Solar Observatory
Authors: Berkefeld, T.; Schmidt, W.; Soltau, D.; Bell, A.;
   Doerr, H. P.; Feger, B.; Friedlein, R.; Gerber, K.; Heidecke, F.;
   Kentischer, T.; v. d. Lühe, O.; Sigwarth, M.; Wälde, E.; Barthol,
   P.; Deutsch, W.; Gandorfer, A.; Germerott, D.; Grauf, B.; Meller, R.;
   Álvarez-Herrero, A.; Knölker, M.; Martínez Pillet, V.; Solanki,
   S. K.; Title, A. M.
2011SoPh..268..103B    Altcode: 2010SoPh..tmp..236B; 2010arXiv1009.3196B
  This paper describes the wave-front correction system developed for
  the Sunrise balloon telescope, and it provides information about its
  in-flight performance. For the correction of low-order aberrations,
  a Correlating Wave-Front Sensor (CWS) was used. It consisted of a
  six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt
  mirror for the compensation of image motion, and an active telescope
  secondary mirror for focus correction. The CWS delivered a stabilized
  image with a precision of 0.04 arcsec (rms), whenever the coarse
  pointing was better than ± 45 arcsec peak-to-peak. The automatic
  focus adjustment maintained a focus stability of 0.01 waves in the
  focal plane of the CWS. During the 5.5 day flight, good image quality
  and stability were achieved during 33 hours, containing 45 sequences,
  which lasted between 10 and 45 min.

---------------------------------------------------------
Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
    Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
   Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
   Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
   J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
   G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
   Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
   Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
2011SoPh..268...35G    Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
  We describe the design of the Sunrise Filter Imager (SuFI) and the
  Image Stabilization and Light Distribution (ISLiD) unit onboard the
  Sunrise balloon borne solar observatory. This contribution provides the
  necessary information which is relevant to understand the instruments'
  working principles, the relevant technical data, and the necessary
  information about calibration issues directly related to the science
  data.

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Title: Adaptive optics development at the German solar telescopes
Authors: Berkefeld, Thomas; Soltau, Dirk; Schmidt, Dirk; von der
   Lühe, Oskar
2010ApOpt..49G.155B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Current concept for the 4m European Solar Telescope (EST)
    optical design
Authors: Sánchez Capuchino, J.; Collados, M.; Soltau, D.; López,
   R.; Rasilla, J. L.; Gelly, B.
2010SPIE.7652E..0SS    Altcode: 2010SPIE.7652E..26S
  The European Solar Telescope (EST) is a 4-m class solar telescope to
  be located in the Canary Islands which is currently in its conceptual
  design study. EST is a pan-european project (with 29 partners, plus 7
  collaborating institutions, from 14 countries) promoted by the European
  Association for Solar Telescopes (EAST). In the current concept,
  the main telescope and its transfer optics assemblies 14 mirrors to
  provide a Science Coudé Focus with an F/50 telecentric beam. It is
  diffraction-limited in a FOV of 1 arcmin with an unvignetted FOV of
  2'x2'. The whole system is being optimized in throughput for several
  instruments observing simultaneously in a spectral range from 0.39
  μm to 2.3 μm. Its innovative concept integrates an optical transfer
  stage assembling multiconjugated adaptive optics with optical field
  de-rotation and with a perfect balance of the whole system in terms
  of polarization being also time and wavelength invariant.

---------------------------------------------------------
Title: Wavefront sensing and wavefront reconstruction for the 4m
    European Solar Telescope EST
Authors: Berkefeld, Thomas; Soltau, Dirk; del Moro, Dario; Löfdahl,
   Mats
2010SPIE.7736E..2JB    Altcode: 2010SPIE.7736E..85B
  We give an overview of the Adaptive Optics (AO) and Multi-conjugate
  Adaptive Optics (MCAO) system of the planned 4m European Solar Telescope
  (EST). The parameter space and the problems of solar MCAO working in the
  visible are explained. The wavefront reconstruction schemes presently
  being considered are explained. First estimates of the expected MCAO
  performance for varying parameter sets are given.

---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
   C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
   E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV    Altcode: 2010SPIE.7733E..18V
  With the integration of a 1-meter Cesic primary mirror the GREGOR
  telescope pre-commissioning started. This is the first time, that
  the entire light path has seen sunlight. The pre-commissioning period
  includes testing of the main optics, adaptive optics, cooling system,
  and pointing system. This time was also used to install a near-infrared
  grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
  range as first-light science instruments. As soon as the final 1.5
  meter primary mirror is installed, commissioning will be completed,
  and an extended phase of science verification will follow. In the near
  future, GREGOR will be equipped with a multi-conjugate adaptive optics
  system that is presently under development at KIS.

---------------------------------------------------------
Title: European Solar Telescope: project status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.;
   Gelly, B.; Grivel-Gelly, C.; Pérez, A.; Socas-Navarro, H.; Soltau,
   D.; Volkmer, R.
2010SPIE.7733E..0HC    Altcode: 2010SPIE.7733E..15C
  The European Solar Telescope is a project for a 4-meter class telescope
  to be located in the Canary Islands. EST is promoted by the European
  Association for Solar Telescopes (EAST). This is a consortium formed
  by a number of research organizations from fifteen European countries
  (Austria, Croatia, Czech Republic, France, Germany, Hungary, Italy,
  the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden,
  Switzerland, and United Kingdom). EST will specialize in high spatial
  and temporal resolution using diverse instruments that can efficiently
  produce two-dimensional spectropolarimetric information of the thermal,
  dynamic and magnetic properties of the plasma over many scale heights
  in the solar atmosphere. In this contribution, the status of the
  development of the Design Study of EST is presented, emphasizing the
  most important aspects of the optical design, mechanical structure, AO
  and MCAO systems for wavefront correction, instruments and polarization
  analysis.

---------------------------------------------------------
Title: Solar multiconjugate adaptive optics at the Dunn Solar
    Telescope
Authors: Rimmele, T. R.; Woeger, F.; Marino, J.; Richards, K.; Hegwer,
   S.; Berkefeld, T.; Soltau, D.; Schmidt, D.; Waldmann, T.
2010SPIE.7736E..31R    Altcode: 2010SPIE.7736E.101R
  Solar observations are performed over an extended field of view and
  the isoplanatic patch over which conventional adaptive optics (AO)
  provides diffraction limited resolution is a severe limitation. The
  development of multi-conjugate adaptive optics (MCAO) for the next
  generation large aperture solar telescopes is thus a top priority. The
  Sun is an ideal object for the development of MCAO since solar structure
  provides multiple "guide stars" in any desired configuration. At the
  Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with
  the goal of developing wellcharacterized, operational MCAO. The MCAO
  system uses two deformable mirrors conjugated to the telescope entrance
  pupil and a layer in the upper atmosphere, respectively. The high
  altitude deformable mirror can be placed at conjugates ranging from
  2km to 10km altitude. We have successfully and stably locked the MCAO
  system on solar granulation and demonstrated the MCAO system's ability
  to significantly extend the corrected field of view. We present results
  derived from analysis of imagery taken simultaneously with conventional
  AO and MCAO. We also present first results from solar Ground Layer AO
  (GLAO) experiments.

---------------------------------------------------------
Title: Site-seeing measurements for the European Solar Telescope
Authors: Berkefeld, Th.; Bettonvil, F.; Collados, M.; López, R.;
   Martín, Y.; Peñate, J.; Pérez, A.; Scharmer, G. B.; Sliepen, G.;
   Soltau, D.; Waldmann, T. A.; van Werkhoven, T.
2010SPIE.7733E..4IB    Altcode: 2010SPIE.7733E.141B
  Seeing measurements are crucial for the optimum design of
  (multi-conjugate) adaptive optics systems operating at solar
  telescopes. For the design study of the 4-meter European Solar
  Telescope, to be located in the Canary Islands, several instruments have
  been constructed and operated, at the Observatorio del Roque de los
  Muchachos (La Palma) and at the Observatorio del Teide (Tenerife),
  to measure the properties of the ground layer and medium-high
  altitude turbulence. Several units of short (42.34 cm) and two long
  (323.06 cm) scintillometer bars are, or are to be, installed at
  both observatories. In addition to them, two wide-field wavefront
  sensors will be attached to the optical beams of the Swedish tower,
  on La Palma, and of the German VTT, on Tenerife, simultaneously used
  with the normal operation of the telescopes. These wavefront sensors
  are of Shack-Hartmann type with ~1 arcminute field of view. In this
  contribution, the instruments setup and their performance are described.

