explanation blue bibcodes open ADS page with paths to full text
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
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
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
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.
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.
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
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
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
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
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.
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
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
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.
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.
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<
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.
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.
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.
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.
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.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. <BR />
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. <BR /> Methods: We present speckle-reconstructed images taken
with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
486 nm and 589 nm bands. We estimate the spatial resolution from the
noise characteristics of the image bursts and obtain 0.08″ at 589
nm. We describe structure details in individual best images as well
as the temporal evolution of selected features. <BR /> Results: We
find branched dark lanes extending along thin (≈1″) light bridges
in sunspots at various heliocentric angles. In thick (≳ 2″) light
bridges the branches are disconnected from the central lane and have a Y
shape with a bright grain toward the umbra. The images reveal that light
bridges exist on varying intensity levels and that their small-scale
features evolve on timescales of minutes. Faint light bridges show
dark lanes outlined by the surrounding bright features. Dark lanes are
very common and are also found in the boundary of pores. They have a
characteristic width of 0.1″ or smaller. Intergranular dark lanes of
that width are seen in active region granulation. <BR /> Conclusions: We
interpret our images in the context of magneto-convective simulations
and findings: while central dark lanes in thin light bridges are
elevated and associated with a density increase above upflows, the dark
lane branches correspond to locations of downflows and are depressed
relative to the adjacent bright plasma. Thick light bridges with central
dark lanes show no projection effect. They have a flat elevated plateau
that falls off steeply at the umbral boundary. There, Y-shaped filaments
form as they do in the inner penumbra. This indicates the presence of
inclined magnetic fields, meaning that the umbral magnetic field is
wrapped around the convective light bridge.
---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. <BR /> Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. <BR /> Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. <BR />
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. <BR /> Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. <BR /> Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. <BR /> Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. <BR /> Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: 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.
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 < 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
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.
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.
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
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
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
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
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.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.
---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.
---------------------------------------------------------
Title: 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.
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.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.
---------------------------------------------------------
Title: The GREGOR adaptive optics system
Authors: Berkefeld , Th.; Schmidt, D.; Soltau, D.; von der Lühe,
O.; Heidecke, F.
2012AN....333..863B Altcode:
The new 1.5-m German solar telescope GREGOR at the Observatorio
del Teide, Tenerife, is equipped with an integrated adaptive optics
system. Although partly still in the commissioning phase, the system is
already being used used for most science observations. It is designed
to provide diffraction-limited observations in the visible-light regime
for seeing better than 1.2 arcsec. We describe the AO system including
the optical design, software, wavefront reconstruction, and performance.
---------------------------------------------------------
Title: Optical design of the new solar telescope GREGOR
Authors: Soltau, D.; Volkmer, R.; von der Lühe, O.; Berkefeld, Th.
2012AN....333..847S Altcode:
This article describes the considerations which led to the current
optical design of the new 1.5 m solar telescope GREGOR. The result
is Gregorian design with two real foci in the optical train. The
telescope includes a relay optic with a pupil image used by a high
order adaptive optics system (AO). The optical design is described in
detail and performance characteristics are given. Finally we show some
verification results which prove that - without atmospheric effects -
the completed telescope reaches a diffraction limited performance.
---------------------------------------------------------
Title: Editors' note
Authors: Denker, Carsten; Feller, Alex; Schmidt, Wolfgang; von der
Lühe, Oskar
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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
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
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
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.
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.
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.
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.
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 < 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
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.
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.
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.
2007AN....328..252K Altcode: 2008arXiv0811.0693K
The objective of this article is to use Fourier-Hankel decomposition as
suggested earlier by Braun & 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.
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.
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.
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.
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&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.
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.
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.
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.
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.
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.
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 & 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.
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.
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<θ<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.
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.
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
2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V
The integration of the three main silicon carbide mirrors into the new
1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
during 2006. We expect first light at the end of 2006. A progress
report about integration of the optics and mechanics and planning of
the commissioning phase of the telescope and post focus instruments
will be presented at the meeting. The GREGOR telescope is build by a
consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
Gottingen and additional national and international Partners.
