Author name code: vonderluehe
ADS astronomy entries on 2022-09-14
author:"von der Luehe, Oskar" 
------------------------------------------------------------------------  

Title: The National Science Foundation's Daniel K. Inouye Solar
    Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
   A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
   Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
   Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
   Mathioudakis, M.; Dkist Team
Bibcode: 2021AAS...23810601R
Altcode:
  The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
  (DKIST) on Haleakala, Maui is now the largest solar telescope in the
  world. DKIST's superb resolution and polarimetric sensitivity will
  enable astronomers to unravel many of the mysteries the Sun presents,
  including the origin of solar magnetism, the mechanisms of coronal
  heating and drivers of flares and coronal mass ejections. Five
  instruments, four of which provide highly sensitive measurements
  of solar magnetic fields, including the illusive magnetic field of
  the faint solar corona. The DKIST instruments will produce large and
  complex data sets, which will be distributed through the NSO/DKIST Data
  Center. DKIST has achieved first engineering solar light in December
  of 2019. Due to COVID the start of the operations commissioning phase
  is delayed and is now expected for fall of 2021. We present a status
  update for the construction effort and progress with the operations
  commissioning phase.

Title: DKIST First-light Instrumentation
Authors: Woeger, F.; Rimmele, T.; Casini, R.; von der Luehe, O.; Lin,
   H.; Kuhn, J.; Dkist Team
Bibcode: 2021AAS...23810602W
Altcode:
  The NSF's Daniel K. Inouye Solar Telescope's (DKIST) four meter aperture
  and state-of-the-art wavefront correction system and instrumentation
  will facilitate new insights into the complexities of the solar
  atmosphere. We will describe the details and status of the diverse
  first light instruments, including the high order adaptive optics
  system, that are being commissioned: The Visible Spectro-Polarimeter
  (ViSP), the Visible Broadband Imager (VBI), the Visible Tunable Filter
  (VTF), the Diffraction-Limited Spectro-Polarimeter (DL-NIRSP) and the
  Cryogenic Spectro-Polarimeter (Cryo-NIRSP). We will present first data
  demonstrating the telescope's instrument systems performance.

Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
   Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
   McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
   von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
   Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
   Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
   Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
   Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
   Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
   Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
   Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
   Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
   D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
   Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
   Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
   Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
   Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
   Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
   Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
   Wampler, Stephen B.; Williams, Timothy R.; White, Charles
Bibcode: 2020SoPh..295..172R
Altcode:
  We present an overview of the National Science Foundation's Daniel
  K. Inouye Solar Telescope (DKIST), its instruments, and support
  facilities. The 4 m aperture DKIST provides the highest-resolution
  observations of the Sun ever achieved. The large aperture of
  DKIST combined with state-of-the-art instrumentation provide the
  sensitivity to measure the vector magnetic field in the chromosphere
  and in the faint corona, i.e. for the first time with DKIST we will
  be able to measure and study the most important free-energy source
  in the outer solar atmosphere - the coronal magnetic field. Over its
  operational lifetime DKIST will advance our knowledge of fundamental
  astronomical processes, including highly dynamic solar eruptions
  that are at the source of space-weather events that impact our
  technological society. Design and construction of DKIST took over two
  decades. DKIST implements a fast (f/2), off-axis Gregorian optical
  design. The maximum available field-of-view is 5 arcmin. A complex
  thermal-control system was implemented in order to remove at prime
  focus the majority of the 13 kW collected by the primary mirror and
  to keep optical surfaces and structures at ambient temperature, thus
  avoiding self-induced local seeing. A high-order adaptive-optics
  system with 1600 actuators corrects atmospheric seeing enabling
  diffraction limited imaging and spectroscopy. Five instruments, four
  of which are polarimeters, provide powerful diagnostic capability
  over a broad wavelength range covering the visible, near-infrared,
  and mid-infrared spectrum. New polarization-calibration strategies
  were developed to achieve the stringent polarization accuracy
  requirement of 5×10<SUP>−4</SUP>. Instruments can be combined and
  operated simultaneously in order to obtain a maximum of observational
  information. Observing time on DKIST is allocated through an open,
  merit-based proposal process. DKIST will be operated primarily in
  "service mode" and is expected to on average produce 3 PB of raw
  data per year. A newly developed data center located at the NSO
  Headquarters in Boulder will initially serve fully calibrated data to
  the international users community. Higher-level data products, such as
  physical parameters obtained from inversions of spectro-polarimetric
  data will be added as resources allow.

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

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

Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
    the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
   R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
   Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
   Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
   Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
   Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
   Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
Bibcode: 2018AAS...23231601R
Altcode:
  The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
  construction on Haleakala, Maui will be the world’s largest solar
  telescope. Designed to meet the needs of critical high resolution and
  high sensitivity spectral and polarimetric observations of the sun,
  this facility will perform key observations of our nearest star that
  matters most to humankind. DKIST’s superb resolution and sensitivity
  will enable astronomers to address many of the fundamental problems
  in solar and stellar astrophysics, including the origin of stellar
  magnetism, the mechanisms of coronal heating and drivers of the
  solar wind, flares, coronal mass ejections and variability in solar
  and stellar output. DKIST will also address basic research aspects of
  Space Weather and help improve predictive capabilities. In combination
  with synoptic observations and theoretical modeling DKIST will unravel
  the many remaining mysteries of the Sun.The construction of DKIST is
  progressing on schedule with 80% of the facility complete. Operations
  are scheduled to begin early 2020. DKIST will replace the NSO
  facilities on Kitt Peak and Sac Peak with a national facility with
  worldwide unique capabilities. The design allows DKIST to operate as
  a coronagraph. Taking advantage of its large aperture and infrared
  polarimeters DKIST will be capable to routinely measure the currently
  illusive coronal magnetic fields. The state-of-the-art adaptive optics
  system provides diffraction limited imaging and the ability to resolve
  features approximately 20 km on the Sun. Achieving this resolution
  is critical for the ability to observe magnetic structures at their
  intrinsic, fundamental scales. Five instruments will be available at
  the start of operations, four of which will provide highly sensitive
  measurements of solar magnetic fields throughout the solar atmosphere
  - from the photosphere to the corona. The data from these instruments
  will be distributed to the world wide community via the NSO/DKIST data
  center located in Boulder. We present examples of science objectives
  and provide an overview of the facility and project status, including
  the ongoing efforts of the community to develop the critical science
  plan for the first 2-3 years of operations.

Title: Facilities for High Resolution Imaging of the Sun
Authors: von der Lühe, Oskar
Bibcode: 2018iss..confE..43V
Altcode:
  The Sun is the only star where physical processes can be observed
  at their intrinsic spatial scales. Even though the Sun in a mere 150
  million km from Earth, it is difficult to resolve fundamental processes
  in the solar atmosphere, because they occur at scales of the order
  of the kilometer. They can be observed only with telescopes which
  have apertures of several meters. The current state-of-the-art are
  solar telescopes with apertures of 1.5 m which resolve 50 km on the
  solar surface, soon to be superseded by telescopes with 4 m apertures
  with 20 km resolution. The US American 4 m DSI Solar Telescope is
  currently constructed on Maui, Hawaii, and is expected to have first
  light in 2020. The European solar community collaborates intensively
  to pursue the 4 m European Solar Telescope with a construction start
  in the Canaries early in the next decade. Solar telescopes with
  slightly smaller are also in the planning by the Russian, Indian
  and Chinese communities. In order to achieve a resolution which
  approaches the diffraction limit, all modern solar telescopes use
  adaptive optics which compensates virtually any scene on the solar
  disk. Multi-conjugate adaptive optics designed to compensate fields
  of the order on one minute of arc have been demonstrated and will
  become a facility feature of the new telescopes. The requirements for
  high precision spectro-polarimetry - about one part in 104 - makes
  continuous monitoring of (MC)AO performance and post-processing image
  reconstruction methods a necessity.

Title: Franz-Ludwig Deubner (1934 - 2017)
Authors: Fleck, Bernhard; von der Lühe, Oskar
Bibcode: 2017SoPh..292..178F
Altcode:
  No abstract at ADS

Title: Simulation algorithm to model the visible tunable filter for
    the Daniel K. Inouye Solar Telescope
Authors: Schubert, Matthias; Kentischer, Thomas; von der Lühe, Oskar
Bibcode: 2017JATIS...3d5002S
Altcode:
  The visible tunable filter is an imaging spectropolarimeter for solar
  observations in visible light. The instrument consists of several
  Fabry-Pérot interferometers (FPIs), a polarization modulator, and a
  prefilter. It will be one of the first light instruments for the Daniel
  K. Inouye Solar Telescope (DKIST) on Haleakaláa, Maui, Hawaii. We
  have developed simulation algorithms to describe the instrument
  and its impact on scientific observations. Our aim is to study the
  expected measurement accuracy and to test calibration algorithms. A
  well-known problem is the surface quality of the glass plates for each
  FPI. We developed algorithms to describe the influence of a surface
  microroughness, reflectivity, and figure errors of the individual
  FPI plates, and the expected total photon flux for scientific data
  acquisition. This tool is used to derive the limits for manufacturing
  processes to achieve the measurement accuracy required for science
  observations with DKIST.

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

Title: Clear widens the field for observations of the Sun with
    multi-conjugate adaptive optics
Authors: Schmidt, Dirk; Gorceix, Nicolas; Goode, Philip R.; Marino,
   Jose; Rimmele, Thomas; Berkefeld, Thomas; Wöger, Friedrich; Zhang,
   Xianyu; Rigaut, François; von der Lühe, Oskar
Bibcode: 2017A&A...597L...8S
Altcode:
  The multi-conjugate adaptive optics (MCAO) pathfinder Clear
  on the New Solar Telescope in Big Bear Lake has provided the
  first-ever MCAO-corrected observations of the Sun that show a
  clearly and visibly widened corrected field of view compared to
  quasi-simultaneous observations with classical adaptive optics (CAO)
  correction. Clear simultaneously uses three deformable mirrors, each
  conjugated to a different altitude, to compensate for atmospheric
  turbulence. While the MCAO correction was most effective over an
  angle that is approximately three times wider than the angle that was
  corrected by CAO, the full 53'' field of view did benefit from MCAO
  correction. We further demonstrate that ground-layer-only correction
  is attractive for solar observations as a complementary flavor of
  adaptive optics for observational programs that require homogenous
  seeing improvement over a wide field rather than diffraction-limited
  resolution. We show illustrative images of solar granulation and
  of a sunspot obtained on different days in July 2016, and present a
  brief quantitative analysis of the generalized Fried parameters of
  the images. <P />The movies associated to Fig. 1 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201629970/olm">http://www.aanda.org</A>

Title: Micro-meteorological contribution to the SHABAR seeing
    retrieval
Authors: Hartogensis, Oscar; Hammerschlag, Robert; Sliepen, Guus;
   Sprung, Detlev; von der Lühe, Oskar; Collados, Manuel
Bibcode: 2017psio.confE.102H
Altcode:
  No abstract at ADS

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

Title: Deep probing of the photospheric sunspot penumbra: no evidence
    of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
   Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
   Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
   O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
   Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
   Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
Bibcode: 2016A&A...596A...2B
Altcode: 2016arXiv160708165B
  Context. Some models for the topology of the magnetic field in
  sunspot penumbrae predict regions free of magnetic fields or with
  only dynamically weak fields in the deep photosphere. <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.

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

Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
   Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
   T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
   Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
   A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
Bibcode: 2016A&A...596A...4F
Altcode: 2016arXiv160800513F
  Context. A significant part of the penumbral magnetic field returns
  below the surface in the very deep photosphere. For lines in the
  visible, a large portion of this return field can only be detected
  indirectly by studying its imprints on strongly asymmetric and
  three-lobed Stokes V profiles. Infrared lines probe a narrow layer
  in the very deep photosphere, providing the possibility of directly
  measuring the orientation of magnetic fields close to the solar
  surface. <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.

Title: Horizontal flow fields in and around a small active region. The
    transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
   Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
   A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
   A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
   Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
   M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
   K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A...3V
Altcode: 2016arXiv160507462V
  Context. The solar magnetic field is responsible for all aspects
  of solar activity. Thus, emergence of magnetic flux at the surface
  is the first manifestation of the ensuing solar activity. <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.

Title: Upper chromospheric magnetic field of a sunspot penumbra:
    observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
   M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
   H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
   Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
   O.; Waldmann, T.
Bibcode: 2016A&A...596A...8J
Altcode: 2016arXiv160801988J
  <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.

Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
   Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
   Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
   Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
   T.; Kneer, F.; Nicklas, H.; Sobotka, M.
Bibcode: 2016A&A...596A...7S
Altcode: 2016arXiv160707094S
  Context. The various mechanisms of magneto-convective energy transport
  determine the structure of sunspots and active regions. <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.
Bibcode: 2016A&A...596A...6L
Altcode: 2016arXiv160506324L
  Context. Investigations of the magnetism of the quiet Sun are hindered
  by extremely weak polarization signals in Fraunhofer spectral
  lines. Photon noise, straylight, and the systematically different
  sensitivity of the Zeeman effect to longitudinal and transversal
  magnetic fields result in controversial results in terms of the strength
  and angular distribution of the magnetic field vector. <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.
Bibcode: 2016AN....337.1090V
Altcode:
  Improved measurements of the photospheric and chromospheric
  three-dimensional magnetic and flow fields are crucial for a precise
  determination of the origin and evolution of active regions. We present
  an illustrative sample of multi-instrument data acquired during a
  two-week coordinated observing campaign in August 2015 involving,
  among others, the GREGOR solar telescope (imaging and near-infrared
  spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
  and Interface Region Imaging Spectrograph (IRIS). The observations
  focused on the trailing part of active region NOAA 12396 with complex
  polarity inversion lines and strong intrusions of opposite polarity
  flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
  spectral profiles in the photospheric Si I λ1082.7 nm line, the
  chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
  λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
  provided maps of Doppler velocity and magnetic field at different
  atmospheric heights. We compare quick-look maps with those obtained
  with the ``Stokes Inversions based on Response functions'' (SIR)
  code, which furnishes deeper insight into the magnetic properties
  of the region. We find supporting evidence that newly emerging flux
  and intruding opposite polarity flux are hampering the formation
  of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
  expected after cessation of flux emergence in proximity to the sunspots.

Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
   Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
   Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
   Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
   R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
   S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
   von der Lühe, O.; Waldmann, T.
Bibcode: 2016A&A...596A..59F
Altcode: 2016arXiv161104803F
  Context. Active regions are the most prominent manifestations of solar
  magnetic fields; their generation and dissipation are fundamental
  problems in solar physics. Light bridges are commonly present during
  sunspot decay, but a comprehensive picture of their role in the
  removal of the photospheric magnetic field is still lacking. <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.
Bibcode: 2016A&A...596A...5M
Altcode: 2018arXiv180410089M
  Context. Over the past 20 yr, the quietest areas of the solar surface
  have revealed a weak but extremely dynamic magnetism occurring
  at small scales (&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.
Bibcode: 2016AN....337.1057G
Altcode: 2016arXiv160300679G
  The new generation of solar instruments provides better
  spectral, spatial, and temporal resolution for a better
  understanding of the physical processes that take place on the
  Sun. Multiple-component profiles are more commonly observed with these
  instruments. Particularly, the He I 10830 Å triplet presents such
  peculiar spectral profiles, which give information on the velocity
  and magnetic fine structure of the upper chromosphere. The purpose
  of this investigation is to describe a technique to efficiently fit
  the two blended components of the He I 10830 Å triplet, which are
  commonly observed when two atmospheric components are located within
  the same resolution element. The observations used in this study were
  taken on 2015 April 17 with the very fast spectroscopic mode of the
  GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
  telescope, located at the Observatorio del Teide, Tenerife, Spain. We
  apply a double-Lorentzian fitting technique using Levenberg-Marquardt
  least-squares minimization. This technique is very simple and much
  faster than inversion codes. Line-of-sight Doppler velocities can
  be inferred for a whole map of pixels within just a few minutes. Our
  results show sub- and supersonic downflow velocities of up to 32 km
  s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
  filamentary structures. The slow component presents velocities close
  to rest.

Title: Development of high reflectivity coatings for large format
    Fabry-Perot etalons
Authors: Sigwarth, M.; Baumgartner, J.; Bell, A.; Cagnoli, G.; Fischer,
   A.; Halbgewachs, C.; Heidecke, F.; Kentischer, Th. J.; Kestner, B.;
   Kuschnir, P.; von der Lühe, O.; Pinard, L.; Michel, Ch.; Reichman,
   W. J.; Sassolas, B.; Scheiffelen, Th.; Schmidt, W.
Bibcode: 2016SPIE.9908E..4FS
Altcode:
  The Visible Tunable Filter (VTF) is a diffraction-limited narrowband
  tunable instrument for imaging spectropolarimetry in the wavelength
  range between 520 and 860 nm. It is based on large-format Fabry
  Perot. The instrument will be one of the first-light instruments of
  the 4m aperture Daniel K. Inoue Solar Telescope (DKIST). To provide a
  field of view of 1 arcmin and a spectral resolution λ/Δλ of about
  100.000, the required free aperture of the Fabry Perot is 250mm. The
  high reflectivity coatings for the Etalon plates need to meet the
  specifications for the reflectivity over the entire wavelength range
  and preserve the plate figure specifications of better λ/300, and
  a micro roughness of &lt; 0.4 nm rms. Coated surfaces with similar
  specifications have successfully been made for reflecting mirrors on
  thick substrates but not for larger format Fabry-Perot systems. Ion Beam
  Sputtering (IBS) based coatings provide stable, homogeneous, and smooth
  coatings. But IBS coatings also introduce stresses to the substrate
  that influence the plate figure in our case at the nm level. In a joint
  effort with an industry partner and a French CNRS research laboratory,
  we developed and tested processes on small and full size substrates,
  to provide coated Etalon plates to the required specifications. Zygo
  Extreme Precision Optics, Richmond, CA, USA, is polishing and figuring
  the substrates, doing the metrology and FE analysis. LMA (Laboratoire
  Matériaux Avancés, Lyon, France) is designing and making the IBS
  coatings and investigating the detailed behavior of the coatings and
  related processes. Both partners provide experience from manufacturing
  coated plane optics for gravitational wave detection experiments
  and EUV optics. The Kiepenheuer-Institut für Sonnenphysik, Freiburg,
  Germany is designing and building the VTF instrument and is leading the
  coating development. We present the characteristics of the coatings
  and the substrate processing concept, as well as results from tests
  on sample size and from full size substrate processing. We demonstrate
  that the tight specifications for a single Etalon can be reached.

Title: End-to-end simulations of the visible tunable filter for the
    Daniel K. Inouye Solar Telescope
Authors: Schmidt, Wolfgang; Schubert, Matthias; Ellwarth, Monika;
   Baumgartner, Jörg; Bell, Alexander; Fischer, Andreas; Halbgewachs,
   Clemens; Heidecke, Frank; Kentischer, Thomas; von der Lühe, Oskar;
   Scheiffelen, Thomas; Sigwarth, Michael
Bibcode: 2016SPIE.9908E..4NS
Altcode: 2016arXiv160706767S
  The Visible Tunable Filter (VTF) is a narrowband tunable filter system
  for imaging spectroscopy and spectropolarimetry based. The instrument
  will be one of the first-light instruments of the Daniel K. Inouye Solar
  Telescope that is currently under construction on Maui (Hawaii). The
  VTF is being developed by the Kiepenheuer Institut fuer Sonnenphysik in
  Freiburg as a German contribution to the DKIST. We perform end-to-end
  simulations of spectropolarimetric observations with the VTF to
  verify the science requirements of the instrument. The instrument
  is simulated with two Etalons, and with a single Etalon. The clear
  aperture of the Etalons is 250 mm, corresponding to a field of view with
  a diameter of 60 arcsec in the sky (42,000 km on the Sun). To model
  the large-scale figure errors we employ low-order Zernike polynomials
  (power and spherical aberration) with amplitudes of 2.5 nm RMS. We use
  an ideal polarization modulator with equal modulation coefficients
  of 3<SUP>-1/2</SUP> for the polarization modulation We synthesize
  Stokes profiles of two iron lines (630.15 nm and 630.25 nm) and for
  the 854.2 nm line of calcium, for a range of magnetic field values
  and for several inclination angles. We estimated the photon noise on
  the basis of the DKIST and VTF transmission values, the atmospheric
  transmission and the spectral flux from the Sun. For the Fe 630.25 nm
  line, we obtain a sensitivity of 20 G for the longitudinal component
  and for 150 G for the transverse component, in agreement with the
  science requirements for the VTF.

Title: Qualification of HEIDENHAIN linear encoders for picometer
    resolution metrology in VTF Etalons
Authors: Halbgewachs, Clemens; Kentischer, Thomas J.; Sändig, Karsten;
   Baumgartner, Joerg; Bell, Alexander; Fischer, Andreas; Funk, Stefan;
   Heidecke, Frank; Scheiffelen, Thomas; Schmidt, Wolfgang; Spanner,
   Erwin; Speckbacher, Peter; von der Lühe, Oskar F.
Bibcode: 2016SPIE.9908E..4HH
Altcode:
  The Visible Tunable Filter (VTF) is a narrowband tunable instrument
  for imaging spectropolarimetry in the wavelength range between 520 and
  870 nm. It is based on large-format Fabry Perots with a free aperture
  of 250 mm. The instrument will be one of the first-light instruments
  of the 4 m aperture Daniel K. Inoue Solar Telescope (DKIST) that is
  currently under construction on Maui (Hawaii). To provide stable and
  repeatable spectral scanning by tuning the air gap distance of the
  Etalons, a metrology system with 20 pm resolution and drift stability
  of better 100 pm per hour is needed. The integration of the metrology
  system must preserve the tight optical specifications of the Etalon
  plates. The HEIDENHAIN LIP 382 linear encoder system has a selected
  linear scale for low noise high signal interpolation. The signal period
  is 128nm and the interpolated signal from the sensor can be read out
  at 128 nm/ 14 bit = 7.8125 pm. To qualify the LIP 382 system for the
  VTF, we investigated the resolution and stability under nominal VTF
  operation conditions and verified a mounting concept for the sensor
  heads. We present results that demonstrate that the LIP 382 system
  fulfills the requirements for the VTF Etalons. We also present a design
  for the sensor head mounts.

