explanation      blue bibcodes open ADS page with paths to full text
Author name code: keller
ADS astronomy entries on 2022-09-14
author:"Keller, Christoph U." 

---------------------------------------------------------
Title: Upgrading the high contrast imaging facility SPHERE: science
    drivers and instrument choices
Authors: Boccaletti, A.; Chauvin, G.; Wildi, F.; Milli, J.; Stadler,
   E.; Diolaiti, E.; Gratton, R.; Vidal, F.; Loupias, M.; Langlois, M.;
   Cantalloube, F.; N'Diaye, M.; Gratadour, D.; Ferreira, F.; Tallon, M.;
   Mazoyer, J.; Segransan, D.; Mouillet, D.; Beuzit, J. -L.; Bonnefoy,
   M.; Galicher, R.; Vigan, A.; Snellen, I.; Feldt, M.; Desidera, S.;
   Rousseau, S.; Baruffolo, A.; Goulas, C.; Baudoz, P.; Bechet, C.;
   Benisty, M.; Bianco, A.; Carry, B.; Cascone, E.; Charnay, B.; Choquet,
   E.; Christiaens, V.; Cortecchia, F.; de Caprio, V.; De Rosa, A.;
   Desgrange, C.; D'Orazi, V.; Douté, S.; Frangiamore, M.; Gendron, E.;
   Ginski, C.; Huby, E.; Keller, C.; Kulcsár, C.; Landman, R.; Lagarde,
   S.; Lagadec, E.; Lagrange, A. -M.; Kasper, M. Lombini M.; Ménard,
   F.; Magnard, Y.; Malaguti, G.; Maurel, D.; Mesa, D.; Morgante, G.;
   Pantin, E.; Pichon, T.; Potier, A.; Rabou, P.; Rochat, S.; Terenzi,
   L.; Thiébaut, E.; Tallon-Bosc, I.; Raynaud, H. -F.; Rouan, D.; Sevin,
   A.; Schiavone, F.; Schreiber, L.; Zanutta, A.
2022arXiv220902092B    Altcode:
  SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT,
  which is intended to boost the current performances of detection and
  characterization for exoplanets and disks. SPHERE+ will also serve as a
  demonstrator for the future planet finder (PCS) of the European ELT. The
  main science drivers for SPHERE+ are 1/ to access the bulk of the young
  giant planet population down to the snow line ($3-10$ au), to bridge
  the gap with complementary techniques (radial velocity, astrometry); 2/
  to observe fainter and redder targets in the youngest ($1-10$\,Myr)
  associations compared to those observed with SPHERE to directly
  study the formation of giant planets in their birth environment; 3/
  to improve the level of characterization of exoplanetary atmospheres
  by increasing the spectral resolution in order to break degeneracies
  in giant planet atmosphere models. Achieving these objectives requires
  to increase the bandwidth of the xAO system (from $\sim$1 to 3\,kHz)
  as well as the sensitivity in the infrared (2 to 3\,mag). These
  features will be brought by a second stage AO system optimized in the
  infrared with a pyramid wavefront sensor. As a new science instrument,
  a medium resolution integral field spectrograph will provide a spectral
  resolution from 1000 to 5000 in the J and H bands. This paper gives
  an overview of the science drivers, requirements and key instrumental
  trade-off that were done for SPHERE+ to reach the final selected
  baseline concept.

---------------------------------------------------------
Title: Joint optimization of wavefront sensing and reconstruction
    with automatic differentiation
Authors: Landman, Rico; Keller, Christoph; Por, Emiel H.; Haffert,
   Sebastiaan; Doelman, David; Stockmans, Thijs
2022arXiv220905904L    Altcode:
  High-contrast imaging instruments need extreme wavefront control to
  directly image exoplanets. This requires highly sensitive wavefront
  sensors which optimally make use of the available photons to sense the
  wavefront. Here, we propose to numerically optimize Fourier-filtering
  wavefront sensors using automatic differentiation. First, we optimize
  the sensitivity of the wavefront sensor for different apertures and
  wavefront distributions. We find sensors that are more sensitive than
  currently used sensors and close to the theoretical limit, under the
  assumption of monochromatic light. Subsequently, we directly minimize
  the residual wavefront error by jointly optimizing the sensing and
  reconstruction. This is done by connecting differentiable models of
  the wavefront sensor and reconstructor and alternatingly improving them
  using a gradient-based optimizer. We also allow for nonlinearities in
  the wavefront reconstruction using Convolutional Neural Networks, which
  extends the design space of the wavefront sensor. Our results show
  that optimization can lead to wavefront sensors that have improved
  performance over currently used wavefront sensors. The proposed
  approach is flexible, and can in principle be used for any wavefront
  sensor architecture with free design parameters.

---------------------------------------------------------
Title: Spectropolarimetry of life: airborne measurements from a hot
    air balloon
Authors: Mulder, Willeke; Patty, C. H. Lucas; Spadaccia, Stefano;
   Pommerol, Antoine; Demory, Brice-Olivier; Keller, Christoph U.; Kühn,
   Jonas G.; Snik, Frans; Stam, Daphne M.
2022arXiv220802317M    Altcode:
  Does life exist outside our Solar System? A first step towards
  searching for life outside our Solar System is detecting life
  on Earth by using remote sensing applications. One powerful and
  unambiguous biosignature is the circular polarization resulting
  from the homochirality of biotic molecules and systems. We aim to
  investigate the possibility of identifying and characterizing life on
  Earth by using airborne spectropolarimetric observations from a hot
  air balloon during our field campaign in Switzerland, May 2022. In
  this work we present the optical-setup and the data obtained from
  aerial circular spectropolarimetric measurements of farmland, forests,
  lakes and urban sites. We make use of the well-calibrated FlyPol
  instrument that measures the fractionally induced circular polarization
  ($V/I$) of (reflected) light with a sensitivity of $<10^{-4}$. The
  instrument operates in the visible spectrum, ranging from 400 to
  900 nm. We demonstrate the possibility to distinguish biotic from
  abiotic features using circular polarization spectra and additional
  broadband linear polarization information. We review the performance
  of our optical-setup and discuss potential improvements. This sets
  the requirements on how to perform future airborne spectropolarimetric
  measurements of the Earth's surface features from several elevations.

---------------------------------------------------------
Title: Detecting life outside our solar system with a large
    high-contrast-imaging mission
Authors: Snellen, Ignas A. G.; Snik, F.; Kenworthy, M.; Albrecht, S.;
   Anglada-Escudé, G.; Baraffe, I.; Baudoz, P.; Benz, W.; Beuzit, J. -L.;
   Biller, B.; Birkby, J. L.; Boccaletti, A.; van Boekel, R.; de Boer,
   J.; Brogi, Matteo; Buchhave, L.; Carone, L.; Claire, M.; Claudi, R.;
   Demory, B. -O.; Désert, J. -M.; Desidera, S.; Gaudi, B. S.; Gratton,
   R.; Gillon, M.; Grenfell, J. L.; Guyon, O.; Henning, T.; Hinkley,
   S.; Huby, E.; Janson, M.; Helling, C.; Heng, K.; Kasper, M.; Keller,
   C. U.; Krause, O.; Kreidberg, L.; Madhusudhan, N.; Lagrange, A. -M.;
   Launhardt, R.; Lenton, T. M.; Lopez-Puertas, M.; Maire, A. -L.; Mayne,
   N.; Meadows, V.; Mennesson, B.; Micela, G.; Miguel, Y.; Milli, J.;
   Min, M.; de Mooij, E.; Mouillet, D.; N'Diaye, M.; D'Orazi, V.; Palle,
   E.; Pagano, I.; Piotto, G.; Queloz, D.; Rauer, H.; Ribas, I.; Ruane,
   G.; Selsis, F.; Sozzetti, A.; Stam, D.; Stark, C. C.; Vigan, A.;
   de Visser, Pieter
2021ExA...tmp..124S    Altcode:
  In this White Paper, which was submitted in response to the European
  Space Agency (ESA) Voyage 2050 Call, we recommend the ESA plays a
  proactive role in developing a global collaborative effort to construct
  a large high-contrast imaging space telescope, e.g. as currently
  under study by NASA. Such a mission will be needed to characterize a
  sizable sample of temperate Earth-like planets in the habitable zones
  of nearby Sun-like stars and to search for extraterrestrial biological
  activity. We provide an overview of relevant European expertise,
  and advocate ESA to start a technology development program towards
  detecting life outside the Solar System.

---------------------------------------------------------
Title: LOUPE: Observing the Earth from the Moon to prepare for
    detecting life on Earth-like exoplanets
Authors: Klindžić, Dora; Stam, Daphne; Snik, Frans; Keller,
   Christoph; Pallichadath, Vidhya; van Dijk, Chris; Esposito, Marco;
   van Dam, Dirk
2021EPSC...15..657K    Altcode:
  LOUPE, the Lunar Observatory for Unresolved Polarimetry of the Earth,
  is a small, robust spectro-polarimeter for observing the Earth as if
  it were an exoplanet, designed to accompany any landing, roving or
  orbiting mission to the Moon. Detecting Earth-like planets in stellar
  habitable zones is one of the key challenges of modern exoplanetary
  science. Characterizing such planets and searching for traces of life
  requires the direct detection of their signals. LOUPE provides unique
  spectral flux and polarization data of sunlight reflected by Earth,
  the only planet known to harbour life. These data will be used to
  test numerical codes to predict signals of Earth-like exoplanets, to
  test algorithms that retrieve planet properties, and to fine-tune the
  design and observational strategies of future space observatories.We
  present a novel spectropolarimetric instrument design: LOUPE, the
  Lunar Observatory for Unresolved Polarimetry of the Earth (Klindžić,
  2020), which aims to observe the Earth from the Moon as if it were
  an exoplanet and perform spectropolarimetric measurements spanning
  the full range of phase angles. Various reasons make observing the
  Earth from the Moon or from a Lunar orbit, rather than a low Earth
  orbit, crucial to the experiment:The Moon is sufficiently far away
  to allow a spatially unresolved view of the whole Earth. For a lander
  on the Lunar surface, the Earth is always visible in a confined area
  in the sky. From the Moon, the Earth can be observed at all phase
  angles during a month. From the Moon, the Earth's daily rotation
  can be captured. LOUPE's science requirements include:Perform
  near-instantaneous (snapshot) spectropolarimetry of the entire
  Earth. Detect the presence of liquid water oceans and clouds. Derive
  and monitor atmospheric properties, e.g. via Rayleigh scattering,
  for potential climate research applications. Detect the O₂A band in
  flux and polarization and its variance with cloud cover, altitude and
  phase angle. Detect the Chlorophyll Green Bump and Vegetation Red Edge,
  the spectroscopic signature of plant life. Derive a map of continents
  from the disk-integrated signal and identify notable features,
  such as rainforests, deserts and ice caps. LOUPE shall perform its
  science goals by recording and demodulating the disk-integrated
  Stokes vector of sunlight reflected from the Earth. The leading
  instrument design principle adopted for LOUPE is to create a compact,
  low-mass, low-volume, space-ready hyperspectropolarimeter with no
  moving parts. These constraints require creative solutions from the
  cutting edge of hyperspectral and polarimetric instrument design,
  where polarimeters traditionally used active rotating optics (temporal
  modulation) or beam-splitting (spatial modulation).The latest LOUPE
  concept (Fig. 1.) utilizes Patterned Liquid Crystal (PLC) plates for
  encoding polarization information as a modulation orthogonal to the
  spectral flux measurement, enabling the linear-Stokes vector of a target
  to be recorded in one single "snapshot", as shown in Fig. 2. Unlike a
  traditional rotating-retarder polarimeter, polarization is modulated in
  the cross-spectral direction, meaning polarimetry can be performed at
  full spectral resolution, which is not possible in the case of channeled
  spectropolarimetry with spectral modulation. This pioneering use of
  Patterned Liquid Crystals makes it possible to forgo the use of moving
  elements, resulting in a compact, space-ready instrument with versatile
  options of installation on a range of landing, roving and orbiting
  missions.Here we discuss our detailed design process and the challenges
  involved in creating a unique space-qualified spectropolarimeter with
  no moving parts, whilst maintaining flexibility for different usage
  scenarios: rovers, landers, orbiters, and more. We present a performance
  trade-off, optical design informed by ray tracing with polarization
  effects, and the development of methods for spectral and polarimetric
  demodulation of simulated Earth observation data.Figure 1: Tentative
  design of LOUPE. Figure 2: Simulated LOUPE measurement. Wavelength
  filtering is applied in the y-direction, and polarization modulation in
  the x-direction. Each dot represents an unresolved image of the Earth.

---------------------------------------------------------
Title: Pale polarized dots: spectropolarimetry of the Earth as an
    exoplanet with LOUPE
Authors: Klindžić, Dora; Snik, Frans; Stam, Daphne M.; Keller,
   Christoph U.; Stockmans, Thijs; Hoeijmakers, H. Jens; van Dam, Dirk
   M.; Willebrands, Michele; Karalidi, Theodora; Pallichadath, Vidhya;
   van Dijk, Chris N.; Esposito, M.
2021SPIE11833E..06K    Altcode:
  We present LOUPE, the Lunar Observatory for Unresolved Polarimetry of
  the Earth, a compact snapshot spectropolarimeter designed to observe
  the Earth from the Moon as if it were an exoplanet. Viewing the Earth
  as it would be seen by a faraway observer will offer novel insight into
  the spectropolarimetric signatures of planets harboring life, as well
  as a chance to refine algorithms for the retrieval of exoplanetary
  properties such as the presence of liquid water, clouds, vegetation,
  and more. LOUPE boasts a novel solid-state design based on patterned
  liquid crystal optics built atop the cosine HyperScout<SUP>®</SUP>,
  a flight-proven hyperspectral imager. Uniquely to LOUPE, a microlens
  array creates a two- dimensional grid of unresolved Earth-images on
  the detector, resulting in an array of "pale (blue) dots" filtered
  spectrally along one direction, with polarization modulation applied
  in the perpendicular direction. The clever use of custom-patterned
  liquid crystals as a passive modulator thus replaces the need for
  classical dispersion elements and polarization modulation optics. This
  pioneering approach enables LOUPE to simultaneously obtain spectral and
  Stokes measurements for the entire Earth, whilst the position of the
  Earth-dots also has the benefit of providing input for angle-dependent
  spectral and polarization calibration. Here we discuss our detailed
  design process and the challenges involved in creating a unique,
  space-qualified spectropolarimeter with no moving parts and no bulky
  optics, whilst maintaining flexibility for different usage scenarios:
  rovers, landers, orbiters, and more. We present a performance trade-off
  and optical design informed by ray tracing with polarization effects,
  to prepare for the demodulation of simulated Earth observation data.

---------------------------------------------------------
Title: Spatial polarization modulators: distinguishing diffraction
    effects from spatial polarization modulation
Authors: Mulder, Willeke; Doelman, David S.; Keller, Christoph U.;
   Patty, C. H. Lucas; Snik, Frans
2021SPIE11833E..0MM    Altcode: 2021arXiv210802538M
  Are we alone? In our quest to find life beyond Earth, we use our own
  planet to develop and verify new methods and techniques to remotely
  detect life. Our Life Signature Detection polarimeter (LSDpol),
  a snapshot full-Stokes spectropolarimeter to be deployed in the
  field and in space, looks for signals of life on Earth by sensing the
  linear and circular polarization states of reflected light. Examples
  of these biosignatures are linear polarization resulting from O2-A
  band and vegetation, e.g. the Red edge and the Green bump, as well
  as circular polarization resulting from the homochirality of biotic
  molecules. LSDpol is optimized for sensing circular polarization. To
  this end, LSDpol employs a spatial light modulator in the entrance slit
  of the spectrograph, a liquid-crystal quarter-wave retarder where the
  fast axis rotates as a function of slit position. The original design
  of LSDpol implemented a dual-beam spectropolarimeter by combining a
  quarter-wave plate with a polarization grating. Unfortunately, this
  design causes significant linear-to-circular cross-talk. In addition,
  it revealed spurious polarization modulation effects. Here, we present
  numerical simulations that illustrate how Fresnel diffraction effects
  can create these spurious modulations. We verified the simulations
  with accurate polarization state measurements in the lab using 100%
  linearly and circularly polarized light.

---------------------------------------------------------
Title: Spectropolarimetry
Authors: Keller, Christoph U.; Snik, Frans
2021hai3.book..239K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Vector-apodizing phase plate coronagraph: design, current
    performance, and future development [Invited]
Authors: Doelman, D. S.; Snik, F.; Por, E. H.; Bos, S. P.; Otten,
   G. P. P. L.; Kenworthy, M.; Haffert, S. Y.; Wilby, M.; Bohn, A. J.;
   Sutlieff, B. J.; Miller, K.; Ouellet, M.; de Boer, J.; Keller, C. U.;
   Escuti, M. J.; Shi, S.; Warriner, N. Z.; Hornburg, K.; Birkby, J. L.;
   Males, J.; Morzinski, K. M.; Close, L. M.; Codona, J.; Long, J.;
   Schatz, L.; Lumbres, J.; Rodack, A.; Van Gorkom, K.; Hedglen, A.;
   Guyon, O.; Lozi, J.; Groff, T.; Chilcote, J.; Jovanovic, N.; Thibault,
   S.; de Jonge, C.; Allain, G.; Vallée, C.; Patel, D.; Côté, O.;
   Marois, C.; Hinz, P.; Stone, J.; Skemer, A.; Briesemeister, Z.;
   Boehle, A.; Glauser, A. M.; Taylor, W.; Baudoz, P.; Huby, E.; Absil,
   O.; Carlomagno, B.; Delacroix, C.
2021ApOpt..60D..52D    Altcode: 2021arXiv210411211D
  Over the last decade, the vector-apodizing phase plate (vAPP)
  coronagraph has been developed from concept to on-sky application in
  many high-contrast imaging systems on 8-m class telescopes. The vAPP is
  an geometric-phase patterned coronagraph that is inherently broadband,
  and its manufacturing is enabled only by direct-write technology for
  liquid-crystal patterns. The vAPP generates two coronagraphic PSFs
  that cancel starlight on opposite sides of the point spread function
  (PSF) and have opposite circular polarization states. The efficiency,
  that is the amount of light in these PSFs, depends on the retardance
  offset from half-wave of the liquid-crystal retarder. Using different
  liquid-crystal recipes to tune the retardance, different vAPPs operate
  with high efficiencies ($&gt;96\%$) in the visible and thermal infrared
  (0.55 $\mu$m to 5 $\mu$m). Since 2015, seven vAPPs have been installed
  in a total of six different instruments, including Magellan/MagAO,
  Magellan/MagAO-X, Subaru/SCExAO, and LBT/LMIRcam. Using two integral
  field spectrographs installed on the latter two instruments, these
  vAPPs can provide low-resolution spectra (R$\sim$30) between 1 $\mu$m
  and 5 $\mu$m. We review the design process, development, commissioning,
  on-sky performance, and first scientific results of all commissioned
  vAPPs. We report on the lessons learned and conclude with perspectives
  for future developments and applications.

---------------------------------------------------------
Title: Self-optimizing adaptive optics control with reinforcement
    learning for high-contrast imaging
Authors: Landman, Rico; Haffert, Sebastiaan Y.; Radhakrishnan, Vikram
   M.; Keller, Christoph U.
2021JATIS...7c9002L    Altcode: 2021arXiv210811332L
  Current and future high-contrast imaging instruments require extreme
  adaptive optics systems to reach contrasts necessary to directly imaged
  exoplanets. Telescope vibrations and the temporal error induced by the
  latency of the control loop limit the performance of these systems. One
  way to reduce these effects is to use predictive control. We describe
  how model-free reinforcement learning can be used to optimize
  a recurrent neural network controller for closed-loop predictive
  control. First, we verify our proposed approach for tip-tilt control in
  simulations and a lab setup. The results show that this algorithm can
  effectively learn to mitigate vibrations and reduce the residuals for
  power-law input turbulence as compared to an optimal gain integrator. We
  also show that the controller can learn to minimize random vibrations
  without requiring online updating of the control law. Next, we show
  in simulations that our algorithm can also be applied to the control
  of a high-order deformable mirror. We demonstrate that our controller
  can provide two orders of magnitude improvement in contrast at small
  separations under stationary turbulence. Furthermore, we show more
  than an order of magnitude improvement in contrast for different wind
  velocities and directions without requiring online updating of the
  control law.

---------------------------------------------------------
Title: Biosignatures of the Earth. I. Airborne spectropolarimetric
    detection of photosynthetic life
Authors: Patty, C. H. Lucas; Kühn, Jonas G.; Lambrev, Petar H.;
   Spadaccia, Stefano; Jens Hoeijmakers, H.; Keller, Christoph; Mulder,
   Willeke; Pallichadath, Vidhya; Poch, Olivier; Snik, Frans; Stam,
   Daphne M.; Pommerol, Antoine; Demory, Brice-Olivier
2021A&A...651A..68P    Altcode: 2021arXiv210600493P
  Context. Homochirality is a generic and unique property of life on Earth
  and is considered a universal and agnostic biosignature. Homochirality
  induces fractional circular polarization in the incident light
  that it reflects. Because this circularly polarized light can be
  sensed remotely, it can be one of the most compelling candidate
  biosignatures in life detection missions. While there are also other
  sources of circular polarization, these result in spectrally flat
  signals with lower magnitude. Additionally, circular polarization
  can be a valuable tool in Earth remote sensing because the circular
  polarization signal directly relates to vegetation physiology. <BR
  /> Aims: While high-quality circular polarization measurements can
  be obtained in the laboratory and under semi-static conditions in
  the field, there has been a significant gap to more realistic remote
  sensing conditions. <BR /> Methods: In this study, we present sensitive
  circular spectropolarimetric measurements of various landscape elements
  taken from a fast-moving helicopter. <BR /> Results: We demonstrate
  that during flight, within mere seconds of measurements, we can
  differentiate (S∕N &gt; 5) between grass fields, forests, and abiotic
  urban areas. Importantly, we show that with only nonzero circular
  polarization as a discriminant, photosynthetic organisms can even be
  measured in lakes. <BR /> Conclusions: Circular spectropolarimetry can
  be a powerful technique to detect life beyond Earth, and we emphasize
  the potential of utilizing circular spectropolarimetry as a remote
  sensing tool to characterize and monitor in detail the vegetation
  physiology and terrain features of Earth itself.

---------------------------------------------------------
Title: A MUSE view of the asymmetric jet from HD 163296
Authors: Xie, C.; Haffert, S. Y.; de Boer, J.; Kenworthy, M. A.;
   Brinchmann, J.; Girard, J.; Snellen, I. A. G.; Keller, C. U.
2021A&A...650L...6X    Altcode: 2021arXiv210601661X
  Context. Jets and outflows are thought to play important roles in
  regulating star formation and disk evolution. An important question
  is how the jets are launched. HD 163296 is a well-studied Herbig Ae
  star that hosts proto-planet candidates, a protoplanetary disk, a
  protostellar jet, and a molecular outflow, which makes it an excellent
  laboratory for studying jets. <BR /> Aims: We aim to characterize
  the jet at the inner regions and check if there are large differences
  with the features at large separations. A secondary objective is to
  demonstrate the performance of Multi Unit Spectroscopic Explorer
  (MUSE) in high-contrast imaging of extended line emission. <BR />
  Methods: MUSE in the narrow field mode (NFM) can provide observations
  at optical wavelengths with high spatial (∼75 mas) and medium
  spectral (R ∼ 2500) resolution. With the high-resolution spectral
  differential imaging technique, we can characterize the kinematic
  structures and physical conditions of jets down to 100 mas. <BR />
  Results: We detect multiple atomic lines in two new knots, B3 and
  A4, at distances of &lt; 4″ from the host star with MUSE. The
  derived \Mdot;<SUB>jet</SUB>/\Mdot;<SUB>acc</SUB> is about 0.08 and
  0.06 for knots B3 and A4, respectively. The observed [Ca II]/[S II]
  ratios indicate that there is no sign of dust grains at distances
  of &lt; 4″. Assuming the A4 knot traced the streamline, we can
  estimate a jet radius at the origin by fitting the half width half
  maximum of the jet, which sets an upper limit of 2.2 au on the size
  of the launching region. Although MUSE has the ability to detect the
  velocity shifts caused by high- and low-velocity components, we found
  no significant evidence of velocity decrease transverse to the jet
  direction in our 500 s MUSE observation. <BR /> Conclusions: Our work
  demonstrates the capability of using MUSE NFM observations for the
  detailed study of stellar jets in the optical down to 100 mas. The
  derived \Mdot;<SUB>jet</SUB>/\Mdot;<SUB>acc</SUB>, no dust grain,
  and jet radius at the star support the magneto-centrifugal models as
  a launching mechanism for the jet.

---------------------------------------------------------
Title: First light of a holographic aperture mask: Observation at
    the Keck OSIRIS Imager
Authors: Doelman, David S.; Wardenier, Joost P.; Tuthill, Peter;
   Fitzgerald, Michael P.; Lyke, Jim; Sallum, Steph; Norris, Barnaby;
   Warriner, N. Zane; Keller, Christoph; Escuti, Michael J.; Snik, Frans
2021A&A...649A.168D    Altcode: 2021arXiv210411210D
  Context. As an interferometric technique, sparse aperture masking
  (SAM) is capable of imaging beyond the diffraction limit of single
  telescopes. This makes SAM an important technique for studying processes
  such as planet formation at Solar System scales. However, it comes at
  the cost of a reduction in throughput, typically by 80-90%. <BR /> Aims:
  We report on the design, construction, and commissioning of a prototype
  aperture masking technology implemented at the Keck OH-Suppressing
  Infrared Integral Field Spectrograph (OSIRIS) Imager: the holographic
  aperture mask. Holographic aperture masking (HAM) aims at (i) increasing
  the throughput of SAM by selectively combining all subapertures across
  a telescope pupil in multiple interferograms using a phase mask, and
  (ii) adding low-resolution spectroscopic capabilities. <BR /> Methods:
  Using liquid-crystal geometric phase patterns, we manufacture a HAM
  mask that uses an 11-hole SAM design as the central component and a
  holographic component comprising 19 different subapertures. Thanks
  to a multilayer liquid-crystal implementation, the mask has a
  diffraction efficiency higher than 96% from 1.1 to 2.5 micron. We
  create a pipeline that extracts monochromatic closure phases from the
  central component as well as multiwavelength closure phases from the
  holographic component. We test the performance of the HAM mask in the
  laboratory and on-sky. <BR /> Results: The holographic component yields
  26 closure phases with spectral resolutions between R ∼ 6.5 and R
  ∼ 15, depending on the interferogram positions. On April 19, 2019,
  we observed the binary star HDS 1507 in the Hbb filter (λ<SUB>0</SUB>
  = 1638 nm and Δλ = 330 nm) and retrieved a constant separation of
  120.9 ± 0.5 mas for the independent wavelength bins, which is in
  excellent agreement with literature values. For both the laboratory
  measurements and the observations of unresolved reference stars, we
  recorded nonzero closure phases - a potential source of systematic
  error that we traced to polarization leakage of the HAM optic. We
  propose a future upgrade that improves the performance, reducing this
  effect to an acceptable level. <BR /> Conclusions: Holographic aperture
  masking is a simple upgrade of SAM with increased throughput and a new
  capability of simultaneous low-resolution spectroscopy that provides new
  differential observables (e.g., differential phases with wavelength).

---------------------------------------------------------
Title: PCS — A Roadmap for Exoearth Imaging with the ELT
Authors: Kasper, M.; Cerpa Urra, N.; Pathak, P.; Bonse, M.; Nousiainen,
   J.; Engler, B.; Heritier, C. T.; Kammerer, J.; Leveratto, S.;
   Rajani, C.; Bristow, P.; Le Louarn, M.; Madec, P. -Y.; Ströbele,
   S.; Verinaud, C.; Glauser, A.; Quanz, S. P.; Helin, T.; Keller, C.;
   Snik, F.; Boccaletti, A.; Chauvin, G.; Mouillet, D.; Kulcsár, C.;
   Raynaud, H. -F.
2021Msngr.182...38K    Altcode: 2021arXiv210311196K
  The Planetary Camera and Spectrograph (PCS) for the Extremely Large
  Telescope (ELT) will be dedicated to detecting and characterising
  nearby exoplanets with sizes from sub-Neptune to Earth-size in the
  neighbourhood of the Sun. This goal is achieved by a combination of
  eXtreme Adaptive Optics (XAO), coronagraphy and spectroscopy. PCS will
  allow us not only to take images, but also to look for biosignatures
  such as molecular oxygen in the exoplanets' atmospheres. This article
  describes the PCS primary science goals, the instrument concept and
  the research and development activities that will be carried out over
  the coming years.

---------------------------------------------------------
Title: A survey of the linear polarization of directly imaged
    exoplanets and brown dwarf companions with SPHERE-IRDIS. First
    polarimetric detections revealing disks around DH Tau B and GSC
    6214-210 B
Authors: van Holstein, R. G.; Stolker, T.; Jensen-Clem, R.; Ginski,
   C.; Milli, J.; de Boer, J.; Girard, J. H.; Wahhaj, Z.; Bohn, A. J.;
   Millar-Blanchaer, M. A.; Benisty, M.; Bonnefoy, M.; Chauvin, G.;
   Dominik, C.; Hinkley, S.; Keller, C. U.; Keppler, M.; Langlois, M.;
   Marino, S.; Ménard, F.; Perrot, C.; Schmidt, T. O. B.; Vigan, A.;
   Zurlo, A.; Snik, F.
2021A&A...647A..21V    Altcode: 2021arXiv210104033V
  Context. Young giant planets and brown dwarf companions emit
  near-infrared radiation that can be linearly polarized up to several
  percent. This polarization can reveal the presence of an (unresolved)
  circumsubstellar accretion disk, rotation-induced oblateness of the
  atmosphere, or an inhomogeneous distribution of atmospheric dust
  clouds. <BR /> Aims: We aim to measure the near-infrared linear
  polarization of 20 known directly imaged exoplanets and brown dwarf
  companions. <BR /> Methods: We observed the companions with the
  high-contrast imaging polarimeter SPHERE-IRDIS at the Very Large
  Telescope. We reduced the data using the IRDAP pipeline to correct
  for the instrumental polarization and crosstalk of the optical system
  with an absolute polarimetric accuracy &lt;0.1% in the degree of
  polarization. We employed aperture photometry, angular differential
  imaging, and point-spread-function fitting to retrieve the polarization
  of the companions. <BR /> Results: We report the first detection of
  polarization originating from substellar companions, with a polarization
  of several tenths of a percent for DH Tau B and GSC 6214-210 B in
  H-band. By comparing the measured polarization with that of nearby
  stars, we find that the polarization is unlikely to be caused by
  interstellar dust. Because the companions have previously measured
  hydrogen emission lines and red colors, the polarization most likely
  originates from circumsubstellar disks. Through radiative transfer
  modeling, we constrain the position angles of the disks and find that
  the disks must have high inclinations. For the 18 other companions,
  we do not detect significant polarization and place subpercent upper
  limits on their degree of polarization. We also present images of
  the circumstellar disks of DH Tau, GQ Lup, PDS 70, β Pic, and HD
  106906. We detect a highly asymmetric disk around GQ Lup and find
  evidence for multiple scattering in the disk of PDS 70. Both disks
  show spiral-like features that are potentially induced by GQ Lup B
  and PDS 70 b, respectively. <BR /> Conclusions: The presence of the
  disks around DH Tau B and GSC 6214-210 B as well as the misalignment of
  the disk of DH Tau B with the disk around its primary star suggest in
  situ formation of the companions. The non-detections of polarization
  for the other companions may indicate the absence of circumsubstellar
  disks, a slow rotation rate of young companions, the upper atmospheres
  containing primarily submicron-sized dust grains, and/or limited cloud
  inhomogeneity. <P />Based on observations collected at the European
  Southern Observatory under ESO programs 098.C-0790, 0101.C-0502,
  0101.C-0635, 0101.C-0855, 0102.C-0453, 0102.C-0466, 0102.C-0871,
  0102.C-0916, and 0104.C-0265.

---------------------------------------------------------
Title: LOUPE: observing Earth from the Moon to prepare for detecting
    life on Earth-like exoplanets
Authors: Klindžić, D.; Stam, D. M.; Snik, F.; Keller, C. U.;
   Hoeijmakers, H. J.; van Dam, D. M.; Willebrands, M.; Karalidi, T.;
   Pallichadath, V.; van Dijk, C. N.; Esposito, M.
2021RSPTA.37990577K    Altcode: 2020arXiv200716078K
  LOUPE, the Lunar Observatory for Unresolved Polarimetry of the
  Earth, is a small, robust spectro-polarimeter for observing the
  Earth as an exoplanet. Detecting Earth-like planets in stellar
  habitable zones is one of the key challenges of modern exoplanetary
  science. Characterizing such planets and searching for traces of life
  requires the direct detection of their signals. LOUPE provides unique
  spectral flux and polarization data of sunlight reflected by Earth,
  the only planet known to harbour life. These data will be used to
  test numerical codes to predict signals of Earth-like exoplanets, to
  test algorithms that retrieve planet properties, and to fine-tune the
  design and observational strategies of future space observatories. From
  the Moon, LOUPE will continuously see the entire Earth, enabling it to
  monitor the signal changes due to the planet's daily rotation, weather
  patterns and seasons, across all phase angles. Here, we present both
  the science case and the technology behind LOUPE's instrumental and
  mission design. <P />This article is part of a discussion meeting issue
  `Astronomy from the Moon: the next decades'.

---------------------------------------------------------
Title: Using the generalised-optical differentiation wavefront sensor
    for laser guide star wavefront sensing
Authors: Haffert, Sebastiaan Y.; Keller, Christoph U.; Dekany, Richard
2020SPIE11448E..1TH    Altcode: 2020arXiv201202336H
  Laser guide stars (LGS) are used in many adaptive optics systems
  to extend sky coverage. The most common wavefront sensor used in
  combination with a LGS is a Shack-Hartmann wavefront sensor (SHWFS). The
  ShackHartmann has a major disadvantage for extended source wavefront
  sensing because it directly samples the image. In this proceeding we
  propose to use the generalized-Optical Differentation Wavefront Sensor
  (g-ODWFS) a wavefront sensor for wavefront sensing of LGS. The g-ODWFS
  uses only 4 pixels per sub-aperture, has little to no aliasing noise
  and therefore no spurious low-order errors and has no need for centroid
  gain calibrations. In this proceeding we show the results of simulations
  that compare the g-ODWFS with the SHWFS.

---------------------------------------------------------
Title: Prediction of the planet yield of the MaxProtoPlanetS
    high-contrast survey for H-alpha protoplanets with MagAO-X based on
    first light contrasts
Authors: Close, Laird M.; Males, Jared; Long, Joseph D.; Van Gorkom,
   Kyle; Hedglen, Alexander D.; Kautz, Maggie; Lumbres, Jennifer; Haffert,
   Sebastiaan Y.; Follette, Katherine; Wagner, Kevin; Miller, Kelsey;
   Apai, Daniel; Wu, Ya-Lin; Guyon, Olivier; Schatz, Lauren; Rodack,
   Alex; Doelman, David; Snik, Frans; Knight, Justin M.; Morzinski,
   Katie; Gasho, Victor; Keller, Christoph; Pearce, Logan; Weinberger,
   Alycia; Pérez, Laura; Doyon, René
2020SPIE11448E..0UC    Altcode:
  Our past GAPplanetS survey over the last 5 years with the MagAO visible
  AO system discovered the first examples of accreting protoplanets
  (by direct observation of H-alpha emission). Examples include LkCa15
  b (Sallum et al. 2015) and PDS70 b (Wagner et al. 2018). In this
  paper we review the science performance of the newly (Dec. 2019)
  commissioned MagAO-X extreme AO system. In particular, we use the vAPP
  coronagraphic contrasts measured during MagAO-X first light. We use the
  Massive Accreting Gap (MAG) protoplanet model of Close 2020 to predict
  the H-alpha contrasts of 19 of the best transitional disk systems
  (ages 1-5 Myr) for the direct detection of H-alpha from accretion of
  hydrogen onto these protoplanets. The MAG protoplanet model applied
  to the observed first light MagAO-X contrasts predict a maximum yield
  of 46+/-7 planets from 19 stars (42 of these planets would be new
  discoveries). This suggests that there is a large, yet, unexplored
  reservoir of protoplanets that can be discovered with an extreme AO
  coronagraphic survey of 19 of the best transitional disk systems. Based
  on our first light contrasts we predict a healthy yield of protoplanets
  from our MaxProtoPlanetS survey of 19 transitional disks with MagAO-X.

---------------------------------------------------------
Title: Focal plane wavefront sensing on SUBARU/SCExAO
Authors: Vievard, S.; Bos, S. P.; Cassaing, F.; Currie, T.; Deo, V.;
   Guyon, O.; Jovanovic, N.; Keller, C. U.; Lamb, M.; Lopez, C.; Lozi,
   J.; Martinache, F.; Miller, K.; Montmerle-Bonnefois, A.; Mugnier,
   L. M.; N'Diaye, M.; Norris, B.; Sahoo, A.; Sauvage, J. -F.; Skaf,
   N.; Snik, F.; Wilby, M. J.; Wong, A.
2020SPIE11448E..6DV    Altcode: 2020arXiv201212417V
  Focal plane wavefront sensing is an elegant solution for wavefront
  sensing since near-focal images of any source taken by a detector show
  distortions in the presence of aberrations. Non-Common Path Aberrations
  and the Low Wind Effect both have the ability to limit the achievable
  contrast of the finest coronagraphs coupled with the best extreme
  adaptive optics systems. To correct for these aberrations, the Subaru
  Coronagraphic Extreme Adaptive Optics instrument hosts many focal plane
  wavefront sensors using detectors as close to the science detector as
  possible. We present seven of them and compare their implementation
  and efficiency on SCExAO. This work will be critical for wavefront
  sensing on next generation of extremely large telescopes that might
  present similar limitations.

---------------------------------------------------------
Title: MagAO-X first light
Authors: Males, Jared R.; Close, Laird M.; Guyon, Olivier; Hedglen,
   Alexander D.; Van Gorkom, Kyle; Long, Joseph D.; Kautz, Maggie;
   Lumbres, Jennifer; Schatz, Lauren; Rodack, Alexander; Miller,
   Kelsey; Doelman, David; Snik, Frans; Bos, Steven; Knight, Justin
   M.; Morzinski, Katie; Gasho, Victor; Keller, Christoph; Haffert,
   Sebastiaan; Pearce, Logan
2020SPIE11448E..4LM    Altcode:
  MagAO-X is a new "extreme" adaptive optics system for the Magellan Clay
  6.5 m telescope which began commissioning in December, 2019. MagAO-X is
  based around a 2040 actuator deformable mirror, controlled by a pyramid
  wavefront sensor operating at up to 3.6 kHz. When fully optimized,
  MagAO-X will deliver high Strehls (&lt; 70%), high resolution (19 mas),
  and high contrast (&lt; 1 × 10<SUP>-4</SUP>) at Hα (656 nm). We
  present a brief review of the instrument design and operations, and
  then report on the results of the first-light run.

---------------------------------------------------------
Title: Self-optimizing adaptive optics control with reinforcement
    learning
Authors: Landman, R.; Haffert, S. Y.; Radhakrishnan, V. M.; Keller,
   C. U.
2020SPIE11448E..49L    Altcode: 2020arXiv201201997L
  Current and future high-contrast imaging instruments require extreme
  Adaptive Optics (XAO) systems to reach contrasts necessary to directly
  image exoplanets. Telescope vibrations and the temporal error induced
  by the latency of the control loop limit the performance of these
  systems. Optimization of the (predictive) control algorithm is crucial
  in reducing these effects. We describe how model-free Reinforcement
  Learning can be used to optimize a Recurrent Neural Network controller
  for closed-loop adaptive optics control. We verify our proposed
  approach for tip-tilt control in simulations and a lab setup. The
  results show that this algorithm can effectively learn to suppress a
  combination of tip-tilt vibrations. Furthermore, we report decreased
  residuals for power-law input turbulence compared to an optimal gain
  integrator. Finally, we demonstrate that the controller can learn
  to identify the parameters of a varying vibration without requiring
  online updating of the control law. We conclude that Reinforcement
  Learning is a promising approach towards data-driven predictive control;
  future research will apply this approach to the control of high-order
  deformable mirrors.

---------------------------------------------------------
Title: Planet formation with all flavors of adaptive optics:
    VLT/MUSE's laser tomography adaptive optics to directly image young
    accreting exoplanets
Authors: Girard, Julien H.; Haffert, Sebastiaan Y.; Bae, Jaehan;
   Zeidler, Peter; de Boer, Jozua; Bohn, Alexander; van Holstein, Rob G.;
   Brinchmann, Jarle; Snellen, Ignas; Bacon, Rolan; Keller, Christoph
2020SPIE11448E..08G    Altcode:
  We present recent results obtained with the VLT/MUSE Integral Field
  Spectrograph fed by the 4LGSF and its laser tomography adaptive
  optics module GALACSI. While this so-called narrow-field mode of
  MUSE was not designed to perform directly imaging of exoplanets
  and outflows, we show that it can be a game changer to detect and
  characterize young exoplanets with a prominent emission lines (i.e Hα,
  tracer of accretion), at moderate contrasts. These performances are
  achieved thanks to the combo of a near-diffraction limited PSF and
  a medium resolution spectrograph and a cross-correlation approach in
  post-processing . We discuss this in the context of ground and space,
  infrared and visible wavelengths, preparing for missions like JWST
  and WFIRST in great synergy and as pathfinder for future ELT/GSMT
  (Extremely Large and/or Giant Segmented Mirror Telescopes) instruments.

---------------------------------------------------------
Title: Multi-core fibre-fed integral-field unit (MCIFU): overview
    and first-light
Authors: Haffert, Sebastiaan Y.; Harris, Robert J.; Zanutta, Alessio;
   Pike, Fraser A.; Bianco, Andrea; Redaelli, Edoardo; Benoît,
   Aurélien; MacLachlan, David G.; Ross, Calum A.; Gris-Sánchez,
   Itandehui; Trappen, Mareike D.; Xu, Yilin; Blaicher, Matthias; Maier,
   Pascal; Riva, Giulio; Sinquin, Baptiste; Kulcsár, Caroline; Bharmal,
   Nazim Ali; Gendron, Eric; Staykov, Lazar; Morris, Tim J.; Barboza,
   Santiago; Muench, Norbert; Bardour, Lisa; Prengère, Léonard; Raynaud,
   Henri-François; Hottinger, Philipp; Anagnos, Theodoros; Osborn,
   James; Koos, Christian; Thompson, Robert R.; Birks, Tim A.; Snellen,
   Ignas A. G.; Keller, Christoph U.; Close, Laird; Males, Jared R.
2020SPIE11448E..4MH    Altcode: 2021arXiv210109766A
  The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited
  near-infrared integral-field unit for exoplanet atmosphere
  characterization with extreme adaptive optics (xAO) instruments. It has
  been developed as an experimental pathfinder for spectroscopic upgrades
  for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0
  um to 1.6um at a resolving power around 5000 for 73 points on-sky. The
  MCIFU uses novel astrophotonic components to make this very compact
  and robust spectrograph. We performed the first successful on-sky test
  with CANARY at the 4.2 meter William Herschel Telescope in July 2019,
  where observed standard stars and several stellar binaries. An improved
  version of the MCIFU will be used with MagAO-X, the new extreme adaptive
  optics system at the 6.5 meter Magellan Clay telescope in Chile. We
  will show and discuss the first-light performance and operations of the
  MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.

---------------------------------------------------------
Title: Design of the life signature detection polarimeter LSDpol
Authors: Keller, Christoph U.; Snik, Frans; Patty, C. H. Lucas;
   Klindžic, Dora; Krasteva, Mariya; Doelman, David S.; Wijnen, Thomas;
   Pallichadath, Vidhya; Stam, Daphne M.; Demory, Brice-Olivier; Kühn,
   Jonas G.; Hoeijmakers, H. Jens; Pommerol, Antoine; Poch, Olivier
2020SPIE11443E..3RK    Altcode: 2020arXiv201209105K
  Many biologically produced chiral molecules such as amino
  acids and sugars show a preference for left or right handedness
  (homochirality). Light reflected by biological materials such as algae
  and leaves therefore exhibits a small amount of circular polarization
  that strongly depends on wavelength. Our Life Signature Detection
  polarimeter (LSDpol) is optimized to measure these signatures of
  life. LSDpol is a compact spectropolarimeter concept with no moving
  parts that instantaneously measures linear and circular polarization
  averaged over the field of view with a sensitivity of better than
  10<SUP>-4</SUP>. We expect to launch the instrument into orbit after
  validating its performance on the ground and from aircraft. LSDpol is
  based on a spatially varying quarter-wave retarder that is implemented
  with a patterned liquid-crystal. It is the first optical element to
  maximize the polarimetric sensitivity. Since this pattern as well as the
  entrance slit of the spectrograph have to be imaged onto the detector,
  the slit serves as the aperture, and an internal field stop limits
  the field of view. The retarder's fast axis angle varies linearly
  along one spatial dimension. A fixed quarter-wave retarder combined
  with a polarization grating act as the disperser and the polarizing
  beam-splitter. Circular and linear polarization are thereby encoded at
  incompatible modulation frequencies across the spectrum, which minimizes
  the potential cross-talk from linear into circular polarization.

---------------------------------------------------------
Title: Searching for proto-planets with MUSE
Authors: Xie, C.; Haffert, S. Y.; de Boer, J.; Kenworthy, M. A.;
   Brinchmann, J.; Girard, J.; Snellen, I. A. G.; Keller, C. U.
2020A&A...644A.149X    Altcode: 2020arXiv201108043X
  Context. Protoplanetary disks contain structures such as gaps, rings,
  and spirals, which are thought to be produced by the interaction
  between the disk and embedded protoplanets. However, only a few
  planet candidates are found orbiting within protoplanetary disks,
  and most of them are being challenged as having been confused
  with disk features. <BR /> Aims: The VLT/MUSE discovery of PDS 70 c
  demonstrated a powerful way of searching for still-forming protoplanets
  by targeting accretion signatures with medium-resolution integral field
  spectroscopy. We aim to discover more proto-planetary candidates with
  MUSE, with a secondary aim of improving the high-resolution spectral
  differential imaging (HRSDI) technique by analyzing the instrumental
  residuals of MUSE. <BR /> Methods: We analyzed MUSE observations of five
  young stars with various apparent brightnesses and spectral types. We
  applied the HRSDI technique to perform high-contrast imaging. The
  detection limits were estimated using fake planet injections. <BR
  /> Results: With a 30 min integration time, MUSE can reach 5σ
  detection limits in apparent Hα line flux down to 10<SUP>-14</SUP>
  and 10<SUP>-15</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP> at 0.075”
  and 0.25”, respectively. In addition to PDS 70 b and c, we did not
  detect any clear accretion signatures in PDS 70, J1850-3147, and V1094
  Sco down to 0.1”. MUSE avoids the small sample statistics problem by
  measuring the noise characteristics in the spatial direction at multiple
  wavelengths. We detected two asymmetric atomic jets in HD 163296 with
  a very high spatial resolution (down to 8 au) and medium spectral
  resolution (R ~ 2500). <BR /> Conclusions: The HRSDI technique when
  applied to MUSE data allows us to reach the photon noise limit at small
  separations (i.e., &lt;0.5”). With the combination of high-contrast
  imaging and medium spectral resolution, MUSE can achieve fainter
  detection limits in apparent line flux than SPHERE/ZIMPOL by a factor
  of ~5. MUSE has some instrumental issues that limit the contrast that
  appear in cases with strong point sources, which can be either a spatial
  point source due to high Strehl observations or a spectral point source
  due to a high line-to-continuum ratio. We modified the HRSDI technique
  to better handle the instrumental artifacts and improve the detection
  limits. To avoid the instrumental effects altogether, we suggest faint
  young stars with relatively low Hα line-to-continuum ratio to be the
  most suitable targets for MUSE to search for potential protoplanets.