---------------------------------------------------------
Title: Multi-conjugate solar adaptive optics with the VTT and GREGOR
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Lühe, Oskar
2006SPIE.6272E..05B Altcode: 2006SPIE.6272E...4B
After the successful demonstration of the solar multi-conjugate adaptive
optics (MCAO) system at the German 70cm Vacuum Tower Telescope (VTT),
Observatorio del Teide, Tenerife, in the last years, we are continuing
the development of the system as a testbed for the future MCAO of the
150cm GREGOR solar telescope. We describe an improved reconstruction
scheme that increases the number of corrected off-axis degrees of
freedom and will be tested at the VTT in September 2006. We present
a modified optical setup of the GREGOR MCAO that has the advantage of
being adjustable to a wide height range of the turbulence.
---------------------------------------------------------
Title: Simulation of adaptive optics for the Vacuum Tower Telescope
Authors: Enmark, Anita; Berkefeld, Thomas; von der Lühe, Oskar;
Andersen, Torben
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.
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
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
2005CRPhy...6.1139V Altcode:
We present a breadboard multi-conjugate adaptive optics (MCAO) system
for high angular resolution solar observations which we operate at
the Vacuum Tower Telescope. We have developed methods to estimate
quantitatively the performance of solar adaptive optics from science
data. Several sets of short exposure images of the solar photosphere
were analyzed to assess the performance of the MCAO. We demonstrate
that a 30 arcsec field of view is substantially improved when the MCAO
system is turned on. This compares favourably with an improvement
of a 10 arcsec field with conventional solar adaptive optics. We
also show how irradiance fluctuations in the MCAO compensated focus
can be suppressed. To cite this article: O. von der Lühe et al.,
C. R. Physique 6 (2005).
---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V Altcode:
The telescope structure including control system and the complete
retractable dome of the new 1.5 m solar telescope GREGOR were
assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
telescope is build by a consortium of the Kiepenheuer Institut fuer
Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
fuer Astrophysik Goettingen and additional national and international
Partners. Pointing, tracking and thermal tests were made to verify
the proposed performance. The results of these tests and a progress
report of the project will be presented.
---------------------------------------------------------
Title: Results of the multi-conjugate adaptive optics system at the
German solar telescope, Tenerife
Authors: Berkefeld, Thomas; Soltau, Dirk; von der Luehe, Oskar
2005SPIE.5903..219B Altcode:
We present the optical setup, reconstruction scheme and observational
results of the Multi-conjugate Adaptive Optics (MCAO) system at
the German 70cm Vacuum Tower Telescope, Observatorio del Teide,
Tenerife. The system serves as a testbed for the future MCAO of the new
1.5m GREGOR solar telescope and is an extension of the conventional
Adaptive Optics (CAO) system. We demonstrate that the use of one
additional MCAO wavefront sensor and one additional deformable mirror
increases the corrected field of view from 10 to 35 arcseconds.
---------------------------------------------------------
Title: 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.
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.
2005ESASP.560..963S Altcode: 2005csss...13..963S
No abstract at ADS
---------------------------------------------------------
Title: Interferometry
Authors: von der Lühe, Oskar
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.
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.
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.
2004SPIE.5490..260B Altcode:
We present the optical setup and properties of the second-generation
adaptive optics (AO) for the 1.5 m solar telescope GREGOR. The system
will consist of a high order AO system correcting about 200 degrees of
freedom on-axis at a bandwith of 200 Hz and a multi-conjugate (MCAO)
extension that uses one additional deformable mirror to correct the
low-order aberrations across a field of one arcminute at a bandwidth
of 50 Hz. Diffraction limited observations will be possible for seeing
better than 1.2 arcsec. First light is expected in 2007.