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

Title: DKIST visible tunable filter control software: connecting
    the DKIST framework to OPC UA
Authors: Bell, Alexander; Halbgewachs, Clemens; Kentischer, Thomas J.;
   Schmidt, Wolfgang; von der Lühe, Oskar; Sigwarth, Michael; Fischer,
   Andreas
Bibcode: 2014SPIE.9152E..1DB
Altcode:
  The Visible Tunable Filter (VTF) is a narrowband tunable filter system
  for imaging spectroscopy and spectropolarimetry based on large-format
  Fabry Perot interferometers that is currently built by the Kiepenheuer
  Institut fuer Sonnenphysik for the Daniel K. Inouye Solar Telescope
  (DKIST). The control software must handle around 30 motorised drives,
  3 etalons, a polarizing modulator, a helium neon laser for system
  calibration, temperature controllers and a multitude of sensors. The
  VTF is foreseen as one of the DKISTs first-light instruments and should
  become operational in 2019. In the design of the control software
  we strongly separate between the high-level part interfacing to the
  DKIST common services framework (CSF) and the low-level control system
  software which guarantees real-time performance and synchronization
  to precision time protocol (PTP) based observatory time. For the
  latter we chose a programmable logic controller (PLC) from Beckhoff
  Automation GmbH which supports a wide set of input and output devices
  as well as distributed clocks for synchronizing signals down to the
  sub-microsecond level. In this paper we present the design of the
  required control system software as well as our work on extending the
  DKIST CSF to use the OPC Unified Architecture (OPC UA) standard which
  provides a cross-platform communication standard for process control
  and automation as an interface between the high-level software and
  the real-time control system.

Title: GREGOR MCAO looking at the Sun
Authors: Schmidt, Dirk; Berkefeld, Thomas; Heidecke, Frank; Fischer,
   Andreas; von der Lühe, Oskar; Soltau, Dirk
Bibcode: 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: A two-dimensional spectropolarimeter as a first-light
    instrument for the Daniel K. Inouye Solar Telescope
Authors: Schmidt, Wolfgang; Bell, Alexander; Halbgewachs, Clemens;
   Heidecke, Frank; Kentischer, Thomas J.; von der Lühe, Oskar;
   Scheiffelen, Thomas; Sigwarth, Michael
Bibcode: 2014SPIE.9147E..0ES
Altcode:
  The Visible Tunable Filter (VTF) is a narrowband tunable filter
  system for imaging spectropolarimetry. The instrument will be one of
  the first-light instruments of the Daniel K. Inouye Solar Telescope
  (DKIST) that is currently under construction on Maui (Hawaii). The
  DKIST has a clear aperture of 4 meters. The VTF is being developed by
  the Kiepenheuer Institut für Sonnenphysik in Freiburg, as a German
  contribution to the DKIST. The VTF is designed as a diffraction-limited
  narrowband tunable instrument for Stokes spectro-polarimetry
  in the wavelength range between 520 and 860 nm. The instrument
  uses large-format Fabry-Perot interferometers (Etalons) as tunable
  monochromators with clear apertures of about 240 mm. To minimize the
  influence of gravity on the interferometer plates, the Fabry-Perots
  are placed horizontally. This implies a complex optical design and a
  three-dimensional support structure instead of a horizontal optical
  bench. The VTF has a field of view of one arc minute squared. With
  4096x4096 pixel detectors, one pixel corresponds to an angle of 0.014"
  on the sky (10 x 10 km on the Sun). The spectral resolution is 6 pm at a
  wavelength of 600 nm. One 2Dspectrum with a polarimetric sensitivity of
  5E-3 will be recorded within 13 seconds. The wavelength range of the VTF
  includes a number of important spectral lines for the measurement flows
  and magnetic fields in the atmosphere of the Sun. The VTF uses three
  identical large-format detectors, two for the polarimetric measurements,
  and one for broadband filtergrams. The main scientific observables
  of the VTF are Stokes polarimetric images to retrieve the magnetic
  field configuration of the observed area, Doppler images to measure
  the line-of-sight flow in the solar photosphere, and monochromatic
  intensity filtergrams to study higher layers of the solar atmosphere.

Title: The Advanced Technology Solar Telescope: Science Drivers and
    Construction Status
Authors: Rimmele, Thomas; Berger, Thomas; McMullin, Joseph; Keil,
   Stephen; Goode, Phil; Knoelker, Michael; Kuhn, Jeff; Rosner, Robert;
   Casini, Roberto; Lin, Haosheng; Woeger, Friedrich; von der Luehe,
   Oskar; Tritschler, Alexandra; Atst Team
Bibcode: 2013EGUGA..15.6305R
Altcode:
  The 4-meter Advance Technology Solar Telescope (ATST) currently
  under construction on the 3000 meter peak of Haleakala on Maui,
  Hawaii will be the world's most powerful solar telescope and the
  leading ground-based resource for studying solar magnetism. The
  solar atmosphere is permeated by a 'magnetic carpet' that constantly
  reweaves itself to control solar irradiance and its effects on Earth's
  climate, the solar wind, and space weather phenomena such as flares and
  coronal mass ejections. Precise measurement of solar magnetic fields
  requires a large-aperture solar telescope capable of resolving a few
  tens of kilometers on the solar surface. With its 4 meter aperture,
  the ATST will for the first time resolve magnetic structure at the
  intrinsic scales of plasma convection and turbulence. The ATST's
  ability to perform accurate and precise spectroscopic and polarimetric
  measurements of magnetic fields in all layers of the solar atmosphere,
  including accurate mapping of the elusive coronal magnetic fields,
  will be transformative in advancing our understanding of the magnetic
  solar atmosphere. The ATST will utilize the Sun as an important astro-
  and plasma-physics "laboratory" demonstrating key aspects of omnipresent
  cosmic magnetic fields. The ATST construction effort is led by the US
  National Solar Observatory. State-of-the-art instrumentation will be
  constructed by US and international partner institutions. The technical
  challenges the ATST is facing are numerous and include the design of the
  off-axis main telescope, the development of a high order adaptive optics
  system that delivers a corrected beam to the instrument laboratory,
  effective handling of the solar heat load on optical and structural
  elements, and minimizing scattered light to enable observations
  of the faint corona. The ATST project has transitioned from design
  and development to its construction phase. The project has awarded
  design and fabrication contracts for major telescope subsystems. Site
  construction has commenced following the successful conclusion of
  the site permitting process. Science goals and construction status of
  telescope and instrument systems will be discussed.

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

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

Title: Gregor@night: The future high-resolution stellar spectrograph
    for the GREGOR solar telescope
Authors: Strassmeier, K. G.; Ilyin, I. V.; Woche, M.; Granzer,
   T.; Weber, M.; Weingrill, J.; Bauer, S. -M.; Popow, E.; Denker, C.;
   Schmidt, W.; von der Lühe, O.; Berdyugina, S.; Collados, M.; Koubsky,
   P.; Hackman, T.; Mantere, M. J.
Bibcode: 2012AN....333..901S
Altcode:
  We describe the future night-time spectrograph for the GREGOR solar
  telescope and present its science core projects. The spectrograph
  provides a 3-pixel resolution of up to R=87 000 in 45 échelle orders
  covering the wavelength range 390-900 nm with three grating settings. An
  iodine cell can be used for high-precision radial velocity work in the
  500-630 nm range. The operation of the spectrograph and the telescope
  will be fully automated without the presence of humans during night-time
  and will be based on the successful STELLA control system. Future
  upgrades include a second optical camera for even higher spectral
  resolution, a Stokes-V polarimeter and a link to the laser-frequency
  comb at the Vacuum Tower Telescope. The night-time core projects are a
  study of the angular-momentum evolution of ``The Sun in Time'' and a
  continuation of our long-term Doppler imaging of active stars.

Title: A retrospective of the GREGOR solar telescope in scientific
    literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
   Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
   Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
   Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
   M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
   Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
   Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
   T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..810D
Altcode: 2012arXiv1210.3167D
  In this review, we look back upon the literature, which had the
  GREGOR solar telescope project as its subject including science cases,
  telescope subsystems, and post-focus instruments. The articles date
  back to the year 2000, when the initial concepts for a new solar
  telescope on Tenerife were first presented at scientific meetings. This
  comprehensive bibliography contains literature until the year 2012,
  i.e., the final stages of commissioning and science verification. Taking
  stock of the various publications in peer-reviewed journals and
  conference proceedings also provides the ``historical'' context
  for the reference articles in this special issue of Astronomische
  Nachrichten/Astronomical Notes.

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

Title: The GREGOR adaptive optics system
Authors: Berkefeld , Th.; Schmidt, D.; Soltau, D.; von der Lühe,
   O.; Heidecke, F.
Bibcode: 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.

Title: Optical design of the new solar telescope GREGOR
Authors: Soltau, D.; Volkmer, R.; von der Lühe, O.; Berkefeld, Th.
Bibcode: 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.

Title: Editors' note
Authors: Denker, Carsten; Feller, Alex; Schmidt, Wolfgang; von der
   Lühe, Oskar
Bibcode: 2012AN....333....1D
Altcode:
  This topical issue of Astronomische Nachrichten/Astronomical Notes is a
  collection of reference articles covering the GREGOR solar telescope,
  its science capabilities, its subsystems, and its dedicated suite
  of instruments for high-resolution observations of the Sun. Because
  ground-based telescopes have life spans of several decades, it is
  only natural that they continuously reinvent themselves. Literally,
  the GREGOR telescope builds on the foundations of the venerable
  Gregory-Coudé Telescope (GCT) at Observatorio del Teide, Tenerife,
  Spain. Acknowledging the fact that new discoveries in observational
  solar physics are driven by larger apertures to collect more photons
  and to scrutinize the Sun in finer detail, the GCT was decommissioned
  and the building was made available to the GREGOR project.

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.
Bibcode: 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.

Title: The GREGOR Broad-Band Imager
Authors: von der Lühe, O.; Volkmer, R.; Kentischer, T. J.; Geißler,
   R.
Bibcode: 2012AN....333..894V
Altcode:
  The design and characteristics of the Broad-Band Imager (BBI) of
  GREGOR are described. BBI covers the visible spectral range with two
  cameras simultaneously for a large field and with critical sampling at
  390 nm, and it includes a mode for observing the pupil in a Foucault
  configuration. Samples of first-light observations are shown.

Title: GRIS: The GREGOR Infrared Spectrograph
Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes,
   M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg,
   A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier,
   K. G.; von der Lühe, O.; Volkmer, R.
Bibcode: 2012AN....333..872C
Altcode:
  This paper describes the main characteristics of GRIS (GREGOR Infrared
  Spectrograph), the grating spectrograph installed in the recently
  inaugurated (May 2012) 1.5-meter GREGOR telescope located at the
  Observatorio del Teide in Tenerife. The spectrograph has a standard
  Czerny-Turner configuration with parabolic collimator and camera mirrors
  that belong to the same conic surface. Although nothing prevents its
  use at visible wavelengths, the spectrograph will be initially used
  in combination with the infrared detector of the Tenerife Infrared
  Polarimeter (TIP-II) in standard spectroscopic mode as well as for
  spectropolarimetric measurements.

Title: The visible tunable filtergraph for the ATST
Authors: Kentischer, T. J.; Schmidt, W.; von der Lühe, O.; Sigwarth,
   M.; Bell, A.; Halbgewachs, C.; Fischer, A.
Bibcode: 2012SPIE.8446E..77K
Altcode:
  The Kiepenheuer-Institut will develop for the Advanced Technology Solar
  Telescope (ATST) a narrowband tunable filter system (Visible Tunable
  Filter, VTF) for imaging spectroscopy and spectropolarimetry based
  on large-format Fabry Perot interferometers. A major challenge for
  the realization of this instrument is the development of large-format
  Fabry-Perots with a free aperture of about 250 mm. The instrument will
  operate in the spectral range between 500 and 900 nm with access to
  a host of magnetically sensitive lines. The instrument is designed to
  match the diffraction limit of the 4m-aperture ATST and will be able to
  observe processes on the sun at spatial scales of 35 km. Its multi-line
  capability, together with a field of view of one arc minute, and the
  ability to measure polarization states of the incoming light allow
  to probe different layers of the solar atmosphere within a couple of
  seconds. The instrument is capable to vary the spectral sampling, the
  integration time, and the temporal cadence over a wide range without
  changing or compromising the opto-mechanical setup. This versatility
  gives unique possibilities to apply different measurement schemes to a
  variety of science questions. The ATST is a fully funded US project,
  with the VTF as the only non-US contribution, and is ready to start
  construction at the Haleakala summit. The VTF is foreseen as one of
  the ATST's firstlight instruments and should become operational in 2018.

Title: Point Spread Function Estimation Using Speckle Reconstructions
    of Solar Surface Images
Authors: Waldmann, T. A.; von der Lühe, O.
Bibcode: 2010SoPh..267..217W
Altcode: 2010SoPh..tmp..169W
  We present a method for retrieving the wavefront phase and estimating
  the point spread function using data from a single imaging channel. The
  method involves a set of short exposures and its speckle reconstruction
  of the observed object, and a parameterized point spread function model
  which is used in order to estimate the wavefront phase and the point
  spread function from the data. Estimates of the wavefront phase and the
  point spread function are computed by minimizing an error function with
  the method of simulated annealing. Results of tests with simulated data
  and with real data are shown. We conclude that the proposed technique
  provides reliable estimates of the instantaneous point spread function
  and is robust against noise.

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

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

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

Title: 2.1 Solar telescopes
Authors: von der Lühe, Oskar
Bibcode: 2010LanB...4A..210V
Altcode:
  This document is part of Subvolume A 'Instruments and Methods' of Volume
  4 'Astronomy, Astrophysics, and Cosmology' of Landolt-Börnstein -
  Group VI 'Astronomy and Astrophysics'.

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.
Bibcode: 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: History of solar telescopes
Authors: von der Lühe, Oskar
Bibcode: 2009ExA....25..193V
Altcode: 2009ExA...tmp...36V
  Solar observations have been done with telescopes since their
  invention—already Galileo looked at the Sun. Despite the
  Sun’s unusual brightness, telescopes which specialize in solar
  observations are fairly recent, dating from the late nineteenth century
  onwards. Today, many solar telescopes have rather little in common with
  nighttime telescopes. They are adapted to high light flux, a limited
  range of declination, and to the specifications of solar spectrographs
  and polarimeters. This paper presents the history of the modern optical
  solar telescope on the ground and in space, the accompanying evolution
  of scientific capabilities, and a brief outlook into the future.

Title: Comparison of geometrical mapping for ring diagram analysis
Authors: Zaatri, Amel; Corbard, Thierry; Roth, Markus; González
   Hernández, Irene; von der Lühe, Oskar
Bibcode: 2008JPhCS.118a2090Z
Altcode:
  Mapping the solar surface is a crucial step in any local helioseismology
  technique. Because the acoustic waves propagate along great circles at
  the solar surface, it has been shown that these circles need to be used
  in the geometrical construction of the plane grid. We study different
  types of projections based on great circles for the calculation of
  sub-surface flows from ring diagram analysis of GONG data. Azimuthal
  equidistant projection, transverse cylindrical projection, gnomonic
  projection and stereographic projection produce almost the same velocity
  fields with standard patch sizes (15°x 15°). The difference between
  the four projections is more noticeable when larger patches (30° x
  30°) are used.

Title: Cross-spectral analysis of solar oscillation time series
Authors: Schad, Ariane; Roth, Markus; Schelter, Björn; von der Lühe,
   Oskar; Timmer, Jens
Bibcode: 2008JPhCS.118a2091S
Altcode:
  Spatial leakage is an unavoidable artifact in the extraction of solar
  oscillation modes by spheric harmonic decomposition from the wavefield
  observed on the solar surface. The determination of solar frequencies by
  spectral analysis is therefore greatly affected by spatial leakage. Here
  we show in which way spatial leakage also influences the cross-spectra
  between different solar oscillation modes. Simulations show that
  spatial leakage induces significant coherences between oscillations
  of degree I and I + 2 with low azimuthal order m.

Title: Calculation of Spectral Darkening and Visibility Functions
    for Solar Oscillations
Authors: Nutto, C.; Roth, M.; Zhugzhda, Y.; Bruls, J.; von der
   Lühe, O.
Bibcode: 2008SoPh..251..179N
Altcode: 2008SoPh..tmp...63N; 2008arXiv0803.1228N
  Calculations of spectral darkening and visibility functions for
  the brightness oscillations of the Sun resulting from global solar
  oscillations are presented. This has been done for a broad range of
  the visible and infrared continuum spectrum. The procedure for the
  calculations of these functions includes the numerical computation of
  depth-dependent derivatives of the opacity caused by p modes in the
  photosphere. A radiative-transport code was used for this purpose to
  get the disturbances of the opacities from temperature and density
  fluctuations. The visibility and darkening functions are obtained
  for adiabatic oscillations under the assumption that the temperature
  disturbances are proportional to the undisturbed temperature of the
  photosphere. The latter assumption is the only way to explore any
  opacity effects since the eigenfunctions of p-mode oscillations have not
  been obtained so far. This investigation reveals that opacity effects
  have to be taken into account because they dominate the violet and
  infrared part of the spectrum. Because of this dominance, the visibility
  functions are negative for those parts of the spectrum. Furthermore,
  the darkening functions show a wavelength-dependent change of sign
  for some wavelengths owing to these opacity effects. However, the
  visibility and darkening functions under the assumptions used contradict
  the observations of global p-mode oscillations, but it is beyond doubt
  that the opacity effects influence the brightness fluctuations of the
  Sun resulting from global oscillations.

Title: Speckle interferometry with adaptive optics corrected
    solar data
Authors: Wöger, F.; von der Lühe, O.; Reardon, K.
Bibcode: 2008A&A...488..375W
Altcode:
  Context: Adaptive optics systems are used on several advanced solar
  telescopes to enhance the spatial resolution of the recorded data. In
  all cases, the correction remains only partial, requiring post-facto
  image reconstruction techniques such as speckle interferometry
  to achieve consistent, near-diffraction limited resolution. <BR
  />Aims: This study investigates the reconstruction properties of
  the Kiepenheuer-Institut Speckle Interferometry Package (KISIP)
  code, with focus on its phase reconstruction capabilities and
  photometric accuracy. In addition, we analyze its suitability for
  real-time reconstruction. <BR />Methods: We evaluate the KISIP
  program with respect to its scalability and the convergence of
  the implemented algorithms with dependence on several parameters,
  such as atmospheric conditions. To test the photometric accuracy of
  the final reconstruction, comparisons are made between simultaneous
  observations of the Sun using the ground-based Dunn Solar Telescope and
  the space-based Hinode/SOT telescope. <BR />Results: The analysis shows
  that near real-time image reconstruction with high photometric accuracy
  of ground-based solar observations is possible, even for observations in
  which an adaptive optics system was utilized to obtain the speckle data.

Title: Metallicity and ages of selected G-K giants
Authors: Pasquini, L.; Döllinger, M.; Setiawan, J.; Hatzes, A.;
   Girardi, L.; da Silva, L.; de Medeiros, J. R.; Weiss, A.; von der
   Lühe, O.
Bibcode: 2008mru..conf..132P
Altcode:
  No abstract at ADS

Title: Planets Around Active Stars
Authors: Setiawan, J.; Weise, P.; Henning, Th.; Hatzes, A. P.;
   Pasquini, L.; da Silva, L.; Girardi, L.; von der Lühe, O.; Döllinger,
   M. P.; Weiss, A.; Biazzo, K.
Bibcode: 2008psa..conf..201S
Altcode: 2007arXiv0704.2145S
  We present the results of radial velocity measurements of two samples
  of active stars. The first sample contains field G and K giants across
  the Red Giant Branch, whereas the second sample consists of nearby
  young stars (d &lt; 150 pc) with ages between 10 and 300 Myrs. The
  radial velocity monitoring program has been carried out with FEROS at
  1.52 m ESO telescope (1999 - 2002) and continued since 2003 at 2.2
  m MPG/ESO telescope. We observed stellar radial velocity variations
  which originate either from the stellar activity or the presence of
  stellar/substellar companions. By means of a bisector technique we are
  able to distinguish the sources of the radial velocity variation. Among
  them we found few candidates of planetary companions, both of young
  stars and G-K giants sample.

Title: Field dependent amplitude calibration of adaptive optics
    supported solar speckle imaging
Authors: Wöger, Friedrich; von der Lühe, Oskar
Bibcode: 2007ApOpt..46.8015W
Altcode:
  Adaptive optics supported solar speckle imaging requires the calibration
  of the source's Fourier amplitudes with the transfer function of
  atmosphere and optics. We present analytical models for the relevant
  transfer functions of an adaptive optics systems. The models include
  the effect of an arbitrary correction as well as anisoplanatism. The
  proposed models have been compared with observational data using
  measurements of α-Orionis and of the solar surface delivering both
  a direct and indirect method (using the spectral ratio technique)
  for validation. We find that measurements and model agree to a
  satisfactory degree.