---------------------------------------------------------
Title: Diffraction-limited integral-field spectroscopy for extreme
    adaptive optics systems with the multicore fiber-fed integral-field
    unit
Authors: Haffert, Sebastiaan Y.; Harris, Robert J.; Zanutta, Alessio;
   Pike, Fraser A.; Bianco, Andrea; Redaelli, Eduardo; Benoît,
   Aurélien; MacLachlan, David G.; Ross, Calum A.; Gris-Sánchez,
   Itandehui; Trappen, Mareike D.; Xu, Yilin; Blaicher, Matthias; Maier,
   Pascal; Riva, Giulio; Sinquin, Baptiste; Kulcsár, Caroline; Bharmal,
   Nazim Ali; Gendron, Eric; Staykov, Lazar; Morris, Tim J.; Barboza,
   Santiago; Muench, Norbert; Bardou, Lisa; Prengère, Léonard; Raynaud,
   Henri-François; Hottinger, Phillip; Anagnos, Theodoros; Osborn,
   James; Koos, Christian; Thomson, Robert R.; Birks, Tim A.; Snellen,
   Ignas A. G.; Keller, Christoph U.
2020JATIS...6d5007H    Altcode: 2020arXiv200903529H
  Direct imaging instruments have the spatial resolution to resolve
  exoplanets from their host star. This enables direct characterization
  of the exoplanets atmosphere, but most direct imaging instruments do
  not have spectrographs with high enough resolving power for detailed
  atmospheric characterization. We investigate the use of a single-mode
  diffraction-limited integral-field unit that is compact and easy to
  integrate into current and future direct imaging instruments for
  exoplanet characterization. This achieved by making use of recent
  progress in photonic manufacturing to create a single-mode fiber-fed
  image reformatter. The fiber link is created with three-dimensional
  printed lenses on top of a single-mode multicore fiber that feeds an
  ultrafast laser inscribed photonic chip that reformats the fiber into
  a pseudoslit. We then couple it to a first-order spectrograph with a
  triple stacked volume phase holographic grating for a high efficiency
  over a large bandwidth. The prototype system has had a successful
  first-light observing run at the 4.2-m William Herschel Telescope. The
  measured on-sky resolving power is between 2500 and 3000, depending
  on the wavelength. With our observations, we show that single-mode
  integral-field spectroscopy is a viable option for current and future
  exoplanet imaging instruments.

---------------------------------------------------------
Title: CS Cha B: A disc-obscured M-type star mimicking a polarised
    planetary companion
Authors: Haffert, S. Y.; van Holstein, R. G.; Ginski, C.; Brinchmann,
   J.; Snellen, I. A. G.; Milli, J.; Stolker, T.; Keller, C. U.;
   Girard, J.
2020A&A...640L..12H    Altcode: 2020arXiv200707831H
  Context. Direct imaging provides a steady flow of newly discovered
  giant planets and brown dwarf companions. These multi-object systems
  can provide information about the formation of low-mass companions
  in wide orbits and/or help us to speculate about possible migration
  scenarios. Accurate classification of companions is crucial for testing
  formation pathways. <BR /> Aims: In this work we further characterise
  the recently discovered candidate for a planetary-mass companion CS
  Cha b and determine if it is still accreting. <BR /> Methods: MUSE is
  a four-laser-adaptive-optics-assisted medium-resolution integral-field
  spectrograph in the optical part of the spectrum. We observed the CS
  Cha system to obtain the first spectrum of CS Cha b. The companion
  is characterised by modelling both the spectrum from 6300 Å to 9300
  Å and the photometry using archival data from the visible to the
  near-infrared (NIR). <BR /> Results: We find evidence of accretion
  and outflow signatures in Hα and OI emission. The atmospheric models
  with the highest likelihood indicate an effective temperature of
  3450 ± 50 K with a log g of 3.6 ± 0.5 dex. Based on evolutionary
  models, we find that the majority of the object is obscured. We
  determine the mass of the faint companion with several methods to
  be between 0.07 M<SUB>⊙</SUB> and 0.71 M<SUB>⊙</SUB> with an
  accretion rate of Ṁ = 4 × 10<SUP>-11±0.4</SUP> M<SUB>⊙</SUB>
  yr<SUP>-1</SUP>. <BR /> Conclusions: Our results show that CS Cha B is
  most likely a mid-M-type star that is obscured by a highly inclined
  disc, which has led to its previous classification using broadband
  NIR photometry as a planetary-mass companion. This shows that it is
  important and necessary to observe over a broad spectral range to
  constrain the nature of faint companions. <P />The extracted spectrum
  of CS Cha B is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/L12">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/L12</A>

---------------------------------------------------------
Title: Two Directly Imaged, Wide-orbit Giant Planets around the Young,
    Solar Analog TYC 8998-760-1
Authors: Bohn, Alexander J.; Kenworthy, Matthew A.; Ginski, Christian;
   Rieder, Steven; Mamajek, Eric E.; Meshkat, Tiffany; Pecaut, Mark J.;
   Reggiani, Maddalena; de Boer, Jozua; Keller, Christoph U.; Snik,
   Frans; Southworth, John
2020ApJ...898L..16B    Altcode: 2020arXiv200710991B
  Even though tens of directly imaged companions have been discovered in
  the past decades, the number of directly confirmed multiplanet systems
  is still small. Dynamical analysis of these systems imposes important
  constraints on formation mechanisms of these wide-orbit companions. As
  part of the Young Suns Exoplanet Survey we report the detection of a
  second planetary-mass companion around the 17 Myr-old, solar-type star
  TYC 8998-760-1 that is located in the Lower Centaurus Crux subgroup
  of the Scorpius-Centaurus association. The companion has a projected
  physical separation of 320 au and several individual photometric
  measurements from 1.1 to 3.8 microns constrain a companion mass of 6
  ± 1 M<SUB>Jup</SUB>, which is equivalent to a mass ratio of q = 0.57
  ± 0.10% with respect to the primary. With the previously detected 14
  ± 3 M<SUB>Jup</SUB> companion that is orbiting the primary at 160 au,
  TYC 8998-760-1 is the first directly imaged multiplanet system that is
  detected around a young, solar analog. We show that circular orbits are
  stable, but that mildly eccentric orbits for either/both components (e
  &gt; 0.1) are chaotic on gigayear timescales, implying in situ formation
  or a very specific ejection by an unseen third companion. Due to the
  wide separations of the companions TYC 8998-760-1 is an excellent
  system for spectroscopic and photometric follow-up with space-based
  observatories such as the James Webb Space Telescope. <SUP>*</SUP>
  Based on observations collected at the European Organisation for
  Astronomical Research in the Southern Hemisphere under ESO programs
  099.C-0698(A), 0101.C-0341(A), 2103.C-5012(B), and 0104.C-0265(A).

---------------------------------------------------------
Title: On-sky verification of Fast and Furious focal-plane wavefront
sensing: Moving forward toward controlling the island effect at
    Subaru/SCExAO
Authors: Bos, S. P.; Vievard, S.; Wilby, M. J.; Snik, F.; Lozi, J.;
   Guyon, O.; Norris, B. R. M.; Jovanovic, N.; Martinache, F.; Sauvage,
   J. -F.; Keller, C. U.
2020A&A...639A..52B    Altcode: 2020arXiv200512097B
  Context. High-contrast imaging (HCI) observations of exoplanets can
  be limited by the island effect (IE). The IE occurs when the main
  wavefront sensor (WFS) cannot measure sharp phase discontinuities
  across the telescope's secondary mirror support structures (also
  known as spiders). On the current generation of telescopes, the IE
  becomes a severe problem when the ground wind speed is below a few
  meters per second. During these conditions, the air that is in close
  contact with the spiders cools down and is not blown away. This can
  create a sharp optical path length difference between light passing on
  opposite sides of the spiders. Such an IE aberration is not measured
  by the WFS and is therefore left uncorrected. This is referred to
  as the low-wind effect (LWE). The LWE severely distorts the point
  spread function (PSF), significantly lowering the Strehl ratio and
  degrading the contrast. <BR /> Aims: In this article, we aim to show
  that the focal-plane wavefront sensing (FPWFS) algorithm, Fast and
  Furious (F&amp;F), can be used to measure and correct the IE/LWE. The
  F&amp;F algorithm is a sequential phase diversity algorithm and a
  software-only solution to FPWFS that only requires access to images
  of non-coronagraphic PSFs and control of the deformable mirror. <BR
  /> Methods: We deployed the algorithm on the SCExAO HCI instrument
  at the Subaru Telescope using the internal near-infrared camera in
  H-band. We tested with the internal source to verify that F&amp;F can
  correct a wide variety of LWE phase screens. Subsequently, F&amp;F
  was deployed on-sky to test its performance with the full end-to-end
  system and atmospheric turbulence. The performance of the algorithm was
  evaluated by two metrics based on the PSF quality: (1) the Strehl ratio
  approximation (SRA), and (2) variance of the normalized first Airy
  ring (VAR). The VAR measures the distortion of the first Airy ring,
  and is used to quantify PSF improvements that do not or barely affect
  the PSF core (e.g., during challenging atmospheric conditions). <BR />
  Results: The internal source results show that F&amp;F can correct
  a wide range of LWE phase screens. Random LWE phase screens with a
  peak-to-valley wavefront error between 0.4 μm and 2 μm were all
  corrected to a SRA &gt; 90% and an VAR ⪅ 0.05. Furthermore, the
  on-sky results show that F&amp;F is able to improve the PSF quality
  during very challenging atmospheric conditions (1.3-1.4″seeing at
  500 nm). Closed-loop tests show that F&amp;F is able to improve the
  VAR from 0.27-0.03 and therefore significantly improve the symmetry
  of the PSF. Simultaneous observations of the PSF in the optical (λ =
  750 nm, Δλ = 50 nm) show that during these tests we were correcting
  aberrations common to the optical and NIR paths within SCExAO. We
  could not conclusively determine if we were correcting the LWE and/or
  (quasi-)static aberrations upstream of SCExAO. <BR /> Conclusions:
  The F&amp;F algorithm is a promising focal-plane wavefront sensing
  technique that has now been successfully tested on-sky. Going forward,
  the algorithm is suitable for incorporation into observing modes,
  which will enable PSFs of higher quality and stability during science
  observations.

---------------------------------------------------------
Title: VizieR Online Data Catalog: CS Cha B spectrum (Haffert+, 2020)
Authors: Haffert, S. Y.; van Holstein, R. G.; Ginski, C.; Brinchmann,
   J.; Snellen, I. A. G.; Milli, J.; Stolker, T.; Keller, C. U.;
   Girard, J.
2020yCat..36409012H    Altcode:
  The extracted MUSE spectrum of CS Cha B. <P />(1 data file).

---------------------------------------------------------
Title: A universal smartphone add-on for portable spectroscopy and
polarimetry: iSPEX 2
Authors: Burggraaff, Olivier; Perduijn, Armand B.; van Hek, Robert F.;
   Schmidt, Norbert; Keller, Christoph U.; Snik, Frans
2020SPIE11389E..2KB    Altcode: 2020arXiv200601519B
  Spectropolarimetry is a powerful technique for remote sensing
  of the environment. It enables the retrieval of particle
  shape and size distributions in air and water to an extent that
  traditional spectroscopy cannot. SPEX is an instrument concept for
  spectropolarimetry through spectral modulation, providing snapshot,
  and hence accurate, hyperspectral intensity and degree and angle
  of linear polarization. Successful SPEX instruments have included
  groundSPEX and SPEX airborne, which both measure aerosol optical
  thickness with high precision, and soon SPEXone, which will fly on
  PACE. Here, we present a low-cost variant for consumer cameras, iSPEX 2,
  with universal smartphone support. Smartphones enable citizen science
  measurements which are significantly more scaleable, in space and time,
  than professional instruments. Universal smartphone support is achieved
  through a modular hardware design and SPECTACLE data processing. iSPEX
  2 will be manufactured through injection molding and 3D printing. A
  smartphone app for data acquisition and processing is in active
  development. Production, calibration, and validation will commence
  in the summer of 2020. Scientific applications will include citizen
  science measurements of aerosol optical thickness and surface water
  reflectance, as well as low-cost laboratory and portable spectroscopy.

---------------------------------------------------------
Title: IRDAP: SPHERE-IRDIS polarimetric data reduction pipeline
Authors: van Holstein, R. G.; Girard, J. H.; de Boer, J.; Snik, F.;
   Milli, J.; Stam, D. M.; Ginski, C.; Mouillet, D.; Wahhaj, Z.; Schmid,
   H. M.; Keller, C. U.; Langlois, M.; Dohlen, K.; Vigan, A.; Pohl, A.;
   Carbillet, M.; Fantinel, D.; Maurel, D.; Origné, A.; Petit, C. Ramos,
   J.; Rigal, F.; Sevin, A.; Boccaletti, A.; Le Coroller, H.; Dominik,
   C.; Henning, T.; Lagadec, E.; Ménard, F.; Turatto, M.; Udry, S.;
   Chauvin, G.; Feldt, M.; Beuzit, J. -L.
2020ascl.soft04015V    Altcode:
  IRDAP (IRDIS Data reduction for Accurate Polarimetry) accurately
  reduces SPHERE-IRDIS polarimetric data. It is a highly-automated
  end-to-end pipeline; its core feature is model-based correction of
  the instrumental polarization effects. IRDAP handles data taken both
  in field- and pupil-tracking mode and using the broadband filters Y,
  J, H and Ks. Data taken with the narrowband filters can be reduced
  as well, although with a somewhat worse accuracy. For pupil-tracking
  observations IRDAP can additionally apply angular differential imaging.

---------------------------------------------------------
Title: The Single-mode Complex Amplitude Refinement (SCAR)
    coronagraph. II. Lab verification, and toward the characterization
    of Proxima b
Authors: Haffert, S. Y.; Por, E. H.; Keller, C. U.; Kenworthy, M. A.;
   Doelman, D. S.; Snik, F.; Escuti, M. J.
2020A&A...635A..56H    Altcode:
  We present the monochromatic lab verification of the newly developed
  SCAR coronagraph that combines a phase plate (PP) in the pupil with
  a microlens-fed single-mode fiber array in the focal plane. The
  two SCAR designs that have been measured, create respectively a
  360 degree and 180 degree dark region from 0.8-2.4λ/D around the
  star. The 360 SCAR has been designed for a clear aperture and the
  180 SCAR has been designed for a realistic aperture with central
  obscuration and spiders. The 360 SCAR creates a measured stellar null
  of 2-3 × 10<SUP>-4</SUP>, and the 180 SCAR reaches a null of 1 ×
  10<SUP>-4</SUP>. Their monochromatic contrast is maintained within a
  range of ±0.16λ/D peak-to-valley tip-tilt, which shows the robustness
  against tip-tilt errors. The small inner working angle and tip-tilt
  stability makes the SCAR coronagraph a very promising technique for
  an upgrade of current high-contrast instruments to characterize and
  detect exoplanets in the solar neighborhood.

---------------------------------------------------------
Title: Original use of MUSE's laser tomography adaptive optics to
    directly image young accreting exoplanets
Authors: Girard, Julien H.; de Boer, Jozua; Haffert, Sebastiaan;
   Zeidler, Peter; Bohn, Alexander; van Holstein, Rob G.; Snellen, Ignas;
   Brinchmann, Jarle; Keller, Christoph; Bacon, Roland; Bae, Jaehan
2020arXiv200302145G    Altcode:
  We present recent results obtained with the VLT/MUSE Integral Field
  Spectrograph fed by the 4LGSF and its laser tomography adaptive optics
  module GALACSI. While this so-called narrow-field mode of MUSE was
  not designed to perform directly imaging of exoplanets and outflows,
  we show that it can be a game changer to detect and characterize
  young exoplanets with a prominent emission lines (i.e H{\alpha},
  tracer of accretion), at moderate contrasts. These performances are
  achieved thanks to the combo of a near-diffraction limited PSF and
  a medium resolution spectrograph and a cross-correlation approach in
  post-processing . We discuss this in the context of ground and space,
  infrared and visible wavelengths, preparing for missions like JWST
  and WFIRST in great synergy and as pathfinder for future ELT/GSMT
  (Extremely Large and/or Giant Segmented Mirror Telescopes) instruments.

---------------------------------------------------------
Title: SPHERE+: Imaging young Jupiters down to the snowline
Authors: Boccaletti, A.; Chauvin, G.; Mouillet, D.; Absil, O.;
   Allard, F.; Antoniucci, S.; Augereau, J. -C.; Barge, P.; Baruffolo,
   A.; Baudino, J. -L.; Baudoz, P.; Beaulieu, M.; Benisty, M.; Beuzit,
   J. -L.; Bianco, A.; Biller, B.; Bonavita, B.; Bonnefoy, M.; Bos, S.;
   Bouret, J. -C.; Brandner, W.; Buchschache, N.; Carry, B.; Cantalloube,
   F.; Cascone, E.; Carlotti, A.; Charnay, B.; Chiavassa, A.; Choquet,
   E.; Clenet, Y.; Crida, A.; De Boer, J.; De Caprio, V.; Desidera, S.;
   Desert, J. -M.; Delisle, J. -B.; Delorme, P.; Dohlen, K.; Doelman,
   D.; Dominik, C.; Orazi, V. D; Dougados, C.; Doute, S.; Fedele, D.;
   Feldt, M.; Ferreira, F.; Fontanive, C.; Fusco, T.; Galicher, R.;
   Garufi, A.; Gendron, E.; Ghedina, A.; Ginski, C.; Gonzalez, J. -F.;
   Gratadour, D.; Gratton, R.; Guillot, T.; Haffert, S.; Hagelberg, J.;
   Henning, T.; Huby, E.; Janson, M.; Kamp, I.; Keller, C.; Kenworthy,
   M.; Kervella, P.; Kral, Q.; Kuhn, J.; Lagadec, E.; Laibe, G.; Langlois,
   M.; Lagrange, A. -M.; Launhardt, R.; Leboulleux, L.; Le Coroller, H.;
   Li Causi, G.; Loupias, M.; Maire, A. L.; Marleau, G.; Martinache,
   F.; Martinez, P.; Mary, D.; Mattioli, M.; Mazoyer, J.; Meheut, H.;
   Menard, F.; Mesa, D.; Meunier, N.; Miguel, Y.; Milli, J.; Min, M.;
   Molliere, P.; Mordasini, C.; Moretto, G.; Mugnier, L.; Muro Arena,
   G.; Nardetto, N.; Diaye, M. N; Nesvadba, N.; Pedichini, F.; Pinilla,
   P.; Por, E.; Potier, A.; Quanz, S.; Rameau, J.; Roelfsema, R.; Rouan,
   D.; Rigliaco, E.; Salasnich, B.; Samland, M.; Sauvage, J. -F.; Schmid,
   H. -M.; Segransan, D.; Snellen, I.; Snik, F.; Soulez, F.; Stadler, E.;
   Stam, D.; Tallon, M.; Thebault, P.; Thiebaut, E.; Tschudi, C.; Udry,
   S.; van Holstein, R.; Vernazza, P.; Vidal, F.; Vigan, A.; Waters,
   R.; Wildi, F.; Willson, M.; Zanutta, A.; Zavagno, A.; Zurlo, A.
2020arXiv200305714B    Altcode:
  SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for
  more than 5 years, demonstrating a high level of performance. SPHERE
  has produced outstanding results using a variety of operating modes,
  primarily in the field of direct imaging of exoplanetary systems,
  focusing on exoplanets as point sources and circumstellar disks as
  extended objects. The achievements obtained thus far with SPHERE
  (~200 refereed publications) in different areas (exoplanets, disks,
  solar system, stellar physics...) have motivated a large consortium
  to propose an even more ambitious set of science cases, and its
  corresponding technical implementation in the form of an upgrade. The
  SPHERE+ project capitalizes on the expertise and lessons learned
  from SPHERE to push high contrast imaging performance to its limits
  on the VLT 8m-telescope. The scientific program of SPHERE+ described
  in this document will open a new and compelling scientific window for
  the upcoming decade in strong synergy with ground-based facilities
  (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and
  WFIRST). While SPHERE has sampled the outer parts of planetary systems
  beyond a few tens of AU, SPHERE+ will dig into the inner regions
  around stars to reveal and characterize by mean of spectroscopy the
  giant planet population down to the snow line. Building on SPHERE's
  scientific heritage and resounding success, SPHERE+ will be a dedicated
  survey instrument which will strengthen the leadership of ESO and the
  European community in the very competitive field of direct imaging
  of exoplanetary systems. With enhanced capabilities, it will enable
  an even broader diversity of science cases including the study of the
  solar system, the birth and death of stars and the exploration of the
  inner regions of active galactic nuclei.

---------------------------------------------------------
Title: The Young Suns Exoplanet Survey: Detection of a wide-orbit
    planetary-mass companion to a solar-type Sco-Cen member
Authors: Bohn, A. J.; Kenworthy, M. A.; Ginski, C.; Manara, C. F.;
   Pecaut, M. J.; de Boer, J.; Keller, C. U.; Mamajek, E. E.; Meshkat,
   T.; Reggiani, M.; Todorov, K. O.; Snik, F.
2020MNRAS.492..431B    Altcode: 2019MNRAS.tmp.3127B; 2019arXiv191204284B
  The Young Suns Exoplanet Survey consists of a homogeneous sample of 70
  young, solar-mass stars located in the Lower Centaurus-Crux subgroup
  of the Scorpius-Centaurus association with an average age of 15 ±
  3 Myr. We report the detection of a co-moving companion around the
  K3IV star TYC 8998-760-1 (2MASSJ13251211-6456207) that is located at a
  distance of 94.6 ± 0.3 pc using SPHERE/IRDIS on the VLT. Spectroscopic
  observations with VLT/X-SHOOTER constrain the mass of the star to
  1.00± 0.02 M_{⊙ } and an age of 16.7± 1.4 Myr. The companion
  TYC 8998-760-1 b is detected at a projected separation of 1.71″,
  which implies a projected physical separation of 162 au. Photometric
  measurements ranging from Y to M band provide a mass estimate of
  14± 3 M_jup by comparison to BT-Settl and AMES-dusty isochrones,
  corresponding to a mass ratio of q = 0.013 ± 0.003 with respect
  to the primary. We rule out additional companions to TYC 8998-760-1
  that are more massive than 12 M_jup and farther than 12 au away from
  the host. Future polarimetric and spectroscopic observations of this
  system with ground and space based observatories will facilitate testing
  of formation and evolution scenarios shaping the architecture of the
  circumstellar environment around this `young Sun'.

---------------------------------------------------------
Title: RefPlanets: Search for reflected light from extrasolar planets
    with SPHERE/ZIMPOL
Authors: Hunziker, S.; Schmid, H. M.; Mouillet, D.; Milli, J.; Zurlo,
   A.; Delorme, P.; Abe, L.; Avenhaus, H.; Baruffolo, A.; Bazzon, A.;
   Boccaletti, A.; Baudoz, P.; Beuzit, J. L.; Carbillet, M.; Chauvin, G.;
   Claudi, R.; Costille, A.; Daban, J. -B.; Desidera, S.; Dohlen, K.;
   Dominik, C.; Downing, M.; Engler, N.; Feldt, M.; Fusco, T.; Ginski,
   C.; Gisler, D.; Girard, J. H.; Gratton, R.; Henning, Th.; Hubin,
   N.; Kasper, M.; Keller, C. U.; Langlois, M.; Lagadec, E.; Martinez,
   P.; Maire, A. L.; Menard, F.; Meyer, M. R.; Pavlov, A.; Pragt, J.;
   Puget, P.; Quanz, S. P.; Rickman, E.; Roelfsema, R.; Salasnich, B.;
   Sauvage, J. -F.; Siebenmorgen, R.; Sissa, E.; Snik, F.; Suarez, M.;
   Szulágyi, J.; Thalmann, Ch.; Turatto, M.; Udry, S.; van Holstein,
   R. G.; Vigan, A.; Wildi, F.
2020A&A...634A..69H    Altcode: 2019arXiv191112759H
  <BR /> Aims: RefPlanets is a guaranteed time observation
  programme that uses the Zurich IMaging POLarimeter (ZIMPOL) of
  Spectro-Polarimetric High-contrast Exoplanet REsearch instrument at
  the Very Large Telescope to perform a blind search for exoplanets
  in wavelengths from 600 to 900 nm. The goals of this study are the
  characterisation of the unprecedented high polarimetic contrast and
  polarimetric precision capabilities of ZIMPOL for bright targets,
  the search for polarised reflected light around some of the closest
  bright stars to the Sun, and potentially the direct detection of an
  evolved cold exoplanet for the first time. <BR /> Methods: For our
  observations of α Cen A and B, Sirius A, Altair, ɛ Eri and τ Ceti
  we used the polarimetricdifferential imaging (PDI) mode of ZIMPOL
  which removes the speckle noise down to the photon noise limit for
  angular separations ≿0.6”. We describe some of the instrumental
  effects that dominate the noise for smaller separations and explain
  how to remove these additional noise effects in post-processing. We
  then combine PDI with angular differential imaging as a final layer
  of post-processing to further improve the contrast limits of our data
  at these separations. <BR /> Results: For good observing conditions
  we achieve polarimetric contrast limits of 15.0-16.3 mag at the
  effective inner working angle of ~0.13”, 16.3-18.3 mag at 0.5”,
  and 18.8-20.4 mag at 1.5”. The contrast limits closer in (≾0.6”)
  display a significant dependence on observing conditions, while in the
  photon-noise-dominated regime (≿0.6”) the limits mainly depend on
  the brightness of the star and the total integration time. We compare
  our results with contrast limits from other surveys and review
  the exoplanet detection limits obtained with different detection
  methods. For all our targets we achieve unprecedented contrast
  limits. Despite the high polarimetric contrasts we are not able to
  find any additional companions or extended polarised light sources
  in the data obtained so far. <P />Based on observations made with
  ESO Telescopes at the La Silla Paranal Observatory under programme
  IDs: 095.C-0312(B), 096.C-0326(A), 097.C-0524(A), 097.C-0524(B),
  098.C-0197(A), 099.C-0127(A), 099.C-0127(B), 0102.C-0435(A).

---------------------------------------------------------
Title: VizieR Online Data Catalog: A planetary-mass companion to a
    solar-type star (Bohn+, 2020)
Authors: Bohn, A. J.; Kenworthy, M. A.; Ginski, C.; Manara, C. F.;
   Pecaut, M. J.; de Boer, J.; Keller, C. U.; Mamajek, E. E.; Meshkat,
   T.; Reggiani, M.; Todorov, K. O.; Snik, F.
2020yCat..74920431B    Altcode:
  Fits images corresponding to the imagery presented in the paper. The
  data are obtained with VLT/SPHERE/IRDIS. The data reduction is performed
  with version 0.8.1 of PynPoint. We detect a co-moving companion around
  The solar-type Sco-Cen member TYC 8998-760-1 with a mass of 14+/-3
  Jupiter masses. The extracted astrometry and photometry is presented
  in this catalogue. <P />(4 data files).

---------------------------------------------------------
Title: Polarimetric imaging mode of VLT/SPHERE/IRDIS. I. Description,
    data reduction, and observing strategy
Authors: de Boer, J.; Langlois, M.; van Holstein, R. G.; Girard,
   J. H.; Mouillet, D.; Vigan, A.; Dohlen, K.; Snik, F.; Keller, C. U.;
   Ginski, C.; Stam, D. M.; Milli, J.; Wahhaj, Z.; Kasper, M.; Schmid,
   H. M.; Rabou, P.; Gluck, L.; Hugot, E.; Perret, D.; Martinez, P.;
   Weber, L.; Pragt, J.; Sauvage, J. -F.; Boccaletti, A.; Le Coroller,
   H.; Dominik, C.; Henning, T.; Lagadec, E.; Ménard, F.; Turatto, M.;
   Udry, S.; Chauvin, G.; Feldt, M.; Beuzit, J. -L.
2020A&A...633A..63D    Altcode: 2019arXiv190913107D
  Context. Polarimetric imaging is one of the most effective techniques
  for high-contrast imaging and for the characterization of protoplanetary
  disks, and it has the potential of becoming instrumental in the
  characterization of exoplanets. The Spectro-Polarimetric High-contrast
  Exoplanet REsearch (SPHERE) instrument installed on the Very Large
  Telescope (VLT) contains the InfraRed Dual-band Imager and Spectrograph
  (IRDIS) with a dual-beam polarimetric imaging (DPI) mode, which offers
  the capability of obtaining linear polarization images at high contrast
  and resolution. <BR /> Aims: We aim to provide an overview of the
  polarimetric imaging mode of VLT/SPHERE/IRDIS and study its optical
  design to improve observing strategies and data reduction. <BR />
  Methods: For H-band observations of TW Hydrae, we compared two data
  reduction methods that correct for instrumental polarization effects in
  different ways: a minimization of the "noise" image (U<SUB>ϕ</SUB>),
  and a correction method based on a polarimetric model that we have
  developed, as presented in Paper II of this study. <BR /> Results:
  We use observations of TW Hydrae to illustrate the data reduction. In
  the images of the protoplanetary disk around this star, we detect
  variability in the polarized intensity and angle of linear polarization
  that depend on the pointing-dependent instrument configuration. We
  explain these variations as instrumental polarization effects and
  correct for these effects using our model-based correction method. <BR
  /> Conclusions: The polarimetric imaging mode of IRDIS has proven to
  be a very successful and productive high-contrast polarimetric imaging
  system. However, the instrument performance is strongly dependent
  on the specific instrument configuration. We suggest adjustments
  to future observing strategies to optimize polarimetric efficiency
  in field-tracking mode by avoiding unfavorable derotator angles. We
  recommend reducing on-sky data with the pipeline called IRDAP, which
  includes the model-based correction method (described in Paper II)
  to optimally account for the remaining telescope and instrumental
  polarization effects and to retrieve the true polarization state of
  the incident light. <P />Based on observations made with ESO Telescopes
  at the La Silla Paranal Observatory under programme ID 095.C-0273(D).

---------------------------------------------------------
Title: Polarimetric imaging mode of
    VLT/SPHERE/IRDIS. II. Characterization and correction of instrumental
    polarization effects
Authors: van Holstein, R. G.; Girard, J. H.; de Boer, J.; Snik, F.;
   Milli, J.; Stam, D. M.; Ginski, C.; Mouillet, D.; Wahhaj, Z.; Schmid,
   H. M.; Keller, C. U.; Langlois, M.; Dohlen, K.; Vigan, A.; Pohl,
   A.; Carbillet, M.; Fantinel, D.; Maurel, D.; Origné, A.; Petit,
   C.; Ramos, J.; Rigal, F.; Sevin, A.; Boccaletti, A.; Le Coroller,
   H.; Dominik, C.; Henning, T.; Lagadec, E.; Ménard, F.; Turatto, M.;
   Udry, S.; Chauvin, G.; Feldt, M.; Beuzit, J. -L.
2020A&A...633A..64V    Altcode: 2019arXiv190913108V
  Context. Circumstellar disks and self-luminous giant exoplanets or
  companion brown dwarfs can be characterized through direct-imaging
  polarimetry at near-infrared wavelengths. SPHERE/IRDIS at the Very
  Large Telescope has the capabilities to perform such measurements,
  but uncalibrated instrumental polarization effects limit the attainable
  polarimetric accuracy. <BR /> Aims: We aim to characterize and correct
  the instrumental polarization effects of the complete optical system,
  that is, the telescope and SPHERE/IRDIS. <BR /> Methods: We created
  a detailed Mueller matrix model in the broadband filters Y, J, H,
  and K<SUB>s</SUB> and calibrated the model using measurements with
  SPHERE's internal light source and observations of two unpolarized
  stars. We developed a data-reduction method that uses the model to
  correct for the instrumental polarization effects, and applied it
  to observations of the circumstellar disk of T Cha. <BR /> Results:
  The instrumental polarization is almost exclusively produced by the
  telescope and SPHERE's first mirror and varies with telescope altitude
  angle. The crosstalk primarily originates from the image derotator
  (K-mirror). At some orientations, the derotator causes severe loss of
  signal (&gt; 90% loss in the H- and K<SUB>s</SUB>-band) and strongly
  offsets the angle of linear polarization. With our correction method
  we reach, in all filters, a total polarimetric accuracy of ≲0.1%
  in the degree of linear polarization and an accuracy of a few degrees
  in angle of linear polarization. <BR /> Conclusions: The correction
  method enables us to accurately measure the polarized intensity and
  angle of linear polarization of circumstellar disks, and is a vital
  tool for detecting spatially unresolved (inner) disks and measuring
  the polarization of substellar companions. We have incorporated the
  correction method in a highly-automated end-to-end data-reduction
  pipeline called IRDAP, which we made publicly available online. <P
  />Based on observations made with ESO telescopes at the La Silla
  Paranal Observatory under program ID 60.A-9800(S), 60.A-9801(S) and
  096.C-0248(C). <P />The data-reduction pipeline IRDAP is available at
  <A href="https://irdap.readthedocs.io">https://irdap.readthedocs.io</A>

---------------------------------------------------------
Title: Overview of focal plane wavefront sensors to correct for the
    Low Wind Effect on SUBARU/SCExAO
Authors: Vievard, Sebastien; Bos, Steven; Cassaing, Frederic; Ceau,
   Alban; Guyon, Olivier; Jovanovic, Nemanja; Keller, Christoph U.; Lozi,
   Julien; Martinache, Frantz; Montmerle-Bonnefois, Aurelie; Mugnier,
   Laurent; NDiaye, Mamadou; Norris, Barnaby; Sahoo, Ananya; Sauvage,
   Jean-Francois; Snik, Frans; Wilby, Michael J.; Wong, Alisson
2019arXiv191210179V    Altcode:
  The Low Wind Effect (LWE) refers to a phenomenon that occurs when
  the wind speed inside a telescope dome drops below $3$m/s creating
  a temperature gradient near the telescope spider. This produces
  phase discontinuities in the pupil plane that are not detected
  by traditional Adaptive Optics (AO) systems such as the pyramid
  wavefront sensor or the Shack-Hartmann. Considering the pupil as
  divided in 4 quadrants by regular spiders, the phase discontinuities
  correspond to piston, tip and tilt aberrations in each quadrant of the
  pupil. Uncorrected, it strongly decreases the ability of high contrast
  imaging instruments utilizing coronagraphy to detect exoplanets at
  small angular separations. Multiple focal plane wavefront sensors are
  currently being developed and tested on the Subaru Coronagraphic Extreme
  Adaptive Optics (SCExAO) instrument at Subaru Telescope: Among them,
  the Zernike Asymmetric Pupil (ZAP) wavefront sensor already showed
  on-sky that it could measure the LWE induced aberrations in focal
  plane images. The Fast and Furious algorithm, using previous deformable
  mirror commands as temporal phase diversity, showed in simulations its
  efficiency to improve the wavefront quality in the presence of LWE. A
  Neural Network algorithm trained with SCExAO telemetry showed promising
  PSF prediction on-sky. The Linearized Analytic Phase Diversity (LAPD)
  algorithm is a solution for multi-aperture cophasing and is studied to
  correct for the LWE aberrations by considering the Subaru Telescope as
  a 4 sub-aperture instrument. We present the different algorithms, show
  the latest results and compare their implementation on SCExAO/SUBARU
  as real-time wavefront sensors for the LWE compensation.

---------------------------------------------------------
Title: Focal-plane wavefront sensing with the vector-Apodizing
    Phase Plate
Authors: Bos, S. P.; Doelman, D. S.; Lozi, J.; Guyon, O.; Keller,
   C. U.; Miller, K. L.; Jovanovic, N.; Martinache, F.; Snik, F.
2019A&A...632A..48B    Altcode: 2019arXiv190908317B
  Context. One of the key limitations of the direct imaging of exoplanets
  at small angular separations are quasi-static speckles that originate
  from evolving non-common path aberrations (NCPA) in the optical train
  downstream of the instrument's main wavefront sensor split-off. <BR />
  Aims: In this article we show that the vector-Apodizing Phase Plate
  (vAPP) coronagraph can be designed such that the coronagraphic point
  spread functions (PSFs) can act as wavefront sensors to measure and
  correct the (quasi-)static aberrations without dedicated wavefront
  sensing holograms or modulation by the deformable mirror. The absolute
  wavefront retrieval is performed with a non-linear algorithm. <BR />
  Methods: The focal-plane wavefront sensing (FPWFS) performance of
  the vAPP and the algorithm are evaluated via numerical simulations to
  test various photon and read noise levels, the sensitivity to the 100
  lowest Zernike modes, and the maximum wavefront error (WFE) that can be
  accurately estimated in one iteration. We apply these methods to the
  vAPP within SCExAO, first with the internal source and subsequently
  on-sky. <BR /> Results: In idealized simulations we show that for
  10<SUP>7</SUP> photons the root mean square (rms) WFE can be reduced to
  ∼λ/1000, which is 1 nm rms in the context of the SCExAO system. We
  find that the maximum WFE that can be corrected in one iteration is
  ∼λ/8 rms or ∼200 nm rms (SCExAO). Furthermore, we demonstrate
  the SCExAO vAPP capabilities by measuring and controlling the 30
  lowest Zernike modes with the internal source and on-sky. On-sky,
  we report a raw contrast improvement of a factor ∼2 between 2
  and 4 λ/D after five iterations of closed-loop correction. When
  artificially introducing 150 nm rms WFE, the algorithm corrects it
  within five iterations of closed-loop operation. <BR /> Conclusions:
  FPWFS with the vAPP coronagraphic PSFs is a powerful technique since
  it integrates coronagraphy and wavefront sensing, eliminating the need
  for additional probes and thus resulting in a 100% science duty cycle
  and maximum throughput for the target.

---------------------------------------------------------
Title: Spatial linear dark field control and holographic modal
    wavefront sensing with a vAPP coronagraph on MagAO-X
Authors: Miller, Kelsey; Males, Jared R.; Guyon, Olivier; Close,
   Laird M.; Doelman, David; Snik, Frans; Por, Emiel; Wilby, Michael J.;
   Keller, Christoph; Bohlman, Chris; Van Gorkom, Kyle; Rodack, Alexander;
   Knight, Justin; Lumbres, Jennifer; Bos, Steven; Jovanovic, Nemanja
2019JATIS...5d9004M    Altcode:
  The Magellan Extreme Adaptive Optics (MagAO-X) Instrument is an extreme
  AO system coming online at the end of 2019 that will be operating
  within the visible and near-IR. With state-of-the-art wavefront sensing
  and coronagraphy, MagAO-X will be optimized for high-contrast direct
  exoplanet imaging at challenging visible wavelengths, particularly
  Hα. To enable high-contrast imaging, the instrument hosts a vector
  apodizing phase plate (vAPP) coronagraph. The vAPP creates a static
  region of high contrast next to the star that is referred to as a dark
  hole; on MagAO-X, the expected dark hole raw contrast is ∼4 × 10<SUP>
  - 6</SUP>. The ability to maintain this contrast during observations,
  however, is limited by the presence of non-common path aberrations
  (NCPA) and the resulting quasi-static speckles that remain unsensed
  and uncorrected by the primary AO system. These quasi-static speckles
  within the dark hole degrade the high contrast achieved by the vAPP
  and dominate the light from an exoplanet. The aim of our efforts here
  is to demonstrate two focal plane wavefront sensing (FPWFS) techniques
  for sensing NCPA and suppressing quasi-static speckles in the final
  focal plane. To sense NCPA to which the primary AO system is blind, the
  science image is used as a secondary wavefront sensor. With the vAPP,
  a static high-contrast dark hole is created on one side of the PSF,
  leaving the opposite side of the PSF unocculted. In this unobscured
  region, referred to as the bright field, the relationship between
  modulations in intensity and low-amplitude pupil plane phase aberrations
  can be approximated as linear. The bright field can therefore be
  used as a linear wavefront sensor to detect small NCPA and suppress
  quasi-static speckles. This technique, known as spatial linear dark
  field control (LDFC), can monitor the bright field for aberrations that
  will degrade the high-contrast dark hole. A second form of FPWFS, known
  as holographic modal wavefront sensing (hMWFS), is also employed with
  the vAPP. This technique uses hologram-generated PSFs in the science
  image to monitor the presence of low-order aberrations. With LDFC and
  the hMWFS, high contrast across the dark hole can be maintained over
  long observations, thereby allowing planet light to remain visible above
  the stellar noise over the course of observations on MagAO-X. Here,
  we present simulations and laboratory demonstrations of both spatial
  LDFC and the hMWFS with a vAPP coronagraph at the University of Arizona
  Extreme Wavefront Control Laboratory. We show both in simulation and in
  the lab that the hMWFS can be used to sense low-order aberrations and
  reduce the wavefront error (WFE) by a factor of 3 - 4 × . We also show
  in simulation that, in the presence of a temporally evolving pupil plane
  phase aberration with 27-nm root-mean-square (RMS) WFE, LDFC can reduce
  the WFE to 18-nm RMS, resulting in factor of 6 to 10 gain in contrast
  that is kept stable over time. This performance is also verified in
  the lab, showing that LDFC is capable of returning the dark hole to
  the average contrast expected under ideal lab conditions. These results
  demonstrate the power of the hMWFS and spatial LDFC to improve MagAO-X's
  high-contrast imaging capabilities for direct exoplanet imaging.

---------------------------------------------------------
Title: A snapshot full-Stokes spectropolarimeter for detecting life
    on Earth
Authors: Snik, Frans; Keller, Christoph U.; Doelman, David S.;
   Kühn, Jonas; Patty, C. H. Lucas; Hoeijmakers, H. Jens; Pallichadath,
   Vidhya; Stam, Daphne M.; Pommerol, Antoine; Poch, Olivier; Demory,
   Brice-Olivier
2019SPIE11132E..0AS    Altcode: 2019arXiv190902283S
  We present the design of a point-and-shoot non-imaging full-Stokes
  spectropolarimeter dedicated to detecting life on Earth from an orbiting
  platform like the ISS. We specifically aim to map circular polarization
  in the spectral features of chorophyll and other biopigments for our
  planet as a whole. These non-zero circular polarization signatures
  are caused by homochirality of the molecular and supramolecular
  configurations of organic matter, and are considered the most
  unambiguous biomarker. To achieve a fully solid-state snapshot design,
  we implement a novel spatial modulation that completely separates the
  circular and linear polarization channels. The polarization modulator
  consists of a patterned liquid-crystal quarter-wave plate inside the
  spectrograph slit, which also constitutes the first optical element of
  the instrument. This configuration eliminates cross-talk between linear
  and circular polarization, which is crucial because linear polarization
  signals are generally much stronger than the circular polarization
  signals. This leads to a quite unorthodox optical concept for the
  spectrograph, in which the object and the pupil are switched. We
  discuss the general design requirements and trade-offs of LSDpol
  (Life Signature Detection polarimeter), a prototype instrument that
  is currently under development.

---------------------------------------------------------
Title: Insights into Terrestrial Planet Compositions and Geophysics
    from Observations of Magma Worlds
Authors: Ridden-Harper, Andrew; Snellen, Ignas; Keller, Christoph;
   Mollière, Paul; De Mooij, Ernst J. W.; Jayawardhana, Ray; de Kok,
   Remco; Hoeijmakers, H. Jens; Brogi, Matteo; Fridlund, Carl Malcolm;
   Vermeersen, Bert; Westrenen, Wim
2019ESS.....431305R    Altcode:
  There exists a remarkable population of short period transiting
  rocky exoplanets with temperatures &gt;2,000 K, and masses ranging
  from about 8 Earth masses, such as the hot super-Earth 55 Cancri
  e, to that of Mercury or smaller, such as K2-22b. These planets
  are thought to have mineral atmospheres that are produced by the
  vaporisation of their magma surfaces, or large exospheres that are
  produced by sputtering of their atmospheres or exposed surfaces by
  intense stellar winds. Additionally, the smaller, low surface gravity
  hot rocky exoplanets have been found to be actively disintegrating
  and forming 'comet-like' dust tails. <P />Since their atmospheres and
  released gas and dust can be observationally constrained, these planets
  present the tantalising prospect of directly probing the composition of
  rocky planets. Sodium and calcium are promising species to detect given
  their low sublimation temperatures, large absorption cross-sections,
  likely presence in terrestrial planet compositions, and presence in
  Mercury's exosphere. <P />This poster presents the insights we gained
  from using high-resolution transmission spectroscopy to search for
  Na and Ca around 55 Cnc e and K2-22 b using several ground based
  telescopes. For 55 Cne e, we detected a tantilizing 5 σ signal of
  Ca+ on one night of observation, but a similar signal has not been
  detected since (despite our unprecedented limits). This may be related
  to variability of the star-planet system and the planet's magnetic
  field. <P />For K2-22 b, we did not detect absorption by Na or Ca+,
  but found lower-limits that are smaller than the expected magnitude
  of the signal based on the planet's estimated mass-loss rate and
  assuming a terrestrial composition. We attribute this non-detection to
  the probed gases being accelerated by the stellar wind and radiation
  pressure to high velocities, resulting in very broad Doppler shifted
  absorption signals that are hard to detect. <P />The implications of
  these results on probing rocky exoplanet compositions, constraining
  planetary magnetic fields, and understanding the environment around
  short-period rocky exoplanets are also outlined.