---------------------------------------------------------
Title: High-precision wavefront sensor for the SUNRISE Telescope
Authors: Schmidt, Wolfgang; Berkefeld, Thomas; Friedlein, Ruediger;
Heidecke, Frank; Kentischer, Thomas; von der Lühe, Oskar F.; Sigwarth,
Michael; Soltau, Dirk; Walde, E.
2004SPIE.5489.1164S Altcode:
SUNRISE is a 1m solar telescope for the visible and near UV wavelength
range. It will be flown in long duration stratospheric balloon flights
in Antarctica, with a first scientific flight in 2007. In this paper,
we describe the development of a wave-front sensing system that
will be used for the automatic in-flight alignment of the SUNRISE
telescope and for high-precision tracking. The system is based on
the principles of an adaptive optics system. A 19-element wavefront
sensor is used to determine low order aberrations of the telescope,
including defocus and spherical aberrations. The correction is achieved
by controlling the position of the telescope secondary and a focusing
mirror in closed-loop. In addition to these quasi-static aberrations,
the system will also measure image motion with a dynamical range of
at least 30 Hz and with a precision of about 0.005 arcs. To this end,
the image displacement measured in all sub-apertures is averaged and
used as tip-tilt correction signal. This signal will feed a second
closed-loop system that drives the tip-tilt mirror assembly. The
tip-tilt mirror unit is designed as a dual-stage system that consists
of a slow component with a large range of 60 arcs and a fast component
with high bandwidth.
---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V Altcode:
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
and other national and international Partners. The refurbishment of
the building is almost finished. The manufacturing of the telescope
structure and the optics is still in progress. After the integration of
the new complete retractable dome in July 2004 the telescope structure,
optic and post focus instruments will be assembled during the rest of
the year. First light is planned during May 2005.
---------------------------------------------------------
Title: GISOT: a giant solar telescope
Authors: Hammerschlag, Robert H.; von der Lühe, Oskar F.; Bettonvil,
Felix C.; Jägers, Aswin P.; Snik, Frans
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.
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.
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.
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} > 60 m s<SUP>-1</SUP>, while giants with B-V
< 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.
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
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
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
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.
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
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.
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
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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
2002SPIE.4538..119B Altcode:
We present the optical setup and wavefront reconstruction algorithms for
the multi-conjugate adaptive optics (MCAO) system at the 70 cm German
Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife. The
system is designed to increase the corrected field of view (FOV) from
about 10 arcseconds to 30 arcseconds in the visible. It will consist of
two Shack-Hartmann wavefront sensors (WFS) and two deformable mirrors
(DMs). Both wavefront sensors will be situated in the pupil plane of
the telescope. One determines the high order wavefront aberrations
for the center of the FOV, the other measures only low order wavefront
aberrations, but covers a large FOV in each subaperture. A 35 actuator
bimorph mirror and a micro mirror will correct the ground layer and
the tropopause, respectively. The system will have first light in
early 2002. Scientific operation is expected to start in the second
half of 2002.
---------------------------------------------------------
Title: Adaptive optics system for a 1.5-m solar telescope
Authors: von der Luehe, Oskar; Berkefeld, Thomas; Soltau, Dirk
2002SPIE.4538..197V Altcode:
We describe an adaptive optics system for the 1.5m diameter solar
telescope GREGOR which is currently developed for the Teide Observatory
on Tenerife. In a first development step, the AO will provide
compensation of 77 modes of wavefront deformation, corresponding
to the first 10 radial degrees of a Karhunen-Loeve decomposition of
wavefront error. We estimate that such a performance will render GREGOR
nearly diffraction limited at visible wavelengths in conditions which
correspond to the best 25% of the seeing In Tenerife. The AO uses
a Shack-Hartmann wavefront sensor which operates on fine structure
anywhere on the solar disk. The required control bandwidth will be
about 200 Hz. We show how such a system can be realized using existing
technology. Substantial increases in performance in terms of corrected
wavefront error and field requires significant technological advances,
in particular in the field of large field high speed detectors.