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

Title: AMBER, the near-infrared spectro-interferometric
    three-telescope VLTI instrument
Authors: Petrov, R. G.; Malbet, F.; Weigelt, G.; Antonelli, P.;
   Beckmann, U.; Bresson, Y.; Chelli, A.; Dugué, M.; Duvert, G.;
   Gennari, S.; Glück, L.; Kern, P.; Lagarde, S.; Le Coarer, E.; Lisi,
   F.; Millour, F.; Perraut, K.; Puget, P.; Rantakyrö, F.; Robbe-Dubois,
   S.; Roussel, A.; Salinari, P.; Tatulli, E.; Zins, G.; Accardo, M.;
   Acke, B.; Agabi, K.; Altariba, E.; Arezki, B.; Aristidi, E.; Baffa,
   C.; Behrend, J.; Blöcker, T.; Bonhomme, S.; Busoni, S.; Cassaing,
   F.; Clausse, J. -M.; Colin, J.; Connot, C.; Delboulbé, A.; Domiciano
   de Souza, A.; Driebe, T.; Feautrier, P.; Ferruzzi, D.; Forveille,
   T.; Fossat, E.; Foy, R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.;
   Gil, C.; Glentzlin, A.; Heiden, M.; Heininger, M.; Hernandez Utrera,
   O.; Hofmann, K. -H.; Kamm, D.; Kiekebusch, M.; Kraus, S.; Le Contel,
   D.; Le Contel, J. -M.; Lesourd, T.; Lopez, B.; Lopez, M.; Magnard,
   Y.; Marconi, A.; Mars, G.; Martinot-Lagarde, G.; Mathias, P.; Mège,
   P.; Monin, J. -L.; Mouillet, D.; Mourard, D.; Nussbaum, E.; Ohnaka,
   K.; Pacheco, J.; Perrier, C.; Rabbia, Y.; Rebattu, S.; Reynaud, F.;
   Richichi, A.; Robini, A.; Sacchettini, M.; Schertl, D.; Schöller,
   M.; Solscheid, W.; Spang, A.; Stee, P.; Stefanini, P.; Tallon, M.;
   Tallon-Bosc, I.; Tasso, D.; Testi, L.; Vakili, F.; von der Lühe,
   O.; Valtier, J. -C.; Vannier, M.; Ventura, N.
Bibcode: 2007A&A...464....1P
Altcode:
  Context: Optical long-baseline interferometry is moving a crucial
  step forward with the advent of general-user scientific instruments
  that equip large aperture and hectometric baseline facilities,
  such as the Very Large Telescope Interferometer (VLTI). <BR />Aims:
  AMBER is one of the VLTI instruments that combines up to three beams
  with low, moderate and high spectral resolutions in order to provide
  milli-arcsecond spatial resolution for compact astrophysical sources
  in the near-infrared wavelength domain. Its main specifications are
  based on three key programs on young stellar objects, active galactic
  nuclei central regions, masses, and spectra of hot extra-solar
  planets. <BR />Methods: These key science goals led to scientific
  specifications, which were used to propose and then validate the
  instrument concept. AMBER uses single-mode fibers to filter the entrance
  signal and to reach highly accurate, multiaxial three-beam combination,
  yielding three baselines and a closure phase, three spectral dispersive
  elements, and specific self-calibration procedures. <BR />Results: The
  AMBER measurements yield spectrally dispersed calibrated visibilities,
  color-differential complex visibilities, and a closure phase allows
  astronomers to contemplate rudimentary imaging and highly accurate
  visibility and phase differential measurements. AMBER was installed
  in 2004 at the Paranal Observatory. We describe here the present
  implementation of the instrument in the configuration with which the
  astronomical community can access it. <BR />Conclusions: .After two
  years of commissioning tests and preliminary observations, AMBER has
  produced its first refereed publications, allowing assessment of its
  scientific potential.

Title: Estimating the solar meridional circulation by normal mode
    decomposition
Authors: Krieger, L.; Roth, M.; von der Lühe, O.
Bibcode: 2007AN....328..252K
Altcode: 2008arXiv0811.0693K
  The objective of this article is to use Fourier-Hankel decomposition as
  suggested earlier by Braun &amp; Fan (1998) to estimate the integrated
  horizontal meridional flow velocity as a function of mode penetration
  depth, and to find ways of potentially improve this technique. We use
  a time series of 43200 (30 days) consecutive full-disk Dopplergrams
  obtained by the MDI (Michelson Doppler Imager) instrument aboard the
  SOHO (Solar Heliospheric Observatory) spacecraft in April 1999. We
  find averaged meridional flow estimates of 15 m/s for modes with a
  penetration depth in the upper 20 Mm of the solar convection zone. This
  reproduces the results of the earlier investigations. Moreover we
  conclude that this method has the potential to become a new technique
  to measure the meridional circulation in the deep convection zone,
  if some improvements will be applied.

Title: An asymmetry detected in the disk of <ASTROBJ>κ Canis
    Majoris</ASTROBJ> with AMBER/VLTI
Authors: Meilland, A.; Millour, F.; Stee, P.; Domiciano de Souza, A.;
   Petrov, R. G.; Mourard, D.; Jankov, S.; Robbe-Dubois, S.; Spang, A.;
   Aristidi, E.; Antonelli, P.; Beckmann, U.; Bresson, Y.; Chelli, A.;
   Dugué, M.; Duvert, G.; Gennari, S.; Glück, L.; Kern, P.; Lagarde,
   S.; Le Coarer, E.; Lisi, F.; Malbet, F.; Perraut, K.; Puget, P.;
   Rantakyrö, F.; Roussel, A.; Tatulli, E.; Weigelt, G.; Zins, G.;
   Accardo, M.; Acke, B.; Agabi, K.; Altariba, E.; Arezki, B.; Baffa,
   C.; Behrend, J.; Blöcker, T.; Bonhomme, S.; Busoni, S.; Cassaing,
   F.; Clausse, J. -M.; Colin, J.; Connot, C.; Delboulbé, A.; Driebe,
   T.; Feautrier, P.; Ferruzzi, D.; Forveille, T.; Fossat, E.; Foy,
   R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.; Gil, C.; Glentzlin,
   A.; Heiden, M.; Heininger, M.; Hernandez Utrera, O.; Hofmann, K. -H.;
   Kamm, D.; Kiekebusch, M.; Kraus, S.; Le Contel, D.; Le Contel, J. -M.;
   Lesourd, T.; Lopez, B.; Lopez, M.; Magnard, Y.; Marconi, A.; Mars, G.;
   Martinot-Lagarde, G.; Mathias, P.; Mège, P.; Monin, J. -L.; Mouillet,
   D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.; Perrier, C.; Rabbia, Y.;
   Rebattu, S.; Reynaud, F.; Richichi, A.; Robini, A.; Sacchettini, M.;
   Schertl, D.; Schöller, M.; Solscheid, W.; Stefanini, P.; Tallon,
   M.; Tallon-Bosc, I.; Tasso, D.; Testi, L.; Vakili, F.; von der Lühe,
   O.; Valtier, J. -C.; Vannier, M.; Ventura, N.
Bibcode: 2007A&A...464...73M
Altcode: 2006astro.ph.11563M
  Aims:We study the geometry and kinematics of the circumstellar
  environment of the Be star κ CMa in the Brγ emission line and its
  nearby continuum. <BR />Methods: We use the AMBER/VLTI instrument
  operating in the K band, which provides a spatial resolution of about 6
  mas with a spectral resolution of 1500, to study the kinematics within
  the disk and to infer its rotation law. To obtain more kinematical
  constraints we also use a high spectral resolution Paβ line profile
  obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and
  we compile V/R line profile variations and spectral energy distribution
  data points from the literature. <BR />Results: Using differential
  visibilities and differential phases across the Brγ line we detect an
  asymmetry in the disk. Moreover, we found that κ CMa seems difficult to
  fit within the classical scenario for Be stars, illustrated recently
  by α Arae observations, i.e. a fast rotating B star close to its
  breakup velocity surrounded by a Keplerian circumstellar disk with
  an enhanced polar wind. We discuss the possibility that κ CMa is a
  critical rotator with a Keplerian rotating disk and examine whether if
  the detected asymmetry can be interpreted within the “one-armed”
  viscous disk framework. <P />Based on observations collected at the
  European Southern Observatory, Paranal, Chile, within the guaranteed
  time programme 074.A-9025(A).

Title: Constraining the wind launching region in Herbig Ae stars:
    AMBER/VLTI spectroscopy of HD 104237
Authors: Tatulli, E.; Isella, A.; Natta, A.; Testi, L.; Marconi, A.;
   Malbet, F.; Stee, P.; Petrov, R. G.; Millour, F.; Chelli, A.; Duvert,
   G.; Antonelli, P.; Beckmann, U.; Bresson, Y.; Dugué, M.; Gennari, S.;
   Glück, L.; Kern, P.; Lagarde, S.; Le Coarer, E.; Lisi, F.; Perraut,
   K.; Puget, P.; Rantakyrö, F.; Robbe-Dubois, S.; Roussel, A.; Weigelt,
   G.; Zins, G.; Accardo, M.; Acke, B.; Agabi, K.; Altariba, E.; Arezki,
   B.; Aristidi, E.; Baffa, C.; Behrend, J.; Blöcker, T.; Bonhomme,
   S.; Busoni, S.; Cassaing, F.; Clausse, J. -M.; Colin, J.; Connot,
   C.; Delboulbé, A.; Domiciano de Souza, A.; Driebe, T.; Feautrier,
   P.; Ferruzzi, D.; Forveille, T.; Fossat, E.; Foy, R.; Fraix-Burnet,
   D.; Gallardo, A.; Giani, E.; Gil, C.; Glentzlin, A.; Heiden, M.;
   Heininger, M.; Hernandez Utrera, O.; Hofmann, K. -H.; Kamm, D.;
   Kiekebusch, M.; Kraus, S.; Le Contel, D.; Le Contel, J. -M.; Lesourd,
   T.; Lopez, B.; Lopez, M.; Magnard, Y.; Mars, G.; Martinot-Lagarde,
   G.; Mathias, P.; Mège, P.; Monin, J. -L.; Mouillet, D.; Mourard,
   D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.; Perrier, C.; Rabbia, Y.;
   Rebattu, S.; Reynaud, F.; Richichi, A.; Robini, A.; Sacchettini, M.;
   Schertl, D.; Schöller, M.; Solscheid, W.; Spang, A.; Stefanini, P.;
   Tallon, M.; Tallon-Bosc, I.; Tasso, D.; Vakili, F.; von der Lühe,
   O.; Valtier, J. -C.; Vannier, M.; Ventura, N.
Bibcode: 2007A&A...464...55T
Altcode: 2006astro.ph..6684T
  Aims:We investigate the origin of the Brγ emission of the Herbig
  Ae star HD 104237 on Astronomical Unit (AU) scales. <BR />Methods:
  Using AMBER/VLTI at a spectral resolution R=1500 we spatially resolve
  the emission in both the Brγ line and the adjacent continuum. <BR
  />Results: The visibility does not vary between the continuum and the
  Brγ line, even though the line is strongly detected in the spectrum,
  with a peak intensity 35% above the continuum. This demonstrates that
  the line and continuum emission have similar size scales. We assume that
  the K-band continuum excess originates in a “puffed-up” inner rim
  of the circumstellar disk, and discuss the likely origin of Brγ. <BR
  />Conclusions: .We conclude that this emission most likely arises from
  a compact disk wind, launched from a region 0.2-0.5 AU from the star,
  with a spatial extent similar to that of the near infrared continuum
  emission region, i.e., very close to the inner rim location. <P />Based
  on observations collected at the European Southern Observatory, Paranal,
  Chile, within the guaranteed time programme 074.A-9025(A).

Title: Disk and wind interaction in the young stellar object
    <ASTROBJ>MWC 297</ASTROBJ> spatially resolved with AMBER/VLTI
Authors: Malbet, F.; Benisty, M.; de Wit, W. -J.; Kraus, S.; Meilland,
   A.; Millour, F.; Tatulli, E.; Berger, J. -P.; Chesneau, O.; Hofmann,
   K. -H.; Isella, A.; Natta, A.; Petrov, R. G.; Preibisch, T.; Stee,
   P.; Testi, L.; Weigelt, G.; Antonelli, P.; Beckmann, U.; Bresson, Y.;
   Chelli, A.; Dugué, M.; Duvert, G.; Gennari, S.; Glück, L.; Kern,
   P.; Lagarde, S.; Le Coarer, E.; Lisi, F.; Perraut, K.; Puget, P.;
   Rantakyrö, F.; Robbe-Dubois, S.; Roussel, A.; Zins, G.; Accardo,
   M.; Acke, B.; Agabi, K.; Altariba, E.; Arezki, B.; Aristidi, E.;
   Baffa, C.; Behrend, J.; Blöcker, T.; Bonhomme, S.; Busoni, S.;
   Cassaing, F.; Clausse, J. -M.; Colin, J.; Connot, C.; Delboulbé,
   A.; Domiciano de Souza, A.; Driebe, T.; Feautrier, P.; Ferruzzi, D.;
   Forveille, T.; Fossat, E.; Foy, R.; Fraix-Burnet, D.; Gallardo, A.;
   Giani, E.; Gil, C.; Glentzlin, A.; Heiden, M.; Heininger, M.; Hernandez
   Utrera, O.; Kamm, D.; Kiekebusch, M.; Le Contel, D.; Le Contel, J. -M.;
   Lesourd, T.; Lopez, B.; Lopez, M.; Magnard, Y.; Marconi, A.; Mars, G.;
   Martinot-Lagarde, G.; Mathias, P.; Mège, P.; Monin, J. -L.; Mouillet,
   D.; Mourard, D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.; Perrier,
   C.; Rabbia, Y.; Rebattu, S.; Reynaud, F.; Richichi, A.; Robini, A.;
   Sacchettini, M.; Schertl, D.; Schöller, M.; Solscheid, W.; Spang,
   A.; Stefanini, P.; Tallon, M.; Tallon-Bosc, I.; Tasso, D.; Vakili,
   F.; von der Lühe, O.; Valtier, J. -C.; Vannier, M.; Ventura, N.
Bibcode: 2007A&A...464...43M
Altcode: 2005astro.ph.10350M
  The young stellar object <ASTROBJ>MWC 297</ASTROBJ> is an embedded
  B1.5Ve star exhibiting strong hydrogen emission lines and a strong
  near-infrared continuum excess. This object has been observed with
  the VLT interferometer equipped with the AMBER instrument during
  its first commissioning run. AMBER/VLTI is currently the only
  near infrared interferometer that can observe spectrally dispersed
  visibilities. <ASTROBJ>MWC 297</ASTROBJ> has been spatially resolved in
  the continuum with a visibility of 0.50<SUP>+0.08</SUP><SUB>-0.10</SUB>
  as well as in the Brγ emission line where the visibility decreases
  to 0.33±0.06. This change in the visibility with wavelength can be
  interpreted by the presence of an optically thick disk responsible for
  the visibility in the continuum and of a stellar wind traced by the
  Brγ emission line and whose apparent size is 40% larger. We validate
  this interpretation by building a model of the stellar environment
  that combines a geometrically thin, optically thick accretion disk
  model consisting of gas and dust, and a latitude-dependent stellar
  wind outflowing above the disk surface. The continuum emission and
  visibilities obtained from this model are fully consistent with the
  interferometric AMBER data. They agree also with existing optical,
  near-infrared spectra and other broad-band near-infrared interferometric
  visibilities. We also reproduce the shape of the visibilities in the
  Brγ line as well as the profile of this line obtained at an higher
  spectral resolution with the VLT/ISAAC spectrograph, and those of
  the Hα and Hβ lines. The disk and wind models yield a consistent
  inclination of the system of approximately 20°. A picture emerges in
  which <ASTROBJ>MWC 297</ASTROBJ> is surrounded by an equatorial flat
  disk that is possibly still accreting and an outflowing wind that has
  a much higher velocity in the polar region than at the equator. The
  AMBER/VLTI unique capability of measuring spectral visibilities
  therefore allows us for the first time to compare the apparent geometry
  of a wind with the disk structure in a young stellar system. <P />Based
  on observations collected at the European Southern Observatory, Paranal,
  Chile, within the commissioning programme 60.A-9054(A).

Title: Near-infrared interferometry of <ASTROBJ>η Carinae</ASTROBJ>
    with spectral resolutions of 1 500 and 12 000 using AMBER/VLTI
Authors: Weigelt, G.; Kraus, S.; Driebe, T.; Petrov, R. G.; Hofmann,
   K. -H.; Millour, F.; Chesneau, O.; Schertl, D.; Malbet, F.; Hillier,
   J. D.; Gull, T.; Davidson, K.; Domiciano de Souza, A.; Antonelli,
   P.; Beckmann, U.; Bresson, Y.; Chelli, A.; Dugué, M.; Duvert, G.;
   Gennari, S.; Glück, L.; Kern, P.; Lagarde, S.; Le Coarer, E.; Lisi,
   F.; Perraut, K.; Puget, P.; Rantakyrö, F.; Robbe-Dubois, S.; Roussel,
   A.; Tatulli, E.; Zins, G.; Accardo, M.; Acke, B.; Agabi, K.; Altariba,
   E.; Arezki, B.; Aristidi, E.; Baffa, C.; Behrend, J.; Blöcker, T.;
   Bonhomme, S.; Busoni, S.; Cassaing, F.; Clausse, J. -M.; Colin, J.;
   Connot, C.; Delboulbé, A.; Feautrier, P.; Ferruzzi, D.; Forveille,
   T.; Fossat, E.; Foy, R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.;
   Gil, C.; Glentzlin, A.; Heiden, M.; Heininger, M.; Hernandez Utrera,
   O.; Kamm, D.; Kiekebusch, M.; Le Contel, D.; Le Contel, J. -M.;
   Lesourd, T.; Lopez, B.; Lopez, M.; Magnard, Y.; Marconi, A.; Mars,
   G.; Martinot-Lagarde, G.; Mathias, P.; Mège, P.; Monin, J. -L.;
   Mouillet, D.; Mourard, D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.;
   Perrier, C.; Rabbia, Y.; Rebattu, S.; Reynaud, F.; Richichi, A.;
   Robini, A.; Sacchettini, M.; Schöller, M.; Solscheid, W.; Spang,
   A.; Stee, P.; Stefanini, P.; Tallon, M.; Tallon-Bosc, I.; Tasso, D.;
   Testi, L.; Vakili, F.; von der Lühe, O.; Valtier, J. -C.; Vannier,
   M.; Ventura, N.; Weis, K.; Wittkowski, M.
Bibcode: 2007A&A...464...87W
Altcode: 2006astro.ph..9715W
  Aims: We present the first NIR spectro-interferometry of the LBV
  <ASTROBJ>η Carinae</ASTROBJ>. The observations were performed with
  the AMBER instrument of the ESO Very Large Telescope Interferometer
  (VLTI) using baselines from 42 to 89 m. The aim of this work is to
  study the wavelength dependence of η Car's optically thick wind
  region with a high spatial resolution of 5 mas (11 AU) and high
  spectral resolution. <BR />Methods: The observations were carried
  out with three 8.2 m Unit Telescopes in the K-band. The raw data are
  spectrally dispersed interferograms obtained with spectral resolutions
  of 1500 (MR-K mode) and 12 000 (HR-K mode). The MR-K observations
  were performed in the wavelength range around both the He I 2.059 μm
  and the Brγ 2.166 μm emission lines, the HR-K observations only in
  the Brγ line region. <BR />Results: The spectrally dispersed AMBER
  interferograms allow the investigation of the wavelength dependence of
  the visibility, differential phase, and closure phase of η Car. In
  the K-band continuum, a diameter of 4.0±0.2 mas (Gaussian FWHM, fit
  range 28-89 m baseline length) was measured for η Car's optically
  thick wind region. If we fit Hillier et al. (2001, ApJ, 553, 837)
  model visibilities to the observed AMBER visibilities, we obtain 50%
  encircled-energy diameters of 4.2, 6.5 and 9.6 mas in the 2.17 μm
  continuum, the He I, and the Brγ emission lines, respectively. In
  the continuum near the Brγ line, an elongation along a position
  angle of 120°±15° was found, consistent with previous VINCI/VLTI
  measurements by van Boekel et al. (2003, A&amp;A, 410, L37). We compare
  the measured visibilities with predictions of the radiative transfer
  model of Hillier et al. (2001), finding good agreement. Furthermore, we
  discuss the detectability of the hypothetical hot binary companion. For
  the interpretation of the non-zero differential and closure phases
  measured within the Brγ line, we present a simple geometric model of
  an inclined, latitude-dependent wind zone. Our observations support
  theoretical models of anisotropic winds from fast-rotating, luminous hot
  stars with enhanced high-velocity mass loss near the polar regions. <P
  />Based on observations collected at the European Southern Observatory,
  Paranal, Chile, within the AMBER guaranteed time programme 074.A-9025
  and the VLTI science demonstration programme 074.A-9024.

Title: Interferometric data reduction with AMBER/VLTI. Principle,
    estimators, and illustration
Authors: Tatulli, E.; Millour, F.; Chelli, A.; Duvert, G.; Acke, B.;
   Hernandez Utrera, O.; Hofmann, K. -H.; Kraus, S.; Malbet, F.; Mège,
   P.; Petrov, R. G.; Vannier, M.; Zins, G.; Antonelli, P.; Beckmann, U.;
   Bresson, Y.; Dugué, M.; Gennari, S.; Glück, L.; Kern, P.; Lagarde,
   S.; Le Coarer, E.; Lisi, F.; Perraut, K.; Puget, P.; Rantakyrö,
   F.; Robbe-Dubois, S.; Roussel, A.; Weigelt, G.; Accardo, M.; Agabi,
   K.; Altariba, E.; Arezki, B.; Aristidi, E.; Baffa, C.; Behrend,
   J.; Blöcker, T.; Bonhomme, S.; Busoni, S.; Cassaing, F.; Clausse,
   J. -M.; Colin, J.; Connot, C.; Delboulbé, A.; Domiciano de Souza,
   A.; Driebe, T.; Feautrier, P.; Ferruzzi, D.; Forveille, T.; Fossat,
   E.; Foy, R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.; Gil, C.;
   Glentzlin, A.; Heiden, M.; Heininger, M.; Kamm, D.; Kiekebusch, M.;
   Le Contel, D.; Le Contel, J. -M.; Lesourd, T.; Lopez, B.; Lopez, M.;
   Magnard, Y.; Marconi, A.; Mars, G.; Martinot-Lagarde, G.; Mathias,
   P.; Monin, J. -L.; Mouillet, D.; Mourard, D.; Nussbaum, E.; Ohnaka,
   K.; Pacheco, J.; Perrier, C.; Rabbia, Y.; Rebattu, S.; Reynaud, F.;
   Richichi, A.; Robini, A.; Sacchettini, M.; Schertl, D.; Schöller,
   M.; Solscheid, W.; Spang, A.; Stee, P.; Stefanini, P.; Tallon, M.;
   Tallon-Bosc, I.; Tasso, D.; Testi, L.; Vakili, F.; von der Lühe,
   O.; Valtier, J. -C.; Ventura, N.
Bibcode: 2007A&A...464...29T
Altcode: 2006astro.ph..3046T
  Aims:In this paper, we present an innovative data reduction method
  for single-mode interferometry. It has been specifically developed
  for the AMBER instrument, the three-beam combiner of the Very Large
  Telescope Interferometer, but it can be derived for any single-mode
  interferometer. <BR />Methods: The algorithm is based on a direct
  modelling of the fringes in the detector plane. As such, it requires
  a preliminary calibration of the instrument in order to obtain the
  calibration matrix that builds the linear relationship between the
  interferogram and the interferometric observable, which is the complex
  visibility. Once the calibration procedure has been performed, the
  signal processing appears to be a classical least-square determination
  of a linear inverse problem. From the estimated complex visibility,
  we derive the squared visibility, the closure phase, and the spectral
  differential phase. <BR />Results: The data reduction procedures have
  been gathered into the so-called amdlib software, now available for
  the community, and are presented in this paper. Furthermore, each
  step in this original algorithm is illustrated and discussed from
  various on-sky observations conducted with the VLTI, with a focus on
  the control of the data quality and the effective execution of the data
  reduction procedures. We point out the present limited performances of
  the instrument due to VLTI instrumental vibrations which are difficult
  to calibrate. <P />Based on observations collected <P />at the European
  Southern Observatory, Paranal, Chile.