---------------------------------------------------------
Title: Adaptive optics for satellite-to-ground laser communication
    at the 1m Telescope of the ESA Optical Ground Station, Tenerife, Spain
Authors: Berkefeld, Thomas; Soltau, Dirk; Czichy, Reinhard; Fischer,
   Edgar; Wandernoth, Bernhard; Sodnik, Zoran
2010SPIE.7736E..4CB    Altcode: 2010SPIE.7736E.146B
  We present the setup including optics and components, the reconstruction
  scheme and performance estimations of an Adaptive Optics (AO) system
  implemented at the 1m telescope of the ESA Optical Ground Station (OGS),
  Observatorio del Teide, Tenerife. The system will be used to improve the
  signal-to-noise ratio of satellite to ground laser communications. It
  operates with coherent laser communication systems at 1064nm. The
  wavefront sensor is an 88-element Shack-Hartmann-sensor (11 subapertures
  across the pupil), matched to a 12×12 actuator "Multi-DM" membrane
  deformable mirror (DM). The system is able to remove a large part of
  the turbulence-induced and static wavefront errors by using more than
  90 degrees of freedom ("modes"). Due to a special high speed infrared
  camera, the control loop can run at speeds up to 20 kHz, achieving a
  0db bandwidth of about 500Hz, depending on the received laser power.

---------------------------------------------------------
Title: Adaptive optics and MCAO for the 4-m European Solar Telescope
    EST
Authors: Soltau, D.; Berkefeld, T.; Sánchez Capuchino, J.; Collados
   Vera, M.; Del Moro, D.; Löfdahl, M.; Scharmer, G.
2010SPIE.7736E..0US    Altcode: 2010SPIE.7736E..27S
  A consortium of more than 20 European solar physics institution from 15
  different countries is conducting a design study for a 4 m class solar
  telescope which shall be situated at the Canary Islands. In this paper
  we introduce the AO and MCAO design concept for EST. A ground layer
  deformable mirror is combined with an arrangement of four deformable
  layer mirrors. A combination of Shack-Hartmann wave front sensors with
  wide and narrow fields of view is used to control the system and to
  achieve a corrected field of view of one arcmin.

---------------------------------------------------------
Title: Current concept for the 4m European Solar Telescope (EST)
    optical design
Authors: Sánchez-Capuchino, J.; Collados, M.; Soltau, D.; López,
   R.; Rasilla, J. L.; Gelly, B.
2010SPIE.7733E..36S    Altcode: 2010SPIE.7733E..99S
  The European Solar Telescope (EST) is a pan-european project (with 29
  partners, plus 7 collaborating institutions, from 14 countries) for the
  conceptual design study of a 4-meter class solar telescope promoted by
  the European Association for Solar Telescopes (EAST) to be located in
  the Canary Islands. The telescope, in the conceptual study, provides a
  Coudé focus with an F/50 telecentric beam. It is diffraction-limited
  in a FOV of 1 arcmin and it will be optimized in throughput for several
  instruments observing simultaneously in a spectral range from 0.39
  μm to 2.3 μm. Its innovative concept integrates an optical transfer
  stage assembling multiconjugated adaptive optics with optical field
  de-rotation and with a perfect balance of the whole system in terms
  of polarization being time and wavelength invariant.

---------------------------------------------------------
Title: NLST: the Indian National Large Solar Telescope
Authors: Hasan, S. S.; Soltau, D.; Kärcher, H.; Süss, M.;
   Berkefeld, T.
2010SPIE.7733E..0IH    Altcode: 2010SPIE.7733E..16H
  India is planning a new solar telescope with an aperture of 2-m for
  carrying out high resolution studies of the Sun. Site characterization
  is underway at high altitude locations in the Himalayan mountains. A
  detailed concept design for NLST (National Large Solar Telescope)
  has been completed. The optical design of the telescope is optimized
  for high optical throughput and uses a minimum number of optical
  elements. A high order AO system is integrated part of the design that
  works with a modest Fried's parameter of 7-cm to give diffraction
  limited performance. The telescope will be equipped with a suite
  of post-focus instruments including a high resolution spectrograph
  and a polarimeter. NLST will also be used for carrying out stellar
  observations during the night. The mechanical design of the telescope,
  building, and the innovative dome is optimized to take advantage of
  the natural air flush which will help to keep the open telescope in
  temperature equilibrium. After its completion (planned for 2014),
  NLST will fill a gap in longitude between the major solar facilities
  in USA and Europe, and it will be for years the largest solar telescope
  in the world

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Title: Flight control software for the wave-front sensor of SUNRISE
    1m balloon telescope
Authors: Bell, Alexander; Barthol, Peter; Berkefeld, Thomas; Feger,
   Bernhard; Gandorfer, Achim M.; Heidecke, Frank; Knoelker, Michael;
   Martinez Pillet, Valentin; Schmidt, Wolfgang; Sigwarth, Michael;
   Solanki, Sami K.; Soltau, Dirk; Title, Alan M.
2010SPIE.7740E..03B    Altcode: 2010SPIE.7740E...2B
  This paper describes the flight control software of the wave-front
  correction system that flew on the 2009 science flight of the Sunrise
  balloon telescope. The software discussed here allowed fully automated
  operations of the wave-front sensor, communications with the adaptive
  optics sub-system, the pointing system, the instrument control unit
  and the main telescope controller. The software was developed using
  modern object oriented analysis and design techniques, and consists
  of roughly 13.000 lines of C++ code not counting code written for the
  on-board communication layer. The software operated error free during
  the 5.5 day flight.

---------------------------------------------------------
Title: European Solar Telescope: Progress status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
   B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2010AN....331..615C    Altcode:
  In this paper, the present status of the development of the design of
  the European Solar Telescope is described. The telescope is devised to
  have the best possible angular resolution and polarimetric performance,
  maximizing the throughput of the whole system. To that aim, adaptive
  optics and multi-conjugate adaptive optics are integrated in the
  optical path. The system will have the possibility to correct for the
  diurnal variation of the distance to the turbulence layers, by using
  several deformable mirrors, conjugated at different heights. The
  present optical design of the telescope distributes the optical
  elements along the optical path in such a way that the instrumental
  polarization induced by the telescope is minimized and independent
  of the solar elevation and azimuth. This property represents a large
  advantage for polarimetric measurements. The ensemble of instruments
  that are planned is also presented.

---------------------------------------------------------
Title: NLST: India's National Large Solar Telescope
Authors: Hasan, S. S.; Soltau, D.; Kärcher, H.; Süß, M.;
   Berkefeld, T.
2010AN....331..628H    Altcode:
  This article introduces the new Indian 2 m telescope which has been
  designed by MT Mechatronics in a detailed conceptual design study
  for the Indian Institute of Astrophysics, Bangalore. We describe
  the background of the project and the science goals which shall be
  addressed with this telescope. NLST is a solar telescope with high
  optical throughput and will be equipped with an integrated Adaptive
  Optics system. It is optimized for a site with the kind of seeing and
  wind conditions as they are expected at a lake site in the Himalayan
  mountains. The telescope can also be used for certain night time
  applications. We also give the scientific rationale for this class
  of telescope.

---------------------------------------------------------
Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
   Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
   D.; Strassmeier, K. G.
2010AN....331..624V    Altcode:
  The integration and verification phase of the GREGOR telescope
  reached an important milestone with the installation of the
  interim 1 m SolarLite primary mirror. This was the first time
  that the entire light path had seen sunlight. Since then extensive
  testing of the telescope and its subsystems has been carried out. The
  integration and verification phase will culminate with the delivery and
  installation of the final 1.5 m Zerodur primary mirror in the summer of
  2010. Observatory level tests and science verification will commence in
  the second half of 2010 and in 2011. This phase includes testing of the
  main optics, adaptive optics, cooling and pointing systems. In addition,
  assuming the viewpoint of a typical user, various observational modes
  of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
  Spectrograph (GRIS), and high-speed camera systems will be tested to
  evaluate if they match the expectations and science requirements. This
  ensures that GREGOR will provide high-quality observations with its
  combination of (multi-conjugate) adaptive optics and advanced post-focus
  instruments. Routine observations are expected for 2012.

---------------------------------------------------------
Title: EST Adaptive optics performance estimations
Authors: Berkefeld, T.; Soltau, D.
2010AN....331..640B    Altcode:
  We give a short overview of the Adaptive Optics (AO) and Multi-conjugate
  Adaptive Optics (MCAO) system of the planned 4 m European Solar
  Telescope (EST). The optimization process of the AO / MCAO parameters
  is shown, including the parameters and layout of the Shack-Hartmann
  wavefront sensor setup and the DMs. We show the expected performance
  of the AO and MCAO system.