---------------------------------------------------------
Title: ESA Voyage 2050 White Paper: Detecting life outside our solar
    system with a large high-contrast-imaging mission
Authors: Snellen, Ignas; Albrecht, Simon; Anglada-Escude, Guillem;
   Baraffe, Isabelle; Baudoz, Pierre; Benz, Willy; Beuzit, Jean-Luc;
   Biller, Beth; Birkby, Jayne; Boccaletti, Anthony; van Boekel, Roy;
   de Boer, Jos; Brogi, Matteo; Buchhave, Lars; Carone, Ludmila;
   Claire, Mark; Claudi, Riccardo; Demory, Brice-Olivier; Desert,
   Jean-Michel; Desidera, Silvano; Gaudi, Scott; Gratton, Raffaele;
   Gillon, Michael; Grenfell, John Lee; Guyon, Olivier; Henning, Thomas;
   Hinkley, Sasha; Huby, Elsa; Janson, Markus; Helling, Christiane;
   Heng, Kevin; Kasper, Markus; Keller, Christoph; Kenworthy, Matthew;
   Krause, Oliver; Kreidberg, Laura; Madhusudhan, Nikku; Lagrange,
   Anne-Marie; Launhardt, Ralf; Lenton, Tim; Lopez-Puertas, Manuel;
   Maire, Anne-Lise; Mayne, Nathan; Meadows, Victoria; Mennesson,
   Bertrand; Micela, Giuseppina; Miguel, Yamila; Milli, Julien; Min,
   Michiel; de Mooij, Ernst; Mouillet, David; N'Diaye, Mamadou; D'Orazi,
   Valentina; Palle, Enric; Pagano, Isabella; Piotto, Giampaolo; Queloz,
   Didier; Rauer, Heike; Ribas, Ignasi; Ruane, Garreth; Selsis, Franck;
   Snik, Frans; Sozzetti, Alessandro; Stam, Daphne; Stark, Christopher;
   Vigan, Arthur; de Visser, Pieter
2019arXiv190801803S    Altcode:
  In this white paper, we recommend the European Space Agency plays a
  proactive role in developing a global collaborative effort to construct
  a large high-contrast imaging space telescope, e.g. as currently
  under study by NASA. Such a mission will be needed to characterize a
  sizable sample of temperate Earth-like planets in the habitable zones
  of nearby Sun-like stars and to search for extraterrestrial biological
  activity. We provide an overview of relevant European expertise,
  and advocate ESA to start a technology development program towards
  detecting life outside the Solar system.

---------------------------------------------------------
Title: Search for gas from the disintegrating rocky exoplanet K2-22b
Authors: Ridden-Harper, A. R.; Snellen, I. A. G.; Keller, C. U.;
   Mollière, P.
2019A&A...628A..70R    Altcode: 2019arXiv190608795R
  Context. The red dwarf star K2-22 is transited every 9.14 h by
  an object which is best explained by being a disintegrating rocky
  exoplanet featuring a variable comet-like dust tail. While the dust is
  thought to dominate the transit light curve, gas is also expected to
  be present, either from being directly evaporated off the planet or by
  being produced by the sublimation of dust particles in the tail. <BR
  /> Aims: Both ionized calcium and sodium have large cross-sections,
  and although present at low abundance, exhibit the strongest atomic
  absorption features in comets. We therefore also identify these species
  as the most promising tracers of circumplanetary gas in evaporating
  rocky exoplanets and search for them in the tail of K2-22 b to constrain
  the gas-loss and sublimation processes in this enigmatic object. <BR
  /> Methods: We observed four transits of K2-22 b with X-shooter on
  the Very Large Telescope operated by ESO to obtain time series of
  intermediate-resolution (R 11 400) spectra. Our analysis focussed on
  the two sodium D lines (588.995 and 589.592 nm) and the Ca<SUP>+</SUP>
  triplet (849.802, 854.209, and 866.214 nm). The stellar calcium and
  sodium absorption was removed using the out-of-transit spectra. We
  searched for planet-related absorption in the velocity rest frame of the
  planet, which changes from approximately -66 to +66 km s<SUP>-1</SUP>
  during the transit. <BR /> Results: Since K2-22 b exhibits highly
  variable transit depths, we analysed the individual nights and their
  average. By injecting signals we reached 5σ upper limits on the
  individual nights that range from 11-13% and 1.7-2.0% for the sodium
  and ionized calcium absorption of the tail, respectively. Night 1 was
  contaminated by its companion star so we considered weighted averages
  with and without Night 1 and quote conservative 5σ limits without
  Night 1 of 9 and 1.4%, respectively. Assuming their mass fractions to
  be similar to those in the Earth's crust, these limits correspond to
  scenarios in which 0.04 and 35% of the transiting dust is sublimated and
  observed as absorbing gas. However, this assumes the gas to be co-moving
  with the planet. We show that for the high irradiation environment of
  K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s
  of km s<SUP>-1</SUP> owing to radiation pressure and entrainment by the
  stellar wind, making these species much more difficult to detect. No
  evidence for such possibly broad and blue-shifted signals are seen in
  our data. <BR /> Conclusions: Future observations aimed at observing
  circumplanetary gas should take into account the possible broad and
  blue-shifted velocity field of atomic and ionized species.

---------------------------------------------------------
Title: Polarimetric imaging of circumstellar disks. I. Artifacts
    due to limited angular resolution
Authors: Heikamp, S.; Keller, C. U.
2019A&A...627A.156H    Altcode:
  Context. Polarimetric images of circumstellar environments,
  even when corrected with adaptive optics, have a limited angular
  resolution. Finite resolution greatly affects polarimetric images
  because of the canceling of adjacent polarization signals with opposite
  signs. In radio astronomy this effect is called beam depolarization and
  is well known. However, radio techniques to mitigate beam depolarization
  are not directly applicable to optical images as a consequence of
  the inherent lack of phase information at optical wavelengths. <BR />
  Aims: We explore the effects of a finite point-spread function (PSF) on
  polarimetric images and the application of Richardson-Lucy deconvolution
  to polarimetric images. <BR /> Methods: We simulated polarimetric
  images of highly simplified, circumstellar disk models and convolved
  these with simulated and actual SPHERE/ZIMPOL PSFs. We attempted
  to deconvolve simulated images in orthogonal linear polarizations
  and polarized intensity images. <BR /> Results: The most significant
  effect of finite angular resolution is the loss of polarimetric signal
  close to the central star where large polarization signals of opposite
  signs average out. The finite angular resolution can also introduce
  polarized light in areas beyond the original, polarized signal such
  as outside of disks. These effects are particularly severe for disks
  that are not rotationally symmetric. The deconvolution of polarimetric
  images is far from trivial. Richardson-Lucy deconvolution applied to
  images in opposite linear polarization states, which are subsequently
  subtracted from each other, cannot recover the signal close to the
  star. Sources that lack rotational symmetry cannot be recovered with
  this deconvolution approach.

---------------------------------------------------------
Title: Two accreting protoplanets around the young star PDS 70
Authors: Haffert, S. Y.; Bohn, A. J.; de Boer, J.; Snellen, I. A. G.;
   Brinchmann, J.; Girard, J. H.; Keller, C. U.; Bacon, R.
2019NatAs...3..749H    Altcode: 2019NatAs.tmp..329H; 2019arXiv190601486H
  Newly forming protoplanets are expected to create cavities and
  substructures in young, gas-rich protoplanetary disks<SUP>1-3</SUP>,
  but they are difficult to detect as they could be confused
  with disk features affected by advanced image analysis
  techniques<SUP>4,5</SUP>. Recently, a planet was discovered
  inside the gap of the transitional disk of the T Tauri star PDS
  70<SUP>6,7</SUP>. Here, we report on the detection of strong Hα
  emission from two distinct locations in the PDS 70 system, one
  corresponding to the previously discovered planet PDS 70 b, which
  confirms the earlier Hα detection<SUP>8</SUP>, and another located
  close to the outer edge of the gap, coinciding with a previously
  identified bright dust spot in the disk and with a small opening
  in a ring of molecular emission<SUP>6,7,9</SUP>. We identify this
  second Hα peak as a second protoplanet in the PDS 70 system. The Hα
  emission spectra of both protoplanets indicate ongoing accretion onto
  the protoplanets<SUP>10,11</SUP>, which appear to be near a 2:1 mean
  motion resonance. Our observations show that adaptive-optics-assisted,
  medium-resolution integral field spectroscopy with MUSE<SUP>12</SUP>
  targeting accretion signatures will be a powerful way to trace ongoing
  planet formation in transitional disks at different stages of their
  evolution. Finding more young planetary systems in mean motion resonance
  would give credibility to the Grand Tack hypothesis in which Jupiter
  and Saturn migrated in a resonance orbit during the early formation
  period of our Solar System<SUP>13</SUP>.

---------------------------------------------------------
Title: Discovery of a directly imaged disk in scattered light around
    the Sco-Cen member Wray 15-788
Authors: Bohn, A. J.; Kenworthy, M. A.; Ginski, C.; Benisty, M.;
   de Boer, J.; Keller, C. U.; Mamajek, E. E.; Meshkat, T.; Muro-Arena,
   G. A.; Pecaut, M. J.; Snik, F.; Wolff, S. G.; Reggiani, M.
2019A&A...624A..87B    Altcode: 2019arXiv190207723B
  Context. Protoplanetary disks are the birth environments of planetary
  systems. Therefore, the study of young, circumstellar environments
  is essential in understanding the processes taking place in planet
  formation and the evolution of planetary systems. <BR /> Aims:
  We detect and characterize circumstellar disks and potential
  companions around solar-type, pre-main sequence stars in the
  Scorpius-Centaurus association (Sco-Cen). <BR /> Methods: As part
  of our ongoing survey we carried out high-contrast imaging with
  VLT/SPHERE/IRDIS to obtain polarized and total intensity images of
  the young (11<SUB>-7</SUB><SUP>+16</SUP> Myr old) K3IV star Wray
  15-788 within the Lower Centaurus Crux subgroup of Sco-Cen. For the
  total intensity images, we remove the stellar halo via an approach
  based on reference star differential imaging in combination with
  principal component analysis. <BR /> Results: Both total intensity
  and polarimetric data resolve a disk around the young, solar-like
  Sco-Cen member Wray 15-788. Modeling of the stellar spectral energy
  distribution suggests that this is a protoplanetary disk at a transition
  stage. We detect a bright outer ring at a projected separation of 370
  mas (≈56 au), hints of inner substructures at 170 mas (≈28 au),
  and a gap in between. Within a position angle range of only 60° &lt;
  ϕ &lt; 240°, we are confident at the 5σ level that we detect actual
  scattered light flux from the outer ring of the disk; the remaining
  part is indistinguishable from background noise. For the detected part
  of the outer ring we determine a disk inclination of i = 21° ± 6°
  and a position angle of φ = 76° ± 16°. Furthermore, we find that
  Wray 15-788 is part of a binary system with the A2V star HD 98363 at a
  separation of 50” (≈6900 au). <BR /> Conclusions: The detection of
  only half of the outer ring might be due to shadowing by a misaligned
  inner disk. A potential substellar companion can cause the misalignment
  of the inner structures and can be responsible for clearing the
  detected gap from scattering material. However, we cannot rule out the
  possibility of a non-detection due to our limited signal-to-noise ratio
  (S/N), combined with brightness azimuthal asymmetry. From our data we
  can exclude companions more massive than 10 M<SUB>jup</SUB> within the
  gap at a separation of 230 mas (≈35 au). Additional data are required
  to characterize the disk's peculiar morphology and to set tighter
  constraints on the potential perturber's orbital parameters and mass. <P
  />Reduced images are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A87">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A87</A>Based
  on observations collected at the European Organisation for Astronomical
  Research in the Southern Hemisphere under ESO programs 099.C-0698(A),
  0101.C-0153(A), and 0101.C-0464(A).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Discovery of a resolved disk
    around Wray 15-788 (Bohn+, 2019)
Authors: Bohn, A. J.; Kenworthy, M. A.; Ginski, C.; Benisty, M.;
   de Boer, J.; Keller, C. U.; Mamajek, E. E.; Meshkat, T.; Muro-Arena,
   G. A.; Pecaut, M. J.; Snik, F.; Wolff, S. G.; Reggiani, M.
2019yCat..36240087B    Altcode:
  Fits images corresponding to the imagery presented in the paper. The
  data are obtained with VLT/SPHERE/IRDIS. The data reduction is performed
  with the latest version of PynPoint. In both total and polarized
  intensity we resolve a disk around the K-type pre-main sequence star
  Wray 15-788. SED analysis suggests that this is a protoplanetary disk
  at a transition stage. <P />(4 data files).

---------------------------------------------------------
Title: SPHERE/ZIMPOL high resolution polarimetric imager. I. System
    overview, PSF parameters, coronagraphy, and polarimetry
Authors: Schmid, H. M.; Bazzon, A.; Roelfsema, R.; Mouillet, D.;
   Milli, J.; Menard, F.; Gisler, D.; Hunziker, S.; Pragt, J.; Dominik,
   C.; Boccaletti, A.; Ginski, C.; Abe, L.; Antoniucci, S.; Avenhaus,
   H.; Baruffolo, A.; Baudoz, P.; Beuzit, J. L.; Carbillet, M.; Chauvin,
   G.; Claudi, R.; Costille, A.; Daban, J. -B.; de Haan, M.; Desidera,
   S.; Dohlen, K.; Downing, M.; Elswijk, E.; Engler, N.; Feldt, M.;
   Fusco, T.; Girard, J. H.; Gratton, R.; Hanenburg, H.; Henning,
   Th.; Hubin, N.; Joos, F.; Kasper, M.; Keller, C. U.; Langlois, M.;
   Lagadec, E.; Martinez, P.; Mulder, E.; Pavlov, A.; Podio, L.; Puget,
   P.; Quanz, S. P.; Rigal, F.; Salasnich, B.; Sauvage, J. -F.; Schuil,
   M.; Siebenmorgen, R.; Sissa, E.; Snik, F.; Suarez, M.; Thalmann, Ch.;
   Turatto, M.; Udry, S.; van Duin, A.; van Holstein, R. G.; Vigan, A.;
   Wildi, F.
2018A&A...619A...9S    Altcode: 2018arXiv180805008S
  Context. The SPHERE "planet finder" is an extreme adaptive optics (AO)
  instrument for high resolution and high contrast observations at the
  Very Large Telescope (VLT). We describe the Zurich Imaging Polarimeter
  (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the
  limits of current AO systems to shorter wavelengths, higher spatial
  resolution, and much improved polarimetric performance. <BR /> Aims:
  We present a detailed characterization of SPHERE/ZIMPOL which should
  be useful for an optimal planning of observations and for improving
  the data reduction and calibration. We aim to provide new benchmarks
  for the performance of high contrast instruments, in particular for
  polarimetric differential imaging. <BR /> Methods: We have analyzed
  SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized
  peak surface brightness, the encircled energy, and the full width half
  maximum (FWHM) for different wavelengths, atmospheric conditions, star
  brightness, and instrument modes. Coronagraphic images are described
  and the peak flux attenuation and the off-axis flux transmission are
  determined. Simultaneous images of the coronagraphic focal plane and the
  pupil plane are analyzed and the suppression of the diffraction rings
  by the pupil stop is investigated. We compared the performance at small
  separation for different coronagraphs with tests for the binary α Hyi
  with a separation of 92 mas and a contrast of Δm ≈ 6<SUP>m</SUP>. For
  the polarimetric mode we made the instrument calibrations using zero
  polarization and high polarization standard stars and here we give a
  recipe for the absolute calibration of polarimetric data. The data
  show small (&lt; 1 mas) but disturbing differential polarimetric
  beam shifts, which can be explained as Goos-Hähnchen shifts from
  the inclined mirrors, and we discuss how to correct this effect. The
  polarimetric sensitivity is investigated with non-coronagraphic and
  deep, coronagraphic observations of the dust scattering around the
  symbiotic Mira variable R Aqr. <BR /> Results: SPHERE/ZIMPOL reaches
  routinely an angular resolution (FWHM) of 22-28 mas, and a normalized
  peak surface brightness of SB<SUB>0</SUB> - m<SUB>star</SUB> ≈
  -6.5<SUP>m</SUP> arcsec<SUP>-2</SUP> for the V-, R- and I-band. The
  AO performance is worse for mediocre ≳1.0″ seeing conditions,
  faint stars m<SUB>R</SUB> ≳ 9<SUP>m</SUP>, or in the presence of the
  "low wind" effect (telescope seeing). The coronagraphs are effective in
  attenuating the PSF peak by factors of &gt; 100, and the suppression
  of the diffracted light improves the contrast performance by a factor
  of approximately two in the separation range 0.06″-0.20″. The
  polarimetric sensitivity is Δp &lt; 0.01% and the polarization zero
  point can be calibrated to better than Δp ≈ 0.1%. The contrast limits
  for differential polarimetric imaging for the 400 s I-band data of R
  Aqr at a separation of ρ = 0.86″ are for the surface brightness
  contrast SB<SUB>pol</SUB>( ρ)-m<SUB>star</SUB> ≈ 8<SUP>m</SUP>
  arcsec<SUP>-2</SUP> and for the point source contrast m<SUB>pol</SUB>(
  ρ)-m<SUB>star</SUB> ≈ 15<SUP>m</SUP> and much lower limits are
  achievable with deeper observations. <BR /> Conclusions: SPHERE/ZIMPOL
  achieves imaging performances in the visual range with unprecedented
  characteristics, in particular very high spatial resolution and very
  high polarimetric contrast. This instrument opens up many new research
  opportunities for the detailed investigation of circumstellar dust,
  in scattered and therefore polarized light, for the investigation of
  faint companions, and for the mapping of circumstellar Hα emission. <P
  />Based on observations collected at La Silla and Paranal Observatory,
  ESO (Chile), Program ID: 60.A-9249 and 60.A-9255.

---------------------------------------------------------
Title: Chromatic transit light curves of disintegrating rocky planets
Authors: Ridden-Harper, A. R.; Keller, C. U.; Min, M.; van Lieshout,
   R.; Snellen, I. A. G.
2018A&A...618A..97R    Altcode: 2018arXiv180707973R
  Context. Kepler observations have revealed a class of short-period
  exoplanets, of which Kepler-1520 b is the prototype, which have
  comet-like dust tails thought to be the result of small, rocky planets
  losing mass. The shape and chromaticity of the transits constrain the
  properties of the dust particles originating from the planet's surface,
  offering a unique opportunity to probe the composition and geophysics
  of rocky exoplanets. <BR /> Aims: We aim to approximate the average
  Kepler long-cadence light curve of Kepler-1520 b and investigate how
  the optical thickness and transit cross section of a general dust tail
  can affect the observed wavelength dependence and depth of transit
  light curves. <BR /> Methods: We developed a new 3D model that ejects
  sublimating particles from the planet surface to build up a dust tail,
  assuming it to be optically thin, and used 3D radiative transfer
  computations that fully treat scattering using the distribution of
  hollow spheres (DHS) method, to generate transit light curves between
  0.45 and 2.5 μm. <BR /> Results: We show that the transit depth is
  wavelength independent of optically thick tails, potentially explaining
  why only some observations indicate a wavelength dependence. From the 3D
  nature of our simulated tails, we show that their transit cross sections
  are related to the component of particle ejection velocity perpendicular
  to the planets orbital plane and use this to derive a minimum ejection
  velocity of 1.2 km s<SUP>-1</SUP>. To fit the average transit depth
  of Kepler-1520 b of 0.87%, we require a high dust mass-loss rate of
  7-80 M<SUB>⊕</SUB> Gyr<SUP>-1</SUP> which implies planet lifetimes
  that may be inconsistent with the observed sample. Therefore, these
  mass loss rates should be considered to be upper limits.

---------------------------------------------------------
Title: Review of high-contrast imaging systems for current and
future ground- and space-based telescopes I: coronagraph design
    methods and optical performance metrics
Authors: Ruane, G.; Riggs, A.; Mazoyer, J.; Por, E. H.; N'Diaye,
   M.; Huby, E.; Baudoz, P.; Galicher, R.; Douglas, E.; Knight, J.;
   Carlomagno, B.; Fogarty, K.; Pueyo, L.; Zimmerman, N.; Absil, O.;
   Beaulieu, M.; Cady, E.; Carlotti, A.; Doelman, D.; Guyon, O.; Haffert,
   S.; Jewell, J.; Jovanovic, N.; Keller, C.; Kenworthy, M. A.; Kuhn, J.;
   Miller, K.; Sirbu, D.; Snik, F.; Wallace, J. Kent; Wilby, M.; Ygouf, M.
2018SPIE10698E..2SR    Altcode: 2018arXiv180707042R
  The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center
  in September 2017 in Leiden, the Netherlands gathered a diverse group
  of 25 researchers working on exoplanet instrumentation to stimulate
  the emergence and sharing of new ideas. In this first installment of a
  series of three papers summarizing the outcomes of the OOC workshop, we
  present an overview of design methods and optical performance metrics
  developed for coronagraph instruments. The design and optimization
  of coronagraphs for future telescopes has progressed rapidly over the
  past several years in the context of space mission studies for Exo-C,
  WFIRST, HabEx, and LUVOIR as well as ground-based telescopes. Design
  tools have been developed at several institutions to optimize a variety
  of coronagraph mask types. We aim to give a broad overview of the
  approaches used, examples of their utility, and provide the optimization
  tools to the community. Though it is clear that the basic function
  of coronagraphs is to suppress starlight while maintaining light
  from off-axis sources, our community lacks a general set of standard
  performance metrics that apply to both detecting and characterizing
  exoplanets. The attendees of the OOC workshop agreed that it would
  benefit our community to clearly define quantities for comparing the
  performance of coronagraph designs and systems. Therefore, we also
  present a set of metrics that may be applied to theoretical designs,
  testbeds, and deployed instruments. We show how these quantities may
  be used to easily relate the basic properties of the optical instrument
  to the detection significance of the given point source in the presence
  of realistic noise.

---------------------------------------------------------
Title: First direct detection of a polarized companion outside a
    resolved circumbinary disk around CS Chamaeleonis
Authors: Ginski, C.; Benisty, M.; van Holstein, R. G.; Juhász,
   A.; Schmidt, T. O. B.; Chauvin, G.; de Boer, J.; Wilby, M.; Manara,
   C. F.; Delorme, P.; Ménard, F.; Pinilla, P.; Birnstiel, T.; Flock,
   M.; Keller, C.; Kenworthy, M.; Milli, J.; Olofsson, J.; Pérez, L.;
   Snik, F.; Vogt, N.
2018A&A...616A..79G    Altcode: 2018arXiv180502261G
  <BR /> Aims: To understand planet formation it is necessary to study
  the birth environment of planetary systems. Resolved imaging of young
  planet forming disks allows us to study this environment in great detail
  and find signs of planet-disk interaction and disk evolution. In the
  present study we aim to investigate the circumstellar environment of
  the spectroscopic binary T Tauri star CS Cha. From unresolved mid-to
  far-infrared photometry it is predicted that CS Cha hosts a disk with
  a large cavity. In addition, spectral energy distribution modeling
  suggests significant dust settling, pointing toward an evolved disk
  that may show signs of ongoing or completed planet formation. <BR />
  Methods: We observed CS Cha with the high contrast imager SPHERE at the
  ESO Very Large Telescope (VLT) in polarimetric differential imaging mode
  to resolve the circumbinary disk in near-infrared scattered light. These
  observations were followed up by VLT/NACO L-band observations and
  complemented by archival VLT/NACO K-band and Hubble Space Telescope
  WFPC2 I-band data. <BR /> Results: We resolve the compact circumbinary
  disk around CS Cha for the first time in scattered light. We find a
  smooth, low inclination disk with an outer radius of 55 au (at 165
  pc). We do not detect the inner cavity but find an upper limit for the
  cavity size of 15 au. Furthermore, we find a faint comoving companion
  with a projected separation of 210 au from the central binary outside
  of the circumbinary disk. The companion is detected in polarized light
  and shows an extreme degree of polarization (13.7 ± 0.4% in the J
  band). The J- and H-band magnitudes of the companion are compatible
  with masses of a few M<SUB>Jup</SUB>. However, K-, L-, and I-band
  data draw this conclusion into question. We explore with radiative
  transfer modeling whether an unresolved circum-companion disk can be
  responsible for the high polarization and complex photometry. We find
  that the set of observations is best explained by a heavily extincted
  low-mass ( 20 M<SUB>Jup</SUB>) brown dwarf or high-mass planet with an
  unresolved disk and dust envelope. <P />Based on observations performed
  with VLT/SPHERE under program ID 098.C-0760(B) and 099.C-0891(B)
  and VLT/NACO under program ID 298.C-5054(B) and 076.C-0292(A)The
  reduced images are only available at the CDS via anonymous ftp to
  <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A79">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A79</A>

---------------------------------------------------------
Title: High contrast imaging for the enhanced resolution imager and
    spectrometer (ERIS)
Authors: Kenworthy, Matthew A.; Snik, Frans; Keller, Christoph U.;
   Doelman, David; Por, Emiel H.; Absil, Olivier; Carlomagno, Brunella;
   Karlsson, Mikael; Huby, Elsa; Glauser, Adrian M.; Quanz, Sascha P.;
   Taylor, William D.
2018SPIE10702E..46K    Altcode: 2020arXiv201201963K
  ERIS is a diffraction limited thermal infrared imager and spectrograph
  for the Very Large Telescope UT4. One of the science cases for ERIS
  is the detection and characterization of circumstellar structures and
  exoplanets around bright stars that are typically much fainter than the
  stellar diffraction halo. Enhanced sensitivity is provided through the
  combination of (i) suppression of the diffraction halo of the target
  star using coronagraphs, and (ii) removal of any residual diffraction
  structure through focal plane wavefront sensing and subsequent active
  correction. In this paper we present the two coronagraphs used for
  diffraction suppression and enabling high contrast imaging in ERIS.

---------------------------------------------------------
Title: On-sky results of the Leiden EXoplanet Instrument (LEXI)
Authors: Haffert, S. Y.; Wilby, M. J.; Keller, C. U.; Snellen,
   I. A. G.; Doelman, D. S.; Por, E. H.; van Kooten, M.; Bos, S. P.;
   Wardenier, J.
2018SPIE10703E..23H    Altcode:
  The Leiden EXoplanet Instrument (LEXI) is a bench-mounted
  high-contrast spectrograph (HCS) and high- contrast imager(HCI). Both
  science instruments are mounted behind a common adaptive optics (AO)
  system. The AO can be controlled by several new wavefront sensors for
  which we will show the first on-sky results. There is a new pupil-plane
  wavefront sensors; the Generalized Optical Differentiation Wavefront
  sensor(g-ODWFS). LEXI can switch between two observing modes, the
  HCI mode or the HD-IFS mode. The spectrograph is very compact because
  it is fed by single-mode fiber. The HD-IFS is an IFS that covers the
  spectral range of 600 800 nm with a constant spectral resolving power
  of 96000. The 2kx3k detector makes it possible to deliver diffraction
  limited spectra of up to 20 input fibers. The high-dispersion spectra
  of the HD-IFS allow for robust post-processing technique to remove
  residual stellar speckles and allows for direct characterization of
  the faint stellar environment. We will show the first sucesful on-sky
  results of the injection into a single-mode fiber with LEXI. In HCI
  mode an Apodizing Phase Plate (APP) is used to create a dark region
  around the star with an average design contrast of 1E-4. The APP is
  multiplexed with holographic modes to create the Coronagraphic Modal
  Wavefront sensor (cMWS) for non-common path error (NCPE) correction. The
  cMWS creates holographic copies in the focal plane that react linearly
  to aberrations. The holographic copies are measured simultaneously with
  the science target. There is no downtime for NCPE correction. We will
  show the first on-sky closed-loop correction of (NCPEs) with the cMWS.

---------------------------------------------------------
Title: Optimization of contrast in adaptive optics for exoplanet
    imaging
Authors: Radhakrishnan, Vikram Mark; Keller, Christoph U.; Doelman,
   Niek
2018SPIE10703E..4NR    Altcode:
  Direct imaging of exoplanets requires overcoming the enormous contrast
  between the exoplanet and its host star, to distinguish the reflected
  light from the exoplanet, from the diffracted light of the star. Direct
  optimization of contrast, using nonlinear optimization techniques
  of the Adaptive Optics (AO) system coupled with coronagraphy, shows
  significant promise in achieving high contrast, beyond the limits of
  what can be achieved with traditional AO systems. Using a coronagraph
  optic as a "static" phase modifying element, and a deformable mirror
  as a "dynamic" element, we create an adaptive coronagraph, capable of
  engineering the point spread function (PSF) of the imaging system,
  to create a deep, dark hole in the focal plane, within which the
  exoplanet can be imaged. We present the results of simulations of a
  system, consisting of a vector Apodizing Phase Plate (vAPP) coronagraph,
  a deformable mirror (DM), and an imaging camera. The vAPP coronagraph
  reroutes starlight within the pupil plane, to create a designated dark
  hole region, which in the ideal case would be devoid of starlight
  in the focal plane. Off-axis exoplanet light is transmitted through
  to the dark hole and hence can be imaged. Atmospheric turbulence is
  simulated to generate a distorted wavefront, and a nonlinear, gradient
  climbing based optimization algorithm is implemented to drive the DM
  to optimize a merit function. This merit function is chosen with a
  dual objective to maximize average raw contrast in the dark hole,
  while maintaining a sufficiently high Strehl ratio. Preliminary
  results show that in a setup with a coronagraph designed to create a
  6×6 (λ/D)<SUP>2</SUP> rectangular dark hole with a raw contrast of
  10<SUP>-5</SUP>, the optimization procedure results in a raw contrast
  of 10<SUP>-7</SUP> at the dark hole while maintaining a Strehl ratio
  above 40%. It is observed that by tweaking the merit function, this
  non-linear optimization procedure can be adjusted to result in either
  higher Strehl or higher contrast. We discuss potential strategies to
  extend the non-linear optimization techniques to real-time, non-linear
  control for the AO system, thereby achieving a real-time, dynamic,
  adaptive coronagraph. Toward this end, we investigate the results
  of using the fast wavefront sensor data to reconstruct the wavefront
  phase, virtually propagate this through the science optical path, and
  optimize contrast on this virtual science image, as opposed to using
  the slower science camera to optimize contrast on the true science
  image. One potential approach to implement true real-time control would
  be to use deep neural networks, trained using deep deterministic policy
  gradients, to identify and remove speckles of diffracted starlight in
  the dark hole region in real-time.

---------------------------------------------------------
Title: Review of high-contrast imaging systems for current and
future ground-based and space-based telescopes: Part II. Common path
    wavefront sensing/control and coherent differential imaging
Authors: Jovanovic, Nemanja; Absil, Olivier; Baudoz, Pierre; Beaulieu,
   Mathilde; Bottom, Michael; Cady, Eric; Carlomagno, Brunella; Carlotti,
   Alexis; Doelman, David; Fogarty, Kevin; Galicher, Raphaël.; Guyon,
   Olivier; Haffert, Sebastiaan; Huby, Elsa; Jewell, Jeffrey; Keller,
   Christoph; Kenworthy, Matthew A.; Knight, Justin; Kühn, Jonas; Miller,
   Kelsey; Mazoyer, Johan; N'Diaye, Mamadou; Por, Emiel; Pueyo, Laurent;
   Riggs, A. J. E.; Ruane, Garreth; Sirbu, Dan; Snik, Frans; Wallace,
   J. K.; Wilby, Michael; Ygouf, Marie
2018SPIE10703E..1UJ    Altcode: 2018arXiv180707043J
  The Optimal Optical Coronagraph (OOC) Workshop held at the Lorentz
  Center in September 2017 in Leiden, the Netherlands, gathered a
  diverse group of 25 researchers working on exoplanet instrumentation
  to stimulate the emergence and sharing of new ideas. In this second
  installment of a series of three papers summarizing the outcomes of
  the OOC workshop, we present an overview of common path wavefront
  sensing/control and Coherent Differential Imaging techniques,
  highlight the latest results, and expose their relative strengths
  and weaknesses. We layout critical milestones for the field with the
  aim of enhancing future ground/space based high contrast imaging
  platforms. Techniques like these will help to bridge the daunting
  contrast gap required to image a terrestrial planet in the zone where
  it can retain liquid water, in reflected light around a G type star
  from space.

---------------------------------------------------------
Title: Laboratory verification of Fast &amp; Furious phase diversity:
    Towards controlling the low wind effect in the SPHERE instrument
Authors: Wilby, M. J.; Keller, C. U.; Sauvage, J. -F.; Dohlen, K.;
   Fusco, T.; Mouillet, D.; Beuzit, J. -L.
2018A&A...615A..34W    Altcode: 2018arXiv180303258W
  Context. The low wind effect (LWE) refers to a characteristic set
  of quasi-static wavefront aberrations seen consistently by the SPHERE
  instrument when dome-level wind speeds drop below 3 ms<SUP>-1</SUP>. The
  LWE produces bright low-order speckles in the stellar point-spread
  function (PSF), which severely limit the contrast performance of SPHERE
  under otherwise optimal observing conditions. <BR /> Aims: In this paper
  we propose the Fast &amp; Furious (F&amp;F) phase diversity algorithm
  as a viable software-only solution for real-time LWE compensation,
  which would utilise image sequences from the SPHERE differential
  tip-tilt sensor (DTTS) and apply corrections via reference slope
  offsets on the AO system's Shack-Hartmann wavefront sensor. <BR />
  Methods: We evaluated the closed-loop performance of F&amp;F on the
  MITHIC high-contrast test-bench, under conditions emulating LWE-affected
  DTTS images. These results were contrasted with predictive simulations
  for a variety of convergence tests, in order to assess the expected
  performance of an on-sky implementation of F&amp;F in SPHERE. <BR />
  Results: The algorithm was found to be capable of returning LWE-affected
  images to Strehl ratios of greater than 90% within five iterations,
  for all appropriate laboratory test cases. These results are highly
  representative of predictive simulations, and demonstrate stability
  of the algorithm against a wide range of factors including low image
  signal-to-noise ratio (S/N), small image field of view, and amplitude
  errors. It was also found in simulation that closed-loop stability can
  be preserved down to image S/N as low as five while still improving
  overall wavefront quality, allowing for reliable operation even on
  faint targets. <BR /> Conclusions: The Fast &amp; Furious algorithm is
  an extremely promising solution for real-time compensation of the LWE,
  which can operate simultaneously with science observations and may
  be implemented in SPHERE without requiring additional hardware. The
  robustness and relatively large effective dynamic range of F&amp;F
  also make it suitable for general wavefront optimisation applications,
  including the co-phasing of segmented ELT-class telescopes.

---------------------------------------------------------
Title: MagAO-X: project status and first laboratory results
Authors: Males, Jared R.; Close, Laird M.; Miller, Kelsey; Schatz,
   Lauren; Doelman, David; Lumbres, Jennifer; Snik, Frans; Rodack, Alex;
   Knight, Justin; Van Gorkom, Kyle; Long, Joseph D.; Hedglen, Alex;
   Kautz, Maggie; Jovanovic, Nemanja; Morzinski, Katie; Guyon, Olivier;
   Douglas, Ewan; Follette, Katherine B.; Lozi, Julien; Bohlman, Chris;
   Durney, Olivier; Gasho, Victor; Hinz, Phil; Ireland, Michael; Jean,
   Madison; Keller, Christoph; Kenworthy, Matt; Mazin, Ben; Noenickx,
   Jamison; Alfred, Dan; Perez, Kevin; Sanchez, Anna; Sauve, Corwynn;
   Weinberger, Alycia; Conrad, Al
2018SPIE10703E..09M    Altcode: 2018arXiv180704315M
  MagAO-X is an entirely new extreme adaptive optics system for the
  Magellan Clay 6.5 m telescope, funded by the NSF MRI program starting
  in Sep 2016. The key science goal of MagAO-X is high-contrast imaging
  of accreting protoplanets at Hα. With 2040 actuators operating at
  up to 3630 Hz, MagAO-X will deliver high Strehls (&gt; 70%), high
  resolution (19 mas), and high contrast (&lt; 1 × 10<SUP>-4 </SUP>)
  at Hα (656 nm). We present an overview of the MagAO-X system, review
  the system design, and discuss the current project status.

---------------------------------------------------------
Title: ERIS: revitalising an adaptive optics instrument for the VLT
Authors: Davies, R.; Esposito, S.; Schmid, H. -M.; Taylor, W.; Agapito,
   G.; Agudo Berbel, A.; Baruffolo, A.; Biliotti, V.; Biller, B.; Black,
   M.; Boehle, A.; Briguglio, B.; Buron, A.; Carbonaro, L.; Cortes,
   A.; Cresci, G.; Deysenroth, M.; Di Cianno, A.; Di Rico, G.; Doelman,
   D.; Dolci, M.; Dorn, R.; Eisenhauer, F.; Fantinel, D.; Ferruzzi, D.;
   Feuchtgruber, H.; Förster Schreiber, N.; Gao, X.; Gemperlein, H.;
   Genzel, R.; George, E.; Gillessen, S.; Giordano, C.; Glauser, A.;
   Glindemann, A.; Grani, P.; Hartl, M.; Heijmans, J.; Henry, D.; Huber,
   H.; Kasper, M.; Keller, C.; Kenworthy, M.; Kühn, J.; Kuntschner,
   H.; Lightfoot, J.; Lunney, D.; MacIntosh, M.; Mannucci, F.; March,
   S.; Neeser, M.; Patapis, P.; Pearson, D.; Plattner, M.; Puglisi, A.;
   Quanz, S.; Rau, C.; Riccardi, A.; Salasnich, B.; Schubert, J.; Snik,
   F.; Sturm, E.; Valentini, A.; Waring, C.; Wiezorrek, E.; Xompero, M.
2018SPIE10702E..09D    Altcode: 2018arXiv180705089D
  ERIS is an instrument that will both extend and enhance the fundamental
  diffraction limited imaging and spectroscopy capability for the VLT. It
  will replace two instruments that are now being maintained beyond their
  operational lifetimes, combine their functionality on a single focus,
  provide a new wavefront sensing module that makes use of the facility
  Adaptive Optics System, and considerably improve their performance. The
  instrument will be competitive with respect to JWST in several regimes,
  and has outstanding potential for studies of the Galactic Center,
  exoplanets, and high redshift galaxies. ERIS had its final design
  review in 2017, and is expected to be on sky in 2020. This contribution
  describes the instrument concept, outlines its expected performance,
  and highlights where it will most excel.

---------------------------------------------------------
Title: Review of high-contrast imaging systems for current and future
ground-based and space-based telescopes III: technology opportunities
    and pathways
Authors: Snik, Frans; Absil, Olivier; Baudoz, Pierre; Beaulieu,
   Mathilde; Bendek, Eduardo; Cady, Eric; Carlomagno, Brunella; Carlotti,
   Alexis; Cvetojevic, Nick; Doelman, David; Fogarty, Kevin; Galicher,
   Raphaël.; Guyon, Olivier; Haffert, Sebastiaan; Huby, Elsa; Jewell,
   Jeffrey; Jovanovic, Nemanja; Keller, Christoph; Kenworthy, Matthew
   A.; Knight, Justin; Kuhn, Jonas; Mazoyer, Johan; Miller, Kelsey;
   N'Diaye, Mamadou; Norris, Barnaby; Por, Emiel; Pueyo, Laurent; Riggs,
   A. J. Eldorado; Ruane, Garreth; Sirbu, Dan; Wallace, J. Kent; Wilby,
   Michael; Ygouf, Marie
2018SPIE10706E..2LS    Altcode: 2018arXiv180707100S
  The Optimal Optical CoronagraphWorkshop at the Lorentz Center in
  September 2017 in Leiden, the Netherlands gathered a diverse group of
  30 researchers working on exoplanet instrumentation to stimulate the
  emergence and sharing of new ideas. This contribution is the final part
  of a series of three papers summarizing the outcomes of the workshop,
  and presents an overview of novel optical technologies and systems that
  are implemented or considered for high-contrast imaging instruments
  on both ground-based and space telescopes. The overall objective
  of high contrast instruments is to provide direct observations
  and characterizations of exoplanets at contrast levels as extreme
  as 10<SUP>-10</SUP>. We list shortcomings of current technologies,
  and identify opportunities and development paths for new technologies
  that enable quantum leaps in performance. Specifically, we discuss the
  design and manufacturing of key components like advanced deformable
  mirrors and coronagraphic optics, and their amalgamation in "adaptive
  coronagraph" systems. Moreover, we discuss highly integrated system
  designs that combine contrast-enhancing techniques and characterization
  techniques (like high-resolution spectroscopy) while minimizing the
  overall complexity. Finally, we explore extreme implementations using
  all-photonics solutions for ground-based telescopes and dedicated huge
  apertures for space telescopes.

---------------------------------------------------------
Title: Multiplexed holographic aperture masking with liquid-crystal
    geometric phase masks
Authors: Doelman, D. S.; Tuthill, P.; Norris, B.; Wilby, M. J.; Por,
   E. H.; Keller, C. U.; Escuti, M. J.; Snik, F.
2018SPIE10701E..0TD    Altcode: 2018arXiv180800751D
  Sparse Aperture Masking (SAM) allows for high-contrast imaging at small
  inner working angles, however the performance is limited by the small
  throughput and the number of baselines. We present the concept and
  first lab results of Holographic Aperture Masking (HAM) with extreme
  liquid-crystal geometric phase patterns. We multiplex subapertures
  using holographic techniques to combine the same subaperture in multiple
  non-redundant PSFs in combination with a non-interferometric reference
  spot. This way arbitrary subaperture combinations and PSF configurations
  can be realized, giving HAM more uv-coverage, better throughput and
  improved calibration as compared to SAM, at the cost of detector space.

---------------------------------------------------------
Title: A Planet with a Disc? A Surprising Detection in Polarised
    Light with VLT/SPHERE
Authors: Ginski, C.; van Holstein, R.; Juhász, A.; Benisty, M.;
   Schmidt, T.; Chauvin, G.; de Boer, J.; Wilby, M.; Manara, C. F.;
   Delorme, P.; Ménard, F.; Muro-Arena, G.; Pinilla, P.; Birnstiel,
   T.; Flock, M.; Keller, C.; Kenworthy, M.; Milli, J.; Olofsson, J.;
   Pérez, L.; Snik, F.; Vogt, N.
2018Msngr.172...27G    Altcode:
  With the Spectro-Polarimetric High- contrast Exoplanet REsearch (SPHERE)
  instrument at ESO's Very Large Telescope (VLT) we can study the linear
  polarisation of directly detected planets and brown dwarfs, to learn
  about their atmospheres and immediate environments. We summarise
  here the recent discovery of a low-mass companion in polarised
  light by Ginski et al. (2018). The object shows an extreme degree of
  polarisation, indicating the presence of a circumplanetary disc.

---------------------------------------------------------
Title: The Single-mode Complex Amplitude Refinement (SCAR)
coronagraph: II. Lab verification, and toward the characterization
    of Proxima b
Authors: Haffert, S. Y.; Por, E. H.; Keller, C. U.; Kenworthy, M. A.;
   Doelman, D. S.; Snik, F.; Escuti, M. J.
2018arXiv180310693H    Altcode:
  We present the monochromatic lab verification of the newly developed
  SCAR coronagraph that combines a phase plate (PP) in the pupil with
  a microlens-fed single-mode fiber array in the focal plane. The two
  SCAR designs that have been measured, create respectively a 360 degree
  and 180 degree dark region from 0.8-2.4 \lambda/D around the star. The
  360 SCAR has been designed for a clear aperture and the 180 SCAR has
  been designed for a realistic aperture with central obscuration and
  spiders. The 360 SCAR creates a measured stellar null of $2-3 \times
  10^{-4}$ , and the 180 SCAR reaches a null of $1 \times 10^{-4}$
  . Their monochromatic contrast is maintained within a range of $\pm$
  0.16 \lambda/D peak-to-valley tip-tilt, which shows the robustness
  against tip-tilt errors. The small inner working angle and tip-tilt
  stability makes the SCAR coronagraph a very promising technique for
  an upgrade of current high-contrast instruments to characterize and
  detect exoplanets in the solar neighborhood.

---------------------------------------------------------
Title: SPEX: a highly accurate spectropolarimeter for atmospheric
    aerosol characterization
Authors: Rietjens, J. H. H.; Smit, J. M.; di Noia, A.; Hasekamp,
   O. P.; van Harten, G.; Snik, F.; Keller, C. U.
2017SPIE10563E..44R    Altcode:
  Global characterization of atmospheric aerosol in terms of the
  microphysical properties of the particles is essential for understanding
  the role aerosols in Earth climate [1]. For more accurate predictions
  of future climate the uncertainties of the net radiative forcing of
  aerosols in the Earth's atmosphere must be reduced [2]. Essential
  parameters that are needed as input in climate models are not only
  the aerosol optical thickness (AOT), but also particle specific
  properties such as the aerosol mean size, the single scattering albedo
  (SSA) and the complex refractive index. The latter can be used to
  discriminate between absorbing and non-absorbing aerosol types, and
  between natural and anthropogenic aerosol. Classification of aerosol
  types is also very important for air-quality and health-related
  issues [3]. Remote sensing from an orbiting satellite platform
  is the only way to globally characterize atmospheric aerosol at a
  relevant timescale of 1 day [4]. One of the few methods that can be
  employed for measuring the microphysical properties of aerosols is to
  observe both radiance and degree of linear polarization of sunlight
  scattered in the Earth atmosphere under different viewing directions
  [5][6][7]. The requirement on the absolute accuracy of the degree
  of linear polarization P<SUB>L</SUB> is very stringent: the absolute
  error in P<SUB>L</SUB> must be smaller then 0.001+0.005.P<SUB>L</SUB>
  in order to retrieve aerosol parameters with sufficient accuracy to
  advance climate modelling and to enable discrimination of aerosol types
  based on their refractive index for air-quality studies [6][7]. In
  this paper we present the SPEX instrument, which is a multi-angle
  spectropolarimeter that can comply with the polarimetric accuracy needed
  for characterizing aerosols in the Earth's atmosphere. We describe
  the implementation of spectral polarization modulation in a prototype
  instrument of SPEX and show results of ground based measurements from
  which aerosol microphysical properties are retrieved.

---------------------------------------------------------
Title: The Spectropolarimeter for Planetary Exploration: SPEX
Authors: Laan, Erik; Stam, Daphne; Snik, Frans; Karalidi, Theodora;
   Keller, Christoph; ter Horst, Rik; Navarro, Ramon; Oomen, Gijsbert;
   de Vries, Johan; Hoogeveen, Ruud
2017SPIE10566E..2GL    Altcode:
  SPEX (Spectropolarimeter for Planetary EXploration) is an innovative,
  compact remotesensing instrument for measuring and characterizing
  aerosols in the atmosphere. The shoebox size instrument is capable of
  accurate full linear spectropolarimetry without moving parts or liquid
  crystals. High precision polarimetry is performed through encoding
  the degree and angle of linear polarization of the incoming light
  in a sinusoidal modulation of the spectrum. Measuring this intensity
  spectrum thus provides the spectral dependence of the degree and angle
  of linear polarization. Polarimetry has proven to be an excellent
  tool to study microphysical properties of atmospheric particles. Such
  information is essential to better understand the weather and climate of
  a planet. Although SPEX can be used to study any planetary atmosphere,
  including the Earth's, the current design of SPEX is tailored to study
  Martian dust and clouds from an orbiting platform. SPEX' 9 entrance
  pupils can simultaneously measure intensity spectra from 0.4 to 0.8
  microns, in different directions along the flight direction (including
  two limb viewing directions). This way, the scattering phase functions
  of dust and cloud particles within a ground pixel are sampled while
  flying over it. SPEX can provide synergy with instruments on rovers and
  landers, as it provides an overview of spatial and temporal variations
  of the Martian atmosphere.