Title: Direct constraint on the distance of γ<SUP>2</SUP> Velorum
    from AMBER/VLTI observations
Authors: Millour, F.; Petrov, R. G.; Chesneau, O.; Bonneau, D.;
   Dessart, L.; Bechet, C.; Tallon-Bosc, I.; Tallon, M.; Thiébaut,
   E.; Vakili, F.; Malbet, F.; Mourard, D.; Antonelli, P.; Beckmann,
   U.; Bresson, Y.; Chelli, A.; Dugué, M.; Duvert, G.; Gennari, S.;
   Glück, L.; Kern, P.; Lagarde, S.; Le Coarer, E.; Lisi, F.; Perraut,
   K.; Puget, P.; Rantakyrö, F.; Robbe-Dubois, S.; Roussel, A.; Tatulli,
   E.; Weigelt, G.; Zins, G.; Accardo, M.; Acke, B.; Agabi, K.; Altariba,
   E.; Arezki, B.; Aristidi, E.; Baffa, C.; Behrend, J.; Blöcker, T.;
   Bonhomme, S.; Busoni, S.; Cassaing, F.; Clausse, J. -M.; Colin, J.;
   Connot, C.; Delboulbé, A.; Domiciano de Souza, A.; Driebe, T.;
   Feautrier, P.; Ferruzzi, D.; Forveille, T.; Fossat, E.; Foy, R.;
   Fraix-Burnet, D.; Gallardo, A.; Giani, E.; Gil, C.; Glentzlin, A.;
   Heiden, M.; Heininger, M.; Hernandez Utrera, O.; Hofmann, K. -H.;
   Kamm, D.; Kiekebusch, M.; Kraus, S.; Le Contel, D.; Le Contel,
   J. -M.; Lesourd, T.; Lopez, B.; Lopez, M.; Magnard, Y.; Marconi,
   A.; Mars, G.; Martinot-Lagarde, G.; Mathias, P.; Mège, P.; Monin,
   J. -L.; Mouillet, D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.; Perrier,
   C.; Rabbia, Y.; Rebattu, S.; Reynaud, F.; Richichi, A.; Robini, A.;
   Sacchettini, M.; Schertl, D.; Schöller, M.; Solscheid, W.; Spang,
   A.; Stee, P.; Stefanini, P.; Tasso, D.; Testi, L.; von der Lühe,
   O.; Valtier, J. -C.; Vannier, M.; Ventura, N.
Bibcode: 2007A&A...464..107M
Altcode: 2006astro.ph.10936M
  Context: Interferometry can provide spatially resolved observations of
  massive star binary systems and their colliding winds, which thus far
  have been studied mostly with spatially unresolved observations. <BR
  />Aims: We present the first AMBER/VLTI observations, taken at
  orbital phase 0.32, of the Wolf-Rayet and O (WR+O) star binary system
  <ASTROBJ>γ2 Velorum</ASTROBJ> and use the interferometric observables
  to constrain its properties. <BR />Methods: The AMBER/VLTI instrument
  was used with the telescopes UT2, UT3, and UT4 on baselines ranging
  from 46 m to 85 m. It delivered spectrally dispersed visibilities,
  as well as differential and closure phases, with a resolution R=1500
  in the spectral band 1.95-2.17 μm. We interpret these data in the
  context of a binary system with unresolved components, neglecting in a
  first approximation the wind-wind collision zone flux contribution. <BR
  />Results: Using WR- and O-star synthetic spectra, we show that the
  AMBER/VLTI observables result primarily from the contribution of the
  individual components of the WR+O binary system. We discuss several
  interpretations of the residuals, and speculate on the detection of an
  additional continuum component, originating from the free-free emission
  associated with the wind-wind collision zone (WWCZ), and contributing at
  most to the observed K-band flux at the 5% level. Based on the accurate
  spectroscopic orbit and the Hipparcos distance, the expected absolute
  separation and position angle at the time of observations were 5.1±0.9
  mas and 66±15°, respectively. However, using theoretical estimates
  for the spatial extent of both continuum and line emission from each
  component, we infer a separation of 3.62<SUP>+0.11</SUP><SUB>-0.30</SUB>
  mas and a position angle of 73<SUP>+9</SUP><SUB>-11</SUB>°, compatible
  with the expected one. Our analysis thus implies that the binary system
  lies at a distance of 368<SUP>+38</SUP><SUB>-13</SUB> pc, in agreement
  with recent spectrophotometric estimates, but significantly larger
  than the Hipparcos value of 258<SUP>+41</SUP><SUB>-31</SUB> pc. <P
  />Based on observations collected at the European Southern Observatory,
  Paranal, Chile, within the guaranteed time programme 074.A-9025(A).

Title: Optical configuration and analysis of the AMBER/VLTI instrument
Authors: Robbe-Dubois, S.; Lagarde, S.; Petrov, R. G.; Lisi,
   F.; Beckmann, U.; Antonelli, P.; Bresson, Y.; Martinot-Lagarde,
   G.; Roussel, A.; Salinari, P.; Vannier, M.; Chelli, A.; Dugué, M.;
   Duvert, G.; Gennari, S.; Glück, L.; Kern, P.; Le Coarer, E.; Malbet,
   F.; Millour, F.; Perraut, K.; Puget, P.; Rantakyrö, F.; Tatulli, E.;
   Weigelt, G.; Zins, G.; Accardo, M.; Acke, B.; Agabi, K.; Altariba,
   E.; Arezki, B.; Aristidi, E.; Baffa, C.; Behrend, J.; Blöcker,
   T.; Bonhomme, S.; Busoni, S.; Cassaing, F.; Clausse, J. -M.; Colin,
   J.; Connot, C.; Delage, L.; Delboulbé, A.; Domiciano de Souza, A.;
   Driebe, T.; Feautrier, P.; Ferruzzi, D.; Forveille, T.; Fossat, E.;
   Foy, R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.; Gil, C.; Glentzlin,
   A.; Heiden, M.; Heininger, M.; Hernandez Utrera, O.; Hofmann, K. -H.;
   Kamm, D.; Kiekebusch, M.; Kraus, S.; Le Contel, D.; Le Contel, J. -M.;
   Lesourd, T.; Lopez, B.; Lopez, M.; Magnard, Y.; Marconi, A.; Mars,
   G.; Mathias, P.; Mège, P.; Monin, J. -L.; Mouillet, D.; Mourard,
   D.; Nussbaum, E.; Ohnaka, K.; Pacheco, J.; Perrier, C.; Rabbia, Y.;
   Rebattu, S.; Reynaud, F.; Richichi, A.; Robini, A.; Sacchettini,
   M.; Schertl, D.; Schöller, M.; Solscheid, W.; Spang, A.; Stee, P.;
   Stefanini, P.; Tallon, M.; Tallon-Bosc, I.; Tasso, D.; Testi, L.;
   Vakili, F.; von der Lühe, O.; Valtier, J. -C.; Ventura, N.
Bibcode: 2007A&A...464...13R
Altcode: 2008arXiv0807.3717R
  Aims:This paper describes the design goals and engineering efforts
  that led to the realization of AMBER (Astronomical Multi BEam
  combineR) and to the achievement of its present performance. <BR
  />Methods: On the basis of the general instrumental concept, AMBER was
  decomposed into modules whose functions and detailed characteristics
  are given. Emphasis is put on the spatial filtering system, a key
  element of the instrument. We established a budget for transmission
  and contrast degradation through the different modules, and made the
  detailed optical design. The latter confirmed the overall performance
  of the instrument and defined the exact implementation of the AMBER
  optics. <BR />Results: The performance was assessed with laboratory
  measurements and commissionings at the VLTI, in terms of spectral
  coverage and resolution, instrumental contrast higher than 0.80,
  minimum magnitude of 11 in K, absolute visibility accuracy of 1%,
  and differential phase stability of 10<SUP>-3</SUP> rad over one minute.

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

Title: Advances, challenges and limitations of speckle reconstruction
    and deconvolution
Authors: Mikurda, K.; von der Lühe, O.; Wöger, F.; Schmidt, W.
Bibcode: 2007msfa.conf..131M
Altcode:
  This paper presents the experiences with speckle imaging and
  deconvolution techniques we have made during the last five years at the
  Kiepenheuer-Institut für Sonnenphysik. We discuss our implementation of
  the above techniques, their tests and application ranges. In addition,
  we summarize our efforts in applying speckle techniques to the data
  taken with the support of the adaptive optics.

Title: Anisoplanatic optical transfer functions for solar adaptive
    optics from simulation using wave front sensor data
Authors: Sailer, M.; von der Lühe, O.
Bibcode: 2007msfa.conf..115S
Altcode:
  Solar observations with online compensation of atmospheric seeing is
  possible at the Vacuum Tower Telescope (VTT) on Tenerife (Spain) with
  the aid of the Kiepenheuer Adaptive Optics (AO) System KAOS. For the
  post-facto speckle image reconstruction methods used at our institutes,
  however, problems arise regarding the photometric accuracy of the
  intensity enhancement at each position of the reconstructed image
  (Puschmann &amp; Sailer 2006), rooting in the lack of knowledge
  about the field dependency of the actual residual wave front
  (WF) after correction and therefore of the instantaneous optical
  transfer functions (OTFs) at the time of each exposure. To process
  more adequately particular sets of image data obtained with KAOS,
  we simulate their OTFs and the according statistically averaged
  quantity for the reconstruction, the speckle transfer function (STF),
  with support of an activity log of the AO system during the time of
  data acquisition. Data regarding the wave front sensor (WFS) and the
  deformable mirror (DM) are analysed to model the atmospheric conditions
  and the average compensation power of the AO system. With this
  information we simulate the propagation of atmospherically distorted
  WFs through the optical elements of the VTT and KAOS, approaching the
  average WF error statistics reflected in the experimental data.

Title: High Resolution Time Series of Narrowband Ca IIK Images in
    the Chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Schmidt, W.; von der
   Lühe, O.
Bibcode: 2006ASPC..354..284W
Altcode:
  We have observed a region of quiet Sun near disk center with the Vacuum
  Tower Telescope (VTT) of the Kiepenheuer-Institut für Sonnenphysik at
  the Observatorio del Teide, Tenerife, Spain in April 2005 in several
  wavelengths. Observations were made at the Ca II K line at 393.3 nm,
  using a Lyot filter with a bandwidth of 30 ± FWHM, centered at the
  K_{2v} emission peak; at the Hα line at 656.3 nm, using a Lyot filter
  (25 ± FWHM) centered at line core, and in the G-band (430.5 nm),
  using an interference filter (1 nm FWHM). We acquired a two-hour long
  sequence of images at a cadence of ten seconds and a spatial resolution
  of about 0.3 arcsec. We present our Ca observations of excellent spatial
  resolution which show morphological structures in internetwork regions
  similar in form, size and lifetime to those present in recent numerical
  models of the solar chromosphere.

Title: Basic physical parameters of a selected sample of evolved stars
Authors: da Silva, L.; Girardi, L.; Pasquini, L.; Setiawan, J.; von der
   Lühe, O.; de Medeiros, J. R.; Hatzes, A.; Döllinger, M. P.; Weiss, A.
Bibcode: 2006A&A...458..609D
Altcode: 2006astro.ph..8160D
  We present the detailed spectroscopic analysis of 72 evolved
  stars, which were previously studied for accurate radial velocity
  variations. Using one Hyades giant and another well studied star as the
  reference abundance, we determine the [Fe/H] for the whole sample. These
  metallicities, together with the T_eff values and the absolute V-band
  magnitude derived from Hipparcos parallaxes, are used to estimate basic
  stellar parameters (ages, masses, radii, (B-V)<SUB>0</SUB> and log g)
  using theoretical isochrones and a Bayesian estimation method. The
  (B-V)<SUB>0</SUB> values so estimated turn out to be in excellent
  agreement (to within ~0.05 mag) with the observed (B-V), confirming
  the reliability of the T_eff-(B-V)<SUB>0</SUB> relation used in the
  isochrones. On the other hand, the estimated log g values are typically
  0.2 dex lower than those derived from spectroscopy; this effect has a
  negligible impact on [Fe/H] determinations. The estimated diameters
  θ have been compared with limb darkening-corrected ones measured
  with independent methods, finding an agreement better than 0.3 mas
  within the 1&lt;θ&lt;10 mas interval (or, alternatively, finding mean
  differences of just 6%). We derive the age-metallicity relation for the
  solar neighborhood; for the first time to our knowledge, such a relation
  has been derived from observations of field giants rather than from open
  clusters and field dwarfs and subdwarfs. The age-metallicity relation
  is characterized by close-to-solar metallicities for stars younger
  than ~4 Gyr, and by a large [Fe/H] spread with a trend towards lower
  metallicities for higher ages. In disagreement with other studies,
  we find that the [Fe/H] dispersion of young stars (less than 1 Gyr)
  is comparable to the observational errors, indicating that stars in
  the solar neighbourhood are formed from interstellar matter of quite
  homogeneous chemical composition. The three giants of our sample which
  have been proposed to host planets are not metal rich; this result
  is at odds with those for main sequence stars. However, two of these
  stars have masses much larger than a solar mass so we may be sampling
  a different stellar population from most radial velocity searches for
  extrasolar planets. We also confirm the previous indication that the
  radial velocity variability tends to increase along the RGB, and in
  particular with the stellar radius.

Title: Observation of a short-lived pattern in the solar chromosphere
Authors: Wöger, F.; Wedemeyer-Böhm, S.; Schmidt, W.; von der
   Lühe, O.
Bibcode: 2006A&A...459L...9W
Altcode: 2006astro.ph..9382W
  Aims.In this work we investigate the dynamic behavior of inter-network
  regions of the solar chromosphere.<BR /> Methods: .We observed the
  chromosphere of the quiet Sun using a narrow-band Lyot filter centered
  at the Ca II K2v emission peak with a bandpass of 0.3 Å. We achieved
  a spatial resolution of on average 0.7 arcsec at a cadence of 10 s.<BR
  /> Results: .In the inter-network we find a mesh-like pattern that
  features bright grains at the vertices. The pattern has a typical
  spatial scale of 1.95 arcsec and a mean evolution time scale of 53 s
  with a standard deviation of 10 s. A comparison of our results with a
  recent three-dimensional radiation hydrodynamical model implies that
  the observed pattern is of chromospheric origin. The measured time
  scales are not compatible with those of reversed granulation in the
  photosphere although the appearance is similar. A direct comparison
  between network and inter-network structure shows that their typical
  time scales differ by at least a factor of two.<BR /> Conclusions:
  .The existence of a rapidly evolving small-scale pattern in the
  inter-network regions supports the picture of the lower chromosphere
  as a highly dynamical and intermittent phenomenon.

Title: Asteroseismology of K giants
Authors: di Mauro, M. P.; Cardini, D.; D'Antona, F.; Weiss, A.;
   Döllinger, M. P.; Pasquini, L.; Girardi, L.; Hatzes, A.; von der
   Lühe, O.; de Medeiros, J. R.; Roth, M.; Setaiwan, J.; da Silva, L.
Bibcode: 2006ESASP.624E.118D
Altcode: 2006soho...18E.118D
  No abstract at ADS

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

Title: Multi-conjugate solar adaptive optics with the VTT and GREGOR
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Lühe, Oskar
Bibcode: 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: Simulation of adaptive optics for the Vacuum Tower Telescope
Authors: Enmark, Anita; Berkefeld, Thomas; von der Lühe, Oskar;
   Andersen, Torben
Bibcode: 2006ExA....21...87E
Altcode: 2006ExA...tmp...45E
  A simulation model of the adaptive optics of the German Vacuum Tower
  Telescope (VTT), Observatorio del Teide, Tenerife, is presented. The
  model uses modules from the integrated model of the Euro50 extremely
  large telescope, and includes submodels of a Shack-Hartmann wavefront
  sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier
  low-pass filters, a reconstructor and a controller. We investigate
  the impact on the closed loop bandwidth of changes in controller
  configuration and certain system parameters, such as low pass filter
  bandwidth and camera integration and readout time. Control strategies
  were tested on simple models before implementation on the full VTT
  model. Using the models, different control strategies are compared.

Title: High resolution solar telescope GREGOR
Authors: Peter, H.; von der Luehe, O.
Bibcode: 2006cosp...36.3628P
Altcode: 2006cosp.meet.3628P
  GREGOR is a new 1 5 m solar telescope assembled on Tenerife Spain by a
  German consortium together with international partners It is designed
  for high-precision measurements of the magnetic field and the gas motion
  in the solar photosphere and chromosphere with a resolution of 70 km on
  the Sun and for high resolution stellar spectroscopy The telescope has a
  Gregorian configuration mounted in an open structure with a retractable
  dome for thermal control and features a multi-conjugate adaptive optics
  system GREGOR will be equipped with several post-focus instruments
  including polarimetric longslit spectrographs for the visible and
  infrared and a high resolution Fabry-Perot filter spectrometer for 3D
  spectroscopy Apart from a report on the present status of the instrument
  the talk will focus on a selection of science goals of GREGOR Among
  these are the emergence evolution and disappearance of small-scale
  magnetic flux the energy budget of sunspots and the structure of their
  penumbrae as well as the dynamics of the chromosphere In this context
  an attempt will be made to put future observations with GREGOR in the
  context of modeling of the photosphere chromosphere and corona

Title: Why are G and K Giants Radial Velocity Variables?
Authors: Doellinger, Michaela Petronilla; Pasquini, Luca; Hatzes,
   Artie Peter; Setiawan, Johny; da Silva, Licio; Renan de Medeiros,
   Jose; von der Luehe, Oskar; Girardi, Leo; di Mauro, Maria Pia; Weiss,
   Achim; Roth, Markus
Bibcode: 2005Msngr.122...39D
Altcode:
  During the past year ESO has coordinated a number of instrument concept
  studies as a complement to the OWL Observatory Design Study. Eight teams
  of scientists and engineers from different institutes in Europe and
  ESO have identified a variety of science programmes at the frontier of
  astrophysics and developed concepts of instruments at OWL which would
  be able to carry them out. This exercise has provided a first view of
  the unique astronomical observations at Blue to IR wavelengths which
  will become possible with a future European Extremely Large Telescope.

Title: Multi-conjugate solar adaptive optics at the Vacuum Tower
    Telescope on Tenerife
Authors: von der Lühe, Oskar; Berkefeld, Thomas; Soltau, Dirk
Bibcode: 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
Bibcode: 2005SPIE.5901...75V
Altcode:
  The telescope structure including control system and the complete
  retractable dome of the new 1.5 m solar telescope GREGOR were
  assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
  telescope is build by a consortium of the Kiepenheuer Institut fuer
  Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
  fuer Astrophysik Goettingen and additional national and international
  Partners. Pointing, tracking and thermal tests were made to verify
  the proposed performance. The results of these tests and a progress
  report of the project will be presented.

Title: Results of the multi-conjugate adaptive optics system at the
    German solar telescope, Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luehe, Oskar
Bibcode: 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: A substellar companion around the intermediate-mass giant
    star HD 11977
Authors: Setiawan, J.; Rodmann, J.; da Silva, L.; Hatzes, A. P.;
   Pasquini, L.; von der Lühe, O.; de Medeiros, J. R.; Döllinger,
   M. P.; Girardi, L.
Bibcode: 2005A&A...437L..31S
Altcode: 2005astro.ph..5510S
  We report the discovery of a substellar companion to the
  intermediate-mass star <ASTROBJ>HD 11977</ASTROBJ> (G5 III). Radial
  velocities of this star have been monitored for five years with FEROS
  at the 1.52-m ESO and later at the 2.2-m MPG/ESO telescope in La Silla,
  Chile. Based on the collected data we calculated an orbital solution
  with a period of P=711 days, a semi-amplitude of K<SUB>1</SUB>=105
  m s<SUP>-1</SUP>, and an eccentricity of e=0.4. The period of the
  radial-velocity variation is longer than that of the estimated stellar
  rotation, rendering it unlikely that rotational modulation is the
  source of the variation in the radial velocity. This hypothesis is
  supported by the absence of a correlation between stellar activity
  indicators and radial-velocity variation. By determining a primary
  stellar mass of M<SUB>star</SUB>=1.91 M<SUB>⊙</SUB>, the best-fit
  minimum mass of the companion and semi-major axis of the orbit are
  m<SUB>2</SUB>sin{i}=6.54 M<SUB>Jup</SUB> and a<SUB>2</SUB>=1.93
  AU, respectively. An upper limit for the mass of the companion of
  m<SUB>2</SUB> ⪉ 65.5 M<SUB>Jup</SUB> has been calculated from
  Hipparcos astrometric measurements. Although the possibility of a
  brown-dwarf companion cannot be excluded, HD 11977 B is one of the
  few planet candidates detected around an intermediate-mass star. The
  progenitor main-sequence star of <ASTROBJ>HD 11977</ASTROBJ> is probably
  an A-type star. This discovery gives an indirect evidence for planetary
  companions around early type main-sequence stars.

Title: Chromospheric activity of red giants
Authors: Setiawan, J.; von der Lühe, O.; Pasquini, L.; da Silva,
   L.; Hatzes, A.; Klotz, F.; Girardi, L.; de Medeiros, J. R.
Bibcode: 2005ESASP.560..963S
Altcode: 2005csss...13..963S
  No abstract at ADS

Title: Interferometry
Authors: von der Lühe, Oskar
Bibcode: 2005ASIB..198..275V
Altcode: 2005opas.conf..275V
  No abstract at ADS

Title: Binaries from FEROS radial velocity survey
Authors: Setiawan, J.; da Silva, L.; Pasquini, L.; Hatzes, A. P.;
   von der Luhe, O.; Girardi, L.; Guenther, E.
Bibcode: 2004ASPC..318..283S
Altcode: 2004ssrc.conf..283S
  At least eleven binary systems have been found from our radial velocity
  (RV) survey (precision ∼ 25 m s<SUP>-1</SUP>) of eighty-three
  G and K evolved stars using FEROS at the 1.52m ESO in La Silla and
  high resolution echelle-spectrograph at 2m-Alfred-Jensch- telescope in
  Tautenburg, Germany. We used the simultaneous calibration method and the
  iodine absorption-cell technique to measure the RV variations. Orbital
  elements have been derived from the RV curves of six binaries. The
  stellar companions have minimum masses (m <P />sin{i}) from 0.1 up to
  0.6 M<SUB>sun</SUB> and orbital semi-major axes between 0.2 and 3.6
  AU. Two special cases are found among them: first, in one system,
  HD 156111, the sin{i} has been determined which permitted us to
  derive the companion's real mass, and second, we found a dependence
  between the RV variation of HD 62644 induced by its companion,
  and chromospheric activity of the primary star. For the remaining
  five stars we do not have enough measurements to obtain the complete
  orbital solutions. Finally, we report two other giants in our sample,
  HD 224533 and HD 27256, which might have brown-dwarf companions.