---------------------------------------------------------
Title: Testbed for the multi-conjugate adaptive optics system of
    the solar telescope GREGOR
Authors: Schmidt, Dirk; Berkefeld, T.; Heidecke, F.; von der Lühe,
   O.; Soltau, D.
2009SPIE.7439E..0XS    Altcode: 2009SPIE.7439E..22S
  We present the latest concept of the multi-conjugate adaptive optics
  system for the 1.5-meter solar telescope Gregor. This system will employ
  three deformable mirrors in order to compensate for seeing introduced by
  the ground layer, and by shear winds in 5 and 15 km above the telescope
  ground. Thus, the compensated field of view will grow compared to ground
  layer compensation only. We describe the design and the used components
  and present a testbed which is used to improve control algorithms and to
  test all the components before installing them at the Gregor telescope.

---------------------------------------------------------
Title: Concepts for Multi-wavelength Observations with the 1.5 m
    Solar Telescope GREGOR
Authors: Schmidt, W.; Beck, C.; Denker, C.; Soltau, D.; Volkmer, R.
2008ESPM...12.2.72S    Altcode:
  The initial instrumentation of the 1.5 m solar telescope GREGOR on
  Tenerife will include a grating spectrograph with a spectro-polarimeter
  for the near infrared and a dual Fabry-Perot filter spectro-polarimeter
  for the "red" wavelength range from 530 to 860 nm. Both instruments
  are based on their predecessors that are presently operated at
  the Vacuum-Tower Telescope on Tenerife. In order to fully exploit
  the scientific capability of GREGOR, simultaneous multi-wavelength
  observations are necessary. Such observations will allow studying the
  coupling of different layers of the solar atmosphere. Simultaneous
  measurements of the magnetic field, using different spectral lines,
  increase the sensitivity and the accuracy of such measurements. <P />We
  present concepts for multi-wavelength observations with GREGOR based
  on the first-light instruments. As a first step, fast large-format CCD
  cameras will be used in the slit-jaw imaging system of the spectrograph
  or in an additional medium-band imaging channel for post-facto image
  restoration combined with the spectro-polarimeter. These observations
  with high spatial resolution would provide the context for the
  spectrally resolved data. Beyond simple time-share concepts, the
  different characteristics of imaging and spectrograph-based instruments
  require more sophisticated approaches, which should neither sacrifice
  adaptive optics performance nor diminish polarimetric efficiency and
  accuracy. Here, we will discuss a beam splitter option and variants
  of scanning spectrograph systems. Finally, we introduce a concept for
  a second-generation instrument the "Blue Imaging Solar Spectrometer"
  (BLISS), a dual Fabry-Perot interferometer to explore the blue solar
  spectrum (from 380 to 530 nm) in tandem with the "red" instrument.

---------------------------------------------------------
Title: GREGOR: the New German Solar Telescope
Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.;
   Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
   C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.;
   Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier,
   K.; Wittmann, A.
2007ASPC..368..605B    Altcode: 2007arXiv0704.2693B
  GREGOR is a new open solar telescope with an aperture of 1.5 m. It
  replaces the former 45-cm Gregory Coudé telescope on the Canary island
  Tenerife. The optical concept is that of a double Gregory system. The
  main and the elliptical mirrors are made from a silicon-carbide material
  with high thermal conductivity. This is important to keep the mirrors
  on the ambient temperature avoiding local turbulence. GREGOR will be
  equipped with an adaptive optics system. The new telescope will be ready
  for operation in 2008. Post-focus instruments in the first stage will be
  a spectrograph for polarimetry in the near infrared and a 2-dimensional
  spectrometer based on Fabry-Pérot interferometers for the visible.

---------------------------------------------------------
Title: New high resolution solar telescope GREGOR
Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.;
   Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
   C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.;
   Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier,
   K.; Wittmann, A. D.
2007msfa.conf...39V    Altcode:
  The 1.5m solar telescope GREGOR is being constructed at Tenerife,
  Spain. Its purpose is to observe with high spatial and spectral
  resolution small-scale dynamic magnetic features on the Sun. The
  telescope is completely open with retractable dome and actively cooled
  primary mirror made of silicon carbide to minimize thermal effects
  on the image quality. After completion it will be one of the most
  powerful solar telescopes. This paper presents a general overview of
  the telescope characteristics and the current status.

---------------------------------------------------------
Title: SUNRISE: high resolution UV/VIS observations of the Sun from
    the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Lites, B. W.;
   Martínez Pillet, V.; Schmidt, W.; Soltau, D.; Title, A. M.
2006SPIE.6267E..0SG    Altcode: 2006SPIE.6267E..25G
  SUNRISE is an international project for the development, construction,
  and operation of a balloon-borne solar telescope with an aperture
  of 1 m, working in the UV/VIS spectral domain. The main scientific
  goal of SUNRISE is to understand the structure and dynamics of the
  magnetic field in the atmosphere of the Sun. SUNRISE will provide
  near diffraction-limited images of the photosphere and chromosphere
  with an unpredecented resolution down to 35 km on the solar surface at
  wavelengths around 220 nm. The focal-plane instrumentation consists of a
  polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
  and a phase-diverse filter imager working in the near UV. The first
  stratospheric long-duration balloon flight of SUNRISE is planned
  in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint
  project of the german Max-Planck-Institut fur Sonnensystemforschung
  (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik
  (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
  USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto,
  USA, and the spanish IMaX consortium. In this paper we will present
  an actual update on the mission and give a brief description of its
  scientific and technological aspects.

---------------------------------------------------------
Title: Auto alignment and image tracking system for the SUNRISE
    telescope
Authors: Schmidt, W.; Berkefeld, T.; Feger, B.; Friedlein, R.; Gerber,
   K.; Heidecke, F.; Kentischer, T.; Lühe, O. v. d.; Sigwarth, M.;
   Soltau, D.; Wälde, E.
2006SPIE.6274E..0HS    Altcode: 2006SPIE.6274E..14S
  The 1m balloon-borne solar telescope Sunrise will be equipped with
  a wave-front sensing system for automatic in-flight focusing and
  alignment of the telescope and for high-precision image tracking. A
  six-element wavefront sensor measures low order aberrations of the
  telescope, including defocus and coma. The correction is achieved by
  moving the focusing mirror and the telescope secondary, respectively,
  in a closed-loop circuit. The same system measures image motion. The
  instrument requirements for the tracking are a dynamical range of
  about 30 Hz and a precision of about 0.005 arcs in the sky. The image
  motion signal feeds a closed-loop control system that drives both the
  tip-tilt mirror assembly and the mirrors that are needed for focusing
  and alignment. The tip-tilt unit is a dual-stage system, built at the
  Kiepenheuer-Insitut, consisting of a slow component with a large range
  of about 60 arcs and a fast component with a short range and high
  bandwidth. A breadboard-version of the Correlating Wavefront Sensor
  has been successfully tested at the German Vacuum Tower Telescope
  on Tenerife in summer of 2005. A closed-loop bandwidth of 80 Hz was
  measured for the tracking system. The wave-front sensor detected image
  aberrations pre-set by the telescope's adaptive optics system with the
  required accuracy. Sunrise will be flown in long duration stratospheric
  balloon flights, with a first scientific flight in 2009.

---------------------------------------------------------
Title: GREGOR AO as a tool for telescope commissioning
Authors: Soltau, D.; Berkefeld, Th.; Volkmer, R.
2006SPIE.6267E..11S    Altcode: 2006SPIE.6267E..34S
  The new German solar 1.5 m telescope (GREGOR) will be equipped
  with an adaptive optic system. GREGOR has a relatively complicated
  optical scheme with small tolerances. We therefore have to expect
  certain aberrations due to misalignments and mechanical/optical
  imperfections. This is why the AO will play an important role as an
  auxiliary tool for telescope alignment from the very beginning of the
  commissioning phase. The paper will cover the alignment strategies
  taking advantage of the AO system.

---------------------------------------------------------
Title: The new 1.5m solar telescope GREGOR: first light and start
    of commissioning
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
   Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
   Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald;
   Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus;
   Sobotka, Michal; Klvana, Miroslav; Collados, Manuel
2006SPIE.6267E..0WV    Altcode: 2006SPIE.6267E..29V
  The integration of the three main silicon carbide mirrors into the new
  1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
  during 2006. We expect first light at the end of 2006. A progress
  report about integration of the optics and mechanics and planning of
  the commissioning phase of the telescope and post focus instruments
  will be presented at the meeting. The GREGOR telescope is build by a
  consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
  the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
  Gottingen and additional national and international Partners.