---------------------------------------------------------
Title: SPEX: the Spectropolarimeter for Planetary Exploration
Authors: Rietjens, J. H. H.; Snik, F.; Stam, D. M.; Smit, J. M.; van
   Harten, G.; Keller, C. U.; Verlaan, A. L.; Laan, E. C.; ter Horst,
   R.; Navarro, R.; Wielinga, K.; Moon, S. G.; Voors, R.
2017SPIE10565E..1CR    Altcode:
  We present SPEX, the Spectropolarimeter for Planetary Exploration,
  which is a compact, robust and low-mass spectropolarimeter designed
  to operate from an orbiting or in situ platform. Its purpose is to
  simultaneously measure the radiance and the state (degree and angle)
  of linear polarization of sunlight that has been scattered in a
  planetary atmosphere and/or reflected by a planetary surface with high
  accuracy. The degree of linear polarization is extremely sensitive to
  the microphysical properties of atmospheric or surface particles (such
  as size, shape, and composition), and to the vertical distribution
  of atmospheric particles, such as cloud top altitudes. Measurements
  as those performed by SPEX are therefore crucial and often the only
  tool for disentangling the many parameters that describe planetary
  atmospheres and surfaces. SPEX uses a novel, passive method for its
  radiance and polarization observations that is based on a carefully
  selected combination of polarization optics. This method, called
  spectral modulation, is the modulation of the radiance spectrum in both
  amplitude and phase by the degree and angle of linear polarization,
  respectively. The polarization optics consists of an achromatic
  quarter-wave retarder, an athermal multiple-order retarder, and a
  polarizing beam splitter. We will show first results obtained with
  the recently developed prototype of the SPEX instrument, and present
  a performance analysis based on a dedicated vector radiative transport
  model together with a recently developed SPEX instrument simulator.

---------------------------------------------------------
Title: Polarization modeling and predictions for DKIST part 2:
    application of the Berreman calculus to spectral polarization fringes
    of beamsplitters and crystal retarders
Authors: Harrington, David M.; Snik, Frans; Keller, Christoph U.;
   Sueoka, Stacey R.; van Harten, Gerard
2017JATIS...3d8001H    Altcode: 2017arXiv171006067H
  We outline polarization fringe predictions derived from an application
  of the Berreman calculus for the Daniel K. Inouye Solar Telescope
  (DKIST) retarder optics. The DKIST retarder baseline design used six
  crystals, single-layer antireflection coatings, thick cover windows,
  and oil between all optical interfaces. This tool estimates polarization
  fringes and optic Mueller matrices as functions of all optical design
  choices. The amplitude and period of polarized fringes under design
  changes, manufacturing errors, tolerances, and several physical factors
  can now be estimated. This tool compares well with observations of
  fringes for data collected with the spectropolarimeter for infrared
  and optical regions at the Dunn Solar Telescope using bicrystalline
  achromatic retarders as well as laboratory tests. With this tool, we
  show impacts of design decisions on polarization fringes as impacted by
  antireflection coatings, oil refractive indices, cover window presence,
  and part thicknesses. This tool helped DKIST decide to remove retarder
  cover windows and also recommends reconsideration of coating strategies
  for DKIST. We anticipate this tool to be essential in designing future
  retarders for mitigation of polarization and intensity fringe errors
  in other high spectral resolution astronomical systems.

---------------------------------------------------------
Title: Combining angular differential imaging and accurate polarimetry
    with SPHERE/IRDIS to characterize young giant exoplanets
Authors: van Holstein, Rob G.; Snik, Frans; Girard, Julien H.;
   de Boer, Jozua; Ginski, C.; Keller, Christoph U.; Stam, Daphne M.;
   Beuzit, Jean-Luc; Mouillet, David; Kasper, Markus; Langlois, Maud;
   Zurlo, Alice; de Kok, Remco J.; Vigan, Arthur
2017SPIE10400E..15V    Altcode: 2017arXiv170907519V
  Young giant exoplanets emit infrared radiation that can be linearly
  polarized up to several percent. This linear polarization can trace:
  1) the presence of atmospheric cloud and haze layers, 2) spatial
  structure, e.g. cloud bands and rotational flattening, 3) the spin axis
  orientation and 4) particle sizes and cloud top pressure. We introduce
  a novel high-contrast imaging scheme that combines angular differential
  imaging (ADI) and accurate near-infrared polarimetry to characterize
  self-luminous giant exoplanets. We implemented this technique at
  VLT/SPHEREIRDIS and developed the corresponding observing strategies,
  the polarization calibration and the data-reduction approaches. The
  combination of ADI and polarimetry is challenging, because the
  field rotation required for ADI negatively affects the polarimetric
  performance. By combining ADI and polarimetry we can characterize
  planets that can be directly imaged with a very high signal-to-noise
  ratio. We use the IRDIS pupil-tracking mode and combine ADI and
  principal component analysis to reduce speckle noise. We take advantage
  of IRDIS' dual-beam polarimetric mode to eliminate differential effects
  that severely limit the polarimetric sensitivity (flat-fielding errors,
  differential aberrations and seeing), and thus further suppress
  speckle noise. To correct for instrumental polarization effects, we
  apply a detailed Mueller matrix model that describes the telescope
  and instrument and that has an absolute polarimetric accuracy &lt;=
  0.1%. Using this technique we have observed the planets of HR 8799 and
  the (sub-stellar) companion PZ Tel B. Unfortunately, we do not detect
  a polarization signal in a first analysis. We estimate preliminary 1σ
  upper limits on the degree of linear polarization of ∼ 1% and ∼ 0.1%
  for the planets of HR 8799 and PZ Tel B, respectively. The achieved
  sub-percent sensitivity and accuracy show that our technique has great
  promise for characterizing exoplanets through direct-imaging polarimetry

---------------------------------------------------------
Title: Three Years of SPHERE: The Latest View of the Morphology and
    Evolution of Protoplanetary Discs
Authors: Garufi, A.; Benisty, M.; Stolker, T.; Avenhaus, H.; de Boer,
   J. .; Pohl, A.; Quanz, S. P.; Dominik, C.; Ginski, C.; Thalmann, C.;
   van Boekel, R.; Boccaletti, A.; Henning, T.; Janson, M.; Salter, G.;
   Schmid, H. M.; Sissa, E.; Langlois, M.; Beuzit, J. -L.; Chauvin, G.;
   Mouillet, D.; Augereau, J. -C.; Bazzon, A.; Biller, B.; Bonnefoy,
   M.; Buenzli, E.; Cheetham, A.; Daemgen, S.; Desidera, S.; Engler,
   N.; Feldt, M.; Girard, J.; Gratton, R.; Hagelberg, J.; Keller, C.;
   Keppler, M.; Kenworthy, M.; Kral, Q.; Lopez, B.; Maire, A. -L.; Menard,
   F.; Mesa, D.; Messina, S.; Meyer, M. R.; Milli, J.; Min, M.; Muller,
   A.; Olofsson, J.; Pawellek, N.; Pinte, C.; Szulagyi, J.; Vigan, A.;
   Wahhaj, Z.; Waters, R.; Zurlo, A.
2017Msngr.169...32G    Altcode: 2017arXiv171002795G
  Spatially resolving the immediate surroundings of young stars is a
  key challenge for the planet formation community. SPHERE on the VLT
  represents an important step forward by increasing the opportunities
  offered by optical or near-infrared imaging instruments to image
  protoplanetary discs. The Guaranteed Time Observation Disc team has
  concentrated much of its efforts on polarimetric differential imaging,
  a technique that enables the efficient removal of stellar light and
  thus facilitates the detection of light scattered by the disc within a
  few au from the central star. These images reveal intriguing complex
  disc structures and diverse morphological features that are possibly
  caused by ongoing planet formation in the disc. An overview of the
  recent advances enabled by SPHERE is presented.

---------------------------------------------------------
Title: Investigating circular patterns in linear polarization
    observations of Venus
Authors: Mahapatra, G.; Stam, D. M.; Rossi, L.; Rodenhuis, M.; Snik,
   F.; Keller, C. U.
2017EPSC...11..885M    Altcode:
  In this work, we report our observations of Venus using the polarized
  flux. Our observations show certain curious looking concentric rings
  around the sub-solar point of Venus. We use our radiative transfer
  model to explain these fluctuations and discuss what the possible
  explanations might be.

---------------------------------------------------------
Title: Rigorous vector wave propagation for arbitrary flat media
Authors: Bos, Steven P.; Haffert, Sebastiaan Y.; Keller, Christoph U.
2017SPIE10407E..09B    Altcode: 2018arXiv181109777B
  Precise modelling of the (off-axis) point spread function (PSF)
  to identify geometrical and polarization aberrations is important for
  many optical systems. In order to characterise the PSF of the system in
  all Stokes parameters, an end-to-end simulation of the system has to
  be performed in which Maxwell's equations are rigorously solved. We
  present the first results of a python code that we are developing
  to perform multiscale end-to-end wave propagation simulations that
  include all relevant physics. Currently we can handle plane-parallel
  near- and far-field vector diffraction effects of propagating waves
  in homogeneous isotropic and anisotropic materials, refraction and
  reflection of flat parallel surfaces, interference effects in thin
  films and unpolarized light. We show that the code has a numerical
  precision on the order of 10<SUP>-16 </SUP>for non-absorbing isotropic
  and anisotropic materials. For absorbing materials the precision is
  on the order of 10<SUP>-8</SUP>. The capabilities of the code are
  demonstrated by simulating a converging beam reflecting from a flat
  aluminium mirror at normal incidence.

---------------------------------------------------------
Title: BP Piscium: its flaring disc imaged with
    SPHERE/ZIMPOL<SUP>★</SUP>
Authors: de Boer, J.; Girard, J. H.; Canovas, H.; Min, M.; Sitko,
   M.; Ginski, C.; Jeffers, S. V.; Mawet, D.; Milli, J.; Rodenhuis, M.;
   Snik, F.; Keller, C. U.
2017MNRAS.466L...7D    Altcode: 2016arXiv161006609D
  Whether BP Piscium (BP Psc) is either a pre-main sequence T Tauri
  star at d ≈ 80 pc, or a post-main sequence G giant at d ≈ 300
  pc is still not clear. As a first-ascent giant, it is the first to
  be observed with a molecular and dust disc. Alternatively, BP Psc
  would be among the nearest T Tauri stars with a protoplanetary disc
  (PPD). We investigate whether the disc geometry resembles typical PPDs,
  by comparing polarimetric images with radiative transfer models. Our
  Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet
  REsearch (SPHERE)/Zurich IMaging Polarimeter (ZIMPOL) observations
  allow us to perform polarimetric differential imaging, reference star
  differential imaging, and Richardson-Lucy deconvolution. We present the
  first visible light polarization and intensity images of the disc of
  BP Psc. Our deconvolution confirms the disc shape as detected before,
  mainly showing the southern side of the disc. In polarized intensity
  the disc is imaged at larger detail and also shows the northern side,
  giving it the typical shape of high-inclination flared discs. We explain
  the observed disc features by retrieving the large-scale geometry with
  MCMAX radiative transfer modelling, which yields a strongly flared
  model, atypical for discs of T Tauri stars.

---------------------------------------------------------
Title: On-sky Performance Analysis of the Vector Apodizing Phase
    Plate Coronagraph on MagAO/Clio2
Authors: Otten, Gilles P. P. L.; Snik, Frans; Kenworthy, Matthew A.;
   Keller, Christoph U.; Males, Jared R.; Morzinski, Katie M.; Close,
   Laird M.; Codona, Johanan L.; Hinz, Philip M.; Hornburg, Kathryn J.;
   Brickson, Leandra L.; Escuti, Michael J.
2017ApJ...834..175O    Altcode: 2017arXiv170204193O
  We report on the performance of a vector apodizing phase plate
  coronagraph that operates over a wavelength range of 2-5 μm and
  is installed in MagAO/Clio2 at the 6.5 m Magellan Clay telescope
  at Las Campanas Observatory, Chile. The coronagraph manipulates the
  phase in the pupil to produce three beams yielding two coronagraphic
  point-spread functions (PSFs) and one faint leakage PSF. The phase
  pattern is imposed through the inherently achromatic geometric phase,
  enabled by liquid crystal technology and polarization techniques. The
  coronagraphic optic is manufactured using a direct-write technique
  for precise control of the liquid crystal pattern and multitwist
  retarders for achromatization. By integrating a linear phase ramp to
  the coronagraphic phase pattern, two separated coronagraphic PSFs are
  created with a single pupil-plane optic, which makes it robust and easy
  to install in existing telescopes. The two coronagraphic PSFs contain
  a 180° dark hole on each side of a star, and these complementary
  copies of the star are used to correct the seeing halo close to the
  star. To characterize the coronagraph, we collected a data set of a
  bright (m<SUB>L</SUB> = 0-1) nearby star with ∼1.5 hr of observing
  time. By rotating and optimally scaling one PSF and subtracting it
  from the other PSF, we see a contrast improvement by 1.46 magnitudes
  at 3.5 λ /D. With regular angular differential imaging at 3.9 μm,
  the MagAO vector apodizing phase plate coronagraph delivers a 5σ {{Δ
  }}{mag} contrast of 8.3 (={10}<SUP>-3.3</SUP>) at 2 λ /D and 12.2
  (={10}<SUP>-4.8</SUP>) at 3.5 λ /D.

---------------------------------------------------------
Title: The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane
    sensor for the high-contrast imaging of circumstellar environments
Authors: Wilby, M. J.; Keller, C. U.; Snik, F.; Korkiakoski, V.;
   Pietrow, A. G. M.
2017A&A...597A.112W    Altcode: 2016arXiv161004235W
  The raw coronagraphic performance of current high-contrast imaging
  instruments is limited by the presence of a quasi-static speckle
  (QSS) background, resulting from instrumental Non-Common Path Errors
  (NCPEs). Rapid development of efficient speckle subtraction techniques
  in data reduction has enabled final contrasts of up to 10<SUP>-6</SUP>
  to be obtained, however it remains preferable to eliminate the
  underlying NCPEs at the source. In this work we introduce the
  coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront sensor
  suitable for real-time NCPE correction. This combines the Apodizing
  Phase Plate (APP) coronagraph with a holographic modal wavefront sensor
  to provide simultaneous coronagraphic imaging and focal-plane wavefront
  sensing with the science point-spread function. We first characterise
  the baseline performance of the cMWS via idealised closed-loop
  simulations, showing that the sensor is able to successfully recover
  diffraction-limited coronagraph performance over an effective dynamic
  range of ±2.5 radians root-mean-square (rms) wavefront error within
  2-10 iterations, with performance independent of the specific choice
  of mode basis. We then present the results of initial on-sky testing
  at the William Herschel Telescope, which demonstrate that the sensor
  is capable of NCPE sensing under realistic seeing conditions via the
  recovery of known static aberrations to an accuracy of 10 nm (0.1
  radians) rms error in the presence of a dominant atmospheric speckle
  foreground. We also find that the sensor is capable of real-time
  measurement of broadband atmospheric wavefront variance (50% bandwidth,
  158 nm rms wavefront error) at a cadence of 50 Hz over an uncorrected
  telescope sub-aperture. When combined with a suitable closed-loop
  adaptive optics system, the cMWS holds the potential to deliver an
  improvement of up to two orders of magnitude over the uncorrected
  QSS floor. Such a sensor would be eminently suitable for the direct
  imaging and spectroscopy of exoplanets with both existing and future
  instruments, including EPICS and METIS for the E-ELT.

---------------------------------------------------------
Title: Dusty tails of evaporating exoplanets. II. Physical modelling
    of the KIC 12557548b light curve
Authors: van Lieshout, R.; Min, M.; Dominik, C.; Brogi, M.; de
   Graaff, T.; Hekker, S.; Kama, M.; Keller, C. U.; Ridden-Harper, A.;
   van Werkhoven, T. I. M.
2016A&A...596A..32V    Altcode: 2016arXiv160900275V
  Context. Evaporating rocky exoplanets, such as KIC 12557548b, eject
  large amounts of dust, which can trail the planet in a comet-like
  tail. When such objects occult their host star, the resulting transit
  signal contains information about the dust in the tail. <BR /> Aims:
  We aim to use the detailed shape of the Kepler light curve of KIC
  12557548b to constrain the size and composition of the dust grains that
  make up the tail, as well as the mass loss rate of the planet. <BR />
  Methods: Using a self-consistent numerical model of the dust dynamics
  and sublimation, we calculated the shape of the tail by following dust
  grains from their ejection from the planet to their destruction due to
  sublimation. From this dust cloud shape, we generated synthetic light
  curves (incorporating the effects of extinction and angle-dependent
  scattering), which were then compared with the phase-folded Kepler light
  curve. We explored the free-parameter space thoroughly using a Markov
  chain Monte Carlo method. <BR /> Results: Our physics-based model is
  capable of reproducing the observed light curve in detail. Good fits
  are found for initial grain sizes between 0.2 and 5.6 μm and dust
  mass loss rates of 0.6 to 15.6 M<SUB>⊕</SUB> Gyr<SUP>-1</SUP> (2σ
  ranges). We find that only certain combinations of material parameters
  yield the correct tail length. These constraints are consistent with
  dust made of corundum (Al<SUB>2</SUB>O<SUB>3</SUB>), but do not agree
  with a range of carbonaceous, silicate, or iron compositions. <BR />
  Conclusions: Using a detailed, physically motivated model, it is
  possible to constrain the composition of the dust in the tails of
  evaporating rocky exoplanets. This provides a unique opportunity to
  probe to interior composition of the smallest known exoplanets.

---------------------------------------------------------
Title: Direct detection of scattered light gaps in the transitional
    disk around HD 97048 with VLT/SPHERE
Authors: Ginski, C.; Stolker, T.; Pinilla, P.; Dominik, C.; Boccaletti,
   A.; de Boer, J.; Benisty, M.; Biller, B.; Feldt, M.; Garufi, A.;
   Keller, C. U.; Kenworthy, M.; Maire, A. L.; Ménard, F.; Mesa, D.;
   Milli, J.; Min, M.; Pinte, C.; Quanz, S. P.; van Boekel, R.; Bonnefoy,
   M.; Chauvin, G.; Desidera, S.; Gratton, R.; Girard, J. H. V.; Keppler,
   M.; Kopytova, T.; Lagrange, A. -M.; Langlois, M.; Rouan, D.; Vigan, A.
2016A&A...595A.112G    Altcode: 2016arXiv160904027G
  <BR /> Aims: We studied the well-known circumstellar disk around the
  Herbig Ae/Be star HD 97048 with high angular resolution to reveal
  undetected structures in the disk which may be indicative of disk
  evolutionary processes such as planet formation. <BR /> Methods: We used
  the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE
  at the ESO/VLT to study the scattered light from the circumstellar disk
  via high resolution polarimetry and angular differential imaging. <BR
  /> Results: We imaged the disk in unprecedented detail and revealed
  four ring-like brightness enhancements and corresponding gaps in the
  scattered light from the disk surface with radii between 39 au and 341
  au. We derived the inclination and position angle as well as the height
  of the scattering surface of the disk from our observational data. We
  found that the surface height profile can be described by a single
  power law up to a separation 270 au. Using the surface height profile
  we measured the scattering phase function of the disk and found that it
  is consistent with theoretical models of compact dust aggregates. We
  discuss the origin of the detected features and find that low mass
  (≤1 M<SUB>Jup</SUB>) nascent planets are a possible explanation. <P
  />Based on data collected at the European Southern Observatory, Chile
  (ESO Programs 096.C-0248, 096.C-0241, 077.C-0106).

---------------------------------------------------------
Title: Multiple rings in the transition disk and companion candidates
    around RX J1615.3-3255. High contrast imaging with VLT/SPHERE
Authors: de Boer, J.; Salter, G.; Benisty, M.; Vigan, A.; Boccaletti,
   A.; Pinilla, P.; Ginski, C.; Juhasz, A.; Maire, A. -L.; Messina,
   S.; Desidera, S.; Cheetham, A.; Girard, J. H.; Wahhaj, Z.; Langlois,
   M.; Bonnefoy, M.; Beuzit, J. -L.; Buenzli, E.; Chauvin, G.; Dominik,
   C.; Feldt, M.; Gratton, R.; Hagelberg, J.; Isella, A.; Janson, M.;
   Keller, C. U.; Lagrange, A. -M.; Lannier, J.; Menard, F.; Mesa, D.;
   Mouillet, D.; Mugrauer, M.; Peretti, S.; Perrot, C.; Sissa, E.; Snik,
   F.; Vogt, N.; Zurlo, A.; SPHERE Consortium
2016A&A...595A.114D    Altcode: 2016arXiv161004038D
  Context. The effects of a planet sculpting the disk from which it formed
  are most likely to be found in disks that are in transition between
  being classical protoplanetary and debris disks. Recent direct imaging
  of transition disks has revealed structures such as dust rings, gaps,
  and spiral arms, but an unambiguous link between these structures and
  sculpting planets is yet to be found. <BR /> Aims: We aim to find signs
  of ongoing planet-disk interaction and study the distribution of small
  grains at the surface of the transition disk around RX J1615.3-3255 (RX
  J1615). <BR /> Methods: We observed RX J1615 with VLT/SPHERE. From these
  observations, we obtained polarimetric imaging with ZIMPOL (R'-band)
  and IRDIS (J), and IRDIS (H2H3) dual-band imaging with simultaneous
  spatially resolved spectra with the IFS (YJ). <BR /> Results: We image
  the disk for the first time in scattered light and detect two arcs,
  two rings, a gap and an inner disk with marginal evidence for an inner
  cavity. The shapes of the arcs suggest that they are probably segments
  of full rings. Ellipse fitting for the two rings and inner disk yield
  a disk inclination I = 47 ± 2° and find semi-major axes of 1.50 ±
  0.01” (278 au), 1.06 ± 0.01” (196 au) and 0.30 ± 0.01” (56 au),
  respectively. We determine the scattering surface height above the
  midplane, based on the projected ring center offsets. Nine point sources
  are detected between 2.1” and 8.0” separation and considered as
  companion candidates. With NACO data we recover four of the nine point
  sources, which we determine to be not co-moving, and therefore unbound
  to the system. <BR /> Conclusions: We present the first detection
  of the transition disk of RX J1615 in scattered light. The height of
  the rings indicate limited flaring of the disk surface, which enables
  partial self-shadowing in the disk. The outermost arc either traces the
  bottom of the disk or it is another ring with semi-major axis ≳ 2.35”
  (435 au). We explore both scenarios, extrapolating the complete shape
  of the feature, which will allow us to distinguish between the two
  in future observations. The most attractive scenario, where the arc
  traces the bottom of the outer ring, requires the disk to be truncated
  at r ≈ 360 au. If the closest companion candidate is indeed orbiting
  the disk at 540 au, then it would be the most likely cause for such
  truncation. This companion candidate, as well as the remaining four,
  all require follow up observations to determine if they are bound to
  the system. <P />Based on observations made with ESO Telescopes at
  the La Silla Paranal Observatory under programme IDs 095.C-0298(A),
  095.C-0298(B), and 095.C-0693(A) during guaranteed and open time
  observations of the SPHERE consortium, and on NACO observations: program
  IDs: 085.C-0012(A), 087.C-0111(A), and 089.C-0133(A). The reduced
  images as FITS files are only available at the CDS via anonymous ftp
  to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A114">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A114</A>

---------------------------------------------------------
Title: The Hera Saturn entry probe mission
Authors: Mousis, O.; Atkinson, D. H.; Spilker, T.; Venkatapathy, E.;
   Poncy, J.; Frampton, R.; Coustenis, A.; Reh, K.; Lebreton, J. -P.;
   Fletcher, L. N.; Hueso, R.; Amato, M. J.; Colaprete, A.; Ferri, F.;
   Stam, D.; Wurz, P.; Atreya, S.; Aslam, S.; Banfield, D. J.; Calcutt,
   S.; Fischer, G.; Holland, A.; Keller, C.; Kessler, E.; Leese, M.;
   Levacher, P.; Morse, A.; Muñoz, O.; Renard, J. -B.; Sheridan, S.;
   Schmider, F. -X.; Snik, F.; Waite, J. H.; Bird, M.; Cavalié, T.;
   Deleuil, M.; Fortney, J.; Gautier, D.; Guillot, T.; Lunine, J. I.;
   Marty, B.; Nixon, C.; Orton, G. S.; Sánchez-Lavega, A.
2016P&SS..130...80M    Altcode: 2015arXiv151007685M
  The Hera Saturn entry probe mission is proposed as an M-class mission
  led by ESA with a contribution from NASA. It consists of one atmospheric
  probe to be sent into the atmosphere of Saturn, and a Carrier-Relay
  spacecraft. In this concept, the Hera probe is composed of ESA
  and NASA elements, and the Carrier-Relay Spacecraft is delivered
  by ESA. The probe is powered by batteries, and the Carrier-Relay
  Spacecraft is powered by solar panels and batteries. We anticipate
  two major subsystems to be supplied by the United States, either by
  direct procurement by ESA or by contribution from NASA: the solar
  electric power system (including solar arrays and the power management
  and distribution system), and the probe entry system (including the
  thermal protection shield and aeroshell). Hera is designed to perform
  in situ measurements of the chemical and isotopic compositions as
  well as the dynamics of Saturn's atmosphere using a single probe, with
  the goal of improving our understanding of the origin, formation, and
  evolution of Saturn, the giant planets and their satellite systems,
  with extrapolation to extrasolar planets. Hera's aim is to probe
  well into the cloud-forming region of the troposphere, below the
  region accessible to remote sensing, to the locations where certain
  cosmogenically abundant species are expected to be well mixed. By
  leading to an improved understanding of the processes by which giant
  planets formed, including the composition and properties of the local
  solar nebula at the time and location of giant planet formation,
  Hera will extend the legacy of the Galileo and Cassini missions by
  further addressing the creation, formation, and chemical, dynamical,
  and thermal evolution of the giant planets, the entire solar system
  including Earth and the other terrestrial planets, and formation of
  other planetary systems.

---------------------------------------------------------
Title: Search for an exosphere in sodium and calcium in the
    transmission spectrum of exoplanet 55 Cancri e
Authors: Ridden-Harper, A. R.; Snellen, I. A. G.; Keller, C. U.; de
   Kok, R. J.; Di Gloria, E.; Hoeijmakers, H. J.; Brogi, M.; Fridlund,
   M.; Vermeersen, B. L. A.; van Westrenen, W.
2016A&A...593A.129R    Altcode: 2016arXiv160608447R
  Context. The atmospheric and surface characterization of rocky
  planets is a key goal of exoplanet science. Unfortunately, the
  measurements required for this are generally out of reach of present-day
  instrumentation. However, the planet Mercury in our own solar system
  exhibits a large exosphere composed of atomic species that have been
  ejected from the planetary surface by the process of sputtering. Since
  the hottest rocky exoplanets known so far are more than an order of
  magnitude closer to their parent star than Mercury is to the Sun,
  the sputtering process and the resulting exospheres could be orders
  of magnitude larger and potentially detectable using transmission
  spectroscopy, indirectly probing their surface compositions. <BR />
  Aims: The aim of this work is to search for an absorption signal from
  exospheric sodium (Na) and singly ionized calcium (Ca<SUP>+</SUP>)
  in the optical transmission spectrum of the hot rocky super-Earth 55
  Cancri e. Although the current best-fitting models to the planet mass
  and radius require a possible atmospheric component, uncertainties in
  the radius exist, making it possible that 55 Cancri e could be a hot
  rocky planet without an atmosphere. <BR /> Methods: High resolution
  (R ~ 110 000) time-series spectra of five transits of 55 Cancri e,
  obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6 m and
  HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium
  H and K lines, the potential planet exospheric signal was filtered out
  from the much stronger stellar and telluric signals, making use of the
  change of the radial component of the orbital velocity of the planet
  over the transit from -57 to +57 km s<SUP>-1</SUP>. <BR /> Results:
  Combining all five transit data sets, we detect a signal potentially
  associated with sodium in the planet exosphere at a statistical
  significance level of 3σ. Combining the four HARPS transits that
  cover the calcium H and K lines, we also find a potential signal from
  ionized calcium (4.1σ). Interestingly, this latter signal originates
  from just one of the transit measurements - with a 4.9σ detection at
  this epoch. Unfortunately, due to the low significance of the measured
  sodium signal and the potentially variable Ca<SUP>+</SUP> signal, we
  estimate the p-values of these signals to be too high (corresponding to
  &lt;4σ) to claim unambiguous exospheric detections. By comparing the
  observed signals with artificial signals injected early in the analysis,
  the absorption by Na and Ca<SUP>+</SUP> are estimated to be at a level
  of ~2.3 × 10<SUP>-3</SUP> and ~7.0 × 10<SUP>-2</SUP> respectively,
  relative to the stellar spectrum. <BR /> Conclusions: If confirmed,
  the 3σ signal would correspond to an optically thick sodium exosphere
  with a radius of 5 R<SUB>⊕</SUB>, which is comparable to the Roche
  lobe radius of the planet. The 4.9σ detection of Ca<SUP>+</SUP>
  in a single HARPS data set would correspond to an optically thick
  Ca<SUP>+</SUP> exosphere approximately five times larger than the
  Roche lobe radius. If this were a real detection, it would imply
  that the exosphere exhibits extreme variability. Although no formal
  detection has been made, we advocate that probing the exospheres of
  hot super-Earths in this way has great potential, also knowing that
  Mercury's exosphere varies significantly over time. It may be a fast
  route towards the first characterization of the surface properties of
  this enigmatic class of planets. <P />Based on observations collected
  at the European Organisation for Astronomical Research in the Southern
  Hemisphere under ESO programmes 092.C-0178 and 288.C-5010 and the
  Telescopio Nazionale Galileo under programme CAT13B_33.

---------------------------------------------------------
Title: HERA: an atmospheric probe to unveil the depths of Saturn
Authors: Mousis, Olivier; Atkinson, David H.; Amato, Michael; Aslam,
   Shahid; Atreya, Sushil K.; Blanc, Michel; Bolton, Scott J.; Brugger,
   Bastien; Calcutt, Simon; Cavalié, Thibault; Charnoz, Sébastien;
   Coustenis, Athena; DELEUIL, Magali; Ferri, Francesca; Fletcher,
   Leigh N.; Guillot, Tristan; Hartogh, Paul; Holland, Andrew; Hueso,
   Ricardo; Keller, Christoph; Kessler, Ernst; Lebreton, Jean-Pierre;
   leese, Mark; Lellouch, Emmanuel; Levacher, Patrick; Marty, Bernard;
   Morse, Andrew; Nixon, Conor; Reh, Kim R.; Renard, Jean-Baptiste;
   Sanchez-Lavega, Agustin; Schmider, François-Xavier; Sheridan, Simon;
   Simon, Amy A.; Snik, Frans; Spilker, Thomas R.; Stam, Daphne M.;
   Venkatapathy, Ethiraj; Vernazza, Pierre; Waite, J. Hunter; Wurz, Peter
2016DPS....4812328M    Altcode:
  The Hera Saturn entry probe mission is proposed as an M-class mission
  led by ESA with a significant collaboration with NASA. It consists
  of a Saturn atmospheric probe and a Carrier-Relay spacecraft. Hera
  will perform in situ measurements of the chemical and isotopic
  compositions as well as the dynamics of Saturn's atmosphere, with
  the goal of improving our understanding of the origin, formation, and
  evolution of Saturn, the giant planets and their satellite systems,
  with extrapolation to extrasolar planets.The primary science objectives
  will be addressed by an atmospheric entry probe that would descend
  under parachute and carry out in situ measurements beginning in the
  stratosphere to help characterize the location and properties of the
  tropopause, and continue into the troposphere to pressures of at least
  10 bars. All of the science objectives, except for the abundance of
  oxygen, which may be only addressed indirectly via observations of
  species whose abundances are tied to the abundance of water, can
  be achieved by reaching 10 bars. As in previous highly successful
  collaborative efforts between ESA and NASA, the proposed mission has a
  baseline concept based on a NASA-provided carrier/data relay spacecraft
  that would deliver the ESA-provided atmospheric probe to the desired
  atmospheric entry point at Saturn. ESA's proposed contribution should
  fit well into the M5 Cosmic Vision ESA call cost envelope.A nominal
  mission configuration would consist of a probe that detaches from
  the carrier one to several months prior to probe entry. Subsequent to
  probe release, the carrier trajectory would be deflected to optimize
  the over-flight phasing of the probe descent location for both probe
  data relay as well as performing carrier approach and flyby science,
  and would allow multiple retransmissions of the probe data for
  redundancy. The Saturn atmospheric entry probe would in many respects
  resemble the Jupiter Galileo probe. It is anticipated that the probe
  architecture for this mission would be battery-powered and accommodate
  a data relay to the carrier for data collection, storage on board the
  carrier/data relay, for later retransmission to Earth.

---------------------------------------------------------
Title: The Leiden EXoplanet Instrument (LEXI): a high-contrast
    high-dispersion spectrograph
Authors: Haffert, S. Y.; Wilby, M. J.; Keller, C. U.; Snellen, I. A. G.
2016SPIE.9908E..67H    Altcode:
  The Leiden EXoplanet Instrument (LEXI) will be the first instrument
  designed for high-contrast, high-dispersion integral field spectroscopy
  at optical wavelengths. High-contrast imaging (HCI) and high-dispersion
  spectroscopy (HDS) techniques are used to reach contrasts of
  10<SUP>-7</SUP>. LEXI will be a bench-mounted, high dispersion integral
  field spectrograph that will record spectra in a small area around the
  star with high spatial resolution and high dynamic range. A prototype
  is being setup to The Leiden EXoplanet Instrument (LEXI) will be the
  first instrument designed for high-contrast, high-dispersion integral
  field spectroscopy at optical wavelengths. High-contrast imaging
  (HCI) and high-dispersion spectroscopy (HDS) techniques are used to
  reach contrasts of 10<SUP>-7</SUP>. LEXI will be a bench-mounted,
  high dispersion integral field spectrograph that will record spectra
  in a small area around the star with high spatial resolution and high
  dynamic range. A prototype is being setup to test the combination of
  HCI+HDS and its first light is expected in 2016.

---------------------------------------------------------
Title: Novel instrument concepts for characterizing directly imaged
    exoplanets
Authors: Keller, Christoph U.
2016SPIE.9908E..9VK    Altcode:
  Current high-contrast exoplanet imagers are optimized to find new
  exoplanets; they minimize diffracted starlight in a large area around a
  star. I present four novel instrumental approaches that are optimized
  to characterize these discoveries by minimizing starlight in a small
  area around the known location of an exoplanet: 1) coronagraphs that
  remove virtually all starlight over an octave in wavelength while
  transmitting more than 90% of the exoplanet signal; 2) holographic
  wavefront sensors that measure aberrations in the science focal plane;
  3) ultra-fast adaptive optics systems that minimize these aberrations;
  and 4) direct minimization of the remaining starlight. By integrating
  these technologies with a high spectral- resolution, integral-field
  spectrograph that can resolve the Doppler shift and the polarization
  difference between the starlight and the reflected light from
  the exoplanet, it will be possible to determine the atmospheric
  composition, temperature and velocity structures of exoplanets and
  their spin rotation rate and orbital velocity. This will ultimately
  allow the upcoming extremely large telescopes to characterize rocky
  exoplanets in the habitable zone to look for signatures of life.

---------------------------------------------------------
Title: End-to-end simulations of the E-ELT/METIS coronagraphs
Authors: Carlomagno, Brunella; Absil, Olivier; Kenworthy, Matthew;
   Ruane, Garreth; Keller, Christoph U.; Otten, Gilles; Feldt, Markus;
   Hippler, Stefan; Huby, Elsa; Mawet, Dimitri; Delacroix, Christian;
   Surdej, Jean; Habraken, Serge; Forsberg, Pontus; Karlsson, Mikael;
   Vargas Catalan, Ernesto; Brandl, Bernhard R.
2016SPIE.9909E..73C    Altcode:
  The direct detection of low-mass planets in the habitable zone of
  nearby stars is an important science case for future E-ELT instruments
  such as the mid-infrared imager and spectrograph METIS, which features
  vortex phase masks and apodizing phase plates (APP) in its baseline
  design. In this work, we present end-to-end performance simulations,
  using Fourier propagation, of several METIS coronagraphic modes,
  including focal-plane vortex phase masks and pupil-plane apodizing
  phase plates, for the centrally obscured, segmented E-ELT pupil. The
  atmosphere and the AO contributions are taken into account. Hybrid
  coronagraphs combining the advantages of vortex phase masks and APPs
  are considered to improve the METIS coronagraphic performance.

---------------------------------------------------------
Title: A "Fast and Furious'" solution to the low-wind effect for
    SPHERE at the VLT
Authors: Wilby, M. J.; Keller, C. U.; Sauvage, J. -F.; Fusco, T.;
   Mouillet, D.; Beuzit, J. -L.; Dohlen, K.
2016SPIE.9909E..6CW    Altcode:
  We present a potential non-invasive solution to sensing the so-called
  low-wind effect (LWE) seen in the SPHERE instrument at the VLT, based on
  the "Fast and Furious (F&amp;F) sequential phase diversity wavefront
  reconstruction algorithm. This uses non-coronagraphic focal-plane
  images available from the near-infra-red Differential Tip-Tilt Sensor
  (DTTS), with the closed-loop correction cycle itself providing the
  necessary phase diversity between frames required to reconstruct
  the full wavefront phase. Crucially, this means F&amp;F does not
  need to apply large artificial phase probes as required by standard
  phase diversity algorithms, allowing it to operate in a real-time (
  10 Hz) correction mode without impacting science observations. In this
  paper we present the results of realistic closed-loop AO simulations
  designed to emulate SPHERE/DTTS observations of the LWE. With this
  we demonstrate that the F&amp;F algorithm is capable of effective
  removal of the characteristic point-spread function (PSF) aberrations
  of strongly LWE-affected images within a few closed-loop iterations,
  with the final wavefront quality limited only by the corrective order of
  the deformable mirror. The ultimate goal of this project is to provide
  an independent, real-time and focal-plane wavefront sensor for SPHERE
  which is capable of detecting and directly compensating the LWE as it
  arises, thus improving coronagraph performance under the best 15-20 %
  of observing conditions where the effect is most pronounced.

---------------------------------------------------------
Title: Focal-plane electric field sensing with pupil-plane holograms
Authors: Por, Emiel H.; Keller, Christoph U.
2016SPIE.9909E..59P    Altcode:
  The direct detection and spectral characterization of exoplanets
  requires a coronagraph to suppress the diffracted star light. Amplitude
  and phase aberrations in the optical train fill the dark zone of
  the coronagraph with quasi-static speckles that limit the achievable
  contrast. Focal-plane electric field sensing, such as phase diversity
  introduced by a deformable mirror (DM), is a powerful tool to minimize
  this residual star light. The residual electric field can be estimated
  by sequentially applying phase probes on the DM to inject star light
  with a well-known amplitude and phase into the dark zone and analyzing
  the resulting intensity images. The DM can then be used to add light
  with the same amplitude but opposite phase to destructively interfere
  with this residual star light. Using a static phase-only pupil-plane
  element we create holographic copies of the point spread function (PSF),
  each superimposed with a certain pupil-plane phase probe. We therefore
  obtain all intensity images simultaneously while still retaining a
  central, unaltered science PSF. The electric field sensing method
  only makes use of the holographic copies, allowing for correction
  of the residual electric field while retaining the central PSF for
  uninterrupted science data collection. In this paper we demonstrate
  the feasibility of this method with numerical simulations.

---------------------------------------------------------
Title: Designing and testing the coronagraphic Modal Wavefront Sensor:
    a fast non-common path error sensor for high-contrast imaging
Authors: Wilby, M. J.; Keller, C. U.; Haffert, S.; Korkiakoski, V.;
   Snik, F.; Pietrow, A. G. M.
2016SPIE.9909E..21W    Altcode:
  Non-Common Path Errors (NCPEs) are the dominant factor limiting
  the performance of current astronomical high-contrast imaging
  instruments. If uncorrected, the resulting quasi-static speckle noise
  floor limits coronagraph performance to a raw contrast of typically
  10<SUP>-4</SUP>, a value which does not improve with increasing
  integration time. The coronagraphic Modal Wavefront Sensor (cMWS)
  is a hybrid phase optic which uses holographic PSF copies to supply
  focal-plane wavefront sensing information directly from the science
  camera, whilst maintaining a bias-free coronagraphic PSF. This
  concept has already been successfully implemented on-sky at the
  William Herschel Telescope (WHT), La Palma, demonstrating both
  real-time wavefront sensing capability and successful extraction of
  slowly varying wavefront errors under a dominant and rapidly changing
  atmospheric speckle foreground. In this work we present an overview of
  the development of the cMWS and recent first light results obtained
  using the Leiden EXoplanet Instrument (LEXI), a high-contrast imager
  and high-dispersion spectrograph pathfinder instrument for the WHT.

---------------------------------------------------------
Title: The ZIMPOL high contrast imaging polarimeter for SPHERE:
    polarimetric high contrast commissioning results
Authors: Roelfsema, Ronald; Bazzon, Andreas; Schmid, Hans Martin;
   Pragt, Johan; Govaert, Alain; Gisler, Daniel; Dominik, Carsten;
   Baruffolo, Andrea; Beuzit, Jean-Luc; Costille, Anne; Dohlen, Kjetil;
   Downing, Mark; Elswijk, Eddy; de Haan, Menno; Hubin, Norbert; Kasper,
   Markus; Keller, Christoph; Lizon, Jean-Louis; Mouillet, David; Pavlov,
   Alexey; Puget, Pascal; Salasnich, Bernardo; Sauvage, Jean-Francois;
   Wildi, Francois
2016SPIE.9909E..27R    Altcode:
  SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is
  a second generation VLT instrument aimed at the direct detection
  of exo-planets. It has received its first light in May 2014. ZIMPOL
  (Zurich Imaging Polarimeter) is the imaging polarimeter subsystem of
  the SPHERE instrument. It's capable of both high accuracy and high
  sensitivity polarimetry but can also be used as a classical imager. It
  is located behind an extreme AO system and a stellar coronagraph. ZIMPOL
  operates at visible wavelengths which is best suited to detect the
  very faint reflected and hence polarized visible light from extra solar
  planets. During the SPHERE fourth commissioning period (October 2014)
  we have made deep coronagraphic observations of the bright star alpha
  Gru (mR = 1.75) to assess the high contrast polarimetric performance
  of SPHERE-ZIMPOL. We have integrated on the target for a total time of
  about 45 minutes during the meridian transit in the Very Broad Band
  filter (600 - 900 nm) with a classical Lyot coronagraph with 3 λ/D
  radius focal mask. We reduce the data by a combination of Polarized
  Background subtraction, Polarimetric Differential Imaging (PDI) and
  Angular Differential Imaging (ADI). We reach contrasts of 10-6 and
  10-7 at a radial distances of respectively 7 and 14 lambda/D from
  the PSF core. At these radial distances we are respectively a factor
  of 10 and 2 above the photon noise limit. We discuss our results by
  considering the temporal and spatial speckle behavior close to the
  PSF core in combination with low order polarimetric aberrations.

---------------------------------------------------------
Title: Instrumemtation
Authors: Keller, Christoph U.; Snik, Frans; Harrington, David M.;
   Packham, Chris
2015psps.book...35K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Combining high-dispersion spectroscopy with high contrast
imaging: Probing rocky planets around our nearest neighbors
Authors: Snellen, I.; de Kok, R.; Birkby, J. L.; Brandl, B.; Brogi,
   M.; Keller, C.; Kenworthy, M.; Schwarz, H.; Stuik, R.
2015A&A...576A..59S    Altcode: 2015arXiv150301136S
  Context. Ground-based high-dispersion (R ~ 100 000) spectroscopy (HDS)
  is proving to be a powerful technique with which to characterize
  extrasolar planets. The planet signal is distilled from the bright
  starlight, combining ral and time-differential filtering techniques. In
  parallel, high-contrast imaging (HCI) is developing rapidly, aimed at
  spatially separating the planet from the star. While HDS is limited by
  the overwhelming noise from the host star, HCI is limited by residual
  quasi-static speckles. Both techniques currently reach planet-star
  contrast limits down to ~10<SUP>-5</SUP>, albeit for very different
  types of planetary systems. <BR /> Aims: In this work, we discuss
  a way to combine HDS and HCI (HDS+HCI). For a planet located at a
  resolvable angular distance from its host star, the starlight can be
  reduced up to several orders of magnitude using adaptive optics and/or
  coronography. In addition, the remaining starlight can be filtered
  out using high-dispersion spectroscopy, utilizing the significantly
  different (or Doppler shifted) high-dispersion spectra of the planet
  and star. In this way, HDS+HCI can in principle reach contrast limits
  of ~10<SUP>-5</SUP> × 10<SUP>-5</SUP>, although in practice this
  will be limited by photon noise and/or sky-background. In contrast to
  current direct imaging techniques, such as Angular Differential Imaging
  and Spectral Differential Imaging, it will work well at small working
  angles and is much less sensitive to speckle noise. For the discovery
  of previously unknown planets HDS+HCI requires a high-contrast adaptive
  optics system combined with a high-dispersion R ~ 100 000 integral field
  spectrograph (IFS). This combination currently does not exist, but is
  planned for the European Extremely Large Telescope. <BR /> Methods:
  We present simulations of HDS+HCI observations with the E-ELT, both
  probing thermal emission from a planet at infrared wavelengths, and
  starlight reflected off a planet atmosphere at optical wavelengths. For
  the infrared simulations we use the baseline parameters of the E-ELT
  and METIS instrument, with the latter combining extreme adaptive
  optics with an R = 100 000 IFS. We include realistic models of
  the adaptive optics performance and atmospheric transmission and
  emission. For the optical simulation we also assume R = 100 000 IFS
  with adaptive optics capabilities at the E-ELT. <BR /> Results: One
  night of HDS+HCI observations with the E-ELT at 4.8 μm (Δλ = 0.07
  μm) can detect a planet orbiting α Cen A with a radius of R = 1.5
  R<SUB>earth</SUB> and a twin-Earth thermal spectrum of T<SUB>eq</SUB>
  = 300 K at a signal-to-noise (S/N) of 5. In the optical, with a Strehl
  ratio performance of 0.3, reflected light from an Earth-size planet
  in the habitable zone of Proxima Centauri can be detected at a S/N of
  10 in the same time frame. Recently, first HDS+HCI observations have
  shown the potential of this technique by determining the spin-rotation
  of the young massive exoplanet β Pictoris b. <BR /> Conclusions:
  The exploration of the planetary systems of our neighbor stars is
  of great scientific and philosophical value. The HDS+HCI technique
  has the potential to detect and characterize temperate rocky planets
  in their habitable zones. Exoplanet scientists should not shy away
  from claiming a significant fraction of the future ELTs to make such
  observations possible.