Title: Adaptive optics for robotic telescopes
Authors: von der Lühe, O.
Bibcode: 2004AN....325..613V
Altcode:
  Adaptive optics is a technology which compensates dynamical
  optical aberrations in an astronomical telescope. The technique
  has matured during the past decade and exists today at any large
  observatory. Adaptive optics improve the spatial resolution, ideally to
  the diffraction limit, and concentrate the source's flux, increasing
  the sensitivity. Both properties can be relevant to science programs
  with robotic telescopes. The hardware for adaptive optics becomes more
  readily available at lower costs, and there are many research groups
  working on their development. We review the current status of adaptive
  optics and discuss its relevance to robotic telescopes.

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.
Bibcode: 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.
Bibcode: 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
Bibcode: 2004SPIE.5489..693V
Altcode:
  GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
  the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
  Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
  and other national and international Partners. The refurbishment of
  the building is almost finished. The manufacturing of the telescope
  structure and the optics is still in progress. After the integration of
  the new complete retractable dome in July 2004 the telescope structure,
  optic and post focus instruments will be assembled during the rest of
  the year. First light is planned during May 2005.

Title: GISOT: a giant solar telescope
Authors: Hammerschlag, Robert H.; von der Lühe, Oskar F.; Bettonvil,
   Felix C.; Jägers, Aswin P.; Snik, Frans
Bibcode: 2004SPIE.5489..491H
Altcode:
  A concept is presented for an extremely large high-resolution solar
  telescope with an aperture of 11 m and diffraction limited for visual
  wavelengths. The structure of GISOT will be transparent to wind and
  placed on a transparent stiff tower. For efficient wind flushing,
  all optics, including the primary mirror, will be located above
  the elevation axis. The aperture will be of the order of 11 m, not
  rotatively symmetrical, but of an elongated shape with dimensions
  11 x 4 m. It consists of a central on-axis 4 m mirror with on both
  sides 3 pieces of 2 m mirrors. The optical layout will be kept simple
  to guarantee quality and minimize stray light. A Coudé room for
  instruments is planned below the telescope. The telescope will not
  be housed in a dome-like construction, which interferes with the open
  principle. Instead the telescope will be protected by a foldable tent
  construction with a diameter of the order of 30 m, which doesn"t form
  any obstruction during observations, but can withstand the severe
  weather circumstances on mountain sites. Because of the nature of
  the solar scene, extremely high resolution in only one dimension is
  sufficient to solve many exciting problems in solar physics and in
  this respect the concept of GISOT is very promising.

Title: Photometric stability of multiconjugate adaptive optics
Authors: von der Luhe, Oskar F. H.
Bibcode: 2004SPIE.5490..617V
Altcode:
  We observe that a multi-conjugate adaptive optics (MCAO) system
  produces rapid fluctuations of irradiance of a few percent in the
  compensated focal plane when observing an extended target, such as
  the solar surface. Such fluctuations are absent in the uncompensated
  focal plane. The fluctuations are apparently correlated with the
  local curvature of deformable mirror in the plane conjugated to
  the high altitude turbulence layer. They can be explained by the
  field dependent change of effective focal length introduced by a high
  altitude turbulence layer, which is related to image distortion. Using
  a simple geometric model of the MCAO system, we are able to reproduce
  the observed irradiance effects. We propose to introduce a slightly
  undersized aperture stop at the location of the nominal exit pupil in
  order to remove the fluctuations in the compensated field.

Title: Mid-infrared sizes of circumstellar disks around Herbig Ae/Be
    stars measured with MIDI on the VLTI
Authors: Leinert, Ch.; van Boekel, R.; Waters, L. B. F. M.; Chesneau,
   O.; Malbet, F.; Köhler, R.; Jaffe, W.; Ratzka, Th.; Dutrey, A.;
   Preibisch, Th.; Graser, U.; Bakker, E.; Chagnon, G.; Cotton, W. D.;
   Dominik, C.; Dullemond, C. P.; Glazenborg-Kluttig, A. W.; Glindemann,
   A.; Henning, Th.; Hofmann, K. -H.; de Jong, J.; Lenzen, R.; Ligori, S.;
   Lopez, B.; Meisner, J.; Morel, S.; Paresce, F.; Pel, J. -W.; Percheron,
   I.; Perrin, G.; Przygodda, F.; Richichi, A.; Schöller, M.; Schuller,
   P.; Stecklum, B.; van den Ancker, M. E.; von der Lühe, O.; Weigelt, G.
Bibcode: 2004A&A...423..537L
Altcode:
  We present the first long baseline mid-infrared interferometric
  observations of the circumstellar disks surrounding Herbig Ae/Be
  stars. The observations were obtained using the mid-infrared
  interferometric instrument MIDI at the European Southern Observatory
  (ESO) Very Large Telescope Interferometer VLTI on Cerro Paranal. The
  102 m baseline given by the telescopes UT1 and UT3 was employed,
  which provides a maximum full spatial resolution of 20 milli-arcsec
  (mas) at a wavelength of 10 μm. The interferometric signal was
  spectrally dispersed at a resolution of 30, giving spectrally
  resolved visibility information from 8 μm to 13.5 μm. We observed
  seven nearby Herbig Ae/Be stars and resolved all objects. The warm
  dust disk of HD 100546 could even be resolved in single-telescope
  imaging. Characteristic dimensions of the emitting regions at 10 μm
  are found to be from 1 AU to 10 AU. The 10 μm sizes of our sample
  stars correlate with the slope of the 10-25 μm infrared spectrum
  in the sense that the reddest objects are the largest ones. Such a
  correlation would be consistent with a different geometry in terms
  of flaring or flat (self-shadowed) disks for sources with strong or
  moderate mid-infrared excess, respectively. We compare the observed
  spectrally resolved visibilities with predictions based on existing
  models of passive centrally irradiated hydrostatic disks made to fit
  the SEDs of the observed stars. We find broad qualitative agreement
  of the spectral shape of visibilities corresponding to these models
  with our observations. Quantitatively, there are discrepancies that
  show the need for a next step in modelling of circumstellar disks,
  satisfying both the spatial constraints such as are now available
  from the MIDI observations and the flux constraints from the SEDs in
  a consistent way. <P />Based on observations made with the Very Large
  Telescope Interferometer at Paranal Observatory.

Title: Precise radial velocity measurements of G and K giants.
    Multiple systems and variability trend along the Red Giant Branch
Authors: Setiawan, J.; Pasquini, L.; da Silva, L.; Hatzes, A. P.;
   von der Lühe, O.; Girardi, L.; de Medeiros, J. R.; Guenther, E.
Bibcode: 2004A&A...421..241S
Altcode:
  We present the results of our radial velocity (RV) measurements of
  G and K giants, concentrating on the presence of multiple systems in
  our sample. Eighty-three giants have been observed for 2.5 years with
  the fiber-fed echelle spectrograph FEROS at the 1.52 m ESO telescope
  in La Silla, Chile. Seventy-seven stars (93%) of the targets have been
  analyzed for RV variability using simultaneous Th-Ar calibration and a
  cross-correlation technique. We estimate the long-term precision of our
  measurement as better than 25 m s<SUP>-1</SUP>. Projected rotational
  velocities have been measured for most stars of the sample. Within
  our time-base only 21 stars (or 27%) show variability below 2\sigma,
  while the others show RV variability with amplitudes up to several km
  s<SUP>-1</SUP>. The large amplitude (several km s<SUP>-1</SUP>) and
  shape (high eccentricity) of the RV variations for 11 of the program
  stars are consistent with stellar companions, and possibly brown dwarf
  companions for two of the program stars. In those systems for which a
  full orbit could be derived, the companions have minimum masses from
  ∼0.6 M<SUB>\sun</SUB> down to 0.1 M<SUB>\sun</SUB>. To these multiple
  systems we add the two candidates of giant planets already discovered
  in the sample. This analysis shows that multiple systems contribute
  substantially to the long-term RV variability of giant stars, with
  about 20% of the sample being composed of multiple systems despite
  screening our sample for known binary stars. After removing binaries,
  the range of RV variability in the whole sample clearly decreases,
  but the remaining stars retain a statistical trend of RV variability
  with luminosity: luminous cool giants with B-V≥1.2 show RV variations
  with \sigma_{/lineRV} &gt; 60 m s<SUP>-1</SUP>, while giants with B-V
  &lt; 1.2 including those in the clump region exhibit less variability
  or they are constant within our accuracy. The same trend is observed
  with respect to absolute visual magnitudes: brighter stars show a
  larger degree of variability and, when plotted in the RV variability
  vs. magnitude diagram a trend of increasing RV scatter with luminosity
  is seen. The amplitude of RV variability does not increase dramatically,
  as predicted, for instance, by simple scaling laws. At least two
  luminous and cooler stars of the sample show a correlation between RV
  and chromospheric activity and bisector asymmetry, indicating that in
  these two objects RV variability is likely induced by the presence of
  (chromospheric) surface structures. <P />Based on observations collected
  at the 1.52 m-ESO telescope at the La Silla Observatory from Oct 1999
  to Feb. 2002 under ESO programs and the ESO-Observatório Nacional,
  Brazil, agreement and in part on observations collected on the Alfred
  Jensch 2 m telescope of the Thüringer Landessternwarte Tautenburg.

Title: Adaptive optics transfer function estimation for solar
    observations.
Authors: Sailer, M.; von der Luehe, O.; Kneer, F.
Bibcode: 2004ANS...325..130S
Altcode: 2004ANS...325..P65S; 2004ANS...325a.130S
  No abstract at ADS

Title: 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
Bibcode: 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: Sensitivity of Active and Passive High Resolution Techniques
Authors: von der Lühe, Oskar
Bibcode: 2003ANS...324...23V
Altcode: 2003ANS...324..C05V
  No abstract at ADS

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

Title: Solar Imaging with an Extended Knox-Thompson Technique
Authors: Mikurda, K.; von der Lühe, O.; Wöger, F.
Bibcode: 2003ANS...324..112M
Altcode: 2003ANS...324..P18M
  No abstract at ADS

Title: Transfer Function Calibration for Speckle Reconstruction
Authors: Sailer, Markus; von der Lühe, Oskar; Kneer, Franz
Bibcode: 2003ANS...324...23S
Altcode: 2003ANS...324..C04S
  No abstract at ADS

Title: Dynamics of the G-band Bright Points
Authors: Mikurda, K.; von der Lühe, O.; Schmidt, W.
Bibcode: 2003ANS...324...24M
Altcode: 2003ANS...324..C06M
  No abstract at ADS

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

Title: Evidence of a sub-stellar companion around HD 47536
Authors: Setiawan, J.; Hatzes, A. P.; von der Lühe, O.; Pasquini,
   L.; Naef, D.; da Silva, L.; Udry, S.; Queloz, D.; Girardi, L.
Bibcode: 2003A&A...398L..19S
Altcode:
  We report evidence of a low-mass companion around the K1III giant
  star HD 47536. This star belongs to our sample of 83 subgiant and
  giant stars studied for their radial velocity variations using the
  FEROS spectrograph at the 1.52 m-ESO telescope on La Silla. We find
  that the radial velocity of HD 47536 exhibits a periodic variation of
  about 712 days with a semi-amplitude of 113 m s<SUP>-1</SUP>. These
  variations are not accompanied by variations in either Ca II emission
  or in the spectral line shapes. A Keplerian orbit due to a sub-stellar
  companion is thus the most viable explanation for the radial velocity
  variation. Assuming a moderate stellar mass of m<SUB>1</SUB>=
  1.1-3.0 M<SUB>sun</SUB> we obtain a minimum mass for the companion of
  m<SUB>2</SUB> sin i= 5.0-9.7 M<SUB>Jup</SUB>, an orbital semi-major axis
  of 1.6-2.3 AU, and an eccentricity of e=0.2. <P />Based on observations
  collected at the ESO 1.52m telescope at the La Silla Observatory from
  July 2000 to February 2002 under ESO programs and the ESO-Observatório
  Nacional, Brazil, agreement.

Title: Lightweight Cesic mirrors and their applications
Authors: Pailer, Norbert M.; Kroedel, Matthias R.; Rosenberg, William
   J.; Schmidt, Wolfgang; von der Luehe, Oskar
Bibcode: 2003SPIE.4853..427P
Altcode:
  Ceramics technologies were successfully applied to a series of
  lightweight mirrors with different sizes and requirements. Several
  joining and optical surface optimizations were applied. Besides the
  classical rib-structured mirrors also the application of sandwich
  mirrors with Cesic foam and/or honeycomb structures are going to be
  tested. For all processes relatively simple straightforward processes
  can be applied which keeps the products relatively cost-effective.

Title: Multi-conjugate Adaptive Optics at the Vacuum Tower Telescope,
    Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Lühe, Oskar
Bibcode: 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: GREGOR - optical design considerations
Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Hofmann, A.;
   Schmidt, W.; Volkmer, R.; Wiehr, E.
Bibcode: 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: MIDI - the 10 \mum instrument on the VLTI
Authors: Leinert, Ch.; Graser, U.; Przygodda, F.; Waters, L. B. F. M.;
   Perrin, G.; Jaffe, W.; Lopez, B.; Bakker, E. J.; Böhm, A.; Chesneau,
   O.; Cotton, W. D.; Damstra, S.; de Jong, J.; Glazenborg-Kluttig,
   A. W.; Grimm, B.; Hanenburg, H.; Laun, W.; Lenzen, R.; Ligori, S.;
   Mathar, R. J.; Meisner, J.; Morel, S.; Morr, W.; Neumann, U.; Pel,
   J. -W.; Schuller, P.; Rohloff, R. -R.; Stecklum, B.; Storz, C.;
   von der Lühe, O.; Wagner, K.
Bibcode: 2003Ap&SS.286...73L
Altcode:
  After more than five years of preparation, the mid-infrared
  interferometric instrument MIDI has been transported to Paranal where
  it will undergo testing and commissioning on the Very Large Telescope
  Interferometer VLTI from the end of 2002 through large part of this year
  2003. Thereafter it will be available as a user instrument to perform
  interferometric observations over the 8 μm-13 μm wavelength range,
  with a spatial resolution of typically 20 milliarcsec, a spectral
  resolution of up to 250, and an anticipated point source sensitivity
  of N = 3-4 mag or 1-2.5 Jy for self - fringe tracking, which will
  be the only observing mode during the first months of operation. We
  describe the layout of the instrument, laboratory tests, and expected
  performance, both for broadband and spectrally resolved observing
  modes. We also briefly outline the planned guaranteed time observations.

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

Title: Precise radial velocity measurements of G and K giants.
    First results
Authors: Setiawan, J.; Pasquini, L.; da Silva, L.; von der Lühe,
   O.; Hatzes, A.
Bibcode: 2003A&A...397.1151S
Altcode:
  We present the first results of our precise radial velocity (RV)
  measurements of G and K giants. A number of stars from our list
  of 80 targets have been observed for 14 months using the fibre-fed
  echelle spectrograph FEROS at the 1.52 m ESO telescope in La Silla,
  Chile. This sample increases the number of giants surveyed with
  precise stellar radial velocity measurements at least by a factor of
  10. During this period we are able to estimate the long-term accuracy
  of our measurement as better than 11 m s<SUP>-1</SUP>. We use the
  simultaneous Th-Ar calibration and cross-correlation technique
  to compute the radial velocity by applying a numerical template
  for K-type stars. Standard deviation sigma of mean radial velocity
  variations between 3 m s<SUP>-1</SUP> and 4 km s<SUP>-1</SUP> with
  timescales between several days and years are measured for 21 of G
  and K giants which are presented in this paper. Fifteen stars show
  definite variability above 3 sigma of our measurement uncertainties. Two
  stars with RV variations above 800 m s<SUP>-1</SUP> are tentatively
  identified as new binaries. Although definitive trends between RV
  variations and stellar evolutionary status cannot yet be established,
  all the luminous cool giants of our sample seem to have significant
  radial velocity variations, while those stars in the giant's clump
  region can be either variable or constant. <P />Based on observations
  collected at the ESO 1.52 m telescope at the La Silla Observatory under
  program ESO No. 64.L-0047, 65.L-0571, 66.D-0592 and from Nov. 99 to
  Feb. 01 under the ESO-Observatório Nacional, Brazil, agreement.}

Title: GREGOR, a 1.5 m Gregory-type telescope for solar observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Soltau, W. Schmidt
   D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
Bibcode: 2002NCimC..25..689K
Altcode:
  No abstract at ADS

Title: Adaptive optics and multi-conjugate adaptive optics with
    the VTT
Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Wöger, F.;
   Schelenz, Th.
Bibcode: 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: Measuring starspots on magnetically active stars with the VLTI
Authors: Wittkowski, M.; Schöller, M.; Hubrig, S.; Posselt, B.;
   von der Lühe, O.
Bibcode: 2002AN....323..241W
Altcode: 2002astro.ph..6090W
  We present feasibility studies to directly image stellar surface
  features, which are caused by magnetic activity, with the Very
  Large Telescope Interferometer (VLTI). We concentrate on late type
  magnetically active stars, for which the distribution of starspots
  on the surface has been inferred from photometric and spectroscopic
  imaging analysis. The study of the surface spot evolution during
  consecutive rotation cycles will allow first direct measurements
  (apart from the Sun) of differential rotation which is the central
  ingredient of magnetic dynamo processes. The VLTI will provide baselines
  of up to 200 m, and two scientific instruments for interferometric
  studies at near- and mid-infrared wavelengths. Imaging capabilities
  will be made possible by closure-phase techniques. We conclude that
  a realistically modeled cool surface spot can be detected on stars
  with angular diameters exceeding ~ 2 mas using the VLTI with the first
  generation instrument AMBER. The spot parameters can then be derived
  with reasonable accuracy. We discuss that the lack of knowledge of
  magnetically active stars of the required angular size, especially in
  the southern hemisphere, is a current limitation for VLTI observations
  of these surface features.

Title: Multiconjugate adaptive optics at the Vacuum Tower Telescope,
    Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luehe, Oskar
Bibcode: 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
Bibcode: 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: GREGOR: a 1.5 m telescope for solar research
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Berkefeld, Th.;
   Kneer, F.; Staude, J.
Bibcode: 2001AN....322..353V
Altcode:
  GREGOR will be a new 1.5 meter solar telescope at the Teide Observatory,
  Izaña, Tenerife. It will provide observations with high polarimetric
  precision at visible and infra-red wavelengths from Earth in the
  solar photosphere and chromosphere with a resolution of 70 km on the
  Sun. GREGOR replaces the 45 cm Gregory Coudé telescope.

Title: Post-focus instrumentation for GREGOR
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
   Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
Bibcode: 2001AN....322..361K
Altcode:
  GREGOR is a high-resolution solar telescope with an aperture of 1.5
  m. It will be equipped with an Adaptive Optics system and is designed
  for high-precision measurements of magnetic fields and plasma motions
  in the solar photosphere and chromosphere with a resolution of 70
  km on the Sun. GREGOR will replace the Gregory Coudé Telescope at
  the Observatorio del Teide on Tenerife. In concert with the other
  solar telescopes at Teide Observatory it will be useful for studying
  the dynamics of the solar atmosphere and the underlying physical
  processes. GREGOR will also serve as a test bed for next generation
  solar telescopes. We discuss briefly the postfocus instrumentation
  of GREGOR.

Title: Visible Imager / Magnetograph: summary of splinter session
Authors: von der Lühe, O.; Fleck, B.
Bibcode: 2001ESASP.493..149V
Altcode: 2001sefs.work..149V
  Both splinter sessions for the Visible Imager and Magnetograph (VIM)
  were well attended by approximately 30 participants. The goals of the
  session was to review the scientific objectives for VIM, to discuss
  specific technological issues, and to refine the approach to science
  operation during all orbital phases. The session was closed by the
  formation of a definition team which will look in detail into these
  matters in order to prepare a VIM Phase A proposal.

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

Title: A proposal for the visible-light imager magnetograph
Authors: von der Lühe, O.; Martinez Pillet, V.; Schmidt, W.;
   Collados, M.
Bibcode: 2001ESASP.493..421V
Altcode: 2001sefs.work..421V
  No abstract at ADS

Title: Solar Instrumentation. An Introduction
Authors: von der Lühe, O.
Bibcode: 2001ASSL..259...43V
Altcode: 2001dysu.conf...43V
  Solar instrumentation is a vast field -- it embraces all experimental
  means to research the Sun. At an observatory -- the most comprehensive
  entity -- several facilities may be operated. Each facility includes
  a telescope, sometimes a specialized telescope, which is equipped
  with one or several post-focus instruments, like spectrographs and
  filtergraphs, and detectors. The equipment is controlled by specific
  hardware and software. The collected data is analyzed using equally
  specialized software packages. An observatory may be ground based or
  space based. All have in common that their prime use is for solar
  research; research on nighttime sources is rarely done with these
  instruments. Most of the time, the equipment collects and detects
  electromagnetic radiation throughout its entire range from gamma
  rays to the radio regime. There are also facilities which detect
  other particles; e.g., the Neutrino observatories or in situ solar
  wind analysis instruments on spacecraft. In this lecture we shall
  confine ourselves only to ground based solar instrumentation related
  to electromagnetic field detection. Instrumentation plays a prominent
  role in the process of physical understanding. The observation is the
  essence of experimental solar physics. What can be observed with which
  precision and accuracy depends mainly on instrumental capabilities,
  which are driven by technological innovations outside the area of solar
  physics and even astrophysics. A good example are modern, moderately
  priced solid state detectors which would have been impossible without
  their use in consumer electronics. The interpretation of the results
  from observations leads to new insights in the form of improved physical
  models of the Sun, which in turn stimulated better understanding of
  physics as a whole.