---------------------------------------------------------
Title: Multi-conjugate solar adaptive optics with the VTT and GREGOR
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Lühe, Oskar
2006SPIE.6272E..05B    Altcode: 2006SPIE.6272E...4B
  After the successful demonstration of the solar multi-conjugate adaptive
  optics (MCAO) system at the German 70cm Vacuum Tower Telescope (VTT),
  Observatorio del Teide, Tenerife, in the last years, we are continuing
  the development of the system as a testbed for the future MCAO of the
  150cm GREGOR solar telescope. We describe an improved reconstruction
  scheme that increases the number of corrected off-axis degrees of
  freedom and will be tested at the VTT in September 2006. We present
  a modified optical setup of the GREGOR MCAO that has the advantage of
  being adjustable to a wide height range of the turbulence.

---------------------------------------------------------
Title: Multi-conjugate solar adaptive optics at the Vacuum Tower
    Telescope on Tenerife
Authors: von der Lühe, Oskar; Berkefeld, Thomas; Soltau, Dirk
2005CRPhy...6.1139V    Altcode:
  We present a breadboard multi-conjugate adaptive optics (MCAO) system
  for high angular resolution solar observations which we operate at
  the Vacuum Tower Telescope. We have developed methods to estimate
  quantitatively the performance of solar adaptive optics from science
  data. Several sets of short exposure images of the solar photosphere
  were analyzed to assess the performance of the MCAO. We demonstrate
  that a 30 arcsec field of view is substantially improved when the MCAO
  system is turned on. This compares favourably with an improvement
  of a 10 arcsec field with conventional solar adaptive optics. We
  also show how irradiance fluctuations in the MCAO compensated focus
  can be suppressed. To cite this article: O. von der Lühe et al.,
  C. R. Physique 6 (2005).

---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
    results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
   Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
   Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
   Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
   Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V    Altcode:
  The telescope structure including control system and the complete
  retractable dome of the new 1.5 m solar telescope GREGOR were
  assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
  telescope is build by a consortium of the Kiepenheuer Institut fuer
  Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
  fuer Astrophysik Goettingen and additional national and international
  Partners. Pointing, tracking and thermal tests were made to verify
  the proposed performance. The results of these tests and a progress
  report of the project will be presented.

---------------------------------------------------------
Title: Results of the multi-conjugate adaptive optics system at the
    German solar telescope, Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luehe, Oskar
2005SPIE.5903..219B    Altcode:
  We present the optical setup, reconstruction scheme and observational
  results of the Multi-conjugate Adaptive Optics (MCAO) system at
  the German 70cm Vacuum Tower Telescope, Observatorio del Teide,
  Tenerife. The system serves as a testbed for the future MCAO of the new
  1.5m GREGOR solar telescope and is an extension of the conventional
  Adaptive Optics (CAO) system. We demonstrate that the use of one
  additional MCAO wavefront sensor and one additional deformable mirror
  increases the corrected field of view from 10 to 35 arcseconds.

---------------------------------------------------------
Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
   Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
   T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
   Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
2005AGUSMSP34A..04H    Altcode:
  The Advanced Technology Solar Telescope (ATST) will be the world's
  largest aperture solar telescope, and is being designed for high
  resolution, IR, and coronal research. It must be located at a site that
  maximizes the scientific return of this substantial investment. We
  present the instrumentation, analysis and results of the ATST site
  survey. Two instrumentation sets were deployed at each of six sites to
  measure seeing as a function of height, and sky brightness as a function
  of wavelength and off-limb position. Analysis software was developed
  to estimate the structure function Cn2 as a function of height near
  the ground, and the results were verified by comparison with in-situ
  measurements. Additional software was developed to estimate the sky
  brightness. The statistics of the conditions at the sites were corrected
  for observing habits and the annualized hours of specific observing
  conditions were estimated. These results were used to identify three
  excellent sites suitable to host the ATST: Haleakala, Big Bear and La
  Palma. Among them, Haleakala is proposed as the optimal location of
  the ATST, La Palma and Big Bear being viable alternative sites.

---------------------------------------------------------
Title: Penumbral Line Asymmetries Using KAOS
Authors: Soltau, Dirk; Berkefeld, Thomas; Schlichenmaier, Rolf;
   Tritschler, Alexandra; Rubio, Luis Ramon Bellot
2005sao..conf..129S    Altcode:
  We analyse and interpret the line asymmetries in a sunspot penumbra
  at a heliocentric angle of 23°. The data, acquired with TESOS [1]
  and KAOS [2] at the VTT, is of high spatial (0.5") and high spectral (
  λ/∆λ = 250 000) resolution. We observed in Fe I 557.6 nm (g=0) [3].

---------------------------------------------------------
Title: Second-generation adaptive optics for the 1.5 m solar telescope
    GREGOR, Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luhe, Oskar F. H.
2004SPIE.5490..260B    Altcode:
  We present the optical setup and properties of the second-generation
  adaptive optics (AO) for the 1.5 m solar telescope GREGOR. The system
  will consist of a high order AO system correcting about 200 degrees of
  freedom on-axis at a bandwith of 200 Hz and a multi-conjugate (MCAO)
  extension that uses one additional deformable mirror to correct the
  low-order aberrations across a field of one arcminute at a bandwidth
  of 50 Hz. Diffraction limited observations will be possible for seeing
  better than 1.2 arcsec. First light is expected in 2007.

---------------------------------------------------------
Title: High-precision wavefront sensor for the SUNRISE Telescope
Authors: Schmidt, Wolfgang; Berkefeld, Thomas; Friedlein, Ruediger;
   Heidecke, Frank; Kentischer, Thomas; von der Lühe, Oskar F.; Sigwarth,
   Michael; Soltau, Dirk; Walde, E.
2004SPIE.5489.1164S    Altcode:
  SUNRISE is a 1m solar telescope for the visible and near UV wavelength
  range. It will be flown in long duration stratospheric balloon flights
  in Antarctica, with a first scientific flight in 2007. In this paper,
  we describe the development of a wave-front sensing system that
  will be used for the automatic in-flight alignment of the SUNRISE
  telescope and for high-precision tracking. The system is based on
  the principles of an adaptive optics system. A 19-element wavefront
  sensor is used to determine low order aberrations of the telescope,
  including defocus and spherical aberrations. The correction is achieved
  by controlling the position of the telescope secondary and a focusing
  mirror in closed-loop. In addition to these quasi-static aberrations,
  the system will also measure image motion with a dynamical range of
  at least 30 Hz and with a precision of about 0.005 arcs. To this end,
  the image displacement measured in all sub-apertures is averaged and
  used as tip-tilt correction signal. This signal will feed a second
  closed-loop system that drives the tip-tilt mirror assembly. The
  tip-tilt mirror unit is designed as a dual-stage system that consists
  of a slow component with a large range of 60 arcs and a fast component
  with high bandwidth.

---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
   Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
   Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
   Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
   Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V    Altcode:
  GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
  the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
  Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
  and other national and international Partners. The refurbishment of
  the building is almost finished. The manufacturing of the telescope
  structure and the optics is still in progress. After the integration of
  the new complete retractable dome in July 2004 the telescope structure,
  optic and post focus instruments will be assembled during the rest of
  the year. First light is planned during May 2005.

---------------------------------------------------------
Title: Detection of neutral sodium above Mercury during the transit
    on 2003 May 7
Authors: Schleicher, H.; Wiedemann, G.; Wöhl, H.; Berkefeld, T.;
   Soltau, D.
2004A&A...425.1119S    Altcode:
  The extent of the exosphere of Mercury above the planet's limb could
  for the first time be observed by detecting an excess absorption
  in the solar sodium line D_2 during the transit of Mercury across
  the solar disk on 2003 May 7. The <P />observations were performed
  with a 2d Fabry-Perot spectrograph of the Vacuum Tower Telescope
  at Izaña, Tenerife. The absorption excess, blue-shifted by 13 pm
  relative to the solar line, is mainly concentrated near the polar
  regions. There, <P />the absorption excess can be traced up to
  ≈700 km above the limb. Between the two polar regions, along the
  eastern limb, a weaker absorption excess can be seen. A possible
  streamer-like feature stretches more than 2000 km above the northern
  region. Assuming the density to decrease exponentially with height,
  we derive for the polar maxima vertical column densities of 3 ×
  10<SUP>10</SUP> cm<SUP>-2</SUP>, volume densities at the surface of 2.5
  × 10<SUP>3</SUP> cm<SUP>-3</SUP>, and a density scale height of 150 km.