---------------------------------------------------------
Title: Magnetic field topology and chemical spot distributions in
    the extreme Ap star HD 75049
Authors: Kochukhov, O.; Rusomarov, N.; Valenti, J. A.; Stempels, H. C.;
   Snik, F.; Rodenhuis, M.; Piskunov, N.; Makaganiuk, V.; Keller, C. U.;
   Johns-Krull, C. M.
2015A&A...574A..79K    Altcode: 2014arXiv1411.7518K
  Context. Intermediate-mass, magnetic chemically peculiar (Ap) stars
  provide a unique opportunity to study the topology of stellar magnetic
  fields in detail and to investigate magnetically driven processes
  of spot formation. <BR /> Aims: Here we aim to derive the surface
  magnetic field geometry and chemical abundance distributions for the
  extraordinary Ap star HD 75049. This object hosts a surface field of
  ~30 kG, one of the strongest known for any non-degenerate star. <BR />
  Methods: We used time-series of high-resolution HARPS intensity and
  circular polarisation observations. These data were interpreted with the
  help of magnetic Doppler imaging and model atmospheres incorporating
  effects of a non-solar chemical composition and a strong magnetic
  field. <BR /> Results: Based on high-precision measurements of the
  mean magnetic field modulus, we refined the rotational period of HD
  75049 to P<SUB>rot</SUB> = 4.048267 ± 0.000036 d. We also derived
  basic stellar parameters, T<SUB>eff</SUB> = 10 250 ± 250 K and log g =
  4.3 ± 0.1. Magnetic Doppler imaging revealed that the field topology
  of HD 75049 is poloidal and dominated by a dipolar contribution with
  a peak surface field strength of 39 kG. At the same time, deviations
  from the classical axisymmetric oblique dipolar configuration are
  significant. Chemical surface maps of Si, Cr, Fe, and Nd show abundance
  contrasts of 0.5-1.4 dex, which is low compared with many other Ap
  stars. Of the chemical elements, Nd is found to be enhanced close to
  the magnetic pole, whereas Si and Cr are concentrated predominantly
  at the magnetic equator. The iron distribution shows low-contrast
  features both at the magnetic equator and the pole. <BR /> Conclusions:
  The morphology of the magnetic field and the properties of chemical
  spots in HD 75049 are qualitatively similar to those of Ap stars with
  weaker fields. Consequently, whatever mechanism forms and sustains
  global magnetic fields in intermediate-mass main-sequence stars, it
  operates in the same way over the entire observed range of magnetic
  field strengths. <P />Based on observations collected at the European
  Southern Observatory, Chile (ESO programs 084.D-0338, 085.D-0296,
  086.D-0240, 088.D-0066, 090.D-0256, 078.D-0192, 080.D-0170).

---------------------------------------------------------
Title: Surprising detection of an equatorial dust lane on the AGB
    star IRC+10216
Authors: Jeffers, S. V.; Min, M.; Waters, L. B. F. M.; Canovas,
   H.; Pols, O. R.; Rodenhuis, M.; de Juan Ovelar, M.; Keller, C. U.;
   Decin, L.
2014A&A...572A...3J    Altcode: 2014arXiv1412.5063J
  <BR /> Aims: Understanding the formation of planetary nebulae remains
  elusive because in the preceding asymptotic giant branch (AGB)
  phase these stars are heavily enshrouded in an optically thick dusty
  envelope. <BR /> Methods: To further understand the morphology of
  the circumstellar environments of AGB stars we observe the closest
  carbon-rich AGB star IRC+10216 in scattered light. <BR /> Results:
  When imaged in scattered light at optical wavelengths, IRC+10216
  surprisingly shows a narrow equatorial density enhancement, in contrast
  to the large-scale spherical rings that have been imaged much further
  out. We use radiative transfer models to interpret this structure
  in terms of two models: firstly, an equatorial density enhancement,
  commonly observed in the more evolved post-AGB stars, and secondly,
  in terms of a dust rings model, where a local enhancement of mass-loss
  creates a spiral ring as the star rotates. <BR /> Conclusions: We
  conclude that both models can be used to reproduce the dark lane in
  the scattered light images, which is caused by an equatorially density
  enhancement formed by dense dust rather than a bipolar outflow as
  previously thought. We are unable to place constraints on the formation
  of the equatorial density enhancement by a binary system. <P />Final
  reduced images (FITS) are available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A3">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A3</A>Based
  on observations made with the William Herschel Telescope operated on the
  island of La Palma by the Isaac Newton Group in the Spanish Observatorio
  del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

---------------------------------------------------------
Title: Mapping atmospheric aerosols with a citizen science network
    of smartphone spectropolarimeters
Authors: Snik, Frans; Rietjens, Jeroen H. H.; Apituley, Arnoud;
   Volten, Hester; Mijling, Bas; Di Noia, Antonio; Heikamp, Stephanie;
   Heinsbroek, Ritse C.; Hasekamp, Otto P.; Smit, J. Martijn; Vonk, Jan;
   Stam, Daphne M.; Harten, Gerard; Boer, Jozua; Keller, Christoph U.
2014GeoRL..41.7351S    Altcode:
  To assess the impact of atmospheric aerosols on health, climate, and
  air traffic, aerosol properties must be measured with fine spatial
  and temporal sampling. This can be achieved by actively involving
  citizens and the technology they own to form an atmospheric measurement
  network. We establish this new measurement strategy by developing
  and deploying iSPEX, a low-cost, mass-producible optical add-on for
  smartphones with a corresponding app. The aerosol optical thickness
  (AOT) maps derived from iSPEX spectropolarimetric measurements of the
  daytime cloud-free sky by thousands of citizen scientists throughout
  the Netherlands are in good agreement with the spatial AOT structure
  derived from satellite imagery and temporal AOT variations derived
  from ground-based precision photometry. These maps show structures
  at scales of kilometers that are typical for urban air pollution,
  indicating the potential of iSPEX to provide information about aerosol
  properties at locations and at times that are not covered by current
  monitoring efforts.

---------------------------------------------------------
Title: Drift scanning technique for mid-infrared background
    subtraction
Authors: Heikamp, Stephanie; Brandl, Bernhard R.; Keller, Christoph
   U.; Venema, Lars; Pantin, Eric; Siebenmorgen, Ralf; Ives, Derek;
   Kerber, Florian
2014SPIE.9147E..9TH    Altcode:
  Accurate calibration of ground-based, mid-infrared observations is
  challenging due to the strong and rapidly varying thermal background
  emission. The classical solution is the chopping/nodding technique where
  the secondary mirror and the telescope are being moved by several tens
  of arcseconds on the sky. However, chopping is generally inefficient and
  limited in accuracy and frequency by the mass and size of the secondary
  mirror. A more elegant solution is a drift scan where the telescope
  slowly drifts across or around the region of interest; the source
  moves on the detector by at least one FWHM of the PSF within the time
  over which the detector performance and the background emission can be
  considered stable. The final image of a drift scan is mathematically
  reconstructed from a series of adjacent short exposures. The drift
  scan approach has recently received a lot of interest, mainly for two
  reasons: first, some of the new, large-format mid-IR Si:As detectors
  (AQUARIUS) suffer from excess low frequency noise (ELFN). To reach the
  nominal performance limit of the detectors, chopping would have to be
  performed at a high frequency, faster than what most telescopes can
  handle; second, the next generation of extremely large telescopes will
  not offer chopping/nodding, and alternative methods need to be developed
  and tested. In this paper we present the results from simulated drift
  scan data. We use drift scanning to simultaneously obtain an accurate
  detector flat field and the sky background. The results are relevant
  for the future operation and calibration of VISIR at the VLT as well
  as for METIS, the thermal infrared instrument for the E-ELT.

---------------------------------------------------------
Title: Focal-plane wavefront sensing with high-order adaptive
    optics systems
Authors: Korkiakoski, Visa; Keller, Christoph U.; Doelman, Niek;
   Kenworthy, Matthew; Otten, Gilles; Verhaegen, Michel
2014SPIE.9148E..5DK    Altcode: 2014arXiv1407.5846K
  We investigate methods to calibrate the non-common path aberrations at
  an adaptive optics system having a wavefront-correcting device working
  with an extremely high resolution (larger than 150x150 correcting
  elements). We use focal-plane images collected successively, the
  corresponding phase-diversity information and numerically efficient
  algorithms to calculate the required wavefront updates. Different
  approaches are considered in numerical simulations, and laboratory
  experiments are shown to confirm the results. We compare the
  performances of the standard Gerchberg-Saxton algorithm, Fast
  and Furious (use of small-phase assumption to take advantage of
  linearisation) and recently proposed phase-retrieval methods based on
  convex optimisation. The results indicate that the calibration task
  is easiest with algorithms similar to Fast and Furious, at least in
  the framework we considered.

---------------------------------------------------------
Title: Fast &amp; Furious focal-plane wavefront sensing
Authors: Korkiakoski, Visa; Keller, Christoph U.; Doelman, Niek;
   Kenworthy, Matthew; Otten, Gilles; Verhaegen, Michel
2014ApOpt..53.4565K    Altcode: 2014arXiv1406.1006K
  We present two complementary algorithms suitable for using
  focal-plane measurements to control a wavefront corrector with
  an extremely high spatial resolution. The algorithms use linear
  approximations to iteratively minimize the aberrations seen by the
  focal-plane camera. The first algorithm, Fast &amp; Furious (FF),
  uses a weak-aberration assumption and pupil symmetries to achieve fast
  wavefront reconstruction. The second algorithm, an extension to FF,
  can deal with an arbitrary pupil shape; it uses a Gerchberg-Saxton
  style error reduction to determine the pupil amplitudes. Simulations and
  experimental results are shown for a spatial light modulator controlling
  the wavefront with a resolution of 170 x 170 pixels. The algorithms
  increase the Strehl ratio from ~0.75 to 0.98-0.99, and the intensity
  of the scattered light is reduced throughout the whole recorded image
  of 320 x 320 pixels. The remaining wavefront rms error is estimated
  to be ~0.15 rad with FF and ~0.10 rad with FF-GS.

---------------------------------------------------------
Title: The ZIMPOL high contrast imaging polarimeter for SPHERE:
    system test results
Authors: Roelfsema, Ronald; Bazzon, Andreas; Schmid, Hans Martin;
   Pragt, Johan; Gisler, Daniel; Dominik, Carsten; Baruffolo, Andrea;
   Beuzit, Jean-Luc; Costille, Anne; Dohlen, Kjetil; Downing, Mark;
   Elswijk, Eddy; de Haan, Menno; Hubin, Norbert; Kasper, Markus; Keller,
   Christoph; Lizon, Jean-Louis; Mouillet, David; Pavlov, Alexey; Puget,
   Pascal; Salasnich, Bernardo; Sauvage, Jean-Francois; Wildi, Francois
2014SPIE.9147E..3WR    Altcode:
  SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a new
  instrument for the VLT aimed at the direct detection of exo-planets. It
  has received its first light in May 2014. ZIMPOL (Zurich Imaging
  Polarimeter) is the imaging polarimeter subsystem of the SPHERE
  instrument. It's capable of both high accuracy and high sensitivity
  polarimetry but can also be used as a classical imager. It is located
  behind an extreme AO system and a stellar coronagraph. ZIMPOL operates
  at visible wavelengths (600-900 nm) which is best suited to detect
  the very faint reflected and hence polarized visible light from extra
  solar planets. It has an instantaneous Field of View of 3 x 3 arcsec2
  (extendable to 8 arcsec diameter) with an angular resolution of 14
  mili-arcsec. We discuss the results that are obtained from the full
  SPHERE-ZIMPOL system testing. In particular the optical, polarimetric
  and high contrast performance.

---------------------------------------------------------
Title: Characterizing instrumental effects on polarization at a
    Nasmyth focus using NaCo
Authors: de Boer, Jozua; Girard, Julien H.; Mawet, Dimitri; Snik,
   Frans; Keller, Christoph U.; Milli, Julien
2014SPIE.9147E..87D    Altcode:
  We propose a new calibration scheme to determine the instrumental
  polarization (IP) and crosstalk induced by either the telescope or
  an instrument at Nasmyth focus. We measure the polarized blue sky at
  zenith with VLT/UT4/NaCo for different NaCo derotator and telescope
  azimuth angles. Taking multiple measurements after rotating both the
  instrument and the telescope with angles of 90° allows use to determine
  the IP and most crosstalk components separately for the telescope and
  the instrument. This separation of the Mueller matrices of UT4 and the
  NaCo is especially important for measurements taken in the conventional
  polarimetric mode (field stabilized), because the rotation of the
  instrument with respect to M3 causes a variation in the IP and crosstalk
  throughout the measurement. The technique allows us to determine the
  IP with an accuracy of 0.4%, and constrain or determine lower or upper
  limits for most crosstalk components. Most notably, the UT4 U --&gt;
  V crosstalk is substantially larger than theory predicts. An angular
  offset in NaCo's half wave plate orientation is a possible source of
  systematic errors. We measure this offset to be 1.8° +/- 0.5°.

---------------------------------------------------------
Title: LOUPE: Spectropolarimetry of the Earth from the surface of
    the Moon
Authors: Hoeijmakers, H. J.; Snik, F.; Stam, D. M.; Keller, C. U.
2014EPSC....9..574H    Altcode:
  We present our prototype for the LOUPE instrument: A small and robust
  imaging spectropolarimeter that can observe the Earth from the surface
  of the moon, with as primary objective to characterize the Earth's
  linear polarization spectrum throughout the Earth's daily rotation
  and monthly phase angle changes. The purpose of LOUPE is to provide
  benchmark data for future polarization observations of possibly
  habitable exoplanets. Our instrument concept has been proven to work
  in a laboratory setting, and efforts are being made to design and
  produce a flight model.

---------------------------------------------------------
Title: Towards Polarimetric Exoplanet Imaging with ELTs
Authors: Keller, C. U.; Korkiakoski, V.; Rodenhuis, M.; Snik, F.
2014ebi..conf..4.6K    Altcode:
  A prime science goal of Extremely Large Telescopes (ELTs) is the
  detection and characterization of exoplanets to answer the question: are
  we alone? ELTs will obtain the first direct images of rocky exoplanets
  in the habitable zone and search for atmospheric biomarkers. However,
  the required instrumental technologies are not yet at a level where an
  instrument could be built that would achieve this goal. Polarimetry will
  be an important ingredient in future high-contrast instruments as it
  will provide a major contrast improvement for planets located within
  the first two Airy rings and offers unique diagnostic capabilities
  for liquid water (ocean glint, water clouds and their rainbows),
  hazes and dust in exoplanetary atmospheres. <P />We will describe
  novel instrumental approaches to improving subsystems, in particular
  polarimetry, wavefront sensing and adaptive optics control. To reach
  contrasts of 10-9 and beyond to image rocky exoplanets from the ground,
  a series of individually optimized subsystems cannot succeed; rather,
  entire combinations of subsystems must be optimized together. We will
  describe our efforts at measuring and controlling wavefronts with 40'000
  degrees of freedom, reaching the photon-noise limit in high-contrast
  polarimetric imaging at telescopes and our plans to reach a contrast of
  at least 10-9 in broadband light under realistic, simulated ground-based
  conditions in the laboratory and to test new approaches at telescopes,
  in particular achromatic aperture and focal-plane coronagraphs,
  focal-plane wavefront-sensing and speckle suppression, integral-field
  polarimetry and high-contrast data reduction algorithms.

---------------------------------------------------------
Title: Instrumental polarisation at the Nasmyth focus of the E-ELT
Authors: de Juan Ovelar, M.; Snik, F.; Keller, C. U.; Venema, L.
2014A&A...562A...8D    Altcode: 2013arXiv1312.6148D; 2013arXiv1312.6148O
  The ~39-m European Extremely Large Telescope (E-ELT) will be the
  largest telescope ever built. This makes it particularly suitable for
  sensitive polarimetric observations, as polarimetry is a photon-starved
  technique. However, the telescope mirrors may severely limit the
  polarimetric accuracy of instruments on the Nasmyth platforms by
  creating instrumental polarisation and/or modifying the polarisation
  signal of the object. In this paper we characterise the polarisation
  effects of the two currently considered designs for the E-ELT Nasmyth
  ports as well as the effect of ageing of the mirrors. By means of
  the Mueller matrix formalism, we compute the response matrices of each
  mirror arrangement for a range of zenith angles and wavelengths. We then
  present two techniques to correct for these effects that require the
  addition of a modulating device at the "polarisation-free" intermediate
  focus that acts either as a switch or as a part of a two-stage
  modulator. We find that the values of instrumental polarisation,
  Stokes transmission reduction and cross-talk vary significantly
  with wavelength, and with pointing, for the lateral Nasmyth case,
  often exceeding the accuracy requirements for proposed polarimetric
  instruments. Realistic ageing effects of the mirrors after perfect
  calibration of these effects may cause polarimetric errors beyond the
  requirements. We show that the modulation approach with a polarimetric
  element located in the intermediate focus reduces the instrumental
  polarisation effects down to tolerable values, or even removes them
  altogether. The E-ELT will be suitable for sensitive and accurate
  polarimetry, provided frequent calibrations are carried out, or a
  dedicated polarimetric element is installed at the intermediate focus.

---------------------------------------------------------
Title: Analysis and interpretation of 15 quarters of Kepler data of
    the disintegrating planet KIC 12557548 b
Authors: van Werkhoven, T. I. M.; Brogi, M.; Snellen, I. A. G.;
   Keller, C. U.
2014A&A...561A...3V    Altcode: 2013arXiv1311.5688V
  Context. The Kepler object KIC 12557548 shows irregular eclipsing
  behaviour with a constant 15.685 h period, but strongly varying
  transit depth. The object responsible for this is believed to be
  a disintegrating planet forming a trailing dust cloud transiting
  the star. A 1D model of an exponentially decaying dust tail was
  found to reproduce the average eclipse in intricate detail. Based
  on radiative hydrodynamic modelling, the upper limit for the planet
  mass was found to be twice the mass of the Moon. <BR /> Aims: In this
  paper we fit individual eclipses, in addition to fitting binned light
  curves, to learn more about the process underlying the eclipse depth
  variation. Additionally, we put forward observational constraints that
  any model of this planet-star system will have to match. <BR /> Methods:
  We manually de-correlated and de-trended 15 quarters of Kepler data,
  three of which were observed in short cadence mode. We determined the
  transit depth, egress depth, and stellar intensity for each orbit and
  search for dependencies between these parameters. We investigated the
  full orbit by comparing the flux distribution of a moving phase window
  of interest versus the out-of-eclipse flux distribution. We fit short
  cadence data on a per-orbit basis using a two-parameter tail model,
  allowing us to investigate potential dust tail property variations. <BR
  /> Results: We find two quiescent spells of ~30 orbital periods each
  where the transit depth is &lt;0.1%, followed by relatively deep
  transits. Additionally, we find periods of on-off behaviour where
  &gt;0.5% deep transits are followed by apparently no transit at
  all. Apart from these isolated events we find neither significant
  correlation between consecutive transit depths nor a correlation
  between transit depth and stellar intensity. We find a three-sigma
  upper limit for the secondary eclipse of 4.9 × 10<SUP>-5</SUP>,
  consistent with a planet candidate with a radius of less than 4600
  km. Using the short cadence data we find that a 1D exponential dust tail
  model is insufficient to explain the data. We improved our model to a
  2D, two-component dust model with an opaque core and an exponential
  tail. Using this model we fit individual eclipses observed in short
  cadence mode. We find an improved fit of the data, quantifying earlier
  suggestions by Budaj (2013, A&amp;A, 557, A72) of the necessity of at
  least two components. We find that deep transits have most absorption
  in the tail, and not in a disk-shaped, opaque coma, but the transit
  depth and the total absorption show no correlation with the tail length.

---------------------------------------------------------
Title: Imaging the circumstellar environment of the young T Tauri
    star SU Aurigae
Authors: Jeffers, S. V.; Min, M.; Canovas, H.; Rodenhuis, M.; Keller,
   C. U.
2014A&A...561A..23J    Altcode: 2013arXiv1311.4832J
  The circumstellar environments of classical T Tauri stars are
  challenging to directly image because of their high star-to-disk
  contrast ratio. One method to overcome this is by using imaging
  polarimetry where scattered and consequently polarised starlight from
  the star's circumstellar disk can be separated from the unpolarised
  light of the central star. We present images of the circumstellar
  environment of SU Aur, a classical T Tauri star at the transition of T
  Tauri to Herbig stars. The images directly show that the disk extends
  out to 500 AU with an inclination angle of ~50°. Using interpretive
  models, we derived very small grains in the surface layers of its disk,
  with a very steep size- and surface-density distribution. Additionally,
  we resolved a large and extended nebulosity in our images that is most
  likely a remnant of the prenatal molecular cloud. The position angle
  of the disk, determined directly from our images, rules out a polar
  outflow or jet as the cause of this large-scale nebulosity.

---------------------------------------------------------
Title: Calibrating a high-resolution wavefront corrector with a
    static focal-plane camera
Authors: Korkiakoski, Visa; Doelman, Niek; Codona, Johanan; Kenworthy,
   Matthew; Otten, Gilles; Keller, Christoph U.
2013ApOpt..52.7554K    Altcode: 2013arXiv1310.1241K
  We present a method to calibrate a high-resolution wavefront-correcting
  device with a single, static camera, located in the focal plane; no
  moving of any component is needed. The method is based on a localized
  diversity and differential optical transfer functions (dOTF) to compute
  both the phase and amplitude in the pupil plane located upstream of the
  last imaging optics. An experiment with a spatial light modulator shows
  that the calibration is sufficient to robustly operate a focal-plane
  wavefront sensing algorithm controlling a wavefront corrector with ~40
  000 degrees of freedom. We estimate that the locations of identical
  wavefront corrector elements are determined with a spatial resolution
  of 0.3% compared to the pupil diameter.

---------------------------------------------------------
Title: Three-dimensional magnetic and abundance mapping of the cool
    Ap star HD 24712 . I. Spectropolarimetric observations in all four
    Stokes parameters
Authors: Rusomarov, N.; Kochukhov, O.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Makaganiuk, V.; Rodenhuis, M.;
   Snik, F.; Stempels, H. C.; Valenti, J. A.
2013A&A...558A...8R    Altcode: 2013arXiv1306.0997R
  Context. High-resolution spectropolarimetric observations provide
  simultaneous information about stellar magnetic field topologies and
  three-dimensional distributions of chemical elements. High-quality
  spectra in the Stokes IQUV parameters are currently available for very
  few early-type magnetic chemically peculiar stars. Here we present
  analysis of a unique full Stokes vector spectropolarimetric data
  set, acquired for the cool magnetic Ap star HD 24712 with a recently
  commissioned spectropolarimeter. <BR /> Aims: The goal of our work
  is to examine the circular and linear polarization signatures inside
  spectral lines and to study variation of the stellar spectrum and
  magnetic observables as a function of rotational phase. <BR /> Methods:
  HD 24712 was observed with the HARPSpol instrument at the 3.6-m ESO
  telescope over a period of 2010-2011. We achieved full rotational phase
  coverage with 43 individual Stokes parameter observations. The resulting
  spectra have a signal-to-noise ratio of 300-600 and resolving power
  exceeding 10<SUP>5</SUP>. The multiline technique of least-squares
  deconvolution (LSD) was applied to combine information from the
  spectral lines of Fe-peak and rare earth elements. <BR /> Results: We
  used the HARPSPol spectra of HD 24712 to study the morphology of the
  Stokes profile shapes in individual spectral lines and in LSD Stokes
  profiles corresponding to different line masks. From the LSD Stokes V
  profiles we measured the longitudinal component of the magnetic field,
  ⟨B<SUB>z</SUB>⟩, with an accuracy of 5-10 G. We also determined the
  net linear polarization from the LSD Stokes Q and U profiles. Combining
  previous ⟨B<SUB>z</SUB>⟩ measurements with our data allowed us to
  determine an improved rotational period of the star, P<SUB>rot</SUB>
  = 12.45812 ± 0.00019 d. We also measured the longitudinal
  magnetic field from the cores of Hα and Hβ lines. The analysis of
  ⟨B<SUB>z</SUB>⟩ measurements showed no evidence for a significant
  radial magnetic field gradient in the atmosphere of HD 24712. We used
  our ⟨B<SUB>z</SUB>⟩ and net linear polarization measurements to
  determine parameters of the dipolar magnetic field topology. We found
  that magnetic observables can be reasonably well reproduced by the
  dipolar model, although significant discrepancies remain at certain
  rotational phases. We discovered rotational modulation of the Hα
  core and related it to a non-uniform surface distribution of rare
  earth elements. <P />Based on observations collected at the European
  Southern Observatory, Chile (ESO programs 084.D-0338, 085.D-0296,
  086.D-0240).Figure 3 and Appendix A are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: The color dependent morphology of the post-AGB star HD 161796
Authors: Min, M.; Jeffers, S. V.; Canovas, H.; Rodenhuis, M.; Keller,
   C. U.; Waters, L. B. F. M.
2013A&A...554A..15M    Altcode: 2013arXiv1303.1704M
  Context. Many protoplanetary nebulae show strong asymmetries in their
  surrounding shells, pointing to asymmetries during the mass loss
  phase. Questions concerning the origin and the onset of deviations
  from spherical symmetry are important for our understanding of the
  evolution of these objects. Here we focus on the circumstellar shell of
  the post-AGB star HD 161796. <BR /> Aims: We aim to detect signatures of
  an aspherical outflow, and to derive its properties. <BR /> Methods: We
  used the imaging polarimeter the Extreme Polarimeter (ExPo), a visitor
  instrument at the William Herschel Telescope, to accurately image the
  dust shell surrounding HD 161796 in various wavelength filters. Imaging
  polarimetry allows us to separate the faint, polarized, light that comes
  from circumstellar material from the bright, unpolarized, light from
  the central star. <BR /> Results: The shell around HD 161796 is highly
  aspherical. A clear signature of an equatorial density enhancement can
  be seen. This structure is optically thick at short wavelengths and
  changes its appearance to optically thin at longer wavelengths. In the
  classification of the two different appearances of planetary nebulae
  from HST images it changes from being classified as DUst-Prominent
  Longitudinally-EXtended (DUPLEX) at short wavelengths to star-obvious
  low-level-elongated (SOLE) at longer wavelengths. This strengthens
  the interpretation that these two appearances are manifestations of
  the same physical structure. Furthermore, we find that the central
  star is hotter than often assumed and the relatively high observed
  reddening is a consequence of circumstellar rather than interstellar
  extinction. <P />Based on observations made with the William Herschel
  Telescope operated on the island of La Palma by the Isaac Newton Group
  in the Spanish Observatorio del Roque de los Muchachos of the Instituto
  de Astrofsicaŋsica de Canarias.

---------------------------------------------------------
Title: Are there tangled magnetic fields on HgMn stars?
Authors: Kochukhov, O.; Makaganiuk, V.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels,
   H. C.; Valenti, J. A.
2013A&A...554A..61K    Altcode: 2013arXiv1304.6717K
  Context. Several recent spectrophotometric studies failed to detect
  significant global magnetic fields in late-B HgMn chemically peculiar
  stars, but some investigations have suggested the presence of strong
  unstructured or tangled fields in these objects. <BR /> Aims: We used
  detailed spectrum synthesis analysis to search for evidence of tangled
  magnetic fields in high-quality observed spectra of eight slowly
  rotating HgMn stars and one normal late-B star. We also evaluated
  recent sporadic detections of weak longitudinal magnetic fields in
  HgMn stars based on the moment technique. <BR /> Methods: Our spectrum
  synthesis code calculated the Zeeman broadening of metal lines in HARPS
  spectra, assuming an unstructured, turbulent magnetic field. A simple
  line formation model with a homogeneous radial field distribution was
  applied to assess compatibility between previous longitudinal field
  measurements and the observed mean circular polarization signatures. <BR
  /> Results: Our analysis of the Zeeman broadening of magnetically
  sensitive spectral lines reveals no evidence of tangled magnetic fields
  in any of the studied HgMn or normal stars. We infer upper limits
  of 200-700 G for the mean magnetic field modulus - much smaller than
  the field strengths implied by studies based on differential magnetic
  line intensification and quadratic field diagnostics. The new HARPSpol
  longitudinal field measurements for the extreme HgMn star HD 65949 and
  the normal late-B star 21 Peg are consistent with zero at a precision of
  3-6 G. Re-analysis of our Stokes V spectra of the spotted HgMn star HD
  11753 shows that the recent moment technique measurements retrieved from
  the same data are incompatible with the lack of circular polarization
  signatures in the spectrum of this star. <BR /> Conclusions: We conclude
  that there is no evidence for substantial tangled magnetic fields on
  the surfaces of studied HgMn stars. We cannot independently confirm
  the presence of very strong quadratic or marginal longitudinal fields
  for these stars, so results from the moment technique are likely to be
  spurious. <P />Based on observations collected at the European Southern
  Observatory, Chile (ESO programmes 084.D-0338, 085.D-0296, 086.D-0240).

---------------------------------------------------------
Title: Magnetically Controlled Accretion on the Classical T Tauri
    Stars GQ Lupi and TW Hydrae
Authors: Johns-Krull, Christopher M.; Chen, Wei; Valenti, Jeff A.;
   Jeffers, Sandra V.; Piskunov, Nikolai E.; Kochukhov, Oleg; Makaganiuk,
   V.; Stempels, H. C.; Snik, Frans; Keller, Christoph; Rodenhuis, M.
2013ApJ...765...11J    Altcode: 2013arXiv1301.3182J
  We present high spectral resolution (R ≈ 108, 000) Stokes V
  polarimetry of the classical T Tauri stars (CTTSs) GQ Lup and TW Hya
  obtained with the polarimetric upgrade to the HARPS spectrometer on
  the ESO 3.6 m telescope. We present data on both photospheric lines
  and emission lines, concentrating our discussion on the polarization
  properties of the He I emission lines at 5876 Å and 6678 Å. The He
  I lines in these CTTSs contain both narrow emission cores, believed
  to come from near the accretion shock region on these stars, and broad
  emission components which may come from either a wind or the large-scale
  magnetospheric accretion flow. We detect strong polarization in the
  narrow component of the two He I emission lines in both stars. We
  observe a maximum implied field strength of 6.05 ± 0.24 kG in the
  5876 Å line of GQ Lup, making it the star with the highest field
  strength measured in this line for a CTTS. We find field strengths in
  the two He I lines that are consistent with each other, in contrast to
  what has been reported in the literature on at least one star. We do
  not detect any polarization in the broad component of the He I lines
  on these stars, strengthening the conclusion that they form over a
  substantially different volume relative to the formation region of
  the narrow component of the He I lines.

---------------------------------------------------------
Title: Sterrekundig Instituut Utrecht: The Last Years
Authors: Keller, C. U.
2013ASPC..470....3K    Altcode: 2012arXiv1208.4095K
  I describe the last years of the 370-year long life of the Sterrekundig
  Instituut Utrecht, which was the second-oldest university observatory in
  the world and was closed in early 2012 after the Faculty of Science and
  the Board of Utrecht University decided, without providing qualitative
  or quantitative arguments, to remove astrophysics from its research
  and education portfolio.

---------------------------------------------------------
Title: Observing Circumstellar Neighbourhoods with the Extreme
    Polarimeter
Authors: Rodenhuis, M.; Canovas, H.; Jeffers, S. V.; Min, M.; Keller,
   C. U.
2013ASPC..470..407R    Altcode:
  The study of circumstellar environments at ever higher contrasts has
  generated considerable interest in recent years. One method to increase
  the contrast is to observe the linearly polarized light scattered by
  the circumstellar material while suppressing the unpolarized stellar
  flux. This paper presents some sample imaging polarimetry results
  obtained with the Extreme Polarimeter (ExPo). ExPo operates in the
  visible part of the spectrum, and currently achieves a polarimetric
  sensitivity of 10<SUP>-4</SUP>. Despite the demise of the Utrecht
  Astronomical Institute, where this instrument was developed, the
  instrument is still being used and upgraded. It has now moved to the
  Leiden Observatory.

---------------------------------------------------------
Title: HARPS Spectropolarimetry of the Classical T Tauri Stars GQ
    Lup and TW Hya
Authors: Johns-Krull, Christopher M.; Chen, W.; Valenti, J. A.;
   Jeffers, S. V.; Piskunov, N. E.; Kochukhov, O.; Makaganiuk, V.;
   Stempels, H. C.; Snik, F.; Keller, C.; Rodenhuis, M.
2013AAS...22125614J    Altcode:
  We present high spectral resolution Stokes V polarimetery of the
  Classical T Tauri stars (CTTSs) GQ Lup and TW Hya obtained with
  the polarimetric upgrade to the HARPS spectrometer on the ESO 3.6 m
  telescope. We present data on both photospheric lines and emission
  lines, concentrating our discussion on the polarization properties
  of the He I emission lines at 5876 A and 6678 A. The He I lines
  in both these CTTS contain both narrow emission cores, believed to
  come from near the accretion shock region on these stars, and broad
  emission components which may come from either a wind or the large
  scale magnetospheric accretion flow. We detect strong polarization in
  the narrow component of both the He I emission lines in both stars. We
  observe a maximum implied field strength of 5.8 +/- 0.3 kG in the 5876
  A line of GQ Lup, the highest field strength measured to date in this
  line for a CTTS. We find field strengths in the two He I lines that
  are consistent with each other, unlike what has been reported in the
  literature on at least one star. We do not detect any polarization in
  the broad component of the He I lines on these stars, strengthening
  the conclusion that they form over a substantially different volume
  relative the formation region of the narrow component of the He I lines.

---------------------------------------------------------
Title: Astronomical Polarimetry: Polarized Views of Stars and Planets
Authors: Snik, Frans; Keller, Christoph U.
2013pss2.book..175S    Altcode:
  Polarization is a fundamental property of light from astronomical
  objects, and measuring that polarization often yields crucial
  information, which is unobtainable otherwise.This chapter reviews the
  useful formalisms for describing polarization in the optical regime,
  the mechanisms for the creation of such polarization, and methods
  for measuring it. Particular emphasis is given on how to implement a
  polarimeter within an astronomical facility, and on how to deal with
  systematic effects that often limit the polarimetric performance.

---------------------------------------------------------
Title: Observing the Earth as an exoplanet with LOUPE, the lunar
    observatory for unresolved polarimetry of Earth
Authors: Karalidi, T.; Stam, D. M.; Snik, F.; Bagnulo, S.; Sparks,
   W. B.; Keller, C. U.
2012P&SS...74..202K    Altcode: 2012arXiv1203.0209K
  The detections of small, rocky exoplanets have surged in recent years
  and will likely continue to do so. To know whether a rocky exoplanet
  is habitable, we have to characterize its atmosphere and surface. A
  promising characterization method for rocky exoplanets is direct
  detection using spectropolarimetry. This method will be based on single
  pixel signals, because spatially resolving exoplanets is impossible with
  current and near-future instruments. Well-tested retrieval algorithms
  are essential to interpret these single pixel signals in terms of
  atmospheric composition, cloud and surface coverage. Observations
  of Earth itself provide the obvious benchmark data for testing such
  algorithms. The observations should provide signals that are integrated
  over the Earth's disk, that capture day and night variations, and
  all phase angles. The Moon is a unique platform from where the Earth
  can be observed as an exoplanet, undisturbed, all of the time. Here,
  we present LOUPE, the Lunar Observatory for Unresolved Polarimetry of
  Earth, a small and robust spectropolarimeter to observe our Earth as
  an exoplanet.

---------------------------------------------------------
Title: Electric Properties of Water Ice doped with Hydrogen Peroxide
(H2O2): Implications for Icy Moons such as Europa
Authors: Keller, C.; Freund, F. T.; Cruikshank, D. P.
2012AGUFM.P51A2026K    Altcode:
  Large floats of ice on Jupiter's moon Europa drift and collide. The
  float boundaries are marked by brownish-reddish colors. The origin
  of these colors is poorly understood. Maybe upwelling of water along
  the active float boundaries brings finely divided suspended matter
  or organic compounds from the ocean below to the surface, where
  the intense, high energy environment in Jupiter's radiation belt
  would lead to photochemical oxidation. At the same time it has been
  suggested that Europa's ice contains traces of H2O2, presumably due to
  micro-meteorite impacts and other processes. We measured the electric
  currents generated in pure and H2O2-doped water ice when we subjected
  one end of ice blocks to uniaxial stress. Ice samples with 0%, 0.3%
  and 0.03% H2O2 were formed in polyethylene troughs, 4.1 x 13.5 x 3.8 cm,
  with Cu contacts at both ends, at 263K (-10°C), 190K (-78°C, dry ice)
  and 77K (-196°C,liquid N2). At 77K the ice samples detached themselves
  from at least one of the Cu contacts, due to thermal contraction. At
  190K, when stressing one end, essentially no currents were produced
  in the pure water ice. By contrast, H2O2-doped ices produced several
  hundred picoamperes (pA) of positive currents, indicating defect
  electrons (holes) flowing down the stress gradient. At 263K the
  results are ambiguous. These (as yet preliminary) results indicate
  that stresses might break the peroxy bonds of imbedded H2O2 molecules,
  releasing the same type of positive hole charge carriers as observed
  during stress experiments with silicate rocks. Since positive holes
  are defect electrons associated with O 2sp levels at the upper edge of
  the valence band, they seem to have the capability to spread through
  the ices. Chemically positive holes are equivalent to highly oxidizing
  oxygen radicals. They may be responsible for oxidation reactions along
  the boundaries of active ice floats on Europa.

---------------------------------------------------------
Title: Unusual Stokes V profiles during flaring activity of a
    delta sunspot
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.; Fletcher, L.;
   Socas-Navarro, H.
2012A&A...547A..34F    Altcode: 2012arXiv1209.0983F
  <BR /> Aims: We analyze a set of full Stokes profile observations of
  the flaring active region NOAA 10808. The region was recorded with
  the Vector-Spectromagnetograph of the Synoptic Optical Long-term
  Investigations of the Sun facility. The active region produced
  several successive X-class flares between 19:00 UT and 24:00 UT on
  September 13, 2005 and we aim to quantify transient and permanent
  changes in the magnetic field and velocity field during one of the
  flares, which has been fully captured. <BR /> Methods: The Stokes
  profiles were inverted using the height-dependent inversion code
  LILIA to analyze magnetic field vector changes at the flaring site. We
  report multilobed asymmetric Stokes V profiles found in the δ-sunspot
  umbra. We fit the asymmetric Stokes V profiles assuming an atmosphere
  consisting of two components (SIR inversions) to interpret the profile
  shape. The results are put in context with Michelson Doppler Imager
  (MDI) magnetograms and reconstructed X-ray images from the Reuven
  Ramaty High Energy Solar Spectroscopic Imager. <BR /> Results: We
  obtain the magnetic field vector and find signs of restructuring
  of the photospheric magnetic field during the flare close to the
  polarity inversion line at the flaring site. At two locations in the
  umbra we encounter strong fields (~3 kG), as inferred from the Stokes
  I profiles, which, however, exhibit a low polarization signal. During
  the flare we observe in addition asymmetric Stokes V profiles at one
  of these sites. The asymmetric Stokes V profiles appear co-spatial
  and co-temporal with a strong apparent polarity reversal observed
  in MDI-magnetograms and a chromospheric hard X-ray source. The
  two-component atmosphere fits of the asymmetric Stokes profiles
  result in line-of-sight velocity differences in the range of ~12 km
  s<SUP>-1</SUP> to 14 km s<SUP>-1</SUP> between the two components in
  the photosphere. Another possibility is that local atmospheric heating
  is causing the observed asymmetric Stokes V profile shape. In either
  case our analysis shows that a very localized patch of ~5″ in the
  photospheric umbra, co-spatial with a flare footpoint, exhibits a
  subresolution fine structure.

---------------------------------------------------------
Title: SPICES: spectro-polarimetric imaging and characterization of
    exoplanetary systems. From planetary disks to nearby Super Earths
Authors: Boccaletti, Anthony; Schneider, Jean; Traub, Wes; Lagage,
   Pierre-Olivier; Stam, Daphne; Gratton, Raffaele; Trauger, John;
   Cahoy, Kerri; Snik, Frans; Baudoz, Pierre; Galicher, Raphael; Reess,
   Jean-Michel; Mawet, Dimitri; Augereau, Jean-Charles; Patience,
   Jenny; Kuchner, Marc; Wyatt, Mark; Pantin, Eric; Maire, Anne-Lise;
   Vérinaud, Christophe; Ronayette, Samuel; Dubreuil, Didier; Min,
   Michiel; Rodenhuis, Michiel; Mesa, Dino; Belikov, Russ; Guyon, Olivier;
   Tamura, Motohide; Murakami, Naoshi; Beerer, Ingrid Mary; SPICES Team;
   Mas, M.; Rouan, D.; Perrin, G.; Lacour, S.; Thébault, P.; Nguyen,
   N.; Ibgui, L.; Arenou, F.; Lestrade, J. F.; N'Diaye, M.; Dohlen, K.;
   Ferrari, M.; Hugot, E.; Beuzit, J. -L.; Lagrange, A. -M.; Martinez,
   P.; Barthelemey, M.; Mugnier, L.; Keller, C.; Marley, M.; Kalas, P.;
   Stapelfeldt, K.; Brown, R.; Kane, S.; Desidera, S.; Sozzetti, A.;
   Mura, A.; Martin, E. L.; Bouy, H.; Allan, A.; King, R.; Vigan, A.;
   Churcher, L.; Udry, S.; Matsuo, T.; Nishikawa, J.; Hanot, C.; Wolf,
   S.; Kaltenegger, L.; Klahr, H.; Pilat-Lohinger, E.
2012ExA....34..355B    Altcode: 2012arXiv1203.0507B; 2012ExA...tmp....8B
  SPICES (Spectro-Polarimetric Imaging and Characterization of
  Exoplanetary Systems) is a five-year M-class mission proposed to ESA
  Cosmic Vision. Its purpose is to image and characterize long-period
  extrasolar planets and circumstellar disks in the visible (450-900
  nm) at a spectral resolution of about 40 using both spectroscopy and
  polarimetry. By 2020/2022, present and near-term instruments will have
  found several tens of planets that SPICES will be able to observe
  and study in detail. Equipped with a 1.5 m telescope, SPICES can
  preferentially access exoplanets located at several AUs (0.5-10 AU)
  from nearby stars (&lt;25 pc) with masses ranging from a few Jupiter
  masses to Super Earths (∼2 Earth radii, ∼10 M<SUB>⊕</SUB>)
  as well as circumstellar disks as faint as a few times the zodiacal
  light in the Solar System.

---------------------------------------------------------
Title: A spectro-polarimetric integral field spectrograph for
    EPICS-EPOL
Authors: Rodenhuis, M.; Sprenger, B.; Keller, C. U.
2012SPIE.8446E..9JR    Altcode:
  Imaging polarimetry offers a way to increase the contrast of light
  scattered from circumstellar material, enabling direct observation of
  exoplanets -possibly rocky- with the E-ELT. To actually characterize
  these planets, some spectral resolution is essential. With sufficient
  resolution -both spectral and spatial- the spectral differential
  imaging technique can be used in addition to the polarimetry to
  detect circumstellar point sources. We present the concept for a
  spectro-polarimetric integral field spectrograph for the EPICS-EPOL
  instrument and our current efforts to demonstrate this concept with
  our existing imaging polarimeter ExPo.

---------------------------------------------------------
Title: Evidence for the disintegration of KIC 12557548 b
Authors: Brogi, M.; Keller, C. U.; de Juan Ovelar, M.; Kenworthy,
   M. A.; de Kok, R. J.; Min, M.; Snellen, I. A. G.
2012A&A...545L...5B    Altcode: 2012arXiv1208.2988B
  Context. The Kepler object KIC 12557548 b is peculiar. It exhibits
  transit-like features every 15.7 h that vary in depth between 0.2% and
  1.2%. Rappaport et al. (2012, ApJ, 752, 1) explain the observations
  in terms of a disintegrating, rocky planet that has a trailing
  cloud of dust created and constantly replenished by thermal surface
  erosion. The variability of the transit depth is then a consequence
  of changes in the cloud optical depth. <BR /> Aims: We aim to
  validate the disintegrating-planet scenario by modeling the detailed
  shape of the observed light curve, and thereby constrain the cloud
  particle properties to better understand the nature of this intriguing
  object. <BR /> Methods: We analyzed the six publicly-available quarters
  of raw Kepler data, phase-folded the light curve and fitted it to
  a model for the trailing dust cloud. Constraints on the particle
  properties were investigated with a light-scattering code. <BR />
  Results: The light curve exhibits clear signatures of light scattering
  and absorption by dust, including a brightening in flux just before
  ingress correlated with the transit depth and explained by forward
  scattering, and an asymmetry in the transit light curve shape, which
  is easily reproduced by an exponentially decaying distribution of
  optically thin dust, with a typical grain size of 0.1 μm. <BR />
  Conclusions: Our quantitative analysis supports the hypothesis that the
  transit signal of KIC 12557548 b is due to a variable cloud of dust,
  most likely originating from a disintegrating object.

---------------------------------------------------------
Title: Searching for signs of habitability with LOUPE, the Lunar
    Observatory of Unresolved Polarimetry of Earth
Authors: Karalidi, T.; Stam, D. M.; Snik, F.; Bagnulo, S.; Sparks,
   W. B.; Keller, C. U.
2012epsc.conf..537K    Altcode: 2012espc.conf..537K
  We present LOUPE, a novel type of spectropolarimeter to measure the
  flux and state of polarization of sunlight that is reflected by the
  Earth from 0.4 to 0.8 μm. LOUPE has been designed as payload of a
  lunar lander. From the moon, the Earth can be observed as a whole,
  during its daily rotation and at all phase angles, just as if it were
  an exoplanet. LOUPE will provide benchmark data for the development
  of instruments for Earth-like exoplanet characterization, and for the
  testing of numerical retrieval algorithms.