Title: Prospects of the Research on Cool Stars with Very Large
Telescopes and New Developments in Instrumentation (CD-ROM Directory:
    contribs/pasquini)
Authors: Pasquini, L.; Hatzes, A.; von der Lühe, O.; Wiedemann, G.
Bibcode: 2001ASPC..223..423P
Altcode: 2001csss...11..423P
  No abstract at ADS

Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
   Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
Bibcode: 2001AGM....18.P223K
Altcode:
  GREGOR is a high-resolution solar telescope with an aperture of 1.5
  m. It will be equipped with an Adaptive Optics system and is designed
  for high-precision measurements of magnetic fields and plasma motions
  in the solar atmosphere and chromosphere with a resolution of 70 km
  on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the
  Observatorio del Teide on Tenerife. We describe the optical design
  and the focal plane instrumentation. In concert with the other solar
  telescopes at Teide Observatory it will be useful for studying the
  dynamics of the solar atmosphere and the underlying processes. GREGOR
  will also serve as a test bed for next generation solar telescopes.

Title: Photospheric Structure from High Resolution Observations
(CD-ROM Directory: contribs/luhe)
Authors: von der Lühe, O.
Bibcode: 2001ASPC..223..153V
Altcode: 2001csss...11..153V
  No abstract at ADS

Title: Where is the Intrinsic Size Limit of Fine Structure in the
Solar Photosphere? (CD-ROM Directory: contribs/bruls)
Authors: Bruls, J. H. M. J.; von der Lühe, O.
Bibcode: 2001ASPC..223..589B
Altcode: 2001csss...11..589B
  No abstract at ADS

Title: A study of the activity of G and K giants through their
    precise radial velocity. Breaking the 10-m/sec accuracy with FEROS.
Authors: Setiawan, J.; Pasquini, L.; da Silva, L.; Hatzes, A.; von der
   Luhe, O.; Kaufer, A.; Girardi, L.; de La, Reza R.; de Medeiros, J. R.
Bibcode: 2000Msngr.102...13S
Altcode:
  Asteroseismology is an indispensable tool that uses the properties of
  stellar oscillations to probe the internal structure of stars. This can
  provide a direct test of stellar structure and evolution theory. Precise
  stellar radial velocity (RV) measurements made in recent years have not
  only discovered the first extra-solar planets, but have also uncovered
  new classes of low-amplitude variable stars. One such is represented
  by the K giant stars which exhibit RV variations with amplitudes in
  the range of 50-300 m/s (Walker et al. 1989, Hatzes &amp; Cochran
  1993,1994 ab). This variability is multi-periodic and occurring on
  two time- scales: less than 10 days and several hundreds of days.

Title: High spatial resolution performance of a triple Fabry-Pérot
    filtergraph
Authors: von der Lühe, O.; Kentischer, Th. J.
Bibcode: 2000A&AS..146..499V
Altcode:
  We investigate the consequences of monochromatic pupil apodisation in
  a filtergraph based on Fabry-Pérot etalons in a telecentric mount,
  an effect which was discovered by Beckers (\cite{beckers1}). The pupil
  apodisation gives rise to systematic changes of the point spread
  function in the presence of strong spectral gradients, like in the
  wings of a Fraunhofer line. These changes are likely to produce spurious
  velocity signals in Dopplergrams generated from high spatial resolution
  filtergrams of the solar surface. We include in our analysis for the
  first time the effects of optical phase changes on pupil apodisation
  which has the tendency to enhance velocity errors. We study the
  resolution and the velocity errors for the three-etalon filtergraph
  TESOS (Kentischer et al. \cite{kenti1}) at the Vacuum Tower Telescope
  on Tenerife. Peak-to-valley velocity errors for solar structure with
  sizes of 2 arcsec and less and a contrast of 15% amount to less than
  50 m/s for the low resolution mode and to less than 10 m/s for the
  high resolution mode of TESOS in the worst case. We conclude that the
  performance of TESOS is not severely compromised by pupil apodisation.

Title: 10-um interferometry on the VLTI with the MIDI instrument:
    a preview
Authors: Leinert, Christopher; Graser, Uwe; Waters, Laurens B.; Perrin,
   Guy; Lopez, Bruno; Coudé du Foresto, Vincent; Glazenborg-Kluttig,
   Annelie W.; de Haas, Johannes C.; Herbst, Thomas M.; Jaffe, Walter;
   Lena, Pierre J.; Lenzen, Rainer; le Poole, Rudolf S.; Ligori,
   Sebastiano; Mundt, Reinhard; Pel, Jan-Willem; Porro, Irene L.; von
   der Luehe, Oskar
Bibcode: 2000SPIE.4006...43L
Altcode:
  We describe principles, design and present status of MIDI, the
  mid-infrared interferometric instrument for the VLTI, which is planned
  to come into operation at the ESO Very Large Telescope Interferometer
  during the second half of 2001.

Title: Science opportunities with AMBER, the near-IR VLTI instrument
Authors: Richichi, Andrea; Bloecker, Thomas; Foy, Renaud; Fraix-Burnet,
   Didier; Lopez, Bruno; Malbet, Fabien; Stee, Philippe; von der Luehe,
   Oskar; Weigelt, Gerd
Bibcode: 2000SPIE.4006...80R
Altcode:
  AMBER is the near-IR instrument for the VLTI, which will offer the
  possibility of combining two or three beams from either the 8 meter
  VLT main telescopes or the 1.8 meter auxiliary telescopes. With
  spectral dispersion up to 10,000 high visibility accuracy and the
  ability to obtain closure phases, AMBER will offer the means to
  perform high quality interferometric measurements in the 1 - 2.5
  micron range initially, with later extensions to other portions
  of the spectrum. These design characteristics, coupled to the VLT
  interferometer potential, open up the access to investigation of several
  classes of objects, from stellar to extragalactic astronomy. We will
  review the projected performance in terms of sensitivity and angular
  resolution, and illustrate the potential applications in some key
  research areas. In particular, we will present the work of the AMBER
  Science Group, which is evaluating simulated data of source models
  and interferometric outputs for the purpose of defining the criteria
  for observations.

Title: Kiepenheuer-Institut für Sonnenphysik. Jahresbericht für
    1999.
Authors: von der Lühe, O.
Bibcode: 2000MitAG..83..209V
Altcode:
  No abstract at ADS

Title: GREGOR: A 1.5m Telescope for Solar Research
Authors: von der Lühe, O.; Schmidt, Wolfgang; Soltau, Dirk; Kneer,
   Franz; Staude, Jurgen
Bibcode: 2000ESASP.463..629V
Altcode: 2000sctc.proc..629V
  No abstract at ADS

Title: Solar Observation with High Spatial and Spectral Resolution
Authors: Krieg, J.; Wunnenberg, M.; Kneer, F.; Koschinsky, M.; Ritter,
   C.; von der Lühe, O.
Bibcode: 1999AGAb...15...88K
Altcode: 1999AGM....15..P03K
  The solar atmosphere is, like stellar atmospheres in general,
  highly dynamic on small scales. To understand, e.g., the generation
  of turbulent motion and waves or chromospheric and coronal heating
  processes, observations with high resolution are needed. We achieve
  both high spatial and spectral resolution with a double Fabry-Perot
  interferometer which allows image restoration with speckle methods. Our
  new results include the height variation of the granular intensity
  pattern and velocity maps of unprecedented spatial resolution.

Title: Estimated Performance for 10-micron Interferometry at the
    VLTI with the MIDI Instrument
Authors: Porro, I. L.; Graser, U.; Leinert, C.; Lopez, B.; von der
   Lühe, O.
Bibcode: 1999ASPC..194..325P
Altcode: 1999wfoi.conf..325P
  The mid-infrared interferometric instrument (MIDI) is planned to become
  operative at the ESO Very Large Telescope Interferometer (VLTI) in the
  year 2001. As for any other interferometers, many effects contribute
  to reduce the fringe visibility of MIDI, and eventually to affect its
  scientific capabilities. We present a preliminary visibility budget
  for MIDI: this is currently used to provide requirements for the
  optical design and in the definition of the scientific performances
  of the instrument. The role of atmospheric and diffraction effects for
  interferometry at mid-infrared wavelengths is also discussed. Finally
  an overview of the scientific objectives of MIDI is presented.

Title: Kiepenheuer-Institut für Sonnenphysik. Jahresbericht für
    1998.
Authors: von der Lühe, O.
Bibcode: 1999MitAG..82..215V
Altcode:
  No abstract at ADS

Title: GREGOR, a 1.5 M Solar Telescope
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
   Staude, J.
Bibcode: 1999AGAb...15....5V
Altcode: 1999AGM....15..A01V
  We present the design of a new large solar telescope which is going to
  be installed at the Observatorio del Teide, in the tower that presently
  houses the 45cm Gregory-Coudé-Telescope. The new telescope has an
  aperture of 1.5 meters and its optical design is basically a Gregorian
  configuration. It will be an open telescope in an azimuthal mount. An
  adaptive optics system is incorporated in the optical design as well as
  a polarimetry package. The feasibility of lightweight optics for the
  primary mirror has been investigated in an industrial pre-study. The
  focal plane instrumentation will include a high resolution filter
  spectrometer similar to the existing TESOS instrument at the VTT and
  a new spectro-polarimeter for the visible and the near UV. The latter
  instrument is presently being developed jointly by the KIS and the
  High Altitude Observatory in Boulder, USA. Budget permitting, detailed
  (Phase-B) planning will start in 2000, and the telescope will be
  developed and built in 2002 and 2003 with first light in spring of 2004.

Title: Adaptive Optics for the German Solar Telescopes
Authors: Soltau, D.; Brunner, R.; von der Lühe, O.
Bibcode: 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: High-resolution observations with the German Vacuum Tower
    Telescope on Tenerife
Authors: von der Lühe, O.
Bibcode: 1998NewAR..42..493V
Altcode:
  The Vacuum Tower Telescope (VTT) on Tenerife has been the main
  ground-based observing facility of the German solar community since
  the late 1980s. We review its main features, performance and potential
  for high-resolution solar physics.

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.
Bibcode: 1998ESASP.421...43D
Altcode: 1998sjcp.conf...43D
  No abstract at ADS

Title: The angular diameter of R Doradus: a nearby Mira-like star
Authors: Bedding, T. R.; Zijlstra, A. A.; von der Luhe, O.; Robertson,
   J. G.; Marson, R. G.; Barton, J. R.; Carter, B. S.
Bibcode: 1997MNRAS.286..957B
Altcode: 1997astro.ph..1021B
  We find the angular diameter of R Doradus to be 57+/-5mas, exceeding
  that of Betelgeuse and implying that R Dor is larger in apparent
  size than every star except the Sun. R Dor is shown to be closely
  related to the Mira variables. We estimate an effective temperature
  of 2740+/-190K, a distance of 61+/-7pc, a luminosity of 6500+/-1400
  Lsolar and a radius of 370+/-50 Rsolar. The characteristics of R Dor are
  consistent with it being near the edge of a Mira instability strip. We
  detect non-zero closure phases from R Dor, indicating an asymmetric
  brightness distribution. We also observed W Hydrae, a small-amplitude
  Mira, for which we find an angular diameter of 44+/-4mas.

Title: Results of studies on the environmental factors affecting
    the VLTI performance
Authors: Koehler, Bertrand; Leveque, Samuel A.; von der Luehe, Oskar
Bibcode: 1997SPIE.2871..544K
Altcode:
  In the last few years, we have undertaken a number of studies and
  experiments to assess the impact of various environmental factors on the
  performance of the ESO very large telescope interferometer (VLTI). The
  investigated topics include atmospheric turbulence, wind loads on the
  telescope structure, vibrations created by equipment, natural thermal
  variation, thermal load from electronics, natural and man-made seismic
  noise, as well as acoustic noise. A first report of this activity
  was given in a previous paper. This paper presents the final results
  obtained in 1995. The main outcome is the very good confidence that
  the VLT 8 m telescope and the infrastructure design is adequate for
  interferometric use at optical wavelengths down to the visible.

Title: R Doradus: the biggest star in the sky.
Authors: Bedding, T. R.; Robertson, J. G.; Marson, R. G.; Zijlstra,
   A. A.; von der Lühe, O.
Bibcode: 1997Msngr..87...34B
Altcode:
  No abstract at ADS

Title: Optical path difference model for the Very Large Telescope
    Interferometer
Authors: Leveque, Samuel A.; Koehler, Bertrand; von der Luehe, Oskar
Bibcode: 1997SPIE.2871..556L
Altcode:
  The optical path difference model (OPD model) determines where to
  position the delay lines in order to compensate for on-axis delay
  as seen from an astronomical object of known coordinates. This model
  is equivalent to a pointing model but applied to the interferometric
  delay. The objective is to reduce the time to search for fringes and to
  improve the delay lines blind tracking accuracy. This aspect is of prime
  importance not only when considering the overall operational efficiency
  of the interferometer but also its ability to quickly observe a set of
  program objects even after relocation of the auxiliary telescopes. The
  optical path difference model is based on a precise knowledge of
  the interferometer configuration by including a set of calibration
  measurements. This paper describes the main characteristics of the model
  and includes the results of a simulation developed to fit telescope
  axis misalignments which contribute to optical path difference errors.

Title: Interferometry with the ESO Very Large Telescope
Authors: von der Luehe, Oskar; Derie, Frederic; Koehler, Bertrand;
   Leveque, Samuel A.; Paresce, Francesco; Verola, Massimo
Bibcode: 1997SPIE.2871..498V
Altcode:
  The interferometric mode of the ESO very large telescope (VLT)
  permits coherent combination of stellar light beams collected by four
  telescopes with 8 m diameter and by several auxiliary telescopes of
  the 2 m class. While the position of the 8 m telescopes is fixed,
  auxiliary telescopes can be moved on rails, and can operate from 30
  stations distributed on the top of the observatory site for efficient
  UV coverage. Coherent beam combination can be achieved with the 8 m
  telescopes alone, with the auxiliary telescopes alone, or with any
  combination, up to eight telescopes in total. A distinct feature
  of the interferometric mode is the high sensitivity due to the 8
  m pupil of the main telescopes, with the potential for adaptive
  optics compensation in the near- infrared spectral regime. The
  VLT interferometer is conceived as an evolutionary program where a
  significant fraction of the interferometer's functionality is initially
  funded, and more capability may be added later while experience is
  gained and further funding becomes available. The scientific program
  is now defined by a team which consists of a VLTI scientist at ESO and
  fifteen astronomers from the VLT community. ESO has recently decided
  to resume the construction of the VLTI which was delayed in December
  1993, in order to achieve first interferometric fringes with two of
  the 8 m telescopes around the year 2000, and routine operation with 2 m
  auxiliary telescopes from 2003 onwards. This paper presents an overview
  of the recent evolution of the project and its future development.

Title: A new plan for the VLTI.
Authors: von der Lühe, O.; Bonaccini, D.; Derie, F.; Koehler, B.;
   Léve^Que, S.; Manil, E.; Michel, A.; Verola, M.
Bibcode: 1997Msngr..87....8V
Altcode:
  The VLTI should acquire first fringes around the turn of the century
  in order to ensure competitiveness with other interferometry programmes.

Title: Simulations of Vlti/visa Imaging Observations of Young Stellar
    Objects at 2.2µm
Authors: Ageorges, N.; von der Lühe, O.
Bibcode: 1997svlt.work..349A
Altcode:
  No abstract at ADS

Title: An Introduction to Interferometry with the ESO Very Large
    Telescope
Authors: von der Lühe, O.
Bibcode: 1997svlt.work...13V
Altcode:
  No abstract at ADS

Title: Pupil Mask Interferometry of M8E-IR
Authors: Löwe, M.; Stecklum, B.; von der Lühe, O.; Quirrenbach, A.
Bibcode: 1997svlt.work..379L
Altcode:
  No abstract at ADS

Title: Interferometry with the ESO Very Large Telescope
Authors: von der Lühe; Dérié, F.; Koehler, Bertrand; Lévêque,
   S.; Paresce, F.; Verola, M.
Bibcode: 1997ioai.book....9V
Altcode:
  No abstract at ADS

Title: Stellar Surface Observations with the Vlti
Authors: von der Lühe, O.
Bibcode: 1997svlt.work..303V
Altcode:
  No abstract at ADS

Title: Results of Studies on the Environmental Factors Affecting
    the Vlti Performance
Authors: Koehler, B.; Lévêque, S.; von der Lühe, O.
Bibcode: 1997svlt.work..369K
Altcode:
  No abstract at ADS

Title: Internal Optical Path Calibration System for Vlti
Authors: Lévêque, S.; Koehler, B.; von der Lühe, O.
Bibcode: 1997svlt.work..375L
Altcode:
  No abstract at ADS

Title: Imaging in interferometry
Authors: von der Lühe, O.; Ageorges, N.
Bibcode: 1997ASIC..501...81V
Altcode: 1997hara.conf...81V
  No abstract at ADS

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.
Bibcode: 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: Kilometric baseline space interferometry
Authors: Bely, Pierre Y.; Laurance, Robin J.; Volonte, Sergio;
   Greenaway, Alan H.; Haniff, Christopher A.; Lattanzi, Mario; Mariotti,
   Jean-Marie; Noordam, Jan E.; Vakili, Farrokh; von der Luehe, Oskar;
   Lambert, Herve; Calvel, Bertrand; Scaddan, Richard J.; Vangasse, Paul
Bibcode: 1996SPIE.2807...59B
Altcode:
  Two versions of a kilometric interferometer with equivalent science
  capabilities have been studied, one located on the Moon and the other
  operating as a free-flyer. It has been found that the Moon is not the
  ideal site for interferometry because of tidal and micro-meteorite
  induced disturbances, the need for long delay lines and the large
  temperature swings from day to night. Automatic deployment of the
  Moon- based interferometer would be difficult and site preparation
  and assistance by man appear to be essential. The free-flyer would
  be implemented as a very accurately controlled cluster of independent
  satellites placed in a halo orbit around the 2nd Lagrange point of the
  Sun-Earth system. Both versions could attain the required scientific
  performances and each one needs the same type of metrology control. The
  free-flyer is intrinsically advantageous because of its reconfiguration
  flexibility, quasi-unlimited baseline length and observation efficiency
  (the Moon-based interferometer cannot be operated during the lunar
  day because of stray light). The free-flyer is better suited for
  implementation in the near or mid-term future, but the Moon-based
  version could be considered in the long term when a human presence
  would permit maintenance and upgrading leading to a longer lifetime
  with continuous performance enhancement.

Title: Longitudinal Dispersion Compensation for the Very Large
    Telescope Interferometer
Authors: Lévêque, Samuel; Koehler, Bertrand; von der Lühe, Oskar
Bibcode: 1996Ap&SS.239..305L
Altcode:
  The Very Large Telescope Interferometer [1,13] will be operated in air
  which will introduce small optical path fluctuations due to internal
  turbulence [4,6] and dispersion effects. Both may contribute to fringe
  contrast decrease. Longitudinal dispersion effects can be corrected
  by inserting an appropriate glass of variable thickness in one arm
  of the interferometer [3,5,11,12]. This paper presents a new method
  applied to VLTI in order to select the optimum glass, according to both
  the observing wavelength and the spectral bandpath, and to calculate
  its thickness. Results are presented in terms of improvement on the
  fringe contrast.

Title: Simulations of VLTI/VISA imaging observations of young stellar
    objects at 2.2 μm.
Authors: Ageorges, N.; von der Lühe, O.
Bibcode: 1996Msngr..85...18A
Altcode:
  No abstract at ADS

Title: Kilometric baseline space interferometry. Comparison of
    free-flyer and moon-based versions. Report by the Space Interferometry
    Study Team.
Authors: Bély, P. -Y.; Laurance, R. J.; Volonte, S.; Greenaway,
   A.; Haniff, C.; Lattanzi, M. G.; Mariotti, J. -M.; Noordam, J. E.;
   Vakili, F.; von der Lühe, O.
Bibcode: 1996kbsi.book.....B
Altcode:
  The authors have compared two versions of a kilometric interferometer
  with equivalent science capabilities, one located on the moon and the
  other operating as a free flying instrument. They have concluded that
  the free-flyer is better suited for an implementation in the near or
  mid-term future, but that the moon-based version should be considered
  in the long term in conjunction with a manned lunar infrastructure.

Title: A new start for the VLTI.
Authors: Paresce, F.; Mourard, D.; Bedding, T.; Beletic, J.; Haniff,
   C.; Leinert, C.; Malbet, F.; Mariotti, J. -M.; Mozurkewich, D.; Mundt,
   R.; Petitjean, P.; Quirrenbach, A.; Reinheimer, T.; Richichi, A.;
   Röttgering, H.; von der Lühe, O.; Waters, R.
Bibcode: 1996Msngr..83...14P
Altcode:
  The complexity and ambitious scope of VLTI mean that its astrophysical
  repercussions are difficult to define fully, even for many of its most
  vocal supporters. However, the primary scientic issues that it seeks to
  address are well defined, although there remains a need to present these
  coherently to the wider community in order to justify the significant
  resources which the project requires. Another pressing need is to
  develop an implementation plan that will optimally exploit the various
  technological stages of the project and ensure their compatibility
  with a vigorous, yet realistic and timely, astrophysical programme.

Title: Astrometrie mit dem VLT interferometer der ESO.
Authors: von der Lühe, O.
Bibcode: 1996AGAb...12...76V
Altcode:
  No abstract at ADS

Title: Scientific and technical goals for solar adaptive optics.
Authors: von der Lühe, O.
Bibcode: 1996AGAb...12...86V
Altcode:
  No abstract at ADS

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.
Bibcode: 1996AGAb...12...92S
Altcode:
  No abstract at ADS

Title: Observing stellar surface structure with the ESO-VLT
    interferometer
Authors: von der Luhe, O.; Solanki, S.; Reinheimer, Th.
Bibcode: 1996IAUS..176..147V
Altcode:
  No abstract at ADS

Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
    Heliospheric Observatory
Authors: Kohl, J. L.; Esser, R.; Gardner, L. D.; Habbal, S.; Daigneau,
   P. S.; Dennis, E. F.; Nystrom, G. U.; Panasyuk, A.; Raymond, J. C.;
   Smith, P. L.; Strachan, L.; Van Ballegooijen, A. A.; Noci, G.;
   Fineschi, S.; Romoli, M.; Ciaravella, A.; Modigliani, A.; Huber,
   M. C. E.; Antonucci, E.; Benna, C.; Giordano, S.; Tondello, G.;
   Nicolosi, P.; Naletto, G.; Pernechele, C.; Spadaro, D.; Poletto, G.;
   Livi, S.; Von Der Lühe, O.; Geiss, J.; Timothy, J. G.; Gloeckler,
   G.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.;
   Fowler, W.; Fisher, R.; Jhabvala, M.
Bibcode: 1995SoPh..162..313K
Altcode:
  The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of
  three reflecting telescopes with external and internal occultation and
  a spectrometer assembly consisting of two toric grating spectrometers
  and a visible light polarimeter. The purpose of the UVCS instrument is
  to provide a body of data that can be used to address a broad range
  of scientific questions regarding the nature of the solar corona and
  the generation of the solar wind. The primary scientific goals are
  the following: to locate and characterize the coronal source regions
  of the solar wind, to identify and understand the dominant physical
  processes that accelerate the solar wind, to understand how the coronal
  plasma is heated in solar wind acceleration regions, and to increase the
  knowledge of coronal phenomena that control the physical properties of
  the solar wind as determined byin situ measurements. To progress toward
  these goals, the UVCS will perform ultraviolet spectroscopy and visible
  polarimetry to be combined with plasma diagnostic analysis techniques
  to provide detailed empirical descriptions of the extended solar corona
  from the coronal base to a heliocentric height of 12 solar radii.