---------------------------------------------------------
Title: Latest Results from the ATST Site Survey
Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt,
   P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa,
   M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau,
   D.; Streander, K.
2004AAS...204.6909H    Altcode: 2004BAAS...36..795H
  We present the latest results and current status of the site survey
  portion of the Advanced Technology Solar Telescope (ATST) project. The
  ATST will provide high resolution solar data in the visible and IR. The
  site is a major factor determining the performance of the telescope. The
  most critical site characteristics are the statistics of daytime seeing
  quality and sky clarity. These conditions are being measured by a suite
  of instruments at three sites (Big Bear, Haleakala, La Palma). These
  sites were chosen from a set of six that have been tested starting in
  November 2001. The instrumentation includes a solar differential image
  motion monitor, an array of scintillometers, a miniature coronagraph,
  a dust monitor, and a weather station. The analysis of the data provides
  an estimate of the seeing as a function of height near the ground. We
  will present the latest results of the analysis of the survey data set.

---------------------------------------------------------
Title: Solar constraints on new couplings between electromagnetism
    and gravity
Authors: Solanki, S. K.; Preuss, O.; Haugan, M. P.; Gandorfer, A.;
   Povel, H. P.; Steiner, P.; Stucki, K.; Bernasconi, P. N.; Soltau, D.
2004PhRvD..69f2001S    Altcode: 2004gr.qc.....2055S
  The unification of quantum field theory and general relativity is a
  fundamental goal of modern physics. In many cases, theoretical efforts
  to achieve this goal introduce auxiliary gravitational fields, ones
  in addition to the familiar symmetric second-rank tensor potential
  of general relativity, and lead to nonmetric theories because of
  direct couplings between these auxiliary fields and matter. Here,
  we consider an example of a metric-affine gauge theory of gravity in
  which torsion couples nonminimally to the electromagnetic field. This
  coupling causes a phase difference to accumulate between different
  polarization states of light as they propagate through the metric-affine
  gravitational field. Solar spectropolarimetric observations are reported
  and used to set strong constraints on the relevant coupling constant k:
  k<SUP>2</SUP>&lt;(2.5 km)<SUP>2</SUP>.

---------------------------------------------------------
Title: Exosphere of Mercury seen as additional absorption in the Na
    D2 line during the Transit on 2003 May 7.
Authors: Schleicher, H.; Wiedemann, G.; Woehl, H.; Berkefeld, T.;
   Soltau, D.
2004ANS...325...81S    Altcode: 2004ANS...325a..81S; 2004ANS...325..P05S
  No abstract at ADS

---------------------------------------------------------
Title: Optical and thermal design of the main optic of the solar
    telescope GREGOR
Authors: Volkmer, Reiner; von der Luhe, Oskar; Soltau, Dirk; Emde,
   Peter; Krodel, Matthias; Pailer, Norbert; Wiehr, Eberhardt
2003SPIE.5179..270V    Altcode:
  The optical and thermal design of the 1.5 m solar telescope GREGOR is
  presented. The three first main mirrors of GREGOR will be made from
  Cesic, a silicon carbide material. One major constraint of large solar
  telescopes is the thermal load of the structure and the mirrors. The
  mirrors are heated by the solar radiation and introduce potentially
  harmful mirror seeing. GREGOR will use an active mirror cooling
  system and an open telescope structure to reduce these negative
  effects. A thermal analysis shows that the equilibrium temperature
  of the Cesic Mirror without active cooling is 6° above ambient
  temperature. Additional cooling will reduce the temperature difference
  of the optical surface and ambient air to below 0.1° K. With tempered
  airflow (about 2.5 m<SUP>3</SUP>/s per square meter mirror surface)
  the temperature gradient on the surface of the face sheet is less
  than 0.1°K. The telescope will have an open structure and a complete
  retractable dome to support mirror and structure cooling by wind.

---------------------------------------------------------
Title: Current Status of the 1.5m Solar Telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
   Jürgen; Berkfeld, Thomas; Schmidt, Wolfgang; Soltau, Dirk; Nicklas,
   Harald; Wiehr, Eberhardt; Wittman, Axel; Hofmann, Axel; Sobotka,
   Michal; Klvana, Miroslav
2003ANS...324..112V    Altcode: 2003ANS...324..P19V
  No abstract at ADS

---------------------------------------------------------
Title: Comparison of Methods for Fried Parameter Estimation
Authors: Wöger, Friedrich; Berkefeld, Thomas; Soltau, Dirk
2003ANS...324R..22W    Altcode: 2003ANS...324..C03W
  No abstract at ADS

---------------------------------------------------------
Title: Merkur vor der Sonne. Eine Fisternis der besonderen Art
Authors: Mattig, Wolfgang; Soltau, Dirk
2003S&W....42d..66M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: GREGOR: the new 1.5m solar telescope on Tenerife
Authors: Volkmer, Reiner; von der Luehe, Oskar; Kneer, Franz; Staude,
   Juergen; Hofmann, Axel; Schmidt, Wolfgang; Sobotka, Michal; Soltau,
   Dirk; Wiehr, Eberhardt; Wittmann, Axel; Berkefeld, Thomas
2003SPIE.4853..360V    Altcode:
  The new 1.5 m high resolution telescope will be build up on the reused
  solar tower of the German 45 cm Gregory Coudé Telescope at the Teide
  Observatory, Izaña, Tenerife. The new telescope is a Gregory type
  with open telescope structure, alt-azimuth mount, complete retractable
  dome, and a pool of well established and new developed post focus
  instruments. An adaptive optics system provides the capability for
  diffraction limited observations at visible wavelengths and the
  polarimetry device in the secondary focus reduces the perturbation
  due to instrumental polarization in an efficient way. We describe the
  main optical characteristics and the focal plane instrumentation with
  respect to the latest status of the project.

---------------------------------------------------------
Title: Multi-conjugate Adaptive Optics at the Vacuum Tower Telescope,
    Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Lühe, Oskar
2003SPIE.4839..544B    Altcode:
  We present an overview of the optical setup and control algorithms
  for the multi-conjugate adaptive optics (MCAO) system of the
  70cm German Vacuum Tower Telescope (VTT), Observatorio del Teide,
  Tenerife. The system is designed to remove the strong differential
  tip/tilt of the present AO system across a field of 30 arcseconds at
  visible wavelengths. It will consist of two Shack-Hartmann wavefront
  sensors (WFS) and two deformable mirrors (DM) plus a separate Tip/Tilt
  mirror. Both wavefront sensors will be situated in the pupil plane of
  the telescope. One determines the high order wavefront aberrations for
  the center of the field of view (FOV), the other measures only low order
  wavefront aberrations, but covers a large FOV in each subaperture. A 35
  actuator bimorph mirror and a 37 actuator membrane mirror will correct
  the ground layer and the tropopause, respectively. For wavefront
  reconstruction, the mirror eigenmodes will be used. The system will
  have first light in the first quarter of 2003. Scientific operation
  is expected to start in April 2003 or July 2003.

---------------------------------------------------------
Title: KAOS: Adaptive optics system for the Vacuum Tower Telescope
    at Teide Observatory
Authors: van der Luehe, Oskar; Soltau, Dirk; Berkefeld, Thomas;
   Schelenz, Thomas
2003SPIE.4853..187V    Altcode:
  We are completing the integration of a solar adaptive optics system KAOS
  at the 70 cm diameter Vacuum Tower telescope (VTT) on Tenerife. The
  system is capable to compensate some 30 modes of wavefront aberration
  with closed-loop bandwidth of about 100 Hz anywhere on the solar
  disk. We describe the design goals, the main characteristics of KAOS
  and present a first demonstration of its performance.

---------------------------------------------------------
Title: GREGOR - optical design considerations
Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Hofmann, A.;
   Schmidt, W.; Volkmer, R.; Wiehr, E.
2003AN....324..292S    Altcode:
  After many years of successful work the Gregory Coudé Telescope
  (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is
  the result of design considerations which to a wide extent are based
  on new technologies. Special aspects of the design are presented,
  including measures to compensate for optical aberrations caused by
  instrumental and atmospheric effects (Adaptive Optics). First light
  is expected for the end of 2004.