---------------------------------------------------------
Title: GREGOR: a 1.5 m telescope for solar research
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Berkefeld, Th.;
Kneer, F.; Staude, J.
2001AN....322..353V Altcode:
GREGOR will be a new 1.5 meter solar telescope at the Teide Observatory,
Izaña, Tenerife. It will provide observations with high polarimetric
precision at visible and infra-red wavelengths from Earth in the
solar photosphere and chromosphere with a resolution of 70 km on the
Sun. GREGOR replaces the 45 cm Gregory Coudé telescope.
---------------------------------------------------------
Title: Post-focus instrumentation for GREGOR
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2001AN....322..361K Altcode:
GREGOR is a high-resolution solar telescope with an aperture of 1.5
m. It will be equipped with an Adaptive Optics system and is designed
for high-precision measurements of magnetic fields and plasma motions
in the solar photosphere and chromosphere with a resolution of 70
km on the Sun. GREGOR will replace the Gregory Coudé Telescope at
the Observatorio del Teide on Tenerife. In concert with the other
solar telescopes at Teide Observatory it will be useful for studying
the dynamics of the solar atmosphere and the underlying physical
processes. GREGOR will also serve as a test bed for next generation
solar telescopes. We discuss briefly the postfocus instrumentation
of GREGOR.
---------------------------------------------------------
Title: Visible Imager / Magnetograph: summary of splinter session
Authors: von der Lühe, O.; Fleck, B.
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.
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.
2001ESASP.493..421V Altcode: 2001sefs.work..421V
No abstract at ADS
---------------------------------------------------------
Title: Solar Instrumentation. An Introduction
Authors: von der Lühe, O.
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.
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.
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.
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.
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.
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 & 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.
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
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
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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
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
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.
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.
1997svlt.work..349A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Introduction to Interferometry with the ESO Very Large
Telescope
Authors: von der Lühe, O.
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.
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.
1997ioai.book....9V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Surface Observations with the Vlti
Authors: von der Lühe, O.
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.
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.
1997svlt.work..375L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Imaging in interferometry
Authors: von der Lühe, O.; Ageorges, N.
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.
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
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
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.
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.
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.
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.
1996AGAb...12...76V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scientific and technical goals for solar adaptive optics.
Authors: von der Lühe, O.
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.
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.
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.
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.
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
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
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.
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.
1995svlt.conf..100B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Calibration of the VLT Interferometer
Authors: von der Lühe, O.; Quirrenbach, A.
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.
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.
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.
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
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
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
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
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.
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.
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.
1994IAUS..158..143B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Narrow-Band Speckle Imaging
Authors: Keller, C.; von der Lühe, O.
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.
1993Msngr..74....2B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Imaging of the Solar Surface with Interferometric Arrays
Authors: von der Lühe, O.
1993rtpf.conf..150V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Speckle imaging of solar small scale structure. I - Methods
Authors: von der Luehe, O.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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
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.
1989hsrs.conf..191V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar speckle imaging.
Authors: von der Lühe, O.
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
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.
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.
1989RvMA....2..105R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-resolution imaging of the solar photosphere.
Authors: von der Lühe, O.; Pehlemann, E.
1989AGAb....2...34V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A correlation tracker for solar fine scale studies.
Authors: Rimmele, T.; von der Lühe, O.
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.
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.
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
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.
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.
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.
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.
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.
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.
1987iia..conf...37V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photospheric Fine Structure Close to a Sunspot
Authors: von der Lühe, O.
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.
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.
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.
1987iia..conf....9V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Image Stabilization
Authors: von der Luhe, O.
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.
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.
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.
1986BAAS...18..663V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Speckle Masking Transfer Function
Authors: von der Luhe, O.
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.
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.
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.
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.
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.
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.
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.
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.
1981MitAG..54..261V Altcode:
No abstract at ADS