Title: Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory: instrument description and calibration
    overview
Authors: Kohl, J. L.; Esser, R.; Gardner, Larry D.; Habbal, S.;
   Daigneau, P. S.; Nystrom, George U.; Raymond, John C.; Strachan,
   Leonard; van Ballegooijen, A. A.; Noci, G.; Fineschi, Silvano; Romoli,
   Marco; Ciaravella, A.; Modigliani, A.; Huber, Martin C.; Antonucci, E.;
   Benna, C.; Giordano, S.; von der Luehe, Oskar; Tondello, Giuseppe;
   Nicolosi, Piergiorgio; Naletto, Giampiero; Pernechele, Claudio;
   Geiss, J.; Gloeckler, G.; Poletto, G.; Spadaro, D.; Allegra, A.;
   Basile, G.; Brusa, R.; Wood, B.; Siegmund, Oswald H.
Bibcode: 1995SPIE.2517...40K
Altcode:
  The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is
  composed of three reflecting telescopes with external and internal
  occultation and a spectrometer assembly consisting of two toric grating
  spectrometers and a visible light polarimeter. The UVCS will perform
  ultraviolet spectroscopy and visible polarimetry to be combined with
  plasma diagnostic analysis techniques to provide detailed empirical
  descriptions of the extended solar corona from the coronal base to a
  heliographic height of 12 R. In this paper, the salient features of
  the design of the UVCS instrument are described. An overview of the
  UVCS test and calibration activities is presented. The results from
  the calibration activity have demonstrated that the UVCS can achieve
  all its primary scientific observational goals.

Title: Interferometry with the ESO Very Large Telescope
Authors: von der Luehe, Oskar; Derie, Frederic; Ferrand, Didier;
   Koehler, Bertrand; Leveque, Samuel A.; Paresce, Francesco; D'Arcio,
   Luigi
Bibcode: 1995SPIE.2566..124V
Altcode:
  The interferometric mode of the ESO very large telescope (VLT)
  permits coherent combination of stellar light beams collected by
  four telescopes with 8m diameter and by several auxiliary telescopes
  of the 2m class. While the position of the 8m telescopes is fixed,
  auxiliary telescopes can be moved on rails, and can operate from 30
  stations distributed on the top of the observatory site for efficient
  UV coverage. Coherent beam combination can be achieved with the 8m
  telescopes alone, with the auxiliary telescopes alone, or with any
  combination, up to eight telescopes in total. A distinct feature of
  the interferrometric mode is the high sensitivity due to the 8m pupil
  of the main telescopes which will be compensated by adaptive optics
  in the near-infrared spectral regime. The VLT interferometer (VLTI)
  part of the VLT program is conceived as an evolutionary program where a
  significant fraction of the interferometer's functionality is initially
  funded, and more capability may be added later while experience is
  gained and further funding becomes available. Major subsystems of the
  present baseline VLTI include: three auxiliary telescopes, three delay
  lines which permit combining the light from up to four telescopes,
  and a laboratory which contains an imaging beam combiner telescope,
  and enough space to accomodate a number of experimental setups. This
  paper presents a general overview of the recent evolution of the
  project and its future development.

Title: Measurement of optical path fluctuations due to internal
    seeing for the VLTI
Authors: Leveque, Samuel A.; Koehler, Bertrand; von der Luehe, Oskar
Bibcode: 1995SPIE.2566..156L
Altcode:
  The very large telescope interferometer (VLTI) will relay stellar
  beams from each individual telescope to the combining facility through
  an air path, as opposed to vacuum. Internal air turbulence will
  induce optical path fluctuations which have been taken into account
  in the global VLTI error budget and in the expected performance
  of the delay line control system. This paper presents experimental
  data used to validate the assessment of these turbulence effects. A
  comparison with theoretical models developed for the free atmosphere
  is included in order to investigate their applicability in the VLTI
  delay line tunnel. Optical path fluctuations were measured by a laser
  interferometer working in the 0-80m range, in an underground tunnel
  representative of the VLTI beam transport facilities. The derived
  index structure coefficient, Cn<SUP>2</SUP>, inside the tunnel has
  been compared with high sensitivity temperature measurements.

Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
    Hellospheric Observatory
Authors: Raymond, J. C.; Kohl, J. L.; Esser, R.; Gardner, L. D.;
   Habbal, S.; Strachan, L.; van Ballegooijen, A. A.; Noci, G.; Fineschi,
   S.; Romoli, M.; Huber, M. C. E.; Antonucci, E.; Benna, C.; von der
   Luhe, O.; Naletto, G.; Nicolosi, P.; Pernechele, C.; Tondello, G.;
   Geiss, J.; Gloeckler, G.; Spadaro, D.; Daigneau, P. S.; Nystrom,
   G. U.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.
Bibcode: 1995SPD....26..720R
Altcode: 1995BAAS...27..970R
  No abstract at ADS

Title: Imaging the Surfaces of Late-Type Stars
Authors: Bedding, T. R.; von der Lühe, O.; Zijlstra, A. A.
Bibcode: 1995svlt.conf..100B
Altcode:
  No abstract at ADS

Title: Calibration of the VLT Interferometer
Authors: von der Lühe, O.; Quirrenbach, A.
Bibcode: 1995ESOC...53..173V
Altcode: 1995cuhe.conf..173V
  No abstract at ADS

Title: Narrow-Angle Astrometry with the VLT Interferometer
Authors: von der Lühe, O.; Quirrenbach, A.; Koehler, B.
Bibcode: 1995svlt.conf..445V
Altcode:
  No abstract at ADS

Title: Observation of Surface Activity on Cool Giants with the VLT
    Interferometer
Authors: von der Lühe, O.; Schüssler, M.; Solanki, S. K.; Caligari,
   P.
Bibcode: 1995svlt.conf...94V
Altcode:
  No abstract at ADS

Title: The MPE imaging beam combiner simulator COSI
Authors: Boeker, T.; Cruzalebes, P.; Hofmann, R.; Katterloher, R.;
   Eckart, A.; Genzel, R.; Drapatz, S.; von der Luehe, O.
Bibcode: 1994A&A...288..656B
Altcode:
  We present first interferograms and reconstructed images obtained with
  the MPE imaging beam combiner simulator COSI. The purpose of COSI is to
  simulate the imaging beam combiner at the coherent focus of the ESO VLTI
  in multi-speckle mode or under conditions of partial or full correction
  of the single telescope wave front by adaptive optics. COSI consists of
  a 1 m telescope and a near-infrared continuum light source to simulate
  the radiation from astronomical objects. Two flat mirrors allow us to
  use one half of the telescope as a transmitter and the other half as
  a receiver. In the receiving focus we have installed the MPE speckle
  camera SHARP, which uses a HgCdTe 256^2^ NICMOS 3 array. A pupil mask
  over the aperture allows us to simulate various telescope configurations
  with a beam compression factor of 100 as it will be used for the ESO VLT
  interferometer. COSI is used to explore NIR array detector properties
  and their suitability for interferometric measurements and to generate
  data to explore image reconstruction algorithms. First interferograms of
  single and multiple objects were taken early this year (1993). Employing
  various deconvolution and Fourier-inversion methods, a diffraction
  limited image of the pin-hole sources can be successfully recovered
  which experimentally demonstrates the feasibility of interferometric
  imaging with a beam combiner. Thus, we have demonstrated that COSI is
  an excellent test bed to investigate methods of image recovery and to
  investigate how the methods are influenced by effects like atmospheric
  turbulence, expected optical imperfections and detector characteristics.

Title: Interferometric mode of the European Southern Observatory
    Very Large Telescope
Authors: von der Luehe, Oskar; Ferrand, Didier; Koehler, Bertrand;
   Zhu, N.; Reinheimer, Thorsten
Bibcode: 1994SPIE.2200..168V
Altcode: 1994aisi.conf..168V
  The interferometric mode of the ESO Very Large Telescope (VLT)
  permits coherent combination of stellar light beams collected by four
  telescopes with 8-m diameter and by several auxiliary telescopes of the
  2-m class. While the position of the 8-m telescopes is fixed, auxiliary
  telescopes can be moved on rails, and can operate from 30 distributed
  on the top of the Observatory site for efficient UV coverage. Coherent
  beam combination can be achieved with the 8-m telescopes alone, with
  the auxiliary telescopes alone, or with any combination, up to eight
  telescopes in total. A distinct feature of the interferometric mode
  is the high sensitivity due to the 8-m pupil of the main telescopes
  which will be compensated by adaptive optics in the near-IR spectral
  regime. The VLT Interferometer (VLTI) part of the VLT Programme is
  conceived as an evolutionary program where a significant fraction of
  the interferometer's functionality is funded, and more capability may
  be added later while experience is gained and further funding becomes
  available. Major subsystems of the present baseline VLTI include:
  three auxiliary telescopes, three delay lines which permit combining
  the light from up to four telescopes, and a laboratory which contains
  an imaging beam combiner telescope and enough space to accommodate a
  number of experimental setups. This paper presents a general overview
  of the recent evolution of the project and its future development.

Title: Engineering aspects of the environmental factors affecting
    the VLTI performance
Authors: Koehler, Bertrand; von der Luehe, Oskar
Bibcode: 1994SPIE.2200..180K
Altcode: 1994aisi.conf..180K
  The stringent and specific requirements associated with visible aperture
  synthesis projects call for a sound engineering effort in the design
  and development phase to assess the instrumental performance. An
  important area of effort concerns the influence of the natural or
  man-made environmental factors on the global performance of the
  interferometer. This paper discusses the major environmental factors
  affecting the Very Large Telescope Interferometer (VLTI) and presents
  the results of a number of studies aimed at evaluating the effects of
  such environmental factors.

Title: Highly variable curvature mirrors for the Very Large Telescope
    Interferometer
Authors: Ferrari, Marc; Lemaitre, Gerard R.; Mazzanti, Silvio;
   von der Luehe, Oskar; di Biagio, Bernard; Montiel, Pierre; Revest,
   Daniel; Joulie, Patrice; Carre, Jean-Francois
Bibcode: 1994SPIE.2201..811F
Altcode:
  The design of two holosteric configurations have been optimized for a
  maximum center/edge de-flexure of 400 micrometers . Their thickness
  distribution is given for active zones of 16 mm in diameter. The
  curvature action is obtained from an air-pressure chamber that generates
  onto the rear side of the mirrors (1) a uniform pressure up to 9 Atm
  or (2) a central force up to 11 daN. The control of the curvature
  is made by an accurate pressure gauge. Some preliminary results are
  shown as obtained on metal prototype VCMs from a first fabrication
  cycle as well as an X-ray device for testing the machining validity
  of the boundaries at the edge of mirrors.

Title: Estimating residual aberrations from images taken at the user
    focus of a telescope compensated by adaptive optics
Authors: von der Luehe, Oskar; Theodore, Bertrand
Bibcode: 1994SPIE.2201..989V
Altcode:
  We present a simple procedure which estimates aberrations in the exit
  pupil from point source images taken at the compensated focus. The
  procedure is based on an iterative technique described by J. Fienup. The
  measured point spread function of the system produced with a reference
  source at the input to the adaptive optics system, and the exact,
  properly scaled shape of the (centrally obscured) exit pupil is all that
  is needed for the procedure to perform. The results can be obtained
  quickly, e.g., as part of a daily maintenance procedure. We present
  some sample cases which were produced with the Come-On Plus adaptive
  optics system at the ESO 3.6 m telescope on La Silla.

Title: Speckle imaging of solar small scale structure. 2: Study of
    small scale structure in active regions
Authors: von der Luehe, O.
Bibcode: 1994A&A...281..889V
Altcode:
  The speckle imaging technique which is described in the first paper
  of this series (von der Luehe 1993) was used to analyze time series
  of high angular resolution images of solar small scale structure at a
  wavelength of 585 nm in active regions with the 76 cm diameter vacuum
  tower telescope at National Solar Observatory (NSO)/Sac Peak. Two
  sets of reconstructed images with a field of 4 by 4 arcsec which
  cover a period of 36 min and 83 min were generated and analyzed. The
  image reconstructions are supplemented with simultaneous large field
  photographs taken within a 15 A passband centered on the Ca II K
  (3933) line. The prime objective of the observing program was the
  study of the structure and the dynamics of the continuum wavelength
  counterpart of facular points which appear with high contrast in the
  Ca pictures, i.e., continuum bright points (CBPs). In addition to CBPs,
  the reconstructions allow studying other small scale phenomena. Results
  of the studies are given.

Title: First Images with the MPE Imaging Beam Combiner Simulator COSI
Authors: Böker, T.; Cruzalèbes, P.; Hofmann, R.; Katterloher, R.;
   Eckart, A.; Genzel, R.; Drapatz, S.; Beckers, J.; von der Lühe, O.;
   Merkle, F.
Bibcode: 1994ESOC...48..161B
Altcode: 1994aao..conf..161B
  No abstract at ADS

Title: The VLT Interferometer [invited]
Authors: Bedding, T. R.; Beckers, J. M.; Faucherre, M.; Hubin, N.;
   Koehler, B.; von der Lühe, O.; Merkle, F.; Zhu, N.
Bibcode: 1994IAUS..158..143B
Altcode:
  No abstract at ADS

Title: Narrow-Band Speckle Imaging
Authors: Keller, C.; von der Lühe, O.
Bibcode: 1993rtpf.conf..129K
Altcode:
  No abstract at ADS

Title: First light from the NTT interferometer.
Authors: Bedding, T. R.; von der Lühe, O.; Zijlstra, A. A.; Eckart,
   A.; Tacconi-Garman, L. E.
Bibcode: 1993Msngr..74....2B
Altcode:
  No abstract at ADS

Title: Imaging of the Solar Surface with Interferometric Arrays
Authors: von der Lühe, O.
Bibcode: 1993rtpf.conf..150V
Altcode:
  No abstract at ADS

Title: Speckle imaging of solar small scale structure. I - Methods
Authors: von der Luehe, O.
Bibcode: 1993A&A...268..374V
Altcode:
  Speckle interferometry and imaging methods can improve considerably
  the angular resolution of images observed with a solar telescope. This
  paper describes in detail an implementation of the Knox-Thompson speckle
  imaging technique which has been developed specifically for the needs
  of solar imaging, in order to produce photometrically accurate maps of
  the intensity of solar small-scale features. The technique can recover
  fields of view of arbitrary size, i.e., fields which may be much larger
  than the isoplanatic patch. A number of problems which are peculiar to
  solar observations have been identified and were solved in the course of
  development of the imaging procedures. These problems and their solution
  are also described in detail. It is demonstrated that the application
  of speckle imaging to solar data results in near-diffraction-limited
  performance with a 76 cm telescope at a wavelength of 600 nm +/- 3 nm
  when seeing conditions are good, but not necessarily exceptionally good.

Title: Solar speckle polarimetry
Authors: Keller, C. U.; von der Luehe, O.
Bibcode: 1992A&A...261..321K
Altcode:
  The combination of a polarimeter with real-time frame selection
  and differential speckle imaging results in diffraction-limited
  magnetograms that provide new insight into the morphology of solar
  small-scale magnetic fields. The method to record diffraction limited
  narrow-band filtergrams of solar features is based on two cameras
  taking simultaneous short exposure images through a broad-band and
  a narrow-band filter, respectively. Speckle imaging reconstructs the
  image in the broad-band channel. This reconstruction determines the
  instantaneous optical transfer function (OTF) for each individual
  broad-band exposure. Each simultaneously recorded image in the
  narrow-band channel is then corrected for the instantaneous OTE To
  recover all spatial frequencies in the narrow-band channel the so
  corrected single images are averaged. We have applied the method
  to polarimetric observations of a solar active region by tuning
  the narrow-band filter to the wing of a Zeeman sensitive spectral
  line. The most active part of the region shows no more normal granules
  but features with a diameter of 0.3 to 0.5 arcsec. The smallest
  magnetic fields are concentrated in regions with sizes at or below
  the diffraction limit of the telescope.

Title: Application of Differential Speckle Imaging to Solar
    Polarimetry
Authors: Keller, C. U.; von der Luhe, O.
Bibcode: 1992ESOC...39..453K
Altcode: 1992hrii.conf..453K
  No abstract at ADS

Title: The Configuration of the VLT Interferometer on the Paranal Site
Authors: von der Luhe, O.; Beckers, J. M.; Braun, R.
Bibcode: 1992ESOC...39..959V
Altcode: 1992hrii.conf..959V
  No abstract at ADS

Title: A Progress Report on the Implementation of the VLT
    Interferometer
Authors: Beckers, J. M.; Faucherre, M.; Koehler, B.; von der Luhe, O.
Bibcode: 1992ESOC...39..775B
Altcode: 1992hrii.conf..775B
  No abstract at ADS

Title: Coudé Near Infrared Camera Instrument Contract Signed
Authors: Lenzen, R.; von der Lühe, O.
Bibcode: 1992Msngr..67...17L
Altcode:
  No abstract at ADS

Title: High Spatial Resolution Magnetograms of Solar Active Regions
Authors: Keller, C. U.; Stenflo, J. O.; von der Luhe, O.
Bibcode: 1992A&A...254..355K
Altcode:
  Using the Universal Birefringent Filter at the Sacramento Peak Vacuum
  Tower Telescope we have obtained simultaneous observations of left and
  right circular polarization in various solar magnetic features with a
  resulting spatial resolution of 0".7 in the magnetograms. We describe
  the data reduction in some detail and discuss the various instrumental
  effects. In particular we show that seeing can create features in
  magnetograms. A penumbra near disk center shows small-scale features in
  the magnetogram which are associated with the bright filaments. Bright
  features in the umbra of a small spot exhibit considerable polarization
  signals. In a pore region opposite polarities are found within a few
  seconds of arc.

Title: High spatial resolution techniques.
Authors: von der Luehe, O.
Bibcode: 1992soti.book....1V
Altcode:
  Contents: (1) Introduction. (2) Basic considerations and concepts:
  diffraction and optical transfer; coherence, Van Cittert-Zernike
  theorem. (3) Wave propagation through the atmosphere: statistics of
  index of refraction fluctuations; mutual intensity of a wave disturbed
  by turbulence; structure functions; the instantaneous optical transfer
  function. (4) Single frame analysis: data collection and preparation;
  image selection; single picture restoration; time series analysis. (5)
  Interferometry: Michelson interferometry; interferometric arrays;
  speckle interferometry; the Labeyrie method; seeing calibration;
  noise calibration; speckle imaging, Knox-Thompson; speckle imaging,
  speckle masking; speckle interferometry and anisoplanatism. (6) Active
  wavefront compensation: image motion compensation; adaptive optics. (7)
  Other methods: radio observations; high resolution observations from
  space; solar optical universal polarimeter; orbiting solar laboratory;
  solar and heliospheric observatory.

Title: Solar feature correlation tracker.
Authors: Rimmele, Th.; von der Luehe, O.; Wiborg, P. H.; Widener,
   A. L.; Dunn, R. B.; Spence, G.
Bibcode: 1991SPIE.1542..186R
Altcode:
  The authors present a tracking system that stabilizes atmospheric
  and instrumental image motion at the vacuum tower telescopes of the
  National Solar Observatory at Sacramento Peak and the Kiepenheuer
  Institut für Sonnenphysik at Tenerife. A matrix diode array rapidly
  scans the scene of interest, usually with a field of 5 arcsec. Images
  are cross-correlated in real time with a previously recorded reference
  image of the same area. Reference pictures are updated every 30
  s. Recent performance tests show that the residual image motion in the
  tracked image is 0.05 arcsec rms compared to a typical 0.5 arcsec rms
  for the untracked image. The correlation tracker also includes a seeing
  monitor providing a relative seeing measure at a two millisecond rate,
  which can be used for frame selection and shutter control.

Title: LEST Mini-Workshop: Entrance windows of solar
    telescopes. Summary and conclusions.
Authors: von der Lühe, O.
Bibcode: 1991ewst.conf...47V
Altcode:
  The main conclusion that can be drawn from the workshop is that the
  LEST entrance window is no longer a critical factor of the telescope
  design. There is a lot of confidence that the window is feasible,
  and as a result the discussions have concentrated on special issues
  and have gone into considerable detail. The presentations given at the
  workshop can be categorized into four broad topics: manufacture of the
  window, control of the window surface reflectivity, thermal control
  of the window, and polarization effects. The author will address each
  of the topics in this sequence.

Title: Coronal observations with SOHO
Authors: Huber, Martin C. E.; von der Luehe, Oskar
Bibcode: 1991AdSpR..11a.339H
Altcode: 1991AdSpR..11..339H
  The Solar and Heliospheric Observatory (SOHO) will carry a set of
  solar physics experiments which permit a thorough investigation of
  the solar corona. The emphasis of the mission is on the measurement
  of the physical properties of coronal structures and the processes
  occurring therein, leading - it is hoped - to an understanding of
  the mechanism(s) by which the solar corona is heated and the solar
  wind is accelerated. The observations will be made from a halo orbit
  around the L1 Lagrange point on the Earth-Sun line and will range from
  magnetic field measurements in the photosphere through spectroscopic
  plasma diagnostics of chromospheric, transition-zone and coronal
  structures with high spatial and spectral resolution, to coronagraphic
  observations out to 30 solar radii and to mass spectrometry of the
  solar wind near one astronomical unit. <P />SOHO is part of the Solar
  Terrestrial Science Programme (STSP), the first `Cornerstone' in ESA's
  long-term scientific programme `Space Science - Horizon 2000', and
  will therefore be flown in connection with the other STSP component,
  the four-spacecraft Cluster mission, which will investigate plasma
  structures and processes in the magnetosphere in three dimensions. <P
  />Both STSP missions, i.e. SOHO and Cluster will address the physics of
  plasma structures and processes, that are accessible to investigation
  in the solar-terrestrial context, yet are thought to be examples of
  plasma processes and structures that are ubiquitous in the cosmos. It
  is hoped that a cross-fertilisation between the scientific communities
  associated with SOHO and Cluster will take place, as they investigate
  the physics of the coronal and magnetospheric plasma with complementary
  methods and techniques - globally by remote observations, and in detail,
  by multi-point in-situ measurements.