---------------------------------------------------------
Title: Multi-conjugate adaptive optics for the 1.5 m GREGOR telescope
Authors: Berkefeld, T.; Soltau, D.; von der Lühe, O.
2003AN....324..296B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Adaptive optics and multi-conjugate adaptive optics with
    the VTT
Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Wöger, F.;
   Schelenz, Th.
2002AN....323..236S    Altcode:
  We are currently developing adaptive optics (AO) system with a
  multi-conjugate extension for the German solar vacuum tower telescope
  (VTT) at the Teide Observatory on Tenerife. Multi-conjugate adaptive
  optics (MCAO) is a technique for increasing the field of view by
  compensating atmospheric turbulence along several, adjacent lines
  of sight. A conventional AO system compensates only a single line of
  sight in the direction of the lock point of its wavefront sensor. At
  larger field angles, the light from the source transverses higher
  layers of turbulence which are not sampled by the conventional
  system. Measurements at the VTT indicate that full compensation
  is typically restricted to a field of about 10 arcsec in diameter
  at visible wavelengths. An MCAO uses (at least) a second deformable
  mirror close to the focal plane of the telescope to compensate a larger
  field. The sun is a privileged target for an MCAO because the wavefront
  errors at larger field angles are easily measured. We intend to extend
  our existing AO system with a second deformable mirror and a second
  wavefront sensor which enables us to extend the compensated field by
  a factor of three in diameter. We present and discuss our concept.

---------------------------------------------------------
Title: Multiconjugate adaptive optics at the Vacuum Tower Telescope,
    Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luehe, Oskar
2002SPIE.4538..119B    Altcode:
  We present the optical setup and wavefront reconstruction algorithms for
  the multi-conjugate adaptive optics (MCAO) system at the 70 cm German
  Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife. The
  system is designed to increase the corrected field of view (FOV) from
  about 10 arcseconds to 30 arcseconds in the visible. It will consist of
  two Shack-Hartmann wavefront sensors (WFS) and two deformable mirrors
  (DMs). Both wavefront sensors will be situated in the pupil plane of
  the telescope. One determines the high order wavefront aberrations
  for the center of the FOV, the other measures only low order wavefront
  aberrations, but covers a large FOV in each subaperture. A 35 actuator
  bimorph mirror and a micro mirror will correct the ground layer and
  the tropopause, respectively. The system will have first light in
  early 2002. Scientific operation is expected to start in the second
  half of 2002.

---------------------------------------------------------
Title: Adaptive optics system for a 1.5-m solar telescope
Authors: von der Luehe, Oskar; Berkefeld, Thomas; Soltau, Dirk
2002SPIE.4538..197V    Altcode:
  We describe an adaptive optics system for the 1.5m diameter solar
  telescope GREGOR which is currently developed for the Teide Observatory
  on Tenerife. In a first development step, the AO will provide
  compensation of 77 modes of wavefront deformation, corresponding
  to the first 10 radial degrees of a Karhunen-Loeve decomposition of
  wavefront error. We estimate that such a performance will render GREGOR
  nearly diffraction limited at visible wavelengths in conditions which
  correspond to the best 25% of the seeing In Tenerife. The AO uses
  a Shack-Hartmann wavefront sensor which operates on fine structure
  anywhere on the solar disk. The required control bandwidth will be
  about 200 Hz. We show how such a system can be realized using existing
  technology. Substantial increases in performance in terms of corrected
  wavefront error and field requires significant technological advances,
  in particular in the field of large field high speed detectors.

---------------------------------------------------------
Title: MCAO at the German solar vacuum telescope
Authors: Berkerfled, Thomas; Soltau, Dirk
2002ESOC...58..461B    Altcode: 2002bcao.conf..461B
  No abstract at ADS

---------------------------------------------------------
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.
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: 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.
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: GREGOR: high resolution solar observations from 1 AU
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
   Staude, J.; Pailer, N.
2001ESASP.493..417V    Altcode: 2001sefs.work..417V
  No abstract at ADS

---------------------------------------------------------
Title: Dynamics of the solar granulation - On the Time Variation of
    the Granular Flow
Authors: Nesis, A.; Hammer, R.; Roth, M.; Schleicher, H.; Soltau,
   D.; Staiger, J.
2001SoPh..200...11N    Altcode:
  The emergence and evolution of large granules shows thegranular dynamics
  particularly well. We therefore investigate the time dependence of
  the convective flows within a regular and an exploding granule. The
  observational material for this study was taken at the center of the
  solar disk with the German VTT in Izaña (Tenerife, Spain) during
  an observing campaign in the year 1994. It consists of series of
  spectrograms of high spatial resolution, which were digitized and
  processed with wavelet techniques. Among other features, our data show
  the dynamical portrait of a regular and an exploding granule. We can
  follow their temporal evolution over more than 12 min. Using absorption
  lines of different strength we are able to see the dynamical change
  of both granules at several heights within the first 200 km above
  τ<SUB>5000</SUB>=1. The observations reveal significant changes of
  the convective flow of both granules over time as well as over height,
  which are discussed in detail.

---------------------------------------------------------
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.
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: Preliminary study of the evolution of solar magnetic structures
    and photospheric horizontal velocity fields
Authors: UeNo, S.; Kitai, R.; Ichimoto, K.; Sakurai, T.; Soltau, D.;
   Brandt, P. N.
2001AdSpR..26.1793U    Altcode:
  In October 1997, we made a coordinated observation of the solar
  photosphere and chromosphere at Hida observatory (Kyoto university,
  Japan) and at Teide observatory (Tenerife) over a 10 day. We obtained
  imaging data series continuously during 6 hr 45 min in G-band (4308 Å)
  observed with the Domeless Solar Telescope (DST) at Hida on 24th October
  (effective FOV; 96″×99″). Additionally, in this observation,
  we simultaneously observed image series of the chromosphere during
  the latter 4 hr 10 min in H α line center and H α ±0.6 Å. From
  these data set, we could detect that emerging flux tubes crossed
  the photosphere to the chromosphere and that 'convective collapse'
  phenomena appeared at the stage of the spot formation. Moreover,
  we confirmed that the lifetime of mesogranulation was about 4000 sec
  (70 min) from the temporal evolution of velocity patterns. We show
  here only a summary of these observations.

---------------------------------------------------------
Title: Penumbral Stokes-V Asymmetries of Fe I 1564.8 nm
Authors: Schlichenmaier, R.; Soltau, D.; Lühe, O. V. D.; Collados, M.
2001ASPC..236..579S    Altcode: 2001aspt.conf..579S
  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
2000ESASP.463..629V    Altcode: 2000sctc.proc..629V
  No abstract at ADS

---------------------------------------------------------
Title: Shift-and-add reconstruction of solar granulation images
Authors: Baba, N.; Miura, N.; Sakurai, T.; Ichimoto, K.; Soltau, D.;
   Brandt, P.
1999SoPh..188...41B    Altcode:
  To restore an atmospherically degraded image of solar granulation the
  shift-and-add (SAA) method is applied to its specklegrams. It is the
  first time, to the best of our knowledge, that such a technique has
  been used for image reconstruction of solar granulation, a largely
  extended target. SAA, therefore, enables us to monitor restored images
  of solar granulation in a simple and fast way.

---------------------------------------------------------
Title: Resolution Improvement of Solar Images
Authors: Miura, Noriaki; Baba, Naoshi; Sakurai, Takashi; Ichimoto,
   Kiyoshi; Soltau, Dirk; Brandt, Peter
1999SoPh..187..347M    Altcode:
  A method for the improvement of resolution in an observed solar image
  is proposed. A blind deconvolution method is used for restoration of an
  atmospherically-degraded solar image, and a super-resolution method is
  applied to its restored image to improve the resolution. It is confirmed
  that a blind deconvolution process can restore fine structures that are
  blurred in an observed image, and that the super-resolution process
  can make a cutoff frequency in a blind-deconvolved image higher. A
  time series of super-resolved images of a sunspot observed with the
  70-cm Vacuum Tower Telescope at Teide Observatory is presented.

---------------------------------------------------------
Title: TIP: The Tenerife Infrared Polarimeter
Authors: Martínez Pillet, V.; Collados, M.; Bellot Rubio, L. R.;
   Rodríiguez Hidalgo, I.; Ruiz Cobo, B.; Soltau, D.
1999AGAb...15...89M    Altcode: 1999AGM....15..P05M
  The aim of the IAC Tenerife Infrared Polarimeter is to obtain
  quantitative measurements of the polarization state of the solar
  radiation collected in near-infrared wavelengths by the Gregory Coudé
  Telescope and the Vacuum Tower Telescope of the Observatorio del Teide
  (Spain). In this contribution we describe the analyzer, instrumental
  calibration, and detector subsystems of TIP, and give details concerning
  the specifications of the instrument.