---------------------------------------------------------
Title: The extreme polarimeter: design, performance, first results
    and upgrades
Authors: Rodenhuis, M.; Canovas, H.; Jeffers, S. V.; de Juan Ovelar,
   Maria; Min, M.; Homs, L.; Keller, C. U.
2012SPIE.8446E..9IR    Altcode: 2012arXiv1211.6300R
  Well over 700 exoplanets have been detected to date. Only a handful of
  these have been observed directly. Direct observation is extremely
  challenging due to the small separation and very large contrast
  involved. Imaging polarimetry offers a way to decrease the contrast
  between the unpolarized starlight and the light that has become
  linearly polarized after scattering by circumstellar material. This
  material can be the dust and debris found in circumstellar disks, but
  also the atmosphere or surface of an exoplanet. We present the design,
  calibration approach, polarimetric performance and sample observation
  results of the Extreme Polarimeter, an imaging polarimeter for the
  study of circumstellar environments in scattered light at visible
  wavelengths. The polarimeter uses the beam-exchange technique, in
  which the two orthogonal polarization states are imaged simultaneously
  and a polarization modulator is swaps the polarization states of the
  two beams before the next image is taken. The instrument currently
  operates without the aid of Adaptive Optics. To reduce the effects
  of atmospheric seeing on the polarimetry, the images are taken at
  a frame rate of 35 fps, and large numbers of frames are combined to
  obtain the polarization images. Four successful observing runs have
  been performed using this instrument at the 4.2 m William Herschel
  Telescope on La Palma, targeting young stars with protoplanetary disks
  as well as evolved stars surrounded by dusty envelopes. In terms of
  fractional polarization, the instrument sensitivity is better than
  10<SUP>-4</SUP>. The contrast achieved between the central star and
  the circumstellar source is of the order 10<SUP>-6</SUP>. We show that
  our calibration approach yields absolute polarization errors below 1%.

---------------------------------------------------------
Title: Modeling the instrumental polarization of the VLT and E-ELT
    telescopes with the M&amp;m's code
Authors: de Juan Ovelar, M.; Diamantopoulou, S.; Roelfsema, R.;
   van Werkhoven, T.; Snik, F.; Pragt, Johan; Keller, C.
2012SPIE.8449E..12D    Altcode:
  Polarimetry is a particularly powerful technique when imaging
  circumstellar environments. Currently most telescopes include more
  or less advanced polarimetric facilities and large telescopes count
  on it for their planet-finder instruments like SPHERE-ZIMPOL on the
  VLT or EPICS on the future E-ELT. One of the biggest limitations
  of this technique is the instrumental polarization (IP) generated
  in the telescope optical path, which can often be larger than the
  signal to be measured. In most cases this instrumental polarization
  changes over time and is dependent on the errors affecting the optical
  elements of the system. We have modeled the VLT and E-ELT telescope
  layouts to characterize the instrumental polarization generated
  on their optical paths using the M&amp;m's code, an error budget
  and performance simulator for polarimetric systems. In this study
  we present the realistic Mueller matrices calculated with M&amp;m's
  for both systems, with and without the setups to correct for the IP,
  showing that correction can be achieved, allowing for an accurate
  polarimetric performance.

---------------------------------------------------------
Title: Potential of phase-diversity for metrology of active
    instruments
Authors: Korkiakoski, Visa; Venema, Lars; Agocs, Tibor; Keller,
   Christoph U.; Doelman, Niek; Fraanje, Rufus; Andrei, Raluca; Verhaegen,
   Michel
2012SPIE.8450E..5DK    Altcode:
  We investigate the potential of phase-diversity (PD) and
  Gerchberg-Saxton (GS) algorithms in the calibration of active
  instruments. A set of images is recorded with the focal-plane
  scientific camera, each image having a known and unique defocus. The
  phase-retrieval algorithms are used, with those images, to estimate
  the non-common path aberration that needs to be compensated by correct
  alignment of the instrument. We demonstrate by numerical simulations
  that such algorithms, in particular GS, are sufficient detection
  methods to fully correct wavefronts with an rms error at least up to
  6 rad — but this requires several iterative correction stages.

---------------------------------------------------------
Title: Constraining the circumbinary envelope of Z Canis Majoris
    via imaging polarimetry
Authors: Canovas, H.; Min, M.; Jeffers, S. V.; Rodenhuis, M.; Keller,
   C. U.
2012A&A...543A..70C    Altcode: 2012arXiv1205.3784C
  Context. Z CMa is a complex binary system composed of a Herbig Be
  and an FU Ori star. The Herbig star is surrounded by a dust cocoon of
  variable geometry, and the whole system is surrounded by an infalling
  envelope. Previous spectropolarimetric observations have reported a
  preferred orientation of the polarization angle, perpendicular to the
  direction of a very extended, parsec-sized jet associated with the
  Herbig star. <BR /> Aims: The variability in the amount of polarized
  light has been associated to changes in the geometry of the dust cocoon
  that surrounds the Herbig star. We aim to constrain the properties of
  Z CMa by means of imaging polarimetry at optical wavelengths. <BR />
  Methods: Using ExPo, a dual-beam imaging polarimeter that operates at
  optical wavelengths, we have obtained imaging (linear) polarimetric
  data of Z CMa. Our observations were secured during the return to
  quiescence after the 2008 outburst. <BR /> Results: We detect three
  polarized features over Z CMa. Two of these features are related to
  the two jets reported in this system: the large jet associated to the
  Herbig star, and the micro-jet associated to the FU Ori star. Our
  results suggest that the micro-jet extends to a distance ten times
  longer than reported in previous studies. The third feature suggests the
  presence of a hole in the dust cocoon that surrounds the Herbig star
  of this system. According to our simulations, this hole can produce
  a pencil beam of light that we see scattered off the low-density
  envelope surrounding the system. <P />Based on observations made with
  the William Herschel Telescope operated on the island of La Palma by
  the Isaac Newton Group in the Spanish Observatorio del Roque de los
  Muchachos of the Instituto de Astrofísica de Canarias.

---------------------------------------------------------
Title: Linear analytical solution to the phase diversity problem
    for extended objects based on the Born approximation
Authors: Andrei, Raluca M.; Smith, Carlas S.; Fraanje, Rufus;
   Verhaegen, Michel; Korkiakoski, Visa A.; Keller, Christoph U.;
   Doelman, Niek
2012SPIE.8447E..6UA    Altcode:
  In this paper we give a new wavefront estimation technique that
  overcomes the main disadvantages of the phase diversity (PD)
  algorithms, namely the large computational complexity and the fact
  that the solutions can get stuck in a local minima. Our approach gives
  a good starting point for an iterative algorithm based on solving a
  linear system, but it can also be used as a new wavefront estimation
  method. The method is based on the Born approximation of the wavefront
  for small phase aberrations which leads to a quadratic point-spread
  function (PSF), and it requires two diversity images. First we take the
  differences between the focal plane image and each of the two diversity
  images, and then we eliminate the constant object, element-wise,
  from the two equations. The result is an overdetermined set of linear
  equations for which we give three solutions using linear least squares
  (LS), truncated total least squares (TTLS) and bounded data uncertainty
  (BDU). The last two approaches are suited when considering measurements
  affected by noise. Simulation results show that the estimation is
  faster than conventional PD algorithms.

---------------------------------------------------------
Title: The Majorana Demonstrator: A Search for Neutrinoless
    Double-beta Decay of Germanium-76
Authors: Wilkerson, J. F.; Aguayo, E.; Avignone, F. T., Iii; Back,
   H. O.; Barabash, A. S.; Beene, J. R.; Bergevin, M.; Bertrand, F. E.;
   Boswell, M.; Brudanin, V.; Busch, M.; Chan, Y. -D.; Christofferson,
   C. D.; Collar, J. I.; Combs, D. C.; Cooper, R. J.; Detwiler, J. A.;
   Doe, P. J.; Efremenko, Yu; Egorov, V.; Ejiri, H.; Elliott, S. R.;
   Esterline, J.; Fast, J. E.; Fields, N.; Finnerty, P.; Fraenkle, F. M.;
   Gehman, V. M.; Giovanetti, G. K.; Green, M. P.; Guiseppe, V. E.;
   Gusey, K.; Hallin, A. L.; Hazama, R.; Henning, R.; Hoppe, E. W.;
   Horton, M.; Howard, S.; Howe, M. A.; Johnson, R. A.; Keeter, K. J.;
   Keller, C.; Kidd, M. F.; Knecht, A.; Kochetov, O.; Konovalov, S. I.;
   Kouzes, R. T.; LaFerriere, B. D.; LaRoque, B. H.; Leon, J.; Leviner,
   L. E.; Loach, J. C.; MacMullin, S.; Marino, M. G.; Martin, R. D.; Mei,
   D. -M.; Merriman, J. H.; Miller, M. L.; Mizouni, L.; Nomachi, M.;
   Orrell, J. L.; Overman, N. R.; Phillips, D. G., Ii; Poon, A. W. P.;
   Perumpilly, G.; Prior, G.; Radford, D. C.; Rielage, K.; Robertson,
   R. G. H.; Ronquest, M. C.; Schubert, A. G.; Shima, T.; Shirchenko,
   M.; Snavely, K. J.; Steele, D.; Strain, J.; Thomas, K.; Timkin, V.;
   Tornow, W.; Vanyushin, I.; Varner, R. L.; Vetter, K.; Vorren, K.;
   Yakushev, E.; Young, A. R.; Yu, C. -H.; Yumatov, V.; Zhang, C.
2012JPhCS.375d2010W    Altcode:
  The observation of neutrino less double-beta decay would show that
  neutrinos are Majorana particles and provide information on neutrino
  mass. Attaining sensitivities for neutrino masses in the inverted
  hierarchy region requires large, tonne scale detectors with extremely
  low backgrounds, at the level of 10<SUP>-3</SUP> counts keV<SUP>-1</SUP>
  t<SUP>-1</SUP> y<SUP>-1</SUP> or lower in the region of the signal. The
  MAJORANA collaboration is constructing the DEMONSTRATOR, an array
  consisting of 40 kg of p-type point contact germanium detectors, at
  least half of which will be enriched to 86% in <SUP>76</SUP>Ge. The
  primary aim is to show the feasibility for a future tonne scale
  measurement. With a sub-keV energy threshold, the array should also
  be able to search for light WIMP dark matter. This paper presents a
  brief update on the status of constructing the DEMONSTRATOR including
  an electroforming facility that is now operating underground at the
  Sanford Underground Research Facility.

---------------------------------------------------------
Title: Experimental validation of optimization concepts for
    focal-plane image processing with adaptive optics
Authors: Korkiakoski, Visa; Keller, Christoph U.; Doelman, Niek;
   Fraanje, Rufus; Andrei, Raluca; Verhaegen, Michel
2012SPIE.8447E..5ZK    Altcode:
  We show experimental results demonstrating the feasibility of an
  extremely fast sequential phase-diversity (SPD) algorithm for point
  sources. The algorithm can be implemented on a typical adaptive
  optics (AO) system to improve the wavefront reconstruction beyond
  the capabilities of a wavefront sensor by using the information
  from the imaging camera. The algorithm is based on a small-phase
  approximation enabling fast numerical implementation, and it finds the
  optimal wavefront correction by iteratively updating the deformable
  mirror. Our experiments were made at an AO-setup with a 37 actuator
  membrane mirror, and the results show that the algorithm finds an
  optimal image quality in 5-10 iterations, when the initial wavefront
  errors are typical non-common path aberrations having a magnitude of
  1-1.5 rad rms. The results are in excellent agreement with corresponding
  numerical simulations.

---------------------------------------------------------
Title: Dark matter sensitivities of the Majorana Demonstrator
Authors: Giovanetti, G. K.; Aguayo, E.; Avignone, F. T., Iii; Back,
   H. O.; Barabash, A. S.; Beene, J. R.; Bergevin, M.; Bertrand, F. E.;
   Boswell, M.; Brudanin, V.; Busch, M.; Chan, Y. -D.; Christofferson,
   C. D.; Collar, J. I.; Combs, D. C.; Cooper, R. J.; Detwiler, J. A.;
   Doe, P. J.; Efremenko, Yu; Egorov, V.; Ejiri, H.; Elliott, S. R.;
   Esterline, J.; Fast, J. E.; Fields, N.; Finnerty, P.; Fraenkle, F. M.;
   Gehman, V. M.; Green, M. P.; Guiseppe, V. E.; Gusey, K.; Hallin, A. L.;
   Hazama, R.; Henning, R.; Hoppe, E. W.; Horton, M.; Howard, S.; Howe,
   M. A.; Johnson, R. A.; Keeter, K. J.; Keller, C.; Kidd, M. F.; Knecht,
   A.; Kochetov, O.; Konovalov, S. I.; Kouzes, R. T.; LaFerriere, B. D.;
   LaRoque, B. H.; Leon, J.; Leviner, L. E.; Loach, J. C.; MacMullin, S.;
   Marino, M. G.; Martin, R. D.; Mei, D. -M.; Merriman, J. H.; Miller,
   M. L.; Mizouni, L.; Nomachi, M.; Orrell, J. L.; Overman, N. R.;
   Phillips, D. G., Ii; Poon, A. W. P.; Perumpilly, G.; Prior, G.;
   Radford, D. C.; Rielage, K.; Robertson, R. G. H.; Ronquest, M. C.;
   Schubert, A. G.; Shima, T.; Shirchenko, M.; Snavely, K. J.; Steele,
   D.; Strain, J.; Thomas, K.; Timkin, V.; Tornow, W.; Vanyushin, I.;
   Varner, R. L.; Vetter, K.; Vorren, K.; Wilkerson, J. F.; Yakushev,
   E.; Young, A. R.; Yu, C. -H.; Yumatov, V.; Zhang, C.
2012JPhCS.375a2014G    Altcode:
  The Majorana Demonstrator is an array of natural and enriched high
  purity germanium detectors that will search for the neutrinoless
  double-beta decay of Germanium-76 and perform a search for weakly
  interacting massive particles with masses below 10 GeV. To reach the
  background rate goal in the neutrinoless double-beta decay region of
  interest of 4 counts/keV/t/y, the DEMONSTRATOR will utilize a number of
  background reduction strategies, including a time-correlated event cut
  for <SUP>68</SUP>Ge that requires a sub-keV energy threshold. This low
  energy threshold allows the DEMONSTRATOR to extend its physics reach to
  include a search for light WIMPs. We will discuss the detector systems
  and data analysis techniques required to achieve sub-keV thresholds
  as well as present the projected dark matter sensitivities of the
  Majorana Demonstrator.

---------------------------------------------------------
Title: Extremely fast focal-plane wavefront sensing for extreme
    adaptive optics
Authors: Keller, Christoph U.; Korkiakoski, Visa; Doelman, Niek;
   Fraanje, Rufus; Andrei, Raluca; Verhaegen, Michel
2012SPIE.8447E..21K    Altcode: 2012arXiv1207.3273K
  We present a promising approach to the extremely fast sensing and
  correction of small wavefront errors in adaptive optics systems. As
  our algorithm's computational complexity is roughly proportional
  to the number of actuators, it is particularly suitable to
  systems with 10,000 to 100,000 actuators. Our approach is based
  on sequential phase diversity and simple relations between the
  point-spread function and the wavefront error in the case of small
  aberrations. The particular choice of phase diversity, introduced
  by the deformable mirror itself, minimizes the wavefront error as
  well as the computational complexity. The method is well suited for
  high­ contrast astronomical imaging of point sources such as the
  direct detection and characterization of exoplanets around stars, and
  it works even in the presence of a coronagraph that suppresses the
  diffraction pattern. The accompanying paper in these proceedings by
  Korkiakoski et al. describes the performance of the algorithm using
  numerical simulations and laboratory tests.

---------------------------------------------------------
Title: FOAM: the modular adaptive optics framework
Authors: van Werkhoven, T. I. M.; Homs, L.; Sliepen, G.; Rodenhuis,
   M.; Keller, C. U.
2012SPIE.8447E..2VV    Altcode:
  Control software for adaptive optics systems is mostly custom built
  and very specific in nature. We have developed FOAM, a modular adaptive
  optics framework for controlling and simulating adaptive optics systems
  in various environments. Portability is provided both for different
  control hardware and adaptive optics setups. To achieve this, FOAM is
  written in C++ and runs on standard CPUs. Furthermore we use standard
  Unix libraries and compilation procedures and implemented a hardware
  abstraction layer in FOAM. We have successfully implemented FOAM on the
  adaptive optics system of ExPo - a high-contrast imaging polarimeter
  developed at our institute - in the lab and will test it on-sky late
  June 2012. We also plan to implement FOAM on adaptive optics systems
  for microscopy and solar adaptive optics. FOAM is available* under
  the GNU GPL license and is free to be used by anyone.

---------------------------------------------------------
Title: Bilinear solution to the phase diversity problem for extended
    objects based on the Born approximation
Authors: Andrei, Raluca M.; Fraanje, Rufus; Verhaegen, Michel;
   Korkiakoski, Visa A.; Keller, Christoph U.; Doelman, Niek
2012SPIE.8447E..6TA    Altcode:
  We propose a new approach for the joint estimation of aberration
  parameters and unknown object from diversity images with applications
  in imaging systems with extended objects as astronomical ground-based
  observations or solar telescopes. The motivation behind our idea is
  to decrease the computational complexity of the conventional phase
  diversity (PD) algorithm and avoid the convergence to local minima
  due to the use of nonlinear estimation algorithms. Our approach is
  able to give a good starting point for an iterative algorithm or it
  can be used as a new wavefront estimation method. When the wavefront
  aberrations are small, the wavefront can be approximated with a linear
  term which leads to a quadratic point-spread function (PSF) in the
  aberration parameters. The presented approach involves recording two or
  more diversity images and, based on the before mentioned approximation
  estimates the aberration parameters and the object by solving a system
  of bilinear equations, which is obtained by subtracting from each
  diversity image the focal plane image. Moreover, using the quadratic
  PSFs gives improved performance to the conventional PD algorithm through
  the fact that the gradients of the PSFs have simple analytical formulas.

---------------------------------------------------------
Title: Simulation of automotive EMC emission test procedures based
    on cable bundle measurements
Authors: Gonser, M.; Keller, C.; Hansen, J.; Khillkevich, V.;
   Radchenko, A.; Pommerenke, D.; Weigel, R.
2012imsd.conf59432G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: HARPS spectropolarimetry of classical T Tauri stars
Authors: Johns-Krull, C. M.; Valenti, J. A.; Jeffers, S. V.; Piskunov,
   N. E.; Kochukhov, O.; Keller, C.; Snik, F.; Rodenhuis, M.; Makaganiuk,
   V.; Stempels, H.
2012AIPC.1429...43J    Altcode:
  We present high spectral resolution Stokes V polarimetery of the
  Classical T Tauri stars (CTTSs) GQ Lup and TW Hya obtained with
  the polarimetric upgrade to the HARPS spectrometer on the ESO 3.6 m
  telescope. We present data on both photospheric lines and emission
  lines, concentrating our discussion on the polarization properties
  of the He I emission lines at 5876 A and 6678 A. The He I lines
  in both these CTTS contain both narrow emission cores, believed to
  come from near the accretion shock region on these stars, and broad
  emission components which may come from either a wind or the large
  scale magnetospheric accretion flow. We detect strong polarization in
  the narrow component of both the He I emission lines in both stars. We
  observe a maximum implied field strength of 5.8 +/- 0.3 kG in the 5876
  A˚ line of GQ Lup, the highest field strength measured to date in
  this line for a CTTS. We find field strengths in the two He I lines
  that are consistent with each other, unlike what has been reported in
  the literature on at least one star. We do not detect any polarization
  in the broad component of the He I lines on these stars, strengthening
  the conclusion that they form over a substantially different volume
  relative the formation region of the narrow component of the He I lines.

---------------------------------------------------------
Title: SPEX2Earth, a novel spectropolarimeter for remote sensing of
    aerosols and clouds
Authors: Smit, J. M.; Rietjens, J. H. H.; Hasekamp, O.; Stam, D. M.;
   Snik, F.; van Harten, G.; Keller, C. U.; van der Togt, O.; Verlaan,
   A. L.; Moddemeijer, K.; Beijersbergen, M.; Voors, R.; Wielinga, K.;
   Vollmuller, B. -J.
2012EGUGA..1414166S    Altcode:
  Multi-angle spectro-polarimetry is the tool for the remote detection and
  characterization of aerosol and clouds in the Earth's atmosphere. Using
  a novel technique to measure polarization, we have developed a 30 kg
  instrument design to simultaneously measure the intensity and state of
  linear polarization of scattered sunlight, from 400 to 800 nm and 1200
  to 1600 nm, for 30 viewing directions, each with a 30° swath. Aerosols
  affect the climate directly by scattering and absorption of solar
  radiation, and by scattering, absorption, and emission of thermal
  radiation. Aerosols also affect the climate by changing the macro-
  and microphysical properties of clouds (the so-called indirect and
  semi-direct effects). Estimates of aerosol effects on the climate
  are hampered by insufficient knowledge of aerosol properties (size
  distribution, shape, and single scattering albedo) at a global
  scale. From several studies we know that these properties can only be
  determined with sufficient accuracy and unambiguously with satellite
  instruments that measure both intensity and polarization at multiple
  wavelengths and multiple viewing angles1,2.Polarization measurements
  must have a high accuracy, typically better than 0.1%. Achieving global
  coverage requires a large instantaneous field of view. Developing
  an instrument that combines all of these specifications can be
  considered as the most important challenge in polarimetric aerosol
  remote sensing. SPEX2Earth is such an instrument. It has been derived
  from the prototype spectropolarimeter SPEX (Spectro-polarimeter
  for Planetary Exploration), that was originally developed for a Mars
  orbiter. Possible target platforms for SPEX2Earth are the International
  Space Station, or a low-Earth orbit platform. SPEX2Earth uses a
  novel technique for its radiance and polarization measurements:
  through a series of carefully selected birefringent crystals,
  the radiance of scattered sunlight is spectrally modulated3. The
  modulation amplitude and phase are proportional to the degree and
  angle of linear polarization respectively. Two modulated spectra are
  produced per ground pixel, with a 180° degree phase shift between
  their modulations. The sum of the two spectra yields a modulation-free
  high resolution radiance spectrum of the scattered sunlight. The
  birefringent crystals determine the modulation frequency and thereby
  the resolution of the polarization spectrum. The technique is entirely
  passive, i.e. the polarization modulation is established without moving
  parts or active components.. SPEX2Earth's novel polarimetric technique
  allows for achieving the extremely high polarimetric accuracy (~0.001
  in linear polarization) needed to derive properties of aerosol (size,
  shape, refractive index, optical thickness, single scattering albedo)
  and clouds (droplet size, number concentration, optical thickness,
  phase, top/base height, cloud cover) with sufficient accuracy for
  climate research. With its relatively high spectral resolution,
  SPEX2Earth resolves the O2-A absorption band, which is important
  for deriving aerosol and cloud height. The viewing angles sample the
  scattering phase functions of aerosol and cloud particles, resolving
  characteristic angular features, and allowing to distinguish different
  types of particles. We will present the SPEX2Earth instrument, outline
  its spectral modulation principle and discuss its advantages compared
  with traditional polarimetric techniques. Expected performances are
  discussed, and recent performance results of the SPEX prototype are
  presented.

---------------------------------------------------------
Title: Multiwavelength imaging polarimetry of Venus at various
    phase angles
Authors: Einarsen, L. J.; Rodenhuis, M.; Snik, F.; Keller, C. U.;
   Stam, D. M.; de Kok, R. J.; Bianda, M.; Ramelli, R.
2012EGUGA..14.8670E    Altcode:
  Venus is the only planet with an atmosphere that we can observe from the
  ground at a large range of phase angles. Therefore it constitutes an
  important benchmark for direct observations of exoplanets, which will
  soon become available. Moreover, polarimetric observations at various
  phase angles and wavelengths provide a unique way to characterize any
  (exo-)planetary atmosphere. For instance, the famous study by Hansen
  &amp; Hovenier (1974) which combines disk-integrated polarimetric
  observations and modeling has unambiguously shown that Venus' upper
  atmosphere consists of sulphuric acid droplets of ~1 um in diameter. We
  present new spatially resolved observations of Venus using the imaging
  polarimeters ExPo at the William Herschel Telescope and ZIMPOL at the
  IRSOL telescope. These observations are taken in narrow-band filters
  from 364--648 nm, and span phase angles from 10--49 degrees. We
  find that the degree of polarization varies strongly with wavelength
  and phase angle, as generally predicted by the model by Hansen &amp;
  Hovenier. However, the polarization behaviour near the equator differs
  considerably from that at the poles, hinting at different atmospheric
  compositions and/or stratifications. In the intensity images we
  detect a significant shift of the location of maximum intensity with
  wavelength. These observations allow us to refine the model by Hansen
  &amp; Hovenier, and we present the preliminary results of our efforts
  to do so.

---------------------------------------------------------
Title: Observing the Earth as an exoplanet
Authors: Karalidi, T.; Stam, D. M.; Snik, F.; Keller, C. U.; Sparks,
   W. B.; Bagnulo, S.
2012EGUGA..1410571K    Altcode:
  Observations of Solar System planets, including the Earth, have
  shown the power of polarimetry for the characterization of planetary
  atmospheres and surfaces, and its ability to break degeneracies in
  retrievals from flux observations only and is thus essential for
  the full characterization of atmospheres and surfaces of (exo-)
  planets. With the discoveries of the first rocky exoplanets, the
  quest for Earth-like exoplanets and signs of their habitability has
  started. Since exoplanet observations will yield a signal that is
  integrated over the illuminated and visible part of the planet's
  disk, the main challenge for the interpretation of future exoplanet
  observations in terms of habitability will be disentangling the
  contributions from the different surface types and clouds. Numerical
  codes have been developed to model the spectral signals of oceans,
  continents, atmospheric gases, aerosols and clouds, but neither
  these codes nor retrieval algorithms can be validated by lack of
  disk-integrated observations of the Earth at a range of phase angles
  and wavelengths. We present LOUPE (Lunar Observatory for Unresolved
  Polarimetry of the Earth) as an instrument for a lunar lander. LOUPE
  will measure the disk-integrated flux and state of polarization of
  sunlight that is reflected by the Earth. LOUPE will offer a unique
  opportunity to observe the Earth as if it were an exoplanet. Thanks to
  the characteristics of the Moon's orbit around our planet, such a lunar
  observatory will witness the daily rotation of the Earth, with various
  surface types rotating in and out of view. During a month, it will also
  see the Earth through all phase angles, ranging from a full Earth to a
  new or almost new Earth, just as we can expect for observations of an
  exoplanet (depending on its orbital inclination angle). Finally, during
  the year, seasonal variations will become apparent. Such observations
  cannot be obtained by integrating spatially resolved observations
  by Earth remote-sensing satellites, nor by so-called Earthshine
  measurements, which capture sunlight that has first been reflected by
  the Earth and then by the lunar surface, because these can only be done
  when the moon is seen at large phase angles (thus when a large fraction
  of the lunar nightside and hence a large fraction of the Earth dayside
  are in view). Apart from a description of the LOUPE instrument, we will
  show numerically simulated flux and polarization spectra of Earth-like
  exoplanets to 1. illustrate the spectral and temporal variations that
  we can expect to observe from the moon, 2. point out the information
  that could be retrieved from such observations

---------------------------------------------------------
Title: Planetary science: In search of biosignatures
Authors: Keller, Christoph U.; Stam, Daphne M.
2012Natur.483...38K    Altcode:
  An analysis of the intensity and polarization of sunlight reflected
  by Earth reveals signatures of life on our planet. What prospects are
  there for using similar measurements to find life on planets outside the
  Solar System? Planetary scientists offer some answers. See Letter p.64

---------------------------------------------------------
Title: Magnetism, chemical spots, and stratification in the HgMn
    star ϕ Phoenicis
Authors: Makaganiuk, V.; Kochukhov, O.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels,
   H. C.; Valenti, J. A.
2012A&A...539A.142M    Altcode: 2011arXiv1111.6065M
  Context. Mercury-manganese (HgMn) stars have been considered as
  non-magnetic and non-variable chemically peculiar (CP) stars for a
  long time. However, recent discoveries of the variability in spectral
  line profiles have suggested an inhomogeneous surface distribution
  of chemical elements in some HgMn stars. From the studies of other
  CP stars it is known that magnetic field plays a key role in the
  formation of surface spots. All attempts to find magnetic fields in
  HgMn stars have yielded negative results. <BR /> Aims: In this study,
  we investigate the possible presence of a magnetic field in ϕ Phe
  (HD 11753) and reconstruct surface distribution of chemical elements
  that show variability in spectral lines. We also test a hypothesis
  that a magnetic field is concentrated in chemical spots and look into
  the possibility that some chemical elements are stratified with depth
  in the stellar atmosphere. <BR /> Methods: Our analysis is based on
  high-quality spectropolarimetric time-series observations, covering
  a full rotational period of the star. Spectra were obtained with the
  HARPSpol at the ESO 3.6-m telescope. To increase the sensitivity of
  the magnetic field search, we employed the least-squares deconvolution
  (LSD) technique. Using Doppler imaging code INVERS10, we reconstructed
  surface chemical distributions by utilising information from
  multiple spectral lines. The vertical stratification of chemical
  elements was calculated with the DDAFit program. <BR /> Results:
  Combining information from all suitable spectral lines, we set an
  upper limit of 4 G on the mean longitudinal magnetic field. For
  chemical spots, an upper limit on the longitudinal field varies
  between 8 and 15 G. We confirmed the variability of Y, Sr, and Ti
  and detected variability in Cr lines. Stratification analysis showed
  that Y and Ti are not concentrated in the uppermost atmospheric
  layers. <BR /> Conclusions: Our spectropolarimetric observations
  rule out the presence of a strong, globally-organised magnetic field
  in ϕ Phe. This implies an alternative mechanism of spot formation,
  which could be related to a non-equilibrium atomic diffusion. However,
  the typical time scales of the variation in stratification predicted
  by the recent time-dependent diffusion models exceed significantly
  the spot evolution time-scale reported for ϕ Phe. <P />Based on
  observations collected at the European Southern Observatory, Chile
  (ESO programme 084.D-0338). Figures 9-12 are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Direct imaging of a massive dust cloud around R Coronae
    Borealis
Authors: Jeffers, S. V.; Min, M.; Waters, L. B. F. M.; Canovas, H.;
   Rodenhuis, M.; de Juan Ovelar, M.; Chies-Santos, A. L.; Keller, C. U.
2012A&A...539A..56J    Altcode: 2012arXiv1203.1265J
  We present recent polarimetric images of the highly variable star R CrB
  using ExPo and archival WFPC2 images from the HST. We observed R CrB
  during its current dramatic minimum where it decreased more than 9 mag
  due to the formation of an obscuring dust cloud. Since the dust cloud is
  only in the line-of-sight, it mimics a coronograph allowing the imaging
  of the star's circumstellar environment. Our polarimetric observations
  surprisingly show another scattering dust cloud at approximately 1.3”
  or 2000 AU from the star. We find that to obtain a decrease in the
  stellar light of 9 mag and with 30% of the light being reemitted
  at infrared wavelengths (from R CrB's SED) the grains in R CrB's
  circumstellar environment must have a very low albedo of approximately
  0.07%. We show that the properties of the dust clouds formed around R
  CrB are best fitted using a combination of two distinct populations of
  grains size. The first are the extremely small 5 nm grains, formed in
  the low density continuous wind, and the second population of large
  grains (~0.14 μm) which are found in the ejected dust clouds. The
  observed scattering cloud, not only contains such large grains, but
  is exceptionally massive compared to the average cloud. <P />Based on
  observations made with the William Herschel Telescope operated on the
  island of La Palma by the Isaac Newton Group in the Spanish Observatorio
  del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

---------------------------------------------------------
Title: The effects of disk and dust structure on observed polarimetric
    images of protoplanetary disks
Authors: Min, M.; Canovas, H.; Mulders, G. D.; Keller, C. U.
2012A&A...537A..75M    Altcode: 2011arXiv1111.4348M
  Context. Imaging polarimetry is a powerful tool for imaging faint
  circumstellar material. It is a rapidly developing field with great
  promise for diagnostics of both the large-scale structures and the
  small-scale details of the scattering particles. <BR /> Aims: For a
  correct analysis of observations we need to fully understand the effects
  of dust particle parameters, as well as the effects of the telescope,
  atmospheric seeing, and assumptions about the data reduction and
  processing of the observed signal. Here we study the major effects of
  dust particle structure, size-dependent grain settling, and instrumental
  properties. <BR /> Methods: We performed radiative transfer modeling
  using different dust particle models and disk structures. To study the
  influence of seeing and telescope diffraction we ran the models through
  an instrument simulator for the ExPo dual-beam imaging polarimeter
  mounted at the 4.2 m William Herschel Telescope (WHT). <BR /> Results:
  Particle shape and size have a strong influence on the brightness and
  detectability of the disks. In the simulated observations, the central
  resolution element also contains contributions from the inner regions
  of the protoplanetary disk besides the unpolarized central star. This
  causes the central resolution element to be polarized, making simple
  corrections for instrumental polarization difficult. This effect
  strongly depends on the spatial resolution, so adaptive optics
  systems are needed for proper polarization calibration. <BR />
  Conclusions: We find that the commonly employed homogeneous sphere
  model gives results that differ significantly from more realistic
  models. For a proper analysis of the wealth of data available now or
  in the near future, one must properly take the effects of particle
  types and disk structure into account. The observed signal depends
  strongly on the properties of these more realistic models, thus
  providing a potentially powerful diagnostic. We conclude that it
  is important to correctly understand telescope depolarization and
  calibration effects for a correct interpretation of the degree of
  polarization. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Signatures of Water Clouds on Exoplanets: Numerical
    Simulations.
Authors: Karalidi, T.; Stam, D. M.; Keller, C. U.
2011ASPC..450..101K    Altcode:
  Clouds are of crucial importance for a planetary climate, because
  they store atmospheric volatiles, and because they scatter and
  absorb incident starlight and absorb, emit and scatter thermal
  radiation. Consequently, the detection and characterization of
  clouds on a planet can provide us with a wealth of information on
  the conditions on the surface. Here, we present numerically simulated
  flux and polarization spectra, from 0.3 μm to 1.0 μm, of starlight
  reflected by Earth-like exoplanets that are covered by horizontally
  homogeneous water clouds, for different cloud altitudes and particle
  sizes. Our results show that the degree of polarization P is sensitive
  to the particle size, in particular at phase angles between 30° and
  ∼50° and around 90°, and to the cloud top altitude, in particular
  at wavelengths between 0.35 μm and 0.7 μm. The information in P
  should be easier to retrieve than that in F.

---------------------------------------------------------
Title: Innovative Imaging of Young Stars: First Light ExPo
    Observations
Authors: Jeffers, S. V.; Canovas, H.; Keller, C. U.; Min, M.;
   Rodenhuis, M.
2011ASPC..448...15J    Altcode: 2011csss...16...15J
  We have developed an innovative imaging polariemter, ExPo, that excels
  in the imaging of the circumstellar environments of young stars. The
  basic physics that ExPo exploits is that starlight reflected from a
  star's circumstellar environment becomes linearly polarised, making
  it easily separable from unpolarised starlight. Our preliminary
  results, from the William Herschel Telescope in La Palma, show that
  ExPo has successfully detected several known protoplanetary disks out
  to a much larger distance and at a finer resolution than previously
  observed. ExPo has also made a significant number of new detections
  of protoplanetary disks and stellar outflows. We use innovative data
  analysis techniques, related to speckle interferometry, to detect the
  innermost parts of the disk to much closer than any other techniques
  operating at visible wavelengths. In this paper I present highlights
  of ExPo's first light observations.

---------------------------------------------------------
Title: New Insights into Stellar Magnetism from the Spectropolarimetry
    in All Four Stokes Parameters
Authors: Kochukhov, O.; Snik, F.; Piskunov, N.; Jeffers, S. V.;
   Keller, C. U.; Makaganiuk, V.; Valenti, J. A.; Johns-Krull, C. M.;
   Rodenhuis, M.; Stempels, H. C.
2011ASPC..448..245K    Altcode: 2011csss...16..245K
  Development of high-resolution spectropolarimetry has stimulated a
  major progress in our understanding of the magnetism and activity of
  late-type stars. During the last decade magnetic fields were discovered
  and mapped for various types of active stars using spectropolarimetric
  methods. However, these observations and modeling attempts are
  inherently incomplete since they are based on the interpretation of the
  stellar circular polarization alone. Taking advantage of the recently
  commissioned HARPS polarimeter, we obtained the first systematic
  observations of cool active stars in all four Stokes parameters. Here we
  report detection of the magnetically induced linear polarization in the
  RS CVn binary HR 1099 and phase-resolved full Stokes vector observations
  of varepsilon Eri. For the latter star we measured the field strength
  with the precision of ∼0.1 G over a complete rotation cycle and
  reconstructed the global field topology with the help of magnetic
  Doppler imaging. Our observations of the inactive solar-like star α
  Cen A indicate the absence of the global field stronger than 0.2 G.

---------------------------------------------------------
Title: Spectropolarimeter for planetary exploration (SPEX):
    performance measurements with a prototype
Authors: Voors, Robert; Moon, Scott G.; Hannemann, Sandro; Rietjens,
   Jeroen H. H.; van Harten, Gerard; Snik, Frans; Smit, Martijn; Stam,
   Daphne M.; Keller, Christoph U.; Laan, Erik C.; Verlaan, Adrianus L.;
   Vliegenthart, Willem A.; ter Horst, Rik; Navarro, Ramón; Wielenga,
   Klaas
2011SPIE.8176E..0DV    Altcode: 2011SPIE.8176E...9V
  SPEX (Spectropolarimeter for Planetary Exploration) was developed
  in close cooperation between scientific institutes and space
  technological industries in the Netherlands. It is used for measuring
  microphysical properties of aerosols and cloud particles in planetary
  atmospheres. SPEX utilizes a number of novel ideas. The key feature
  is that full linear spectropolarimetry can be performed without the
  use of moving parts, using an instrument of approximately 1 liter
  in volume. This is done by encoding the degree and angle of linear
  polarization (DoLP and AoLP) of the incoming light in a sinusoidal
  modulation of the intensity spectrum. Based on this principle,
  and after gaining experience from breadboard measurements using the
  same principle, a fully functional prototype was constructed. The
  functionality and the performance of the prototype were shown by
  extensive testing. The simulated results and the laboratory measurements
  show striking agreement. SPEX would be a valuable addition to any
  mission that aims to study the composition and structure of planetary
  atmospheres, for example, missions to Mars, Venus, Jupiter, Saturn
  and Titan. In addition, on an Earth-orbiting satellite, SPEX could
  give unique information on particles in our own atmosphere.

---------------------------------------------------------
Title: Data Reduction Approach for the Extreme Polarimeter
Authors: Canovas, H.; Rodenhuis, M.; Jeffers, S. V.; Keller, C. U.
2011ASPC..449...79C    Altcode:
  ExPo (Extreme Polarimeter) is an imaging polarimeter that we are
  building at Utrecht University, The Netherlands. It will detect
  polarized light from circumstellar disks and extrasolar planets,
  initially at the 4.2 m WHT and later at other telescopes. We have
  developed a data reduction approach that minimizes the influence of
  instrumental and atmospherical effects by using a partially transmitting
  coronagraph focal-plane mask. The approach has been tested with a
  laboratory simulator and an ExPo prototype.

---------------------------------------------------------
Title: Simulating Polarized Light from Exoplanets
Authors: Jeffers, S. V.; Miesen, N.; Rodenhuis, M.; Keller, C. U.;
   Canovas, H.
2011ASPC..449..391J    Altcode:
  In Utrecht we are building an imaging polarimeter, ExPo (Extreme
  Polarimeter), to image circumstellar disk and characterize extra-solar
  planets. To test and calibrate ExPo, we have built a laboratory-based
  simulator that mimicks a star with a Jupiter-like exoplanet as seen by
  the 4.2 m William-Herschel Telescope. The star and planet are simulated
  using two single-mode fibres in close proximity that are fed with a
  broadband arc lamp. The unpolarized star has a flux of 10<SUP>11</SUP>
  photons s<SUP>-1</SUP>, to simulate a mv=0 star, and the planet is
  partially linearly polarized, with a flux of as little as 10<SUP>2</SUP>
  photons s<SUP>-1</SUP> to simulate reflected star light with a contrast
  ratio of as much as 10<SUP>-9</SUP>. The telescope is simulated with
  two lenses, and seeing can be included with a rotating glass plate
  covered with hairspray, while dispersion is approximated with a wedge
  prism. These are the first realistic laboratory simulations of imaging
  polarimetry for exoplanet detection and characterization.

---------------------------------------------------------
Title: Design and Prototype Results of the ExPo Imaging Polarimeter
Authors: Rodenhuis, M.; Canovas, H.; Jeffers, S.; Keller, C.
2011ASPC..449...33R    Altcode:
  We present the design and prototype laboratory results of ExPo, an
  imaging polarimeter for the study of circumstellar disks and possibly
  exoplanet detection currently under development at the University of
  Utrecht. The instrument is designed to achieve a contrast ratio of
  10<SUP>-9</SUP> between the unpolarized starlight and the polarized
  source. First light is scheduled for the second half of 2008 at the
  4.2 m William Herschel telescope at La Palma. The instrument is based
  on the dual beam-exchange technique, simultaneously imaging the two
  orthogonal polarization states. It employs a ferro-electric liquid
  crystal retarder and a single electron-multiplying camera for fast
  modulation of the polarization. The instrument operates in the visible
  and has a field of view of (20″ × 20″).

---------------------------------------------------------
Title: M&amp;m's: an error budget and performance simulator code
    for polarimetric systems
Authors: de Juan Ovelar, Maria; Snik, Frans; Keller, Christoph U.
2011SPIE.8160E..0CD    Altcode: 2011SPIE.8160E...8D; 2012arXiv1207.4241O
  Although different approaches to model a polarimeter's accuracy have
  been described before, a complete error budgeting tool for polarimetric
  systems has not been yet developed. Based on the framework introduced
  by Keller &amp; Snik, in 2009, we have developed the M&amp;m's code
  as a first attempt to obtain a generic tool to model the performance
  and accuracy of a given polarimeter, including all the potential error
  contributions and their dependencies on physical parameters. The main
  goal of the code is to provide insight on the combined influence of many
  polarization errors on the polarimetric accuracy of any polarimetric
  instrument. In this work we present the mathematics and physics based
  on which the code is developed as well as its general structure and
  operational scheme. Discussion of the advantages of the M&amp;m's
  approach to error budgeting and polarimetric performance simulation
  is carried out and a brief outlook of further development of the code
  is also given.

---------------------------------------------------------
Title: Prototyping for the Spectropolarimeter for Planetary
EXploration (SPEX): calibration and sky measurements
Authors: van Harten, Gerard; Snik, Frans; Rietjens, Jeroen H. H.; Smit,
   J. Martijn; de Boer, Jozua; Diamantopoulou, Renia; Hasekamp, Otto P.;
   Stam, Daphne M.; Keller, Christoph U.; Laan, Erik C.; Verlaan, Ad L.;
   Vliegenthart, Willem A.; ter Horst, Rik; Navarro, Ramón; Wielinga,
   Klaas; Hannemann, Sandro; Moon, Scott G.; Voors, Robert
2011SPIE.8160E..0ZV    Altcode: 2011SPIE.8160E..28V
  We present the Spectropolarimeter for Planetary EXploration (SPEX),
  a high-accuracy linear spectropolarimeter measuring from 400 to 800 nm
  (with 2 nm intensity resolution), that is compact (~ 1 liter), robust
  and lightweight. This is achieved by employing the unconventional
  spectral polarization modulation technique, optimized for linear
  polarimetry. The polarization modulator consists of an achromatic
  quarter-wave retarder and a multiple-order retarder, followed by a
  polarizing beamsplitter, such that the incoming polarization state
  is encoded as a sinusoidal modulation in the intensity spectrum,
  where the amplitude scales with the degree of linear polarization,
  and the phase is determined by the angle of linear polarization. An
  optimized combination of birefringent crystals creates an athermal
  multiple-order retarder, with a uniform retardance across the field
  of view. Based on these specifications, SPEX is an ideal, passive
  remote sensing instrument for characterizing planetary atmospheres
  from an orbiting, air-borne or ground-based platform. By measuring the
  intensity and polarization spectra of sunlight that is scattered in
  the planetary atmosphere as a function of the single scattering angle,
  aerosol microphysical properties (size, shape, composition), vertical
  distribution and optical thickness can be derived. Such information is
  essential to fully understand the climate of a planet. A functional
  SPEX prototype has been developed and calibrated, showing excellent
  agreement with end-to-end performance simulations. Calibration tests
  show that the precision of the polarization measurements is at least
  2 • 10<SUP>-4</SUP>. We performed multi-angle spectropolarimetric
  measurements of the Earth's atmosphere from the ground in conjunction
  with one of AERONET's sun photometers. Several applications exist for
  SPEX throughout the solar system, a.o. in orbit around Mars, Jupiter
  and the Earth, and SPEX can also be part of a ground-based aerosol
  monitoring network.

---------------------------------------------------------
Title: The ZIMPOL high contrast imaging polarimeter for SPHERE:
    sub-system test results
Authors: Roelfsema, Ronald; Gisler, Daniel; Pragt, Johan; Schmid,
   Hans Martin; Bazzon, Andreas; Dominik, Carsten; Baruffolo, Andrea;
   Beuzit, Jean-Luc; Charton, Julien; Dohlen, Kjetil; Downing, Mark;
   Elswijk, Eddy; Feldt, Markus; de Haan, Menno; Hubin, Norbert; Kasper,
   Markus; Keller, Christoph; Lizon, Jean-Louis; Mouillet, David; Pavlov,
   Alexey; Puget, Pascal; Rochat, Sylvain; Salasnich, Bernardo; Steiner,
   Peter; Thalmann, Christian; Waters, Rens; Wildi, François
2011SPIE.8151E..0NR    Altcode: 2011SPIE.8151E..21R
  SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is
  one of the first instruments which aim for the direct detection from
  extra-solar planets. The instrument will search for direct light from
  old planets with orbital periods of several months to several years
  as we know them from our solar system. These are planets which are in
  or close to the habitable zone. ZIMPOL (Zurich Imaging Polarimeter)
  is the high contrast imaging polarimeter subsystem of the ESO SPHERE
  instrument. ZIMPOL is dedicated to detect the very faint reflected and
  hence polarized visible light from extrasolar planets. The search for
  reflected light from extra-solar planets is very demanding because
  the signal decreases rapidly with the orbital separation. For a
  Jupiter-sized object and a separation of 1 AU the planet/star contrast
  to be achieved is on the order of 10<SUP>-8</SUP> for a successful
  detection. This is much more demanding than the direct imaging of young
  self-luminous planets. ZIMPOL is located behind an extreme AO system
  (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light
  at the VLT at the end of 2012. ZIMPOL is currently in the subsystem
  testing phase. We describe the results of verification and performance
  testing done at the NOVA-ASTRON lab. We will give an overview of
  the system noise performance, the polarimetric accuracy and the high
  contrast testing. For the high contrast testing we will describe the
  impact of crucial system parameters on the contrast performance. SPHERE
  is an instrument designed and built by a consortium consisting of IPAG,
  MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA,
  ONERA and ASTRON in collaboration with ESO.