Title: High spatial resolution techniques.
Authors: von der Luehe, O.
Bibcode: 1991sia..book..688V
Altcode:
  Observations of the solar surface from the ground are severely affected
  by turbulence of the Earth's atmosphere. Beside selecting observatory
  sites for excellent atmospheric quality, the careful design of the
  observing equipment, and the application of modern methods that undo
  the effects of the atmosphere or recover degraded data provide a wealth
  of information on small-scale processes. The effects of atmospheric
  turbulence on solar observations are reviewed, and methods that
  achieve high angular resolution on the Sun, such as adaptive optics
  and interferometry, are discussed. Some experiments that provide solar
  observations of high spatial resolution are presented.

Title: Solar adaptive optics
Authors: von der Luehe, O.
Bibcode: 1991AdSpR..11e.275V
Altcode: 1991AdSpR..11..275V
  Ground-based observations of solar small-scale structure is severely
  degraded by thermal fluctuations in the Earth's atmosphere. Adaptive
  optics systems can compensate in real time the aberrations caused by
  seeing, permitting observations close to the diffraction limit of the
  telescope. There are adaptive optical systems with varying degrees
  of complexity, ranging from simple fast guiders for high-contrast,
  confined targets to sophisticated systems that undo high degree
  wavefront deformations. This paper reviews the main principles of
  adaptive optics, addresses issues peculiar to solar adaptive systems,
  and presents current developments in this area.

Title: Adaptive Optik für die Sonnenbeobachtung.
Authors: Rimmele, Thomas; von der Luehe, Oskar
Bibcode: 1990S&W....29..520R
Altcode:
  The present status is reviewed of efforts to construct an earth-based
  solar observatory which will compensate for the distorting effects
  of the earth's atmosphere on solar observations. Image movement
  compensation techniques are described, including the recently developed
  Correlation Tracker. Efforts being made in the area of higher-order
  adaptive optics are addressed.

Title: Solar feature correlation tracker for ground-based telescopes
Authors: von der Luehe, O.; Widener, A. L.; Rimmele, Th.; Spence,
   G.; Dunn, R. B.
Bibcode: 1989A&A...224..351V
Altcode:
  A tracking system that stabilizes atmospheric and instrumental image
  motion has been tested at the vacuum tower telescope of the National
  Solar Observatory at Sacramento Peak. The system locks anywhere on
  the sun, using solar granulation or other small scale structures as
  tracers. A matrix diode array rapidly scans the scene of interest;
  pictures are cross-correlated in real time with a previously recorded
  reference image of the same area on the sun.

Title: Solar Ultraviolet Network: an interferometric investigation
    of the fundamental solar astrophysical scales
Authors: Dame, Luc; Moreau, Bernard G.; Cornwell, Timothy J.;
   Visser, H.; Title, Alan M.; Acton, Loren W.; Aime, Claude; Braam,
   Bart M.; Bruner, Marilyn E.; Connes, Pierre; Faucherre, Michel; Foing,
   B. H.; Haisch, Bernhard M.; Hoekstra, Roel; Heyvaerts, Jean; Jalin,
   Rene; Lemaire, Philippe; Martic, Milena; Muller, R.; Noens, J. C.;
   Porteneuve, Jacques; Schulz-Luepertz, E.; von der Luehe, Oskar
Bibcode: 1989SPIE.1130..126D
Altcode:
  The Solar UV Network (SUN) presently proposed is an interferometric
  system, based on the principles of stabilized interferometry, which
  will be capable of solar observations with spatial resolutions better
  than 0.013 arcsec. SUN will consist of four 20-cm diameter telescopes
  aligned nonredundantly on a 2-m baseline. SUN is judged to be ideally
  deployable by the NASA Space Station, if implemented on a pointing
  platform whose performance is of the order of the Instrument Pointing
  System flown on Spacelab 2. The compact, nonredundant configuration of
  SUN's telescopes will allow high-resolution imaging of a 2 x 2 arcsec
  field on the solar disk.

Title: Prospects for solar interferometry.
Authors: von der Lühe, O.; Zirker, J. B.
Bibcode: 1989hsrs.conf..191V
Altcode:
  No abstract at ADS

Title: Solar speckle imaging.
Authors: von der Lühe, O.
Bibcode: 1989hsrs.conf..147V
Altcode:
  This paper discusses the application of extensions of Labeyrie's
  speckle interferometry method to solar observations. These extensions
  fully reconstruct a picture of the source.

Title: High spatial resolution solar observations
Authors: von der Luehe, Oskar
Bibcode: 1989hsrs.conf.....V
Altcode:
  No abstract at ADS

Title: Technical aspects of the speckle masking phase reconstruction
    algorithm
Authors: Pehlemann, E.; von der Luehe, O.
Bibcode: 1989A&A...216..337P
Altcode:
  Technical problems that arise when the full four-dimensional speckle
  masking algorithm is implemented to reconstruct diffraction-limited
  two-dimensional images of astronomical objects are discussed,
  with particular emphasis on extended sources. The symmetries
  of the four-dimensional speckle masking bispectrum are used
  to relax computer memory requirements of the algorithm without
  loss of information. Further limits on the bispectrum reduce it to
  manageable sizes, but imply a loss of information. Various approaches
  of bispectrum truncation and the consequences for the phase recovery
  process are discussed, phase consistency and phase number diagrams
  are introduced as tools for quality assessment of the algorithm and
  the reconstruction. Different sequences for the phase recovery process
  are discussed as well. Sample reconstructions of a point source and of
  an extended object (a section of the solar photosphere) are presented.

Title: A Correlation Tracker for Solar Fine Scale Studies.
Authors: Rimmele, Th.; von der Luehe, O.
Bibcode: 1989RvMA....2..105R
Altcode:
  No abstract at ADS

Title: High-resolution imaging of the solar photosphere.
Authors: von der Lühe, O.; Pehlemann, E.
Bibcode: 1989AGAb....2...34V
Altcode:
  No abstract at ADS

Title: A correlation tracker for solar fine scale studies.
Authors: Rimmele, T.; von der Lühe, O.
Bibcode: 1989amts.conf..105R
Altcode:
  A solar feature correlation tracker was designed, built, and
  successfully tested in a joint effort of the National Solar Observatory
  in Sunspot, USA, and the Kiepenheuer Institut, Freiburg, Germany. The
  purpose of the system is stabilizing image motion which is caused
  by telescope shake and by seeing at the post-focus instruments of
  vacuum tower telescopes in Sunspot and in Izana. The tracker system
  features a matrix diode array as detector, fast digital processors,
  and an agile mirror as the optical active element. The processor
  consists of commercial and in-house built hardware.

Title: Wavefront error measurement technique using extended,
    incoherent light sources
Authors: von der Luhe, O.
Bibcode: 1988OptEn..27.1078V
Altcode:
  A technique for measuring wavefront errors in an optical system that
  receives light from a spatially extended, arbitrarily structured,
  incoherent source is described. If a suitable transparent mask is
  placed at an image plane of the system, the structure in the light
  source serves as a tracer for wavefront errors. The slope of the
  wavefront error can be detected in the form of intensity variations
  in a pupil image that follows the mask. One-dimensional numerical
  simulations of the method as well as the analytical treatment of the
  proposed principle are presented. The application of the technique as a
  wavefront sensor in an adaptive optical system for solar observations,
  in which aberrations are caused by atmospheric turbulence in the light
  path, is discussed as an example.

Title: Measurements of characteristics of image motion with a solar
    image stabilizing device
Authors: von der Luhe, O.
Bibcode: 1988A&A...205..354V
Altcode:
  An image motion stabilizer that locks on confined areas which are
  brighter or darker than the surrounding photosphere was used to measure
  some characteristics of atmospheric image motion at the Vacuum Tower
  telescope of the National Solar Observatory. The device stabilizes
  images of sunspots, pores, and faculae. Recordings of the drive signals
  were analyzed. Image motion between 0.3 and 0.5 arcsec rms was measured,
  power spectra of the recordings show roughly the behavior predicted
  theoretically for frequencies below 1 Hz and a much steeper decrease
  for frequencies larger than 5 Hz. Residual motion measured at various
  distances away from the stabilized area shows an increase over some 100
  arcsec. The residual rms motion is less than the theoretical resolution
  of the telescope within roughly 30 arcsec around the stabilized area.

Title: Signal transfer function of the Knox-Thompson speckle imaging
    technique
Authors: von der Luhe, Oskar
Bibcode: 1988JOSAA...5..721V
Altcode: 1988OSAJ....5..721V
  The transfer function associated with the Knox-Thompson speckle imaging
  technique is investigated. Numerical model transfer functions using
  log-normal statistics for perturbation of the complex wave front, the
  near-field approximation, and a Kolmogorov spectrum for atmospheric
  turbulence statistics are presented. Simple approximations for the
  transfer function are discussed. As with the transfer function of
  Labeyrie's speckle interferometry technique, the portion beyond
  the seeing limit can be represented as the transfer function of an
  unaberrated telescope times a seeing-dependent constant. An additional
  factor depends on the frequency shift of the Knox-Thompson cross
  spectra. The influence of the frequency shift on the reconstructed
  phase error is discussed for simple reconstruction problems.

Title: Scientific goals for solar interferometry.
Authors: von der Lühe, O.; Zirker, J. B.
Bibcode: 1988ESOC...29...77V
Altcode: 1988hrii.conf...77V
  The authors review scientific programs for solar research that can be
  carried out using interferometric techniques. They establish boundary
  conditions for interferometric experiments. The performance and
  achievable resolution of interferometry is studied using an empirical
  model spectrum of the intensity fluctuation of solar granualtion as an
  example of extended, low-contrast small scale structure. The authors
  conclude that, with interferometric techniques, a ten-fold increase
  in resolution beyound today's seeing-limited performance is possible.

Title: Speckle masking imaging of extended sources.
Authors: von der Lühe, O.; Pehlemann, E.
Bibcode: 1988ESOC...29..159V
Altcode: 1988hrii.conf..159B
  The authors have developed a computer code to calculate speckle
  masking image reconstructions from two-dimensional observations of
  extended sources. The code was applied to specklegrams of solar small
  scale structure. The authors report on first results obtained with
  this code and compare reconstructions with those obtained using the
  Knox-Thompson technique.

Title: First results with the NOAO 2-D speckle camera for infrared
    wavelengths.
Authors: Beckers, J. M.; Christou, J. C.; Probst, R. G.; Ridgway,
   S. T.; von der Lühe, O.
Bibcode: 1988ESOC...29..393B
Altcode: 1988hrii.conf..393B
  The authors have constructed an infrared speckle camera using the NOAO
  SBRC 58×62 InSb array detector. The camera and detector can be used
  anywhere in the 1 to 5 μm wavelength region. The authors describe the
  first observations. These observations illustrate the performance of
  the camera for an unresolved object, for a double star (ζ Aqr) and
  for a resolved object (the "Red Rectangle"). The authors have analyzed
  the observations using shift-and-add, power spectrum/autocorrelation
  function, and Knox-Thompson methods.

Title: Solar granulation power spectra from speckle interferometry
Authors: von der Luhe, O.; Dunn, R. B.
Bibcode: 1987A&A...177..265V
Altcode:
  Granulation was observed with a CCD array at the SPO tower telescope
  in a quiet region near the solar center. Time series of short exposure
  (4 ms) pictures of a 14 by 14 arcsec region were taken. Consecutive
  frames were separated by 0.55 s in time. Labeyrie's (1970) speckle
  interferometry technique was applied in order to recover power spectra
  of the intensity fluctuations at high spatial frequencies. The spectral
  ratio technique (von der Luhe, 1984) was applied to correct for seeing
  attenaution of the power spectra. It is possible to recover a signal
  up to spatial frequency of 2.5 line pairs per arcsec, corresponding
  to a wave number of 22/Mm or 40 percent of the diffraction limit of
  the telescope under 1.3 arcsec average seeing conditions. A corrected
  rms granulation contrast of 0.127 + or - 0.01 is estimated, and an
  exponential falloff of power density toward higher spatial frequencies
  is observed.

Title: Photon noise analysis for a LEST multidither adaptive optical
    system.
Authors: von der Lühe, O.
Bibcode: 1987LFTR...28..255V
Altcode:
  A simple analysis to assess the influence of photon noise in a solar
  adaptive optic based on a multidither wavefront detection principle is
  carried out. It is argued that the performance should be practically
  independent of the type of control (modal or zonal). The performance
  of such a system increases slightly with the telescope diameter. It
  should be possible to control a few dozen modes or zones with a system
  working at a 2.4m diameter LEST.

Title: Application of the Knox-Thompson Method to Solar Observations
Authors: von der Luhe, O.
Bibcode: 1987iia..conf...37V
Altcode:
  No abstract at ADS

Title: Photospheric Fine Structure Close to a Sunspot
Authors: von der Lühe, O.
Bibcode: 1987rfsm.conf..156V
Altcode:
  Facular points, which typically have angular scales smaller than one
  arc second, are believed to represent the footpoints of magnetic flux
  tubes in the photosphere. The author made observations of facular points
  in the continuum and tried to resolve them using the Knox-Thompson
  speckle imaging technique. The objective was to measure the spatial
  extent of facular points and, if possible, to resolve their internal
  structure. Also, by using a time series of images, the lifetime
  of facular points can be determined and their interaction with the
  surrounding medium can be examined.

Title: A wavefront sensor for extended, incoherent targets.
Authors: von der Lühe, O.
Bibcode: 1987LFTR...28..155V
Altcode:
  The author proposes a novel method for sensing wavefront errors in
  an aberrated solar telescope. The wavefront sensor consists of a
  transparent mask located at an image plane. A difference image of the
  scene under observation is encoded in density on the mask. Wavefront
  error slopes can be detected in a pupil image following the mask
  in the form of intensity variations. The principle of the method
  is described and results of one-dimensional simulation calculations
  are presented. It is demonstrated that the proposed method is very
  sensitive and requires only a few percent of the incident light for
  a photon-noise limited null state measurement.

Title: Study of Sizes Brightnesses and Dynamics of Solar Facular
    Points
Authors: von der Luhe, O.
Bibcode: 1987iia..conf..225V
Altcode:
  This paper presents first results of an ongoing project to study the
  structure and the dynamics of small faculae.

Title: Calibration Problems in Solar Speckle Interferometry
Authors: von der Luhe, O.
Bibcode: 1987iia..conf....9V
Altcode:
  No abstract at ADS

Title: Solar Image Stabilization
Authors: von der Luhe, O.
Bibcode: 1986BAAS...18..924V
Altcode:
  No abstract at ADS

Title: Initial Solar Observations at Sacramento Peak Using the
    Lockheed Active Optics System
Authors: Smithson, R. C.; Sharbaugh, R. J.; Ramsey, H. E.; Acton,
   D. S.; Pari, M.; Keil, S. L.; Radick, R. R.; Simon, G. W.; von der
   Luehe, O.; Zirker, J. B.
Bibcode: 1986BAAS...18..933S
Altcode:
  No abstract at ADS

Title: Speckle Image Reconstructions of Solar Pore Images taken in
    Hα 6563
Authors: Conde, A. L.; von der Luhe, O.; Radick, R. R.
Bibcode: 1986BAAS...18R.933C
Altcode:
  No abstract at ADS

Title: Image Enhancement Techniques Applied to Solar Granulation Data
Authors: von der Luehe, O.; Dunn, R. B.; November, L. J.
Bibcode: 1986BAAS...18..663V
Altcode:
  No abstract at ADS

Title: The Speckle Masking Transfer Function
Authors: von der Luhe, O.
Bibcode: 1985A&A...150..229V
Altcode:
  The transfer function for the speckle masking image reconstruction
  technique (Weigelt, 1977; Weigelt et al., 1983; Lohman et al., 1983
  has been analyzed. The regions relevent to the speckle masking signal
  turn out to be proportional to (r<SUB>0</SUB>/D)<SUP>4</SUP>, where
  r<SUB>0</SUB> is Fried's seeing parameter and D is the diameter of
  the telescope entrance pupil.

Title: Adaptive Image Stabilization of Solar Observations: a Review
Authors: von der Luehe, O.
Bibcode: 1985LNP...233...62V
Altcode: 1985hrsp.proc...62V
  Active wavefront correction techniques for solar imaging are
  discussed. The basic elements of all systems include: a wavefront
  error detector, servo logic, and an active optical element. The use
  of image motion (IM) control in image displacement detection and
  active element design for adaptive control systems is analyzed. The
  spot and correlation tracking methods of displacement detection are
  studied. The spot tracking uses a four-point limit guider, is based
  on local intensity maxima, and is applicable for observing sunspots
  and pores. The correlation trackers are designed to continuously scan
  an image detector and to compare the image with reference images
  in order to obtain the error signals. The application of agile,
  high quality mirrors either piezoelectrically or electrodynamically
  driven, to IM control is investigated. Research is being conducted on
  utilizing a real-time atmospheric compensation system in wavefront
  correction. Hardy's (1980) model, which consists of a rotational
  shearing interferometer as the wavefront sensor, monolithic
  piezoelectric mirrors as the active element, and analog logic to
  generate the drive signal, and the Smithson (1983) design, which uses
  a wavefront sensor that is a combination of the Hartmann test principle
  and the spot tracking principle, are examined.

Title: High Resolution Speckle Imaging of Solar Small-Scale Structure:
    the Influence of Anisoplanatism
Authors: von der Luehe, O.
Bibcode: 1985LNP...233...96V
Altcode: 1985hrsp.proc...96V
  The effects of anisoplanatism on image reconstructions developed
  with the Knox and Thompson (1974) technique are investigated. The
  procedures for reconstruction are described. A time series of 30
  solar granulation images covering 14 x 14 arcsec and 15 s of time
  were analyzed. The four reconstructions derived from the series are:
  (1) the entire field centered in an area of 32 x 32 pixels, (2) the
  series without anisoplantic image motion, (3) the field restricted
  to the center 64 x 64 pixels covering approximately 7 x 7 arcsec,
  and (4) the center 40 x 40 pixels corresponding to a 4 x 4 arcsec
  square. Consistency tests were performed on the reconstructions. The
  comparisons of the reconstructions with a sample frame reveal that
  the Knox and Thompson technique is not useful when the field is larger
  than the isoplantic patch.

Title: Estimating Fried's parameter from a time series of an arbitrary
    resolved object imaged through atmospheric turbulence.
Authors: von der Luehe, O.
Bibcode: 1984JOSAA...1..510V
Altcode: 1984OSAJ....1..510V
  A method to obtain an estimate of Fried's seeing parameter r<SUB>0</SUB>
  from time series of an arbitrarily shaped, resolved structure
  that exhibits degradation resulting from atmospheric turbulence is
  presented. The basic idea is to evaluate the ratio of the observed
  squared modulus of the average Fourier transform and the observed
  average power spectrum. The theory of the method is developed, and
  the influence of noise on the ratio is discussed. The method has
  been applied to five consecutive time series of observations of solar
  granulation under different seeing conditions. The power spectra, which
  are reconstructed with appropriate theoretical modulation transfer
  functions, converge.

Title: A Method to Estimate Fried's Seeing Parameter from a Time
    Series of Arbitrary Resolved Structures Imaged Through the Atmosphere
Authors: von der Luhe, O.
Bibcode: 1984vlti.conf..203V
Altcode: 1984IAUCo..79..203V
  A method is presented that allows to estimate the effective MTF from
  the observation of arbitrary structure with the use of Fried-Korff
  theory. The ratio of the squared modulus of the average Fourier
  transform and the average power spectrum serves as an estimator for the
  Fried parameter r<SUB>0</SUB>. To a first approximation, this ratio
  is independent from the observed object. Additionally, the behaviour
  of the ratio in regions beyond the seeing limit in the Fourier plane
  may be analyzed to obtain an estimate of the speckle interferometry
  signal-to-noise ratio.

Title: A study of a correlation tracking method to improve imaging
    quality of ground-based solar telescopes
Authors: von der Luehe, O.
Bibcode: 1983A&A...119...85V
Altcode:
  The measurement and correction of image motion introduced by the earth's
  atmosphere is undertaken, in order to improve solar imaging, by means
  of a correlation-tracking method designed to guide ground-based solar
  telescopes during the study of small scale, low contrast photospheric
  structures. A time series of digitized images was obtained with
  a two-dimensional CCD camera of 32 x 32 pixels. Image motion was
  determined from the locations of the cross-correlation function peaks
  of an arbitrarily chosen reference image, and the tracking method
  was simulated off-line by computer methods. Analysis results indicate
  that image motion may be suppressed to a residual rms value as low as
  1/18th of the theoretical Rayleigh limit of telescopic resolution. The
  correlation method is found to work on arbitrary structures with
  rms constant values as low as a few percent under acceptable seeing
  conditions.

Title: Adaptive optical systems for LEST.
Authors: von der Lühe, O.
Bibcode: 1983LFTR....2.....V
Altcode:
  Some fundamental properties of adaptive optical systems and some basic
  design considerations for such a system on LEST have been discussed.

Title: A comparison of optical and digital Fourier transformation
    of solar granulation
Authors: von der Luehe, O.
Bibcode: 1981A&A...101..277V
Altcode:
  The application of an optical Fourier transformation setup to solar
  granulation transparencies is examined. An analysis of the photographic
  process makes it possible to derive calibrated radial power spectra of
  the granulation intensity fluctuations. The results are compared with
  power spectra of the same pictures obtained via microdensitometry and
  fast Fourier algorithms. It is found that the two independent methods
  lead to essentially the same quantitative results in the medium to
  high spatial wavenumber regions (2.5 to 10 per Mm). Disturbances due
  to the film supporting the granulation transmission pattern do not
  permit any significant optical power density estimates in the lower
  wavenumber regions (below 2.5 per Mm). It is concluded, however, that
  optical Fourier transformation, may be a useful alternative to other
  techniques in this field.

Title: Ein Vergleich zwischen optischer und digitaler
    Fouriertransformation von Sonnengranulationsaufnahmen
Authors: von der Lühe, O.
Bibcode: 1981MitAG..54..261V
Altcode:
  No abstract at ADS