---------------------------------------------------------
Title: GREGOR, a 1.5 M Solar Telescope
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
   Staude, J.
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: TIP (Tenerife Infrared Polarimeter): a near IR full Stokes
    Polarimeter for the German Solar Telescopes at Observatorio del Teide
Authors: Collados, M.; Rodríguez Hidalgo, I.; Bellot Rubio, L.;
   Ruiz Cobo, B.; Soltau, D.
1999AGAb...15Q..11C    Altcode: 1999AGM....15..A13C
  In this contribution, the main characteristics of the=20 Tenerife
  Infrared Polarimeter (TIP), recently built at the Instituto de
  Astrofísica de Canarias, to be operated at the German Solar
  Telescopes (GCT and VTT) of the Observatorio del Teide (Tenerife)
  are presented. Especial emphasis is put on the modulation scheme,
  polarisation efficiencies, signal-to-noise ratio, spatial and spectral
  resolution, and instrumental polarisation cross-talk. Some examples
  of data recently obtained are presented, which give an idea of the
  performance and capabilities of this instrument.

---------------------------------------------------------
Title: Adaptive Optics for the German Solar Telescopes
Authors: Soltau, D.; Brunner, R.; von der Lühe, O.
1999AGAb...15....6S    Altcode: 1999AGM....15..A03S
  Adaptive Optics is a precondition to get high resolution observations
  near the diffraction limit when the integration times become larger than
  a few milliseconds At the KIS there is a project to upgrade the Vacuum
  Tower Telescope at Tenerife with an adaptive optics system (KAOS =
  Kiepenheuer-Institut adaptives Optiksystem). The optical concept is
  discussed and first measurements with the KAOS wavefront sensor and
  their implications are presented. Considerations with respect to AO
  for the future GREGOR telescope are also discussed.

---------------------------------------------------------
Title: LPSP &amp; TIP: Full Stokes Polarimeters for the Canary
    Islands Observatories
Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.;
   González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.;
   Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D.
1999ASPC..183..264M    Altcode: 1999hrsp.conf..264M
  No abstract at ADS

---------------------------------------------------------
Title: The Helium Spectrum in the Quiet Sun: The January 16/17 and
    May 7-13 1997 Coordinated SOHO/Ground-Based Observational Campaigns
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Muglach, Karin;
   Garcia, Adriana; Jones, Harrison P.; Penn, Matthew J.; Soltau, Dirk
1998ASPC..155..336A    Altcode: 1998sasp.conf..336A
  No abstract at ADS

---------------------------------------------------------
Title: Simultaneous observations of spicules with SOHO/CDS and the
    Fabry-Perot interferometer at the VTT
Authors: de Pontieu, B.; von der Lühe, O.; Soltau, D.; Kentisher, Th.
1998ESASP.421...43D    Altcode: 1998sjcp.conf...43D
  No abstract at ADS

---------------------------------------------------------
Title: Investigating the Formation of the Helium Spectrum in the
    Solar Atmosphere
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Muglach, Karin;
   Garcia, Adriana; Jones, Harrison P.; Soltau, Dirk
1998ASPC..154..559A    Altcode: 1998csss...10..559A
  We present the first results of coordinated observations with SOHO
  (Solar Heliospheric Observatory) and ground-based observatories aimed
  at investigating the mechanisms responsible for the formation of helium
  lines in the quiescent solar atmosphere. The observations described
  here were taken on 7-13 May 1997; the SOHO instruments involved were
  CDS, SUMER and EIT, while ground-based support was provided by the
  German Vacuum Tower Telescope on Tenerife (He 1 lambda10830 and Ca 2
  lambda8498 spectra-spectroheliograms), Coimbra Solar Observatory (Hα
  spectroheliograms), and NASA/NSO Vacuum Tower Telescope on Kitt Peak
  (Ca 2 lambda8542 spectra-spectroheliograms and polarimetry).

---------------------------------------------------------
Title: Stokes I and V observations of magnetic knots using bright
    CA II K network points as tracers.
Authors: Soltau, D.
1997A&A...317..586S    Altcode:
  This paper uses bright Ca II K points as markers for isolated magnetic
  features in the underlying solar photosphere. Stokes V polarimetry
  in selected photospheric lines applied to a large number of Ca II
  K targets yield some average results: These magnetic features are
  2 to 3arcsec in diameter, dark at disk center and bright at the
  limb. Their magnetic field strength is typically 1400Gauss, with the
  field vertically oriented on average. Their magnetic filling factor is
  large (=~40%). Our targets share these properties with the magnetic
  knots introduced by Beckers &amp; Schroeter (1968SPh.....4..142B).We
  therefore conclude that magnetic knots can be found anywhere on
  the solar disk and not only near active regions. These features may
  contribute significantly to the total solar magnetic flux.

---------------------------------------------------------
Title: Adaptive Optics at the German VTT on Tenerife
Authors: Soltau, D.; Acton, D. S.; Kentischer, Th.; Roser, M.; Schmidt,
   W.; Stix, M.; von der Luhe, O.
1997ASPC..118..351S    Altcode: 1997fasp.conf..351S
  Experiences and considerations are presented which play an important
  role for an Adaptive Optics system at our telescope.

---------------------------------------------------------
Title: Spectroscopic Observation of the Solar Active Regions in Hel
    10830 A Line
Authors: Tohmura, Ichirah; Kitai, Reizaburo; Suematsu, Yoshinori;
   Soltau, Dirk
1996JKASS..29..333T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Full-field wavefront measurements with phase diversity.
Authors: Acton, D. S.; Soltau, D.; Schmidt, W.
1996A&A...309..661A    Altcode:
  We apply phase diversity techniques to focused and defocused images
  of solar granulation to make full-field measurements of the wavefront
  errors due to atmospheric turbulence. From these measured wavefronts,
  we estimate that the size of the isoplanatic patch is between 9 and
  14 arcseconds. We form a two-layer model of the atmospheric turbulence
  in an attempt to separate the near and far-field effects. We show that
  this model does not adequately separate the observed turbulence, unless
  the measured field of view is quite large. We conclude that there is
  a strong layer of turbulence near the telescope, and a weaker layer
  of turbulence centered at about 4km above the telescope. The measured
  wavefronts are averaged in order to quantify the fixed aberrations
  present in the telescope.

---------------------------------------------------------
Title: Adaptive optics for a 70 cm solar telescope.
Authors: Soltau, D.; Acton, D. S.; Kentischer, T.; Röser, M.; Schmidt,
   W.; Stix, M.; von der Lühe, O.
1996AGAb...12...92S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: He I 10830 Angstroms in Solar Active Regions and its
    Correlation with Chromospheric Lines
Authors: Kitai, R.; Tohmura, I.; Suematsu, Y.; Akioka, M.; Soltau, D.
1996mpsa.conf..435K    Altcode: 1996IAUCo.153..435K
  No abstract at ADS

---------------------------------------------------------
Title: Solar Observations Near 1.6 μm with the German Telescopes
    at Tenerife
Authors: Soltau, D.
1995itsa.conf..407S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Peculiar magnetic field evolution of active region NOAA 7562
    in August 1993 - results from campaign observation with Yohkoh
Authors: Sakurai, T.; Suematsu, Y.; Ichimoto, K.; Kurokawa, H.; Kitai,
   R.; Akioka, M.; Tohmura, I.; Soltau, D.; Mickey, D. L.; Zhang, H.;
   Li, W.; Zirin, H.; Tang, F.
1994ESASP.373..337S    Altcode: 1994soho....3..337S
  No abstract at ADS

---------------------------------------------------------
Title: Instrumental polarization effects of the German Vacuum Tower
    Telescope (VTT) at Tenerife
Authors: Soltau, Dirk
1994SPIE.2265..463S    Altcode:
  Polarimetry is an important method to investigate the physics of the
  solar atmosphere. If the magnetic field strength is not strong enough
  to produce completely split Zeeman profiles the degree of polarization
  is a measure for the field strength. Measuring both the circular
  and linear polarization allows in principle the construction of the
  magnetic field vector including magnitude and direction. Unfortunately
  these highly desired measurements are in many cases affected by the
  instrument's optic itself. Especially telescopes which don't have a
  rotation symmetry with respect to their optical axis suffer from these
  problems. This is also the case with our German Vacuum Tower Telescope
  at Tenerife and this paper shall show the instrumental effects which
  are to be expected. One of the effects is crosstalk between linear and
  circular polarization. We show a method where this crosstalk can be
  considered as a tool and may be used--under certain assumptions--to
  derive the true size of magnetic elements which may cover only a
  fraction of the resolution element.