---------------------------------------------------------
Title: No magnetic field in the spotted HgMn star μ Leporis
Authors: Kochukhov, O.; Makaganiuk, V.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels,
   H. C.; Valenti, J. A.
2011A&A...534L..13K    Altcode: 2011arXiv1110.0829K
  Context. Chemically peculiar stars of the mercury-manganese (HgMn)
  type represent a new class of spotted late-B stars, in which evolving
  surface chemical inhomogeneities are apparently unrelated to the
  presence of strong magnetic fields but are produced by some hitherto
  unknown astrophysical mechanism. <BR /> Aims: The goal of this study
  is to perform a detailed line profile variability analysis and carry
  out a sensitive magnetic field search for one of the brightest HgMn
  stars - μ Lep. <BR /> Methods: We acquired a set of very high-quality
  intensity and polarization spectra of μ Lep with the HARPSpol
  polarimeter. These data were analyzed with the multiline technique
  of least-squares deconvolution in order to extract information on
  the magnetic field and line profile variability. <BR /> Results:
  Our spectra show very weak but definite variability in the lines
  of Sc, all Fe-peak elements represented in the spectrum of μ Lep,
  as well as Y, Sr, and Hg. Variability might also be present in the
  lines of Si and Mg. Anomalous profile shapes of Ti ii and Y ii lines
  suggest a dominant axisymmetric distribution of these elements. At
  the same time, we found no evidence of the magnetic field in μ Lep,
  with the 3σ upper limit of only 3 G for the mean longitudinal magnetic
  field. This is the most stringent upper limit on the possible magnetic
  field derived for a spotted HgMn star. <BR /> Conclusions: The very
  weak variability detected for many elements in the spectrum μ Lep
  suggests that low-contrast chemical inhomogeneities may be common in
  HgMn stars and that they have not been recognized until now due to the
  limited precision of previous spectroscopic observations and a lack
  of time-series data. The null result of the magnetic field search
  reinforces the conclusion that formation of chemical spots in HgMn
  stars is not magnetically driven. <P />Based on observations collected
  at the European Southern Observatory, Chile (ESO programs 084.D-0338,
  086.D-0240).

---------------------------------------------------------
Title: Fast horizontal flows in a quiet sun MHD simulation and their
    spectroscopic signatures
Authors: Vitas, N.; Fischer, C. E.; Vögler, A.; Keller, C. U.
2011A&A...532A.110V    Altcode:
  Numerical simulations of solar surface convection have predicted
  the existence of supersonic horizontal flows in the photospheric
  granulation. Recently, the detection of such flows in data from the
  Hinode satellite was reported. We study supersonic granular flows in
  detail to understand their signatures in spectral lines and to test
  the observational detection method used to identify these flows in
  the Hinode observations. We perform time-dependent 3D radiative MHD
  numerical simulations and synthesize the Fe i 6302 Å spectral lines at
  the resolution of the Hinode data for different viewing angles covering
  the center-limb variation. There is very large variation in the detailed
  shape of the emergent line profiles depending on the viewing angle and
  the particular flow properties and orientation. At the full simulation
  resolution the supersonic flows can even produce distinct satellite
  lines. After smearing to the Hinode resolution sufficient signature
  of supersonic motion remains. Our analysis shows that the detection
  method used to analyze the Hinode data is indeed applicable. However,
  the detection is very sensitive to ad hoc parameter choices and can
  also misidentify supersonic flows.

---------------------------------------------------------
Title: The search for magnetic fields in mercury-manganese stars
Authors: Makaganiuk, Vitalii; Kochukhov, Oleg; Piskunov, Nikolai;
   Jeffers, Sandra V.; Johns-Krull, Christopher M.; Keller, Christoph
   U.; Rodenhuis, Michiel; Snik, Frans; Stempels, Henricus C.; Valenti,
   Jeff A.
2011IAUS..272..202M    Altcode:
  Mercury-manganese (HgMn) stars were considered to be non-magnetic,
  showing no evidence of surface spots. However, recent investigations
  revealed that some stars in this class possess an inhomogeneous
  distribution of chemical elements on their surfaces. According to
  our current understanding, the most probable mechanism of spot
  formation involves magnetic fields. Taking the advantage of a
  newly-built polarimeter attached to the HARPS spectrometer at the
  ESO 3.6m-telescope, we performed a high-precision spectropolarimetric
  survey of a large group of HgMn stars. The main purpose of this study
  was to find out how typical it is for HgMn stars to have weak magnetic
  fields. We report no magnetic field detection for any of the studied
  objects, with a typical precision of the longitudinal field measurements
  of 10 G and down to 1 Gauss for some of the stars. We conclude that HgMn
  stars lack large-scale magnetic fields typical of spotted magnetic Ap
  stars and probably lack any fields capable of creating and sustaining
  chemical spots. Our study confirms that alongside the magnetically
  altered atomic diffusion, there must be other structure formation
  mechanism operating in the atmospheres of late-B main sequence stars.

---------------------------------------------------------
Title: Data-reduction techniques for high-contrast imaging
    polarimetry. Applications to ExPo
Authors: Canovas, H.; Rodenhuis, M.; Jeffers, S. V.; Min, M.; Keller,
   C. U.
2011A&A...531A.102C    Altcode: 2011arXiv1105.2961C
  Context. Imaging polarimetry is a powerful tool for detecting and
  characterizing exoplanets and circumstellar environments. Polarimetry
  allows a separation of the light coming from an unpolarized source
  such as a star and the polarized source such as a planet or a
  protoplanetary disk. Future facilities like SPHERE at the VLT or
  EPICS at the E-ELT will incorporate imaging polarimetry to detect
  exoplanets. The Extreme Polarimeter (ExPo) is a dual-beam imaging
  polarimeter that can currently reach contrast ratios of 10<SUP>5</SUP>,
  enough to characterize circumstellar environments. <BR /> Aims: We
  present the data-reduction steps for a dual-beam imaging polarimeter
  that can reach contrast ratios of 10<SUP>5</SUP>. <BR /> Methods: The
  data obtained with ExPo at the William Herschel Telescope (WHT) are
  analyzed. Instrumental artifacts and noise sources are discussed for
  an unpolarized star and for a protoplanetary disk (AB Aurigae). <BR />
  Results: The combination of fast modulation and dual-beam techniques
  allows us to minimize instrumental artifacts. A proper data processing
  and alignment of the images is fundamental when dealing with high
  contrasts. Imaging polarimetry proves to be a powerful method to
  resolve circumstellar environments even without a coronagraph mask or
  an adaptive optics system.

---------------------------------------------------------
Title: Spectral and polarimetric characterization of gazeous and
    telluric planets with SEE COAST
Authors: Boccaletti, A.; Baudoz, P.; Mawet, D.; Schneider, J.;
   Tinetti, G.; Galicher, R.; Stam, D.; Cavarroc, C.; Hough, J.; Doel,
   P.; Pinfield, D.; Keller, C. -U.; Beuzit, J. -L.; Udry, S.; Ferrari,
   A.; Martin, E.; Ménard, F.; Sein, E.
2011EPJWC..1607002B    Altcode:
  SEE COAST stands for Super Earth Explorer - Coronagraphic Off-Axis
  Space Telescope. The concept was initially proposed to ESA for
  Cosmic Vision. None of the direct detection exoplanet proposals were
  selected in 2007 and we are now pursuing our efforts to consolidate
  the astrophysical program and the technical developments for the next
  call for proposal. The prime objective of SEE COAST is to contribute
  to the understanding of the formation and evolution of planetary
  systems. Exploring the diversity of these objects is therefore the
  main driver to define the instrumentation. In the next decade the
  improvement of radial velocity instruments and obviously temporal
  coverage will provide us with a large numbers of long period giants as
  well as telluric planets, namely Super Earths. Obtaining the spectral
  and polarimetric signatures of these objects in the visible range
  to measure atmospheric parameters (molecular composition, clouds,
  soils, …) will be unique and with important scientific returns. A
  space mission complementary to near IR instruments like SPHERE, GPI,
  JWST and later ELTs for the full characterization of giants and Super
  Earths is a first secure step towards the longer term goal that is
  the characterization of telluric planets with mass and atmosphere
  comparable to that of the Earth. An overview of the astrophysical
  motivation and the trade-off that lead to a simple integrated concept
  of a space-based high contrast imaging instrument are given here.

---------------------------------------------------------
Title: Chemical spots in the absence of magnetic field in the binary
    HgMn star 66 Eridani
Authors: Makaganiuk, V.; Kochukhov, O.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels,
   H. C.; Valenti, J. A.
2011A&A...529A.160M    Altcode: 2011arXiv1102.4661M
  Context. According to our current understanding, a subclass of the
  upper main-sequence chemically peculiar stars, called mercury-manganese
  (HgMn), is non-magnetic. Nevertheless, chemical inhomogeneities were
  recently discovered on their surfaces. At the same time, no global
  magnetic fields stronger than 1-100 G are detected by systematic
  studies. <BR /> Aims: The goals of our study are to search for a
  magnetic field in the HgMn binary system 66 Eri and to investigate
  chemical spots on the stellar surfaces of both components. <BR />
  Methods: Our analysis is based on high-quality spectropolarimetric
  time-series observations obtained during 10 consecutive nights with
  the HARPSpol instrument at the ESO 3.6-m telescope. To increase the
  sensitivity of the magnetic field search we employed a least-squares
  deconvolution (LSD). We used spectral disentangling to measure radial
  velocities and study the line profile variability. Chemical spot
  geometry was reconstructed using multi-line Doppler imaging. <BR />
  Results: We report a non-detection of magnetic field in 66 Eri, with
  error bars 10-24 G for the longitudinal field. Circular polarization
  profiles also do not indicate any signatures of complex surface
  magnetic fields. For a simple dipolar field configuration we estimated
  an upper limit of the polar field strength to be 60-70 G. For the
  HgMn component we found variability in spectral lines of Ti, Ba,
  Y, and Sr with the rotational period equal to the orbital one. The
  surface maps of these elements reconstructed with the Doppler imaging
  technique show a relative underabundance on the hemisphere facing the
  secondary component. The contrast of chemical inhomogeneities ranges
  from 0.4 for Ti to 0.8 for Ba. <P />Based on observations collected
  at the European Southern Observatory, Chile (ESO program 084.D-0338).

---------------------------------------------------------
Title: First Detection of Linear Polarization in the Line Profiles
    of Active Cool Stars
Authors: Kochukhov, O.; Makaganiuk, V.; Piskunov, N.; Snik, F.;
   Jeffers, S. V.; Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.;
   Valenti, J. A.
2011ApJ...732L..19K    Altcode: 2011arXiv1103.6028K
  The application of high-resolution spectropolarimetry has led to major
  progress in understanding the magnetism and activity of late-type
  stars. During the last decade, magnetic fields have been discovered and
  mapped for many types of active cool stars using spectropolarimetric
  data. However, these observations and modeling attempts are
  fundamentally incomplete since they are based on the interpretation of
  the circular polarization alone. Taking advantage of the newly built
  HARPS polarimeter, we have obtained the first systematic observations
  of several cool active stars in all four Stokes parameters. Here we
  report the detection of magnetically induced linear polarization for
  the primary component of the very active RS CVn binary HR 1099 and
  for the moderately active K dwarf ɛ Eri. For both stars the amplitude
  of linear polarization signatures is measured to be ~10<SUP>-4</SUP>
  of the unpolarized continuum, which is approximately a factor of 10
  lower than for circular polarization. This is the first detection of
  the linear polarization in line profiles of cool active stars. Our
  observations of the inactive solar-like star α Cen A show neither
  circular nor linear polarization above the level of ~10<SUP>-5</SUP>,
  indicating the absence of a net longitudinal magnetic field stronger
  than 0.2 G. <P />Based on observations obtained at the European Southern
  Observatory (ESO programs 083.D-1000(A) and 084.D-0338(A)).

---------------------------------------------------------
Title: The Polarization Optics for the European Solar Telescope
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
   Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
   Snik, F.; Socas-Navarro, H.
2011ASPC..437..329B    Altcode:
  EST, the European Solar Telescope, is a 4-m class solar telescope,
  which will be located at the Canary Islands. It is currently in the
  conceptual design phase as a European funded project. In order to
  fulfill the stringent requirements for polarimetric sensitivity
  and accuracy, the polarimetry has been included in the design
  work from the very beginning. The overall philosophy has been to
  use a combination of techniques, which includes a telescope with
  low (and stable) instrumental polarization, optimal full Stokes
  polarimeters, differential measurement schemes, fast modulation
  and demodulation, and accurate calibration, and at the same time not
  giving up flexibility. The current baseline optical layout consists of a
  14-mirror layout, which is polarimetrically compensated and non-varying
  in time. In the polarization free F2 focus ample space is reserved for
  calibration and modulators and a polarimetric switch. At instrument
  level the s-, and p-planes of individual components are aligned,
  resulting in a system in which eigenvectors can travel undisturbed
  through the system.

---------------------------------------------------------
Title: The HARPS Polarimeter
Authors: Snik, F.; Kochukhov, O.; Piskunov, N.; Rodenhuis, M.; Jeffers,
   S.; Keller, C.; Dolgopolov, A.; Stempels, E.; Makaganiuk, V.; Valenti,
   J.; Johns-Krull, C.
2011ASPC..437..237S    Altcode: 2010arXiv1010.0397S
  We recently commissioned the polarimetric upgrade of the HARPS
  spectrograph at ESO's 3.6-m telescope at La Silla, Chile. The HARPS
  polarimeter is capable of full Stokes spectropolarimetry with large
  sensitivity and accuracy, taking advantage of the large spectral
  resolution and stability of HARPS. In this paper we present the
  instrument design and its polarimetric performance. The first HARPSpol
  observations show that it can attain a polarimetric sensitivity
  of ∼10<SUP>-5</SUP> (after addition of many lines) and that no
  significant instrumental polarization effects are present.

---------------------------------------------------------
Title: HARPSpol — The New Polarimetric Mode for HARPS
Authors: Piskunov, N.; Snik, F.; Dolgopolov, A.; Kochukhov, O.;
   Rodenhuis, M.; Valenti, J.; Jeffers, S.; Makaganiuk, V.; Johns-Krull,
   C.; Stempels, E.; Keller, C.
2011Msngr.143....7P    Altcode:
  The HARPS spectrograph can now perform a full polarisation analysis
  of spectra. It has been equipped with a polarimetric unit, HARPSpol,
  which was jointly designed and produced by Uppsala, Utrecht and Rice
  Universities and by the STScI. Here we present the new instrument,
  demonstrate its polarisation capabilities and show the first scientific
  results.

---------------------------------------------------------
Title: The search for magnetic fields in mercury-manganese stars
Authors: Makaganiuk, V.; Kochukhov, O.; Piskunov, N.; Jeffers, S. V.;
   Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels,
   H. C.; Valenti, J. A.
2011A&A...525A..97M    Altcode: 2010arXiv1010.3931M
  Context. A subclass of the upper main-sequence chemically peculiar
  stars, mercury-manganese (HgMn) stars were traditionally considered to
  be non-magnetic, showing no evidence of variability in their spectral
  line profiles. However, discoveries of chemical inhomogeneities on
  their surfaces imply that this assumption should be investigated. In
  particular, spectroscopic time-series of AR Aur, α And, and five other
  HgMn stars indicate the presence of chemical spots. At the same time,
  no signatures of global magnetic fields have been detected. <BR />
  Aims: We attempt to understand the physical mechanism that causes the
  formation of chemical spots in HgMn stars and gain insight into the
  potential magnetic field properties at their surfaces; we performed a
  highly sensitive search for magnetic fields for a large set of HgMn
  stars. <BR /> Methods: With the aid of a new polarimeter attached
  to the HARPS spectrometer at the ESO 3.6 m-telescope, we obtained
  high-quality circular polarization spectra of 41 single and double HgMn
  stars. Using a multi-line analysis technique on each star, we co-added
  information from hundreds of spectral lines to ensure significantly
  greater sensitivity to the presence of magnetic fields, including very
  weak fields. <BR /> Results: For the 47 individual objects studied,
  including six components of SB2 systems, we do not detect any magnetic
  fields at greater than the 3σ level. The lack of detection in the
  circular polarization profiles indicates that if strong fields are
  present on these stars, they must have complex surface topologies. For
  simple global fields, our detection limits imply upper limits to the
  fields present of 2-10 Gauss in the best cases. <BR /> Conclusions:
  We conclude that HgMn stars lack large-scale magnetic fields, which
  is typical of spotted magnetic Ap stars, of sufficient strength to
  form and sustain the chemical spots observed on HgMn stars. Our study
  confirms that in addition to magnetically altered atomic diffusion,
  there exists another differentiation mechanism operating in the
  atmospheres of late-B main sequence stars that can produce compositional
  inhomogeneities on their surfaces. <P />Based on observations collected
  at the European Southern Observatory, Chile (ESO programs 083.D-1000,
  084.D-0338, 085.D-0296).Figure 5 is only available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Imaging polarimetry of circumstellar environments with the
    Extreme Polarimeter
Authors: Rodenhuis, M.; Canovas, H.; Jeffers, S. V.; Min, M.; Keller,
   C. U.
2010lyot.confE..20R    Altcode:
  Three successful observation campaigns have been conducted with
  the Extreme Polarimeter, an imaging polarimeter for the study of
  circumstellar environments in scattered light at visible wavelengths. A
  contrast ratio between the central star and the circumstellar source
  of 10-5 can be achieved with polarimetry, with a Lyot coronograph
  capable of increasing this contrast by several orders of magnitude. The
  instrument currently operates without an adaptive optics system. An
  Adaptive Optics system under development for ExPo is expected to
  increase the contrast further. The polarimeter uses the dual-beam
  exchange technique, in which the two orthogonal polarisation states
  are imaged simultaneously after which a polarisation modulator is used
  to swap the polarisation states of the two beams before the next image
  is taken. The imaging polarimetry technique developed with ExPo will
  be used in the polarimetry arm of the EPICS exoplanet characterisation
  instrument proposed for the E-ELT. Here we present the results from the
  first observation campaigns, highlighting observations of protoplanetary
  disks around several young stars. Systematic effects that limit the
  polarimetric sensitivity, and the strategies we employ to overcome
  them, are discussed in detail. In particular, the advantages of the
  dual-beam exchange polarimetry method are demonstrated.

---------------------------------------------------------
Title: EPOL: the exoplanet polarimeter for EPICS at the E-ELT
Authors: Snik, F.; Keller, C.; Ovelar, M. J.; Rodenhuis, M.;
   Korkiakoski, V.; Venema, L.; Jager, R.; Rigal, F.; Hanenburg, H.;
   Roelfsema, R.; Schmidt, H. M.; Verinaud, C.; Kasper, M.; Martinez,
   P.; Yaitskova, N.
2010lyot.confE..82S    Altcode:
  EPOL is the imaging polarimeter part of EPICS (Exoplanet Imaging
  Camera and Spectrograph) for the 42-m E-ELT. It is based on sensitive
  imaging polarimetry to differentiate between linearly polarized
  light from exoplanets and unpolarized, scattered starlight and to
  characterize properties of exoplanet atmospheres and surfaces that
  cannot be determined from intensity observations alone. EPOL consists
  of a coronagraph and a dual-beam polarimeter with a liquid-crystal
  retarder to exchange the polarization of the two beams. The polarimetry
  thereby increases the contrast between star and exoplanet by 3 to 5
  orders of magnitude over what the extreme adaptive optics and the EPOL
  coronagraph alone can achieve. EPOL operates between 600 and 900 nm,
  can select more specific wavelength bands with filters and aims at
  having an integral field unit to obtain linearly polarized spectra of
  known exoplanets. We present the conceptual design of EPOL along with
  an analysis of its performance.

---------------------------------------------------------
Title: Imaging polarimetry of protoplanetary disks: feasibility
    and usability
Authors: Min, M.; Jeffers, S. V.; Rodenhuis, M.; Canovas, H.; Buenzli,
   E.; Keller, C. U.; Waters, L. B. F. M.; Dominik, C.
2010lyot.confE..34M    Altcode:
  Imaging polarimetry is one of the most promising tools to map the
  structure of faint protoplanetary disks. In this contribution we
  discuss the feasibility of imaging polarimetry of protoplanetary
  disks and the usability to answer the scientific questions in the
  field. From the theoretical side we do this by simulations of disks of
  various geometries and dust properties. We model the expected signal and
  detailed predictions for current and upcoming imaging polarimeters. This
  way we can address the question what the diagnostic value of polarimetry
  is for the structure of the disk and the characteristics of the grains
  in it. We compare extremely fluffy aggregated grains and compact
  homogeneous grains and show that their expected signal is significantly
  different. In combination with infrared/mm observations this could
  allow us to obtain grain properties in addition to mapping of the
  disk geometry. From the observational side we address the issues by
  discussing some of the early results from the Extreme Polarimeter
  (ExPo). ExPo is a sensitive imaging polarimeter designed to be a
  pathfinding instrument for the large imaging polarimetry projects
  planned for the VLT and the ELT. Already it proves to be a pioneering
  instrument in the field of imaging polarimetry of circumstellar matter.

---------------------------------------------------------
Title: Observations of solar scattering polarization at high spatial
    resolution
Authors: Snik, F.; de Wijn, A. G.; Ichimoto, K.; Fischer, C. E.;
   Keller, C. U.; Lites, B. W.
2010A&A...519A..18S    Altcode: 2010arXiv1005.5042S
  Context. The weak, turbulent magnetic fields that supposedly
  permeate most of the solar photosphere are difficult to observe,
  because the Zeeman effect is virtually blind to them. The Hanle
  effect, acting on the scattering polarization in suitable lines,
  can in principle be used as a diagnostic for these fields. However,
  the prediction that the majority of the weak, turbulent field resides
  in intergranular lanes also poses significant challenges to scattering
  polarization observations because high spatial resolution is usually
  difficult to attain. <BR /> Aims: We aim to measure the difference
  in scattering polarization between granules and intergranules. We
  present the respective center-to-limb variations, which may serve as
  input for future models. <BR /> Methods: We perform full Stokes filter
  polarimetry at different solar limb positions with the CN band filter
  of the Hinode-SOT Broadband Filter Imager, which represents the first
  scattering polarization observations with sufficient spatial resolution
  to discern the granulation. Hinode-SOT offers unprecedented spatial
  resolution in combination with high polarimetric sensitivity. The CN
  band is known to have a significant scattering polarization signal,
  and is sensitive to the Hanle effect. We extend the instrumental
  polarization calibration routine to the observing wavelength,
  and correct for various systematic effects. <BR /> Results: The
  scattering polarization for granules (i.e., regions brighter than
  the median intensity of non-magnetic pixels) is significantly larger
  than for intergranules. We derive that the intergranules (i.e., the
  remaining non-magnetic pixels) exhibit (9.8±3.0)% less scattering
  polarization for 0.2 &lt; μ ≤ 0.3, although systematic effects cannot
  be completely excluded. <BR /> Conclusions: These observations constrain
  MHD models in combination with (polarized) radiative transfer in terms
  of CN band line formation, radiation anisotropy, and magnetic fields.

---------------------------------------------------------
Title: The ZIMPOL high-contrast imaging polarimeter for SPHERE:
    design, manufacturing, and testing
Authors: Roelfsema, Ronald; Schmid, Hans Martin; Pragt, Johannes;
   Gisler, Daniel; Waters, Rens; Bazzon, Andreas; Baruffolo, Andrea;
   Beuzit, Jean-Luc; Boccaletti, Anthony; Charton, Julien; Cumani,
   Claudio; Dohlen, Kjetil; Downing, Mark; Elswijk, Eddy; Feldt, Markus;
   Groothuis, Charlotte; de Haan, Menno; Hanenburg, Hiddo; Hubin, Norbert;
   Joos, Franco; Kasper, Markus; Keller, Christoph; Kragt, Jan; Lizon,
   Jean-Louis; Mouillet, David; Pavlov, Aleksej; Rigal, Florence; Rochat,
   Sylvain; Salasnich, Bernardo; Steiner, Peter; Thalmann, Christian;
   Venema, Lars; Wildi, François
2010SPIE.7735E..4BR    Altcode: 2010SPIE.7735E.144R
  ZIMPOL is the high contrast imaging polarimeter subsystem of the
  ESO SPHERE instrument. ZIMPOL is dedicated to detect the very
  faint reflected and hence polarized visible light from extrasolar
  planets. ZIMPOL is located behind an extreme AO system (SAXO) and a
  stellar coronagraph. SPHERE is foreseen to have first light at the
  VLT at the end of 2011. ZIMPOL is currently in the manufacturing,
  integration and testing phase. We describe the optical, polarimetric,
  mechanical, thermal and electronic design as well as the design
  trade offs. Specifically emphasized is the optical quality of the key
  performance component: the Ferro-electric Liquid Crystal polarization
  modulator (FLC). Furthermore, we describe the ZIMPOL test setup and
  the first test results on the achieved polarimetric sensitivity and
  accuracy. These results will give first indications for the expected
  overall high contrast system performance. SPHERE is an instrument
  designed and built by a consortium consisting of LAOG, MPIA, LAM,
  LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA, ONERA and
  ASTRON in collaboration with ESO.

---------------------------------------------------------
Title: SPEX: the spectropolarimeter for planetary exploration
Authors: Snik, Frans; Rietjens, Jeroen H. H.; van Harten, Gerard;
   Stam, Daphne M.; Keller, Christoph U.; Smit, J. Martijn; Laan, Erik
   C.; Verlaan, Ad L.; Ter Horst, Rik; Navarro, Ramón; Wielinga, Klaas;
   Moon, Scott G.; Voors, Robert
2010SPIE.7731E..1BS    Altcode: 2010SPIE.7731E..34S
  SPEX (Spectropolarimeter for Planetary EXploration) is an innovative,
  compact instrument for spectropolarimetry, and in particular for
  detecting and characterizing aerosols in planetary atmospheres. With
  its ~1-liter volume it is capable of full linear spectropolarimetry,
  without moving parts. The degree and angle of linear polarization
  of the incoming light is encoded in a sinusoidal modulation of the
  intensity spectrum by an achromatic quarter-wave retarder, an athermal
  multiple-order retarder and a polarizing beam-splitter in the entrance
  pupil. A single intensity spectrum thus provides the spectral dependence
  of the degree and angle of linear polarization. Polarimetry has proven
  to be an excellent tool to study microphysical properties (size, shape,
  composition) of atmospheric particles. Such information is essential
  to better understand the weather and climate of a planet. The current
  design of SPEX is tailored to study Martian dust and ice clouds
  from an orbiting platform: a compact module with 9 entrance pupils
  to simultaneously measure intensity spectra from 400 to 800 nm, in
  different directions along the flight direction (including two limb
  viewing directions). This way, both the intensity and polarization
  scattering phase functions of dust and cloud particles within a ground
  pixel are sampled while flying over it. We describe the optical and
  mechanical design of SPEX, and present performance simulations and
  initial breadboard measurements. Several flight opportunities exist
  for SPEX throughout the solar system: in orbit around Mars, Jupiter
  and its moons, Saturn and Titan, and the Earth.

---------------------------------------------------------
Title: EPICS: direct imaging of exoplanets with the E-ELT
Authors: Kasper, Markus; Beuzit, Jean-Luc; Verinaud, Christophe;
   Gratton, Raffaele G.; Kerber, Florian; Yaitskova, Natalia; Boccaletti,
   Anthony; Thatte, Niranjan; Schmid, Hans Martin; Keller, Christoph;
   Baudoz, Pierre; Abe, Lyu; Aller-Carpentier, Emmanuel; Antichi, Jacopo;
   Bonavita, Mariangela; Dohlen, Kjetil; Fedrigo, Enrico; Hanenburg,
   Hiddo; Hubin, Norbert; Jager, Rieks; Korkiakoski, Visa; Martinez,
   Patrice; Mesa, Dino; Preis, Olivier; Rabou, Patrick; Roelfsema,
   Ronald; Salter, Graeme; Tecza, Mathias; Venema, Lars
2010SPIE.7735E..2EK    Altcode: 2010SPIE.7735E..81K
  Presently, dedicated instruments at large telescopes (SPHERE for the
  VLT, GPI for Gemini) are about to discover and explore self-luminous
  giant planets by direct imaging and spectroscopy. The next generation
  of 30m-40m ground-based telescopes, the Extremely Large Telescopes
  (ELTs), have the potential to dramatically enlarge the discovery space
  towards older giant planets seen in reflected light and ultimately
  even a small number of rocky planets. EPICS is a proposed instrument
  for the European ELT, dedicated to the detection and characterization
  of Exoplanets by direct imaging, spectroscopy and polarimetry. ESO
  completed a phase-A study for EPICS with a large European consortium
  which - by simulations and demonstration experiments - investigated
  state-of-the-art diffraction and speckle suppression techniques to
  deliver highest contrasts. The paper presents the instrument concept and
  analysis as well as its main innovations and science capabilities. EPICS
  is capable of discovering hundreds of giant planets, and dozens of
  lower mass planets down to the rocky planets domain.

---------------------------------------------------------
Title: EPOL: the exoplanet polarimeter for EPICS at the E-ELT
Authors: Keller, Christoph U.; Schmid, Hans Martin; Venema, Lars B.;
   Hanenburg, Hiddo; Jager, Rieks; Kasper, Markus; Martinez, Patrice;
   Rigal, Florence; Rodenhuis, Michiel; Roelfsema, Ronald; Snik, Frans;
   Verinaud, Christophe; Yaitskova, Natalia
2010SPIE.7735E..6GK    Altcode: 2010SPIE.7735E.212K
  EPOL is the imaging polarimeter part of EPICS (Exoplanet Imaging
  Camera and Spectrograph) for the 42-m E-ELT. It is based on sensitive
  imaging polarimetry to differentiate between linearly polarized
  light from exoplanets and unpolarized, scattered starlight and to
  characterize properties of exoplanet atmospheres and surfaces that
  cannot be determined from intensity observations alone. EPOL consists
  of a coronagraph and a dual-beam polarimeter with a liquid-crystal
  retarder to exchange the polarization of the two beams. The polarimetry
  thereby increases the contrast between star and exoplanet by 3 to 5
  orders of magnitude over what the extreme adaptive optics and the EPOL
  coronagraph alone can achieve. EPOL operates between 600 and 900 nm,
  can select more specific wavelength bands with filters and aims at
  having an integral field unit to obtain linearly polarized spectra of
  known exoplanets. We present the conceptual design of EPOL along with
  an analysis of its performance.

---------------------------------------------------------
Title: The polarization optics for the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
   Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
   Snik, F.; Socas-Navarro, H.
2010SPIE.7735E..6IB    Altcode: 2010SPIE.7735E.214B
  EST (European Solar Telescope) is a 4-m class solar telescope, which
  is currently in the conceptual design phase. EST will be located at
  the Canary Islands and aims at observations with the best possible
  spectral, spatial and temporal resolution and best polarimetric
  performance, of the solar photosphere and chromosphere, using a
  suite of instruments that can efficiently produce two-dimensional
  spectropolarimetric information of the thermal, dynamic and magnetic
  properties of the plasma over many scale heights, and ranging from
  λ=350 until 2300 nm. In order to be able to fulfill the stringent
  requirements for polarimetric sensitivity and accuracy, from the very
  beginning the polarimetry has been included in the design work. The
  overall philosophy has been to use a combination of techniques, which
  includes a telescope with low (and stable) instrumental polarization,
  optimal full Stokes polarimeters, differential measurement schemes,
  fast modulation and demodulation, and accurate calibration. The
  current baseline optical layout consists of a 14-mirror layout,
  which is polarimetrically compensated and nonvarying in time. In the
  polarization free F2 focus ample space is reserved for calibration and
  modulators and a polarimetric switch. At instrument level the s-, and
  p-planes of individual components are aligned, resulting in a system
  in which eigenvectors can travel undisturbed through the system.

---------------------------------------------------------
Title: Prediction of underground argon content for dark matter
    experiments
Authors: Mei, D. -M.; Yin, Z. -B.; Spaans, J.; Koppang, M.; Hime,
   A.; Keller, C.; Gehman, V. M.
2010PhRvC..81e5802M    Altcode: 2009arXiv0912.5368M
  In this paper, we demonstrate the use of physical models to evaluate the
  production of Ar39 and Ar40 underground. Considering both cosmogenic
  Ar39 production and radiogenic Ar40 production in situ and from
  external sources, we can derive the ratio of Ar39 to Ar40 in underground
  sources. We show for the first time that the Ar39 production underground
  is dominated by stopping negative muon capture on K39 and (α,n) induced
  subsequent K39(n,p)Ar39 reactions. The production of Ar39 is shown as
  a function of depth. We demonstrate that argon depleted in Ar39 can
  be obtained only if the depth of the underground resources is greater
  than 500 m.w.e. below the surface. Stopping negative muon capture on
  K39 dominates over radiogenic production at depths of less than 2000
  m.w.e., and that production by muon-induced neutrons is subdominant at
  any depth. The depletion factor depends strongly on both radioactivity
  level and potassium content in the rock. We measure the radioactivity
  concentration and potassium concentration in the rock for a potential
  site of an underground argon source in South Dakota. Depending on the
  probability of Ar39 and Ar40 produced underground being dissolved in the
  water, the upper limit of the concentration of Ar39 in the underground
  water at this site is estimated to be in a range of a factor of 1.6 to
  155 less than the Ar39 concentration in the atmosphere. The calculation
  tools presented in this paper are also critical to the dating method
  with Ar39.

---------------------------------------------------------
Title: Inversions of High-Cadence SOLIS-VSM Stokes Observations
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.
2010ASSP...19..515F    Altcode: 2010mcia.conf..515F
  We have processed full-Stokes observations made with the SOLIS-VSM
  using Fe I 630.15 and Fe I 630.25 nm. The data have high spectral and
  temporal resolution, moderate spatial resolution, and large polarimetric
  sensitivity and accuracy. We use the code LILIA, an LTE inversion code
  written by Socas-Navarro (2001), in order to invert the data in vector
  magnetic fields. The 180-degree ambiguity in magnetic field orientation
  is solved by using the Non-Potential Field Calculation (NPFC) method
  of Georgoulis (2005). The output product are maps of the fullmagnetic
  field vector at the photospheric level, as illustrated in Fig. 1. We
  performed such inversions for observations of active region NOAA 10808
  taken during an X-class flare in September 2005. Details of the data
  processing and the first results are given in the proceedings of the
  Fifth Solar PolarizationWorkshop (ASP Conf. Ser., in press).

---------------------------------------------------------
Title: EPICS, the exoplanet imager for the E-ELT
Authors: Kasper, M.; Beuzit, J. -L.; Verinaud, C.; Baudoz, P.;
   Boccaletti, A.; Gratton, R.; Keller, C.; Kerber, F.; Schmid, H. M.;
   Thatte, N.; Venema, L.; Yaitskova, N.
2010aoel.confE2009K    Altcode:
  Very soon, dedicated instruments developments at large telescopes
  (SPHERE for the VLT, GPI for Gemini) are about to discover and explore
  self-luminous giant planets by direct imaging and spectroscopy in
  significant numbers. The next generation of 30m-40m ground-based
  telescopes, the Extremely Large Telescopes (ELTs), have the potential
  to dramatically enlarge the discovery space towards older giant planets
  seen in reflected light and ultimately even a small number of rocky
  planets. EPICS is a proposed instrument for the European ELT, dedicated
  to the detection and characterization of expolanets by direct imaging
  and spectroscopy. EPICS is currently mid-way through a phase-A study
  carried out by a large European consortium which - by simulations
  and demonstration experiments - will investigate state-of-the-art
  diffraction and speckle suppression techniques to deliver highest
  contrasts. The final result of the study early 2010 will be a conceptual
  design and a development plan for the instrument. We will present the
  EPICS concept including the performance analysis and first results from
  prototyping experiments and discuss the main challenges and science
  capabilities of EPICS.

---------------------------------------------------------
Title: Two Ways of Improving Stokes Inversions
Authors: Becher, H. -M.; Fischer, C.; Keller, C.
2009ASPC..415..160B    Altcode:
  Performing Stokes inversion on single pixels can be difficult due to
  seeing and instrumental smearing. We present two different techniques
  to improve Stokes inversions. The first method, REGIONS, is a code that
  finds pixels that are likely to contain signal from the same magnetic
  element. The second method, mCLEAN, reconstructs a magnetogram if the
  point spread function (PSF) of the instrument and seeing is known.

---------------------------------------------------------
Title: Statistics of Convective Collapse Events in the Photosphere
    and Chromosphere Observed with the HINODE SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
   Keller, C. U.
2009ASPC..415..127F    Altcode:
  Convective collapse, a theoretically predicted process that
  intensifies existing weak magnetic fields in the solar atmosphere,
  was first directly observed in a single event by Nagata et al. (2008)
  using the high resolution Solar Optical Telescope (SOT) of the Hinode
  satellite. Using the same space telescope, we observed 49 such events
  and present a statistical analysis of convective collapse events. Our
  data sets consist of high resolution time series of polarimetric
  spectral scans of two iron lines formed in the lower photosphere and
  filter images in Mg I b<SUB>2</SUB> and Ca II H. We were thus able
  to study the implication of convective collapse events on the high
  photospheric and the chromospheric layers. The physical parameters from
  the full Stokes profiles were obtained with the MERLIN Milne-Eddington
  inversion code. For each of the 49 events we determined the duration,
  maximum photospheric downflow, and field strength increase. We found
  event durations of about 10 minutes and field strengths of up to
  1.65 kG.

---------------------------------------------------------
Title: Statistics of convective collapse events in the photosphere
    and chromosphere observed with the Hinode SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
   Keller, C. U.
2009A&A...504..583F    Altcode: 2009arXiv0906.2308F
  Convective collapse, a theoretically predicted process that intensifies
  existing weak magnetic fields in the solar atmosphere, was first
  directly observed in a single event by Nagata et al. (2008, ApJ,
  677, L145) using the high resolution Solar Optical Telescope (SOT)
  of the Hinode satellite. Using the same space telescope, we observed
  49 such events and present a statistical analysis of convective
  collapse events. Our data sets consist of high resolution time series
  of polarimetric spectral scans of two iron lines formed in the lower
  photosphere and filter images in Mg I b{2} and Ca II H, spectral lines
  that are formed in the high photosphere and the lower chromosphere,
  respectively. We were thus able to study the implication of convective
  collapse events on the high photospheric and the chromospheric
  layers. We found that in all cases, the event was accompanied by a
  continuum bright point and nearly always by a brightening in the Ca
  II H images. The magnesium dopplergram exhibits a strong downflow in
  about three quarters of the events that took place within the field
  of view of the magnesium dopplergram. The physical parameters from
  the full Stokes profiles were obtained with the MERLIN Milne-Eddington
  inversion code. For each of the 49 events we determined the duration,
  maximum photospheric downflow, field strength increase and size. We
  found event durations of about 10 min, magnetic element radii of about
  0.43 arcsec and 0.35 arcsec, before and after the event, respectively,
  and field strengths of up to 1.65 kG.

---------------------------------------------------------
Title: The case for spectropolarimetry with SPEX on EJSM
Authors: Stam, D. M.; Smit, J. M.; Snik, F.; Keller, C. U.
2009epsc.conf..536S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Polarimetric Measurements of Protoplanetary Disks with ExPo
Authors: Canovas, H.; Rodenhuis, M.; Jeffers, S. V.; Keller, C. U.
2009AIPC.1158..381C    Altcode:
  Polarimetry is a powerful tool for detecting and characterizing
  exoplanets and protoplanetary disks as light scattered from
  circumstellar material is linearly polarized. We present the first
  light results of ExPo (Extreme Polarimeter) [1], a sensitive imaging
  polarimeter developed at Utrecht University that works in the
  visible part of the spectrum. Our first light observations at the
  4.2-meter William Herschel Telescope (WHT) show that ExPo can reach
  the high-contrast ratios that are necessary to observe protoplanetary
  disks. We present images of the protoplanetary disks around the Herbig
  Ae star AB Aurigae and the T Tauri star SU Aurigae. Our results show
  the power of polarimetry for future projects e.g. the ZIMPOL arm of
  SPHERE, and the EPOL part of EPICS.

---------------------------------------------------------
Title: An IFU for diffraction-limited 3D spectroscopic imaging:
    laboratory and on-site tests
Authors: Ren, Deqing; Keller, Christoph; Plymate, Claude
2009SPIE.7438E..18R    Altcode: 2009SPIE.7438E..35R
  We have developed a state-of-the-art image slicer Integral Field Unit
  (IFU) for the McMath-Pierce Solar Telescope (McMP) located at Kitt Peak
  National Solar Observatory. The IFU will be used for high-resolution
  3-dimensional spectroscopy and polarimetry over a small field of
  view that is well corrected by adaptive optics. It consists of 19
  effective slices that correspond to a field of view of 6.27"x 7". The
  IFU delivers a 152" long slit to an existing spectrograph producing
  diffraction-limited 3-dimensional spectroscopy. The 3-D instrument is
  being used for highspatial and high-temporal resolution imaging of the
  Sun, which is crucial for the magnetic field and spectroscopic studies
  of 2-dimensional solar fine structures. We discuss the instrument
  construction, laboratory test and on-site trial observations with
  the McMP.

---------------------------------------------------------
Title: A Brief History of the Second Solar Spectrum
Authors: Keller, C. U.
2009ASPC..405...29K    Altcode:
  The development of the ZIMPOL principle at ETH Zurich led to a dramatic
  increase in our observational knowledge of the solar scattering
  polarization spectrum, now known as the Second Solar Spectrum. This
  contribution summarizes the historical developments of this field with
  a special focus on the observational events between 1994 and 1996 when
  many interesting things happened that cannot be found in the literature.

---------------------------------------------------------
Title: Bioaccumulated manganese and nickel in endemic plants from
    New Caledonian mining soils
Authors: Pouschat, P.; Rose, J.; Alliot, I.; Dominici, C.; Keller,
   C.; Olivi, L.; Rabier, J.; Ambrosi, J. -P.
2009GeCAS..73R1049P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Polarimetry from the Ground Up
Authors: Keller, C. U.; Snik, F.
2009ASPC..405..371K    Altcode: 2008arXiv0809.2772K
  Ground-based solar polarimetry has made great progress over the last
  decade. Nevertheless, polarimetry is still an afterthought in most
  telescope and instrument designs, and most polarimeters are designed
  based on experience and rules of thumb rather than using more formal
  systems engineering approaches as is common in standard optical design
  efforts. Here we present the first steps in creating a set of systems
  engineering approaches to the design of polarimeters that makes sure
  that the final telescope-instrument-polarimeter system is more than
  the sum of its parts.

---------------------------------------------------------
Title: The Prototype of the Small Synoptic Second Solar Spectrum
    Telescope (S^5T)
Authors: Snik, F.; Melich, R.; Keller, C. U.
2009ASPC..405..383S    Altcode: 2009arXiv0903.2730S
  We present the design and the prototype of the Small Synoptic Second
  Solar Spectrum Telescope (S^5T), which can autonomously measure
  scattering polarization signals on a daily basis with large sensitivity
  and accuracy. Its data will be used to investigate the nature of weak,
  turbulent magnetic fields through the Hanle effect in many lines. Also
  the relation between those fields and the global solar dynamo can be
  revealed by spanning the observations over a significant fraction of
  a solar cycle. The compact instrument concept is enabled by a radial
  polarization converter that allows for “one-shot” polarimetry over the
  entire limb of the Sun. A polarimetric sensitivity of ∼10<SUP>-5</SUP>
  is achieved by minimizing the instrumental polarization and by
  FLC modulation in combination with a fast line-scan camera in the
  fiber-fed spectrograph. The first prototype results successfully show
  the feasibility of the concept.

---------------------------------------------------------
Title: Vector Magnetic Field Inversions of High Cadence SOLIS-VSM Data
Authors: Fischer, C. E.; Keller, C. U.; Snik, F.
2009ASPC..405..311F    Altcode:
  We have processed full Stokes observations from the SOLIS VSM in the
  photospheric lines Fe I 630.15 nm and 630.25 nm. The data sets have
  high spectral and temporal resolution, moderate spatial resolution,
  and large polarimetric sensitivity and accuracy. We used the LILIA, an
  LTE code written by \citet{fischer_Navarro2001} to invert the data. We
  also applied the non-potential magnetic field calculation method
  of \citet{fischer_Manolis2005} in order to resolve the 180 degree
  ambiguity. The output are maps of the full magnetic field vector at
  the photospheric level. Here we present the first inversions of the
  active region NOAA 10808 during an X-class flare, which occurred on
  13 September 2005.

---------------------------------------------------------
Title: SOLIS Vector Spectromagnetograph: Status and Science
Authors: Henney, C. J.; Keller, C. U.; Harvey, J. W.; Georgoulis,
   M. K.; Hadder, N. L.; Norton, A. A.; Raouafi, N. -E.; Toussaint, R. M.
2009ASPC..405...47H    Altcode: 2008arXiv0801.0013H
  The Vector Spectromagnetograph (VSM) instrument has recorded
  photospheric and chromospheric magnetograms daily since August
  2003. Full-disk photospheric vector magnetograms are observed
  at least weekly and, since November 2006, area-scans of active
  regions daily. Quick-look vector magnetic images, plus X3D and FITS
  formated files, are now publicly available daily. In the near future,
  Milne-Eddington inversion parameter data will also be available and
  a typical observing day will include three full-disk photospheric
  vector magnetograms. Besides full-disk observations, the VSM is
  capable of high temporal cadence area-scans of both the photosphere
  and chromosphere. Carrington rotation and daily synoptic maps are
  also available from the photospheric magnetograms and coronal hole
  estimate images.

---------------------------------------------------------
Title: Polarization Properties of Real Aluminum Mirrors, I. Influence
    of the Aluminum Oxide Layer
Authors: van Harten, G.; Snik, F.; Keller, C. U.
2009PASP..121..377V    Altcode: 2009arXiv0903.2740V
  In polarimetry, it is important to characterize the polarization
  properties of the instrument itself to disentangle real astrophysical
  signals from instrumental effects. This article deals with the
  accurate measurement and modeling of the polarization properties
  of real aluminum mirrors, as used in astronomical telescopes. Main
  goals are the characterization of the aluminum oxide layer thickness
  at different times after evaporation, and its influence on the
  polarization properties of the mirror. The full polarization properties
  of an aluminum mirror are measured with Mueller matrix ellipsometry at
  different incidence angles and wavelengths. The best fit of theoretical
  Mueller matrices to all measurements simultaneously is obtained by
  taking into account a model of bulk aluminum with a thin aluminum
  oxide film on top of it. Full Mueller matrix measurements of a mirror
  are obtained with an absolute accuracy of ∼1% after calibration. The
  determined layer thicknesses indicate logarithmic growth in the first
  few hours after evaporation, but stability at a value of 4.12 ± 0.08
  nm in the long term. Although the aluminum oxide layer is established
  to be thin, it is necessary to consider it to accurately describe the
  mirror’s polarization properties.