---------------------------------------------------------
Title: Sunspot observations (Invited Review)
Authors: Soltau, D.
1994smf..conf..155S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On Intensity; Magnetic Field and Velocities of Small Bright
    Points in the CA Network
Authors: Soltau, D.
1993ASPC...46..225S    Altcode: 1993IAUCo.141..225S; 1993mvfs.conf..225S
  No abstract at ADS

---------------------------------------------------------
Title: The German solar telescopes on Tenerife
Authors: Soltau, Dirk
1991AdSpR..11e.133S    Altcode: 1991AdSpR..11..133S
  In 1989 the last of the three German Telescopes in the Observatorio
  del Teide (Tenerife) the Vacuum Tower Telescope (VTT) became
  operational. With emphasis on this instrument a description of the
  telescopes is given and their performance is demonstrated. The postfocus
  equipment is described briefly.

---------------------------------------------------------
Title: Windows of the German Vacuum Tower Telescope.
Authors: Soltau, D.
1991ewst.conf...23S    Altcode:
  This paper deals with the various effects which may play a role if one
  introduces a plane parallel transmitting plate (i.e. a window) into
  an optical system. In this particular case the system is the German
  Vacuum Tower Telescope (VTT) which is operated on Tenerife. Only some
  of the possible effects are important for the VTT but this compilation
  together with a number of useful formulae and our experiences may help
  to treat this kind of problems for LEST.

---------------------------------------------------------
Title: Observations of Magnetic Features with the German Solar
    Telescopes at the Observatorio-Del / Tenerife
Authors: Kneer, F.; Soltau, D.; Wiehr, E.
1990IAUS..142..113K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: High resolution observations with the new German VTT on
    Teneriffe
Authors: Soltau, D.
1989hsrs.conf....3S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Status of the Latest German Solar Facility on Tenerife
Authors: Soltau, D.
1989ASIC..263...17S    Altcode: 1989ssg..conf...17S
  No abstract at ADS

---------------------------------------------------------
Title: Construction of the German Solar Telescopes in the Observatorio
del Teide, Tenerife: The Vacuum Tower Telescope
Authors: Schmidt, W.; Soltau, D.
1987MitAG..68..184S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Present and Future Observational Facilities of the German
    Vacuum Tower Telescope
Authors: Soltau, D.
1987rfsm.conf..362S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The German solar telescopes at the observatorio del Teide
Authors: Schroeter, E. H.; Soltau, D.; Wiehr, E.
1985VA.....28..519S    Altcode:
  This article gives a survey of the German solar telescope installations
  which are going to be operational in 1985 (Gregory Coudé Telescope)
  and in 1986 (Vacuum Tower Telescope) respectively.

---------------------------------------------------------
Title: The German 60-cm Vacuum Tower Telescope and Its Post-Focus
    Facilities
Authors: Soltau, D.
1985spit.conf.1191S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Time-dependence of umbral oscillations
Authors: Soltau, D.; Wiehr, E.
1984A&A...141..159S    Altcode:
  Doppler shifts of the magnetically insensitive line Fe 7090.4 are
  observed in two sunspot umbrae on three days over time intervals up
  to 8.5 h. The temporal power spectra show a large variety of periods
  whose pattern reoccurs periodically. Neither the 300 s nor the 180 s
  periods are preferred umbral modes. Conspicuous power near 0.8 m Hz
  closely corresponds to the known 20 min time scale of umbral dots. A
  240 s period from the revolution of the telescope's RA drive screw
  indicates the occasional existence of a structured umbral velocity
  field; its relation to intensity structures, e.g. the dots, is seen from
  the 240 s power peak in the simultaneously recorded continuum intensity.

---------------------------------------------------------
Title: Oszillationen in Flecken-Umbren
Authors: Soltau, D.; Balthasar, H.; Koch, A.; Küveler, G.; Wiehr, E.
1983MitAG..60..225S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A morphological study of some umbral fine structures
Authors: Soltau, D.
1982A&A...107..211S    Altcode:
  Photographic analysis of a high resoluted white-light photograph of a
  big sunspot (Mount Wilson No. 20551) shows that there is a morphological
  relation between bright penumbral filaments and umbral dots. Within
  the umbra evidence is found for the existence of features which are
  considerably bigger than umbral dots and which may be identified with
  earlier found 'umbral granulation'.

---------------------------------------------------------
Title: Guiding and Image Stabilization of the 60 cm VTT by Means of
    a Fourth-Order Servo System
Authors: Soltau, D.
1981siwn.conf..600S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: An attempt to compare the differential rotation of the
    Ca<SUP>+</SUP>-network with that of the photospheric plasma.
Authors: Schroeter, E. H.; Woehl, H.; Soltau, D.; Vazquez, M.
1978SoPh...60..181S    Altcode:
  In this third paper of a series we report on results obtained
  from almost simultaneous observations of the differential
  rotation of the Ca<SUP>+</SUP>-chromosphere and the photospheric
  plasma. The observations (tracings of Ca<SUP>+</SUP>-mottles,
  Doppler-shift-measurements in a photospheric line) were performed
  at the Locarno station during two extended periods in 1976. Both
  data sets were used to search for a large scale circulation
  pattern. A regular long-lived pattern could not be detected, but a
  single cell with radial outflow (∼40 ms<SUP>-1</SUP>) extending
  over more than 50° in longitude has been found. Statistically
  significant temporal changes of the differential rotation law of the
  Ca<SUP>+</SUP>-chromosphere correlated with changes of meridional
  motions and differences in the rotation of the two hemispheres
  were observed. The data of 1976 show no significant difference in
  the equatorial velocity of the Ca<SUP>+</SUP>-chromosphere and the
  photosphere. A comparison of temporal variations of the rotation
  velocity of the Ca<SUP>+</SUP>-mottles and the photospheric plasma
  yielded no significant correlation. Finally, we correlated the
  measurements of the photospheric rotation performed within the
  equatorial belts at Locarno with those obtained at Mt. Wilson by a
  different method during the same periods. The Locarno data show small
  temporal variations (±50 m<SUP>-1</SUP>s) with no correlation between
  the two hemispheres, while from the Mt. Wilson data larger variations
  (±100 m s<SUP>-1</SUP>) with a very high correlation between the two
  hemispheres have been found. A comparison of both sets of data yielded
  no correlation at all demonstrating the need for further coordinated
  observations and a drastic increase of internal accuracy.

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Title: Zum Problem der Evershedströmungen in Penumbra-Feinstrukturen
Authors: Wiehr, E.; Stellmacher, G.; Soltau, D.
1977MitAG..42..117W    Altcode:
  The use of a two-flow model in the interpretation of the solar
  Evershed flows reported by Schroeter (1965) leads to contradictions
  with respect to recent measurements regarding the flow characteristics
  in the penumbra fine structures. Stellmacher and Wiehr (1971) have
  found in an analysis of line asymmetries based on such a model that
  the line main component must be related to slow-flowing bright penumbra
  structures. The line satellite, on the other hand, must be related to
  fast-flowing dark penumbra structures. A series of nonsplitting lines
  in two long-term individual spots were recorded in connection with a
  more detailed investigation of this model concept. The asymmetrical
  penumbral line profiles were decomposed with the aid of a computer
  calculation into a main component and a satellite. The significance of
  the results is discussed. It is found that the observational phenomena
  can be very well reconciled with a depth-dependent flow concept for
  the penumbra proposed by Maltby (1964).

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Title: On velocity oscillations in sunspot umbrae.
Authors: Soltau, D.; Schroeter, E. H.; Woehl, H.
1976A&A....50..367S    Altcode:
  We report results from a power spectrum analysis of photographic
  measurements of velocity oscillations in two sunspot umbrae. We find
  oscillations with 3 regimes, of periods: 470-300 s, 196-164 s and
  123-110 s with a peak to peak amplitude of about 0.6 km/sec. Whereas
  the two long period oscillations agree well with the findings of
  previous authors the detection of the short period oscillations is
  new. We find significant power for the 300 s oscillations in a purely
  umbral molecular line, 6496.2 A (TiO), which establishes the umbral
  origin of this oscillation mode.

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Title: On the time behaviour of oscillations in sunspot umbrae.
Authors: Schroeter, E. H.; Soltau, D.
1976A&A....49..463S    Altcode:
  The time behavior of oscillations in a sunspot umbra is studied using
  Doppler-compensator velocity records with high time resolution. A
  power-spectrum analysis yields modes with different periods. It is
  found that during time periods when the spot umbra oscillated with the
  180-s period, the 300-s period was strongly suppressed and vice versa.