---------------------------------------------------------
Title: Super earth explorer: a coronagraphic off-axis space telescope
Authors: Schneider, J.; Boccaletti, A.; Mawet, D.; Baudoz, P.; Beuzit,
   J. -L.; Doyon, R.; Marley, M.; Stam, D.; Tinetti, G.; Traub, W.;
   Trauger, J.; Aylward, A.; Cho, J. Y. -K.; Keller, C. -U.; Udry, S.;
   SEE-COAST Team
2009ExA....23..357S    Altcode: 2008arXiv0811.3908S
  The Super-Earth Explorer is an Off-Axis Space Telescope (SEE-COAST)
  designed for high contrast imaging. Its scientific objective is to
  make the physico-chemical characterization of exoplanets possibly
  down to 2 Earth radii. For that purpose it will analyze the spectral
  and polarimetric properties of the parent starlight reflected by the
  planets, in the wavelength range 400-1,250 nm.

---------------------------------------------------------
Title: An analytical model to demonstrate the reliability of
    reconstructed `active longitudes'.
Authors: Jeffers, S. V.; Keller, C. U.
2009AIPC.1094..664J    Altcode: 2009csss...15..664J
  Photometric light curves show apparent spot concentrations separated
  by 180 degrees in longitude that are commonly referred to as `active
  longitudes'. These spot concentrations have been observed to change in
  strength resulting in the `flip-flop' effect. We use a simple analytical
  model to calculate the light curve of a star with an arbitrary spot
  pattern to show that `active longitudes' are a likely consequence of
  the limited information content contained in a light curve. We also
  show that the same effects apply to heavily spotted stars.

---------------------------------------------------------
Title: Characterization of Extra-solar Planets with Direct-Imaging
    Techniques
Authors: Tinetti, Giovanna; Cash, Webster; Glassman, Tiffany; Keller,
   C.; Oakley, Phil; Snik, F.; Stam, Daphne; Turnbull, Margret
2009astro2010S.296T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Polarimetry of Mars with SPEX, an Innovative Spectropolarimeter
Authors: Stam, D. M.; Laan, E.; Snik, F.; Karalidi, T.; Keller, C.; Ter
   Horst, R.; Navarro, R.; Aas, C.; de Vries, J.; Oomen, G.; Hoogeveen, R.
2008LPICo1447.9078S    Altcode:
  We present SPEX, an innovative, compact, and robust spectropolarimeter
  that measures fluxes and polarization of sunlight reflected by Mars from
  400 to 800 nm. With simulations we'll show how with SPEX atmospheric
  dust and the surface can be studied.

---------------------------------------------------------
Title: A New Era in Solar Thermal-IR Astronomy: the NSO Array Camera
    (NAC) on the McMath-Pierce Telescope
Authors: Ayres, T.; Penn, M.; Plymate, C.; Keller, C.
2008ESPM...12.2.74A    Altcode:
  The U.S. National Solar Observatory Array Camera (NAC) is a
  cryogenically cooled 1Kx1K InSb “Aladdin" array that recently became
  operational at the McMath-Pierce facility on Kitt Peak, a high dry site
  in the southwest U.S. (Arizona). The new camera is similar to those
  already incorporated into instruments on nighttime telescopes, and has
  unprecedented sensitivity, low noise, and excellent cosmetics compared
  with the Amber Engineering (AE) device it replaces. (The latter was
  scavenged from a commercial surveillance camera in the 1990's: only
  256X256 format, high noise, and annoying flatfield structure). The
  NAC focal plane is maintained at 30 K by a mechanical closed-cycle
  helium cooler, dispensing with the cumbersome pumped--solid-N2 40 K
  system used previously with the AE camera. The NAC linearity has been
  verified for exposures as short as 1 ms, although latency in the data
  recording holds the maximum frame rate to about 8 Hz (in "streaming
  mode"). The camera is run in tandem with the Infrared Adaptive
  Optics (IRAO) system. Utilizing a 37-actuator deformable mirror, IRAO
  can--under moderate seeing conditions--correct the telescope image to
  the diffraction limit longward of 2.3 mu (if a suitable high contrast
  target is available: the IR granulation has proven too bland to reliably
  track). IRAO also provides fine control over the solar image for spatial
  scanning in long-slit mode with the 14 m vertical "Main" spectrograph
  (MS). A 1'X1' area scan, with 0.5" steps orthogonal to the slit
  direction, requires less than half a minute, much shorter than p-mode
  and granulation evolution time scales. A recent engineering test run,
  in April 2008, utilized NAC/IRAO/MS to capture the fundamental (4.6 mu)
  and first-overtone (2.3 mu) rovibrational bands of CO, including maps
  of quiet regions, drift scans along the equatorial limbs (to measure
  the off-limb molecular emissions), and imaging of a fortuitous small
  sunspot pair, a final gasp, perhaps, of Cycle 23. Future work with
  the NAC will emphasize pathfinding toward the next generation of IR
  imaging spectrometers for the Advanced Technology Solar Telescope,
  whose 4 m aperture finally will bring sorely needed high spatial
  resolution to daytime infrared astronomy. In the meantime, the NAC
  is available to qualified solar physicists from around the world to
  conduct forefront research in the 1-5 mu region, on the venerable--but
  infrared friendly--McMath-Pierce telescope.

---------------------------------------------------------
Title: The upgrade of HARPS to a full-Stokes high-resolution
    spectropolarimeter
Authors: Snik, Frans; Jeffers, Sandra; Keller, Christoph; Piskunov,
   Nikolai; Kochukhov, Oleg; Valenti, Jeff; Johns-Krull, Christopher
2008SPIE.7014E..0OS    Altcode: 2008SPIE.7014E..22S
  We present the design of a compact module that converts the HARPS
  instrument at the 3.6-m telescope at La Silla to a full-Stokes
  high-resolution spectropolarimeter. The polarimeter will replace the
  obsolete Iodine cell inside the HARPS Cassegrain adapter. Utilizing
  the two fibers going into the spectrograph, two dual-beam systems
  can be positioned in the beam: one with a rotating superachromatic
  quarter-wave plate for circular polarimetry and one with a rotating
  superachromatic half-wave plate for linear polarimetry. A large
  polarimetric precision is ensured by the beam-exchange technique
  and a minimal amount of instrumental polarization. The polarimeter,
  in combination with the ultra-precise HARPS spectrograph, enables
  unprecedented observations of stellar magnetic fields and circumstellar
  material without compromising the successful planet-finding program.

---------------------------------------------------------
Title: SPHERE ZIMPOL: overview and performance simulation
Authors: Thalmann, Christian; Schmid, Hans M.; Boccaletti, Anthony;
   Mouillet, David; Dohlen, Kjetil; Roelfsema, Ronald; Carbillet,
   Marcel; Gisler, Daniel; Beuzit, Jean-Luc; Feldt, Markus; Gratton,
   Raffaele; Joos, Franco; Keller, Christoph U.; Kragt, Jan, II; Pragt,
   Johan H.; Puget, Pascal; Rigal, Florence; Snik, Frans; Waters, Rens;
   Wildi, François
2008SPIE.7014E..3FT    Altcode: 2008SPIE.7014E.112T
  The ESO planet finder instrument SPHERE will search for the
  polarimetric signature of the reflected light from extrasolar
  planets, using a VLT telescope, an extreme AO system (SAXO),
  a stellar coronagraph, and an imaging polarimeter (ZIMPOL). We
  present the design concept of the ZIMPOL instrument, a single-beam
  polarimeter that achieves very high polarimetric accuracy using fast
  polarization modulation and demodulating CCD detectors. Furthermore,
  we describe comprehensive performance simulations made with the CAOS
  problem-solving environment. We conclude that direct detection of
  Jupiter-sized planets in close orbit around the brightest nearby stars
  is achievable with imaging polarimetry, signal-switching calibration,
  and angular differential imaging.

---------------------------------------------------------
Title: The Extreme Polarimeter (ExPo): design of a sensitive imaging
    polarimeter
Authors: Rodenhuis, M.; Canovas, H.; Jeffers, S. V.; Keller, C. U.
2008SPIE.7014E..6TR    Altcode: 2008SPIE.7014E.227R
  The Extreme Polarimeter (ExPo) is approaching its first deployment
  at the 4.2 m William Herschel Telescope at La Palma. This imaging
  polarimeter, developed at the Astronomical Institute of Utrecht
  University, aims to study circumstellar material at a contrast
  ratio with the central star of 10<SUP>-9</SUP>. Working at visible
  wavelengths, it will provide an inner working angle down to 0.5
  arcsec and a field of view of 20 arcsec diameter. ExPo employs a
  dual beam-exchange technique based on polarimeter designs for solar
  studies. A partially transmitting coronagraph mask placed in the first
  focus reduces the light of the star. The beam is modulated using three
  ferro-electric liquid crystals in a Pancharatnam configuration, then
  split in a polarizing beamsplitter. Both beams are re-imaged onto
  the same Electron-Multiplying CCD camera. We present the design of
  the ExPo instrument, highlighting the elements that are critical to
  the polarimetric performance. Some prototype laboratory experiments
  demonstrating the instrument concept are discussed. These have been
  performed using our realistic exoplanet laboratory simulator.

---------------------------------------------------------
Title: Design of a laboratory simulator to test exoplanet imaging
    polarimetry
Authors: Jeffers, S. V.; Miesen, N.; Rodenhuis, M.; Keller, C. U.
2008SPIE.7014E..7BJ    Altcode: 2008SPIE.7014E.239J
  Research on extrasolar planets is one of the most rapidly advancing
  fields of astrophysics. In just over a decade since the discovery of
  the first extra-solar planet orbiting around 51 Pegasi, 289 extrasolar
  planets have been discovered. This breakthrough is the result of
  the development of a wide range of new observational techniques
  and facilities for the detection and characterisation of extrasolar
  planets. In Utrecht we are building the Extreme Polarimeter (ExPo)
  to image extra-solar planets and circumstellar environments using
  polarimetry at contrast ratio of 10<SUP>-9</SUP>. To test and calibrate
  ExPo, we have built a laboratory-based simulator that mimics a star
  with a Jupiter-like exoplanet as seen by the 4.2m William Herschel
  Telescope. The star and planet are simulated using two single-mode
  fibres in close proximity that are fed with a broadband arc lamp with a
  contrast ratio down to 10<SUP>-9</SUP>. The planet is partially linearly
  polarized. The telescope is simulated with two lenses, and seeing can
  be included with a rotating glass plate covered with hairspray. In this
  paper we present the scientific requirements and the simulator design.

---------------------------------------------------------
Title: SPEX: an in-orbit spectropolarimeter for planetary exploration
Authors: Snik, Frans; Karalidi, Theodora; Keller, Christoph; Laan,
   Erik; ter Horst, Rik; Navarro, Ramon; Stam, Daphne; Aas, Christina;
   de Vries, Johan; Oomen, Gijs; Hoogeveen, Ruud
2008SPIE.7010E..15S    Altcode: 2008SPIE.7010E..35S
  SPEX (Spectropolarimeter for Planetary EXploration) is an innovative,
  compact remote-sensing instrument for detecting and characterizing
  aerosols. With its 1-liter volume it is capable of full linear
  spectropolarimetry, without moving parts. High precision polarimetry is
  performed through encoding the degree and angle of linear polarization
  of the incoming light in a sinusoidal modulation of the intensity
  spectrum. This is achieved by using an achromatic quarter-wave retarder,
  an athermal multiple-order retarder and a polarizing beamsplitter
  behind each entrance pupil. Measuring a single intensity spectrum thus
  provides the spectral dependence of the degree and angle of linear
  polarization. Polarimetry has proven to be an excellent tool to study
  microphysical properties (size, shape, composition) of atmospheric
  particles. Such information is essential to better understand the
  weather and climate of a planet. Although SPEX can be used to study
  any planetary atmosphere, including the Earth's, the current design of
  SPEX is tailored to study Martian dust and ice clouds from an orbiting
  platform: a compact module with 9 entrance pupils to simultaneously
  measure intensity spectra from 350 to 800 nm, in different directions
  along the flight direction (including two limb viewing directions). This
  way, both the intensity and polarization scattering phase functions
  of dust and cloud particles within a ground pixel are sampled while
  flying over it. In the absence of significant amounts of dust and
  clouds, the surface properties can be studied. SPEX provides synergy
  with instruments on rovers and landers, as it provides a global view
  of spatial and temporal variations of the planet.

---------------------------------------------------------
Title: New Observations of the Magnetic Vector Field across the
    Solar Disk
Authors: Keller, C. U.; Harvey, J. W.; Henney, C. J.
2008ASPC..384..166K    Altcode: 2008csss...14..166K
  Full disk solar magnetograms have been available for more than three
  decades. However, those maps only show the line-of-sight magnetic
  flux. The physical quantity we really want to know is the magnetic
  field vector along with the filling factor, i.e. the fractional area
  of the resolution element that is occupied by the magnetic field. Since
  August 2003, the SOLIS Vector-SpectroMagnetograph has been recording the
  photospheric magnetic field vector across the full solar disk with high
  sensitivity and resolution. Some of the data are now becoming available
  for beta testing, and the first science results are emerging. Here we
  provide a brief introduction to the instrument and its data products and
  then present some of the data from the first three years of operation.

---------------------------------------------------------
Title: Science Goals of the Extreme Polarimeter (ExPo)
Authors: Jeffers, S. V.; Keller, C. U.; Rodenhuis, M.; Miesen, N.
2007lyot.confE..42J    Altcode:
  To advance our understanding of the formation, evolution and structure
  of extra-solar planetary systems we are building a high-precision
  imaging polarimeter (ExPo). ExPo will initially be located at the 4.2m
  William Herschel Telescope on La Palma. We will use polarimetric
  techniques similar to those developed for high-precision solar
  polarimetry to reach a sensitivity of 10^-5, to polarimetrically
  image and characterize planets and protoplanetary debris discs. I will
  present a review of the proposed data analysis techniques and science
  goals that will be achievable using the significant improvement in
  polarimetric imaging capabilities.

---------------------------------------------------------
Title: Design Options for the Extreme Polarimeter (ExPo)
Authors: Rodenhuis, M.; Keller, C. U.
2007lyot.confQ..43R    Altcode:
  The Extreme Polarimeter, ExPo, is being developed for the detailed
  study of circumstellar disks and exoplanet characterization at the
  4.2-m William Herschel Telescope at La Palma. This imaging polarimeter
  is designed to measure linear polarization at the 10-5 level around
  bright stars at distances outward of about 0.5 arcsec. We will discuss
  the design options for this instrument as well as the advantages and
  disadvantages of specific components such as the Atmospheric Dispersion
  Compensator, the polarising beamsplitting element, the coronograph mask,
  and the polarisation modulator based on either ferroelectric or nematic
  liquid crystals. The merits and disadvantages of each of these will
  be discussed along with the impact of a certain choice on the overall
  instrument performance. Finally, an analysis of several off-the-shelf
  scientific cameras for the actual image recording will be presented.

---------------------------------------------------------
Title: Seething Horizontal Magnetic Fields in the Quiet Solar
    Photosphere
Authors: Harvey, J. W.; Branston, D.; Henney, C. J.; Keller, C. U.;
   SOLIS Team; GONG Team
2007AAS...21010001H    Altcode: 2007BAAS...39S.227H
  The photospheric magnetic field outside of active regions and the
  network has a ubiquitous and dynamic line-of-sight component that
  strengthens away from disk center as expected for a nearly horizontal
  orientation. This component shows a striking time variation with an
  average temporal rms of 1.7 G at 3 arcsec resolution. In our moderate
  resolution observations the nearly horizontal component has a frequency
  variation power law exponent of -1.4 below 1.5 mHz and is spatially
  patchy on scales up to 15 arcsec. <P />The field may be a manifestation
  of changing magnetic connections between eruptions and evolution of
  small magnetic flux elements in response to convective motions. It shows
  no detectable latitude or longitude variations. Preliminary observations
  show no evidence of this field in the 854.2 nm chromosphere.

---------------------------------------------------------
Title: Seething Horizontal Magnetic Fields in the Quiet Solar
    Photosphere
Authors: Harvey, J. W.; Branston, D.; Henney, C. J.; Keller, C. U.;
   SOLIS and GONG Teams
2007ApJ...659L.177H    Altcode: 2007astro.ph..2415H
  The photospheric magnetic field outside of active regions and the
  network has a ubiquitous and dynamic line-of-sight component that
  strengthens from disk center to limb as expected for a nearly horizontal
  orientation. This component shows a striking time variation with an
  average temporal rms near the limb of 1.7 G at ~3" resolution. In our
  moderate-resolution observations the nearly horizontal component has
  a frequency variation power-law exponent of -1.4 below 1.5 mHz and is
  spatially patchy on scales up to ~15". The field may be a manifestation
  of changing magnetic connections between eruptions and evolution of
  small magnetic flux elements in response to convective motions. It
  shows no detectable latitude or longitude variations.

---------------------------------------------------------
Title: The Ba II 4554 / Hβ Imaging Polarimeter for the Dutch Open
    Telescope
Authors: Snik, F.; Bettonvil, F. C. M.; Jägers, A. P. L.;
   Hammerschlag, R. H.; Rutten, R. J.; Keller, C. U.
2006ASPC..358..205S    Altcode:
  In order to expand the high-resolution, multi-wavelength imaging
  capabilities of the Dutch Open Telescope (DOT), an additional
  polarimetric channel based on a 80 mÅ tunable Lyot filter for Ba
  II 4554 and Hβ has been designed and constructed. The large atomic
  mass and the resulting steep line wings, make Ba II 4554 particularly
  suitable for the creation of photospheric Dopplergrams and Stokes-V
  magnetograms. The line also yields a significant degree of linear
  (scattering) polarization for observations near the limb of the Sun,
  which is modified by both horizontal and vertical weak-field topologies
  through the Hanle effect and hyperfine-structure level crossing. The
  polarimeter is based on liquid crystal variable retarders (LCVRs)
  as polarization modulators in combination with the Lyot filter's
  entrance polarizer. The tunability of the LCVRs is exploited to enable
  specific wavelength calibration, selection of the reference frame of
  linear polarization, and optimization of instrumental polarization
  cross-talk, which for the DOT is constant in time. With the future
  Ba II 4554 photospheric magnetograms, we expect to be able to discern
  magnetic structures of about 150 km with field strengths down to 100 G,
  and that Hanle-type observations can be performed at a resolution of
  about 1 arcsec. The range of applicability of Hβ imaging polarimetry
  has to be explored after installation.

---------------------------------------------------------
Title: SOLIS-VSM Solar Vector Magnetograms
Authors: Henney, C. J.; Keller, C. U.; Harvey, J. W.
2006ASPC..358...92H    Altcode: 2006astro.ph.12584H
  The Vector SpectroMagnetograph (VSM) instrument has recorded full-disk
  photospheric vector magnetograms weekly since August 2003 as part
  of the Synoptic Optical Long-term Investigations of the Sun (SOLIS)
  project. After the full deployment of the VSM data processing system,
  a typical observing day will include three Fe I 630.2 nm full-disk
  photospheric vector magnetograms, one full-disk photospheric and
  three Ca II 854.2 nm chromospheric longitudinal magnetograms, along
  with three He I 1083 nm spectroheliograms. The photospheric vector
  magnetograms will be available over the Internet in two stages: first,
  as a quick-look product within minutes of data acquisition, and then
  as a Milne-Eddington inversion product within a day of each observation.

---------------------------------------------------------
Title: High-Resolution Surface Observations and What They Can Tell
    MHD Simulations
Authors: Keller, C. U.
2006ASPC..354....3K    Altcode:
  I review selected state-of-the art observations of the solar
  photosphere at the highest possible spatial resolution with a special
  emphasis on properties that can directly be compared with current
  MHD simulations. Observations of the solar surface have made big
  advances during the last decade thanks to new telescopes and new
  data processing approaches. I will provide an overview of the latest
  observations and discuss parameters such as the rms contrast and other
  statistical parameters that can be directly related to state-of-the-art
  MHD simulations.

---------------------------------------------------------
Title: Solar Carbon Monoxide, Thermal Profiling, and the Abundances
    of C, O, and Their Isotopes
Authors: Ayres, Thomas R.; Plymate, Claude; Keller, Christoph U.
2006ApJS..165..618A    Altcode: 2006astro.ph..6153A
  A solar photospheric “thermal profiling” analysis is presented,
  exploiting the infrared (2.3-4.6 μm) rovibrational bands of carbon
  monoxide (CO) as observed with the McMath-Pierce Fourier transform
  spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere
  by the Shuttle-borne ATMOS experiment. Visible continuum intensities
  and center-limb behavior constrained the temperature profile of the deep
  photosphere, while CO center-limb behavior defined the thermal structure
  at higher altitudes. The oxygen abundance was self-consistently
  determined from weak CO absorptions (for C/O≡0.5). Our analysis
  was meant to complement recent studies based on three-dimensional
  (3D) convection models, which, among other things, have revised the
  historical solar oxygen (and carbon) abundance downward by a factor
  of nearly 2, although in fact our conclusions do not support such a
  revision. Based on various considerations, an ɛ<SUB>O</SUB>=700+/-100
  ppm (parts per million relative to hydrogen) is recommended; the large
  uncertainty reflects the model sensitivity of CO. New solar isotopic
  ratios also are reported: <SUP>12</SUP>C/<SUP>13</SUP>C=80+/-1,
  <SUP>16</SUP>O/<SUP>17</SUP>O=1700+/-220, and
  <SUP>16</SUP>O/<SUP>18</SUP>O=440+/-6-all significantly lower than
  terrestrial. CO synthesis experiments utilizing a stripped down
  version of the 3D model-which has large temperature fluctuations in the
  middle photosphere, possibly inconsistent with CO “movies” from the
  Infrared Imaging Spectrometer (IRIS), and a steeper mean temperature
  gradient than matches visible continuum center-limb measurements-point
  to a lower oxygen abundance (~500 ppm) and isotopic ratios closer
  to terrestrial. A low oxygen abundance from CO-and other molecules
  like OH-thus hinges on the reality of the theoretically predicted
  midphotospheric convective properties.

---------------------------------------------------------
Title: Design of a polarimeter for extrasolar planetary systems
    characterization
Authors: Keller, Christoph U.
2006SPIE.6269E..0TK    Altcode: 2006SPIE.6269E..26K
  Unpolarized light from the central star that is reflected by exoplanets,
  protoplanetary disks, and debris disks becomes partially polarized by
  the reflection process. Imaging polarimetry is therefore the ideal
  way to discriminate between the polarized light from circumstellar
  environments and the unpolarized light from the nearby central star. A
  sensitivity of 10 <SUP>-5</SUP> (fraction of polarized intensity to the
  total intensity) must be achieved to detect exoplanets; 10 <SUP>-4</SUP>
  is sufficient for disks. Based on extensive experience in precision
  polarimetry of the Sun, the newly formed experimental astrophysics group
  at Utrecht University, The Netherlands, will design, build, and use
  a high-precision imaging polarimeter for use at the 4.2-meter William
  Herschel Telescope. Since systematic errors typically limit conventional
  imaging polarimeters to about 10 <SUP>-3</SUP>, laboratory setups
  and theoretical models will be used to understand and then minimize
  and/or calibrate systematic errors. Published catalogues of exoplanets
  and stars that harbor disks will guide extensive observations with
  this new polarimeter. The effort will focus on retrieving fundamental
  properties of circumstellar environments that cannot be obtained with
  other observational approaches.

---------------------------------------------------------
Title: Development of an IFU for diffraction-limited 3D
    spectropolarimetry
Authors: Ren, Deqing; Keller, Christoph; Plymate, Claude
2006SPIE.6269E..5ZR    Altcode: 2006SPIE.6269E.191R
  Ground-based telescopes can achieve diffraction-limited images when
  equipped with adaptive optics (AO). A major limitation of AO is the
  small field of view, which is due to the limited isoplanatic patch
  size. Nevertheless, conventional long-slit spectrographs cannot sample
  the entire AO-corrected field of view in a single exposure. However,
  equipped with a modern, large detector array, the Integral Field
  Unit (IFU) technique will allow a 3-dimensional (3-D) data cube to
  be recorded simultaneously over the entire AO corrected field of
  view, with a conventional long-slit spectrographs. We are building a
  state-of-the-art image slicer IFU for the National Solar Observatory's
  (NSO) McMath-Pierce Solar Telescope (McMP). This will be the first time
  that an advanced image slicer IFU is used for 3-D spectroscopy and
  polarimetry at a solar telescope. The IFU consists of 25 slices that
  will sample a 6.25" x 8" AO corrected field of view simultaneously,
  and produces a 200" long slit for diffraction-limited 3-D spectroscopy
  and polarimetry. This IFU 3-D technique will provide the most high
  spatial, high temporal resolution with high throughput for solar
  spectroscopy and polarimetry. This is critical for state-of-the-art
  spectral diagnosis of solar velocity and magnetic fields. We discuss
  the design, construction, and testing of this new IFU.

---------------------------------------------------------
Title: Mapping sodium distribution in the exosphere of Mercury with
    tip-tilt image stabilization
Authors: Potter, A. E.; Plymate, C.; Keller, C.; Killen, R. M.;
   Morgan, T. H.
2006AdSpR..38..599P    Altcode:
  Mapping the sodium emission about Mercury is a difficult observational
  problem, since Mercury is seen either against the bright daytime sky,
  or against a dark sky at very high air masses. The distribution of
  sodium emission over the surface of Mercury is non-uniform, and changes
  over time. These effects give clues to the processes that produce
  the sodium and control its distribution, so that improved mapping
  of sodium emissions over the Mercury surface will help clarify their
  relative importance. We have adapted an image stabilizer utilizing a
  piezoelectric driven tip-tilt correction mirror for daytime spectral
  imaging of Mercury. The image stabilizer, which was originally developed
  for solar observations at the McMath Pierce solar telescope, results
  in a noticeable improvement in spatial resolution of our Mercury
  sodium images. In this paper we give initial results from use of
  the tip-tilt image stabilizer for observations of Mercury’s sodium
  exosphere. Further systematic observations and improvements are planned
  for the image stabilizer system, as well as experimental observations
  with a low-order adaptive optics system incorporating a commercially
  available 37-actuator deformable mirror.

---------------------------------------------------------
Title: C3Po --- The Ultimate Focal Plane Array for Imaging Polarimetry
    from 200 nm to 20 μm
Authors: Keller, C. U.
2005ASPC..343...33K    Altcode:
  C^3Po is a novel array detector concept that is optimized for highly
  sensitive and precise differential imaging. Chopping between two
  or more independent image states (such as four linearly independent
  polarization states) can be performed at speeds in the kHz domain to
  provide virtually simultaneous images without the need to read out the
  array at kHz frame rates. This allows the technology to be applied
  to large arrays with precise, slow readouts. All independent image
  planes are observed with the same physical pixel on the detector, which
  renders normalized differences between image planes insensitive to the
  gain of individual pixels. The detector concept has 100% geometrical
  fill factor and a quantum efficiency approaching unity. The technology
  can be applied to silicon to cover the 200--1100 nm wavelength range,
  and to infrared-sensitive materials such as HgCdTe or InSb for the
  1-20 μm wavelength range. The detector concept has a wide range of
  potential applications outside of astronomy.

---------------------------------------------------------
Title: High precision polarimetry with the Advanced Technology
    Solar Telescope
Authors: Socas-Navarro, Hector; Elmore, David F.; Keller, Christoph
   U.; Seagraves, Paul H.; Streander, Kim V.; Card, Gregory L.; Warner,
   Mark; Kuhn, Jeffrey R.; Mickey, Donald L.
2005SPIE.5901...52S    Altcode:
  This paper addresses the issue of calibrating the Advanced Technology
  Solar Telescope for high-precision polarimetry, in particular of the
  optical train above the Gregorian station (where suitable calibration
  optics will be placed). Conventional techniques would not be adequate
  for this telescope given its large aperture. Here we explore two
  different methods that are currently being considered by the design
  team. The first one is the "sub-aperture" method, which uses small
  calibration optics above the primary mirror to calibrate a small
  sub-aperture of the system. This calibration is then extended to the
  full aperture by means of actual observations. The second method is
  based on analyzing the polarization observed in a spectral line with
  a peculiar Zeeman pattern, such as the FeII 614.9 nm line, which does
  not produce any intrinsic linear polarization. Numerical simulations
  are presented that show the robustness of both techniques and their
  respective advantages and disadvantages are discussed.

---------------------------------------------------------
Title: Reduction of SOLIS/Vector Spectromagnetograph He I 1083
    nm Observations
Authors: Jones, H. P.; Malanushenko, O. V.; Harvey, J. W.; Henney,
   C. J.; Keller, C. U.
2005AGUSMSP51A..02J    Altcode:
  The SOLIS/Vector Spectromagnetograph (VSM) now continues the
  three-decade record of full-disk He I 1083 nm spectroheliograms from
  NSO/Kitt Peak (see poster by Henney et al.). Although the sensitivity
  of the VSM interim cameras at 1083 nm is far greater than that of
  previous NSO/KP instruments, the observations are compromised by
  strong interference fringes produced within the detectors. We discuss
  in some detail the extent to which this difficulty is overcome
  in the simple algorithm used to produce the synoptic observations
  and explore methods for removing remaining fringe effects for true
  imaging spectroscopy. These techniques include Fourier and Wavelet
  filtering, the flat-fielding algorithm used for earlier NASA/NSO
  Spectromagnetograph (SPM) observations, and physical modeling of the
  detector fringe pattern.

---------------------------------------------------------
Title: The Solar Oxygen Abundance, and the Rare Isotopes of C and O,
    Derived from Infrared Spectra of Carbon Monoxide
Authors: Ayres, T. R.; Plymate, C.; Keller, C.; Kurucz, R. L.
2005AGUSMSP41B..09A    Altcode:
  A detailed abundance analysis is presented for solar oxygen based on
  the ΔV=1 fundamental (4.6~μm) and ΔV=2 (2.3~μm) first-overtone
  rovibrational bands of carbon monoxide observed above the Earth's
  atmosphere at very high spectral resolution and high signal-to-noise by
  the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional
  observations to define the reference photospheric thermal structure
  were taken of the CO fundamental bands in an atmospheric window at
  2145~cm-1 (4.6~μm) using the 1~m FTS of the McMath-Pierce telescope
  at Kitt Peak and a fast tip/tilt image stabilization system. The latter
  allowed measurements at the extreme limb where the highly slanted rays
  probe into the outer layers of the photosphere. High spatial resolution
  "movies" of weak CO lines at disk center taken under excellent seeing
  conditions with the Infrared Imaging Spectrometer (IRIS), also on
  the McMath-Pierce telescope, further constrained thermal and velocity
  fluctuations in the layers in which the abundance-sensitive CO lines
  form. This work is meant to complement a series of recent studies
  which have revised the previously recommended solar oxygen abundance
  downward by nearly a factor of two; although in fact our conclusions
  do not support such a revision. The oxygen abundance recovered in the
  present work is 700±70~ppm (parts per million relative to hydrogen)
  compared with the proposed downward revision to 460±60~ppm, and the
  recommended value of 650±100~ppm of a decade ago. In our analysis,
  a fixed C/O ratio of 0.5, derived in independent work, was assumed;
  so the associated carbon abundance is 350~ppm. New accurate values
  for the solar abundance ratios of the rare isotopes of C and O also
  are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three
  ratios are lower than terrestrial or meteoritic values (indicating
  higher isotopic abundances). We find no evidence in the ATMOS3 spectra
  for measurable 14C16O lines.

---------------------------------------------------------
Title: Are You Being Served? - Solar Data Management at the National
    Solar Observatory
Authors: Hill, F.; Suarez-Sola, I.; Harvey, J. W.; Henney, C. J.;
   Keller, C.; Wampler, S.
2005AGUSMSH43B..04H    Altcode:
  Solar physics is a data driven field, where no progress can be made
  without multi-wavelength and multi-cadence information about the
  sun's behavior. The National Solar Observatory (NSO) has provided
  data to the research community for over 30 years and thus has
  considerable experience in the areas of data processing, archiving,
  and distribution. This presentation will describe the development of
  NSO's data services, outline what lessons have been learned along the
  way, and attempt to forecast the future of data management at NSO.

---------------------------------------------------------
Title: First-Light Instrumentation for the Advanced Technology
    Solar Telescope
Authors: Rimmele, T.; Balasubramaniam, K.; Berger, T.; Elmore, D.;
   Gary, A.; Keller, C.; Kuhn, J.; Lin, H.; Mickey, D.; Pevtsov, A.;
   Robinson, B.; Sigwarth, M.; Soccas-Navarro, H.
2005AGUSMSP34A..03R    Altcode:
  The 4m Advanced Technology Solar Telescope (ATST) is the next
  generation ground based solar telescope. In this paper we provide
  an overview of the ATST post-focus instrumentation. The majority of
  ATST instrumentation is located in an instrument Coude lab facility,
  where a rotating platform provides image de-rotation. A high order
  adaptive optics system delivers a corrected beam to the Coude lab
  facility. Alternatively, instruments can be mounted at the Nasmyth
  focus. For example, instruments for observing the faint corona
  preferably will be mounted at Nasmyth where maximum throughput
  is achieved. In addition, the Nasmyth focus has minimum telescope
  polarization and minimum stray light. We give an overview of the
  initial set of first generation instruments: the Visible-Light
  Broadband Imager (VLBI), the Visible Spectro-Polarimeter (ViSP),
  the Near-IR Spectro-Polarimeter (NIRSP), which includes a coronal
  module, and the Visible Tunable Filter. We also discuss the unique and
  efficient approach to the ATST instrumentation, which builds on the use
  of common components such as detector systems, polarimetry packages
  and various opto-mechanical components. For example, the science
  requirement for polarimetric sensitivity (10-5 relative to intensity)
  and accuracy (5'10-4 relative to intensity) place strong constraints
  on the polarization analysis and calibration units. Consequently,
  these systems are provided at the facility level, rather than making
  it part of the requirement for each instrument.

---------------------------------------------------------
Title: SOLIS-VSM Synoptic Products
Authors: Henney, C. J.; Harvey, J. W.; Keller, C. U.
2005AGUSMSP51A..04H    Altcode:
  Since August 2003, the Vector Spectromagnetograph (VSM) instrument has
  recorded full-disk photospheric and chromospheric magnetograms along
  with He I 1083 nm spectroheliograms daily as part of the Synoptic
  Optical Long-term Investigations of the Sun (SOLIS) project. In
  addition, the VSM measured full-disk photospheric vector magnetograms
  weekly. After the full deployment of the VSM data processing system,
  a typical observing day will include three full-disk photospheric
  vector magnetograms. Products from observations for the past year
  and half are expected to become available during the year 2005, these
  include Dopplergrams, equivalent width and line depth images. Besides
  individual full-disk images, several derived products are also or
  soon will be available via the SOLIS web site. These products include
  integrated full-disk magnetogram and helium spectroheliogram time
  series. Additionally, Carrington rotation and daily synoptic maps
  are now available from the photospheric magnetograms. Daily coronal
  hole estimate images using VSM data, along with the creation of solar
  wind source maps will also be available. The VSM synoptic products
  are available on the NSO-SOLIS web site cooperatively by NSF/NSO
  and NASA/GSFC. The National Solar Observatory is operated by AURA,
  Inc. under a cooperative agreement with the National Science Foundation.

---------------------------------------------------------
Title: Adaptive Optics Observations of the Sun
Authors: Keller, Christoph U.
2005sao..conf..119K    Altcode:
  Modern solar observations are performed close to the diffraction
  limit of the existing solar telescopes since important, fundamental
  processes on the Sun occur on scales of a tenth of an arc-second
  and smaller. Spatial resolution is therefore paramount in solar
  observations. Even though solar telescopes have relatively small
  apertures as compared to modern night-time telescopes, their spatial
  resolution is still limited by seeing, which is worse during the
  day as compared to at night. Adaptive optics has thus become an
  important addition to almost all large solar telescopes. While the
  first solar adaptive optics system was among the first to be used at
  astronomical telescopes, only in the past few years have such systems
  become available for regular science use. Publications of solar science
  obtained with adaptive optics are therefore still rare, but their number
  is rapidly increasing. Here I discuss the existing solar adaptive optics
  systems and summarize some of the science they have produced to date.

---------------------------------------------------------
Title: Helicity and the SOLIS Vector-Spectromagnetograph
Authors: Keller, Christoph U.; Harvey, John W.; Henney, Carl. J.;
   Jones, Harrison P.
2005HiA....13..126K    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun)
  is a suite of three innovative instruments that greatly improve
  ground-based synoptic solar observations. The main instrument the
  Vector Spectro-Magnetograph (VSM) is a compact high-throughput
  vector-polarimeter that measures the magnetic field strength and
  direction over the full solar disk within 15 minutes. Helicity can
  be directly calculated from the full-disk vector field data provided
  by the Stokes inversion of the observed polarized line profiles. We
  present an anlysis of the difficulties and problems that one faces
  when interpreting the the helicity derived from VSM data.

---------------------------------------------------------
Title: Radio Observations of the Quiet Sun
Authors: Keller, Christoph U.; Krucker, Säam
2004ASSL..314..287K    Altcode:
  While radio observations of the Sun have mostly focused on active
  region phenomena, they also contribute unique data to our knowledge
  of the quiet Sun, in particular through accurate measurements of the
  temperature as a function of height in the atmosphere and through the
  measurement of nonthermal emissions from chromospheric and coronal
  heating events. Here we review observations of the quiet Sun using
  radio telescopes and discuss current science problems that will be
  addressed with future facilities such as the Frequency Agile Solar
  Radiotelescope (FASR).

---------------------------------------------------------
Title: Instrumentation for the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Hubbard, Robert P.; Balasubramaniam,
   K. S.; Berger, Tom; Elmore, David; Gary, G. Allen; Jennings, Don;
   Keller, Christoph; Kuhn, Jeff; Lin, Haosheng; Mickey, Don; Moretto,
   Gilberto; Socas-Navarro, Hector; Stenflo, Jan O.; Wang, Haimin
2004SPIE.5492..944R    Altcode:
  The 4-m aperture Advanced Technology Solar Telescope (ATST) is the
  next generation ground based solar telescope. In this paper we provide
  an overview of the ATST post-focus instrumentation. The majority of
  ATST instrumentation is located in an instrument Coude lab facility,
  where a rotating platform provides image de-rotation. A high order
  adaptive optics system delivers a corrected beam to the Coude lab
  facility. Alternatively, instruments can be mounted at Nasmyth or
  a small Gregorian area. For example, instruments for observing the
  faint corona preferably will be mounted at Nasmyth focus where maximum
  throughput is achieved. In addition, the Nasmyth focus has minimum
  telescope polarization and minimum stray light. We describe the set of
  first generation instruments, which include a Visible-Light Broadband
  Imager (VLBI), Visible and Near-Infrared (NIR) Spectropolarimeters,
  Visible and NIR Tunable Filters, a Thermal-Infrared Polarimeter &amp;
  Spectrometer and a UV-Polarimeter. We also discuss unique and efficient
  approaches to the ATST instrumentation, which builds on the use of
  common components such as detector systems, polarimetry packages and
  various opto-mechanical components.

---------------------------------------------------------
Title: Solar and Space Weather Radiophysics - Current Status and
    Future Developments
Authors: Gary, D. E.; Keller, C. U.
2004ASSL..314.....G    Altcode: 2004sswr.book.....G
  The book explores what can be learned about the Sun and interplanetary
  space using present-day and future radio observations and
  techniques. The emphasis is on interpretation of radio data with high
  spatial and spectral resolution, motivated by the planned construction
  of a new, powerful, solar-dedicated radio array called the Frequency
  Agile Solar Radiotelescope (FASR). The book is unique in exploring a
  broad frequency range, which corresponds to heights ranging from the
  low solar atmosphere out to the Earth. The book contains a thorough
  review of the entire field of solar and Space Weather radio research;
  gives background information suitable for advanced undergraduates,
  graduates, and researchers in solar and Space Weather research and
  related fields; and looks at what new results may be expected in
  the next two decades with FASR and other new instruments now under
  development. The individual chapters are written by international
  experts in each topic, and although each chapter may be read as a
  stand-alone article, the ordering of the chapters and the topical
  development makes the book readable from beginning to end, to provide
  an excellent understanding of the field as a whole.

---------------------------------------------------------
Title: Evaluation of Seeing-Induced Cross Talk in Tip-Tilt-Corrected
    Solar Polarimetry
Authors: Judge, Philip G.; Elmore, David F.; Lites, Bruce W.; Keller,
   Christoph U.; Rimmele, Thomas
2004ApOpt..43.3817J    Altcode:
  We reanalyze the effects of atmosphere-induced image motions on the
  measurement of solar polarized light using a formalism developed by
  Lites. Our reanalysis is prompted by the advent of adaptive optics (AO)
  systems that reduce image motion and higher-order aberrations, by the
  availability of liquid crystals as modulation devices, and by the need
  to understand how best to design polarimeters for future telescopes
  such as the Advanced Technology Solar Telescope. In this first attempt
  to understand the major issues, we analyze the influence of residual
  image motion (tip-tilt) corrections of operational AO systems on the
  cross talk between Stokes parameters and present results for several
  polarization analysis schemes. Higher-order wave-front corrections are
  left for future research. We also restrict our discussion to the solar
  photosphere, which limits several important parameters of interest,
  using some recent magnetoconvection simulations.

---------------------------------------------------------
Title: Improved Spatial Resolution of the Sodium Distribution
    on Mercury
Authors: Potter, A. E.; Plymate, C.; Keller, C.; Killen, R. M.;
   Morgan, T. H.
2004AAS...204.6407P    Altcode: 2004BAAS...36R.780P
  The distribution of sodium emission over the surface of Mercury
  is non-uniform, and changes over time. These non-uniformities and
  time-dependent changes give clues to the processes that produce the
  sodium. However, observations of the distribution of sodium on Mercury
  are hampered by the bad seeing that accompanies the need to observe
  either in daytime, or at extremely large air masses in twilight. In
  an effort to improve this situation, we have developed an image
  stabilizer utilizing a piezoelectric driven tip-tilt correction mirror
  for daytime spectral imaging of Mercury. The system is a modification
  of one that was originally developed for solar observations at the
  McMath-Pierce solar telescope. Use of image stabilization results in
  a noticeable improvement in spatial resolution of our Mercury sodium
  images. A series of sodium images taken over an eight-day period
  show changes in which an emission peak in high southern latitudes
  disappears, and is replaced by an emission peak at high northern
  latitudes. Further systematic observations and improvements are planned
  for the image stabilizer system, as well as experimental observations
  with a low-order adaptive optics system incorporating a commercially
  available 37-actuator deformable mirror. <P />This work was supported
  by the NASA Planetary Astronomy Program.

---------------------------------------------------------
Title: High-accuracy Multiangle Spectropolarimetric Imaging Concept
    for Aerosol Remote Sensing from Space
Authors: Diner, D. J.; Chipman, R. A.; Cairns, B.; Foo, L. D.; Keller,
   C. U.; Macenka, S. A.; Bruce, C. F.
2004AGUSMGC51A..07D    Altcode:
  Satellite remote sensing has a key role in measuring the distribution,
  radiative impact, and regional and global spatial context of
  tropospheric aerosols. A synergistic combination of multispectral,
  multiangle, and polarimetric approaches would improve the accuracies of
  aerosol optical depth and particle property characterizations compared
  to what is achievable using each method by itself. In this paper we
  discuss the science benefits and technical feasibility of combining
  key attributes of multiple aerosol remote sensing instruments into a
  single instrument package. The features of the conceptual instrument
  are: spectral coverage from the near-UV to the shortwave infrared;
  global coverage within a few days; intensity and polarimetric imaging
  simultaneously at multiple view angles; kilometer to sub-kilometer
  spatial resolution; and measurement of the degree of linear polarization
  in one visible and one shortwave-infrared spectral band, i.e., a
  subset of the full spectral complement, with an uncertainty of 0.5%
  or less. The polarimetric accuracy is the driving requirement of the
  instrument design, and is stipulated in order to achieve uncertainty
  goals in optical depth (0.01) and single scattering albedo (0.03) that
  appear difficult to reach given the current state-of-the-art of the
  calibration of intensity-only measurements. Bispectral polarimetry is
  invoked to enable size-resolved retrievals of particle real refractive
  index. After examining many approaches and technologies for imaging
  polarimetry, we conclude that ultrafast time-multiplexing is the best
  option for meeting the instrument performance requirements. The approach
  is based upon innovative advances in high-precision imaging polarimetry
  developed for ground-based solar astronomy. Rapid modulation of the
  linear polarization Stokes components Q and U, coupled with synchronous
  demodulation in a charge-caching focal plane, provides two essential
  benefits: (1) the same detector is used to measure the relative
  proportions of Q or U to the total intensity, thus circumventing
  inaccuracies introduced by detector gain changes or uncertainties in
  flight, and (2) rapid interlacing of the measurements at sub-pixel
  scale insulates against false polarization signals as the spacecraft
  flies over a spatially varying scene. Technology advances needed to
  implement this approach are identified.

---------------------------------------------------------
Title: On the Origin of Solar Faculae
Authors: Keller, C. U.; Schüssler, M.; Vögler, A.; Zakharov, V.
2004ApJ...607L..59K    Altcode:
  Solar faculae appear as bright small features close to the solar
  limb. Recent high-resolution images show these brightenings in
  unprecedented detail. Our analysis of numerical MHD simulations
  reproduces the observed small-scale features. The simulations reveal
  that faculae originate from a thin layer within granules just below
  largely transparent magnetic flux concentrations. This is basically
  the “bright wall” model of Spruit. The dark, narrow lanes often
  associated with faculae occur at the opposite side of the magnetic flux
  concentration and are due to an extended layer with lower-than-average
  temperature.

---------------------------------------------------------
Title: SOLIS-VSM Longitudinal Magnetogram Calibration
Authors: Henney, C. J.; Harvey, J. W.; Keller, C. U.; Jones, H. P.
2004AAS...204.3702H    Altcode: 2004BAAS...36..709H
  The VSM (Vector SpectroMagnetograph) instrument started recording
  daily full-disk magnetograms during August, 2003 at a temporary
  site in Tucson, Arizona. Along with the other instruments that
  constitute the SOLIS (Synoptic Optical Long-term Investigations of
  the Sun) project, the VSM will be relocated to Kitt Peak in April,
  2004. The VSM instrument provides a unique record of solar full-disk
  vector magnetograms along with the high sensitivity photospheric and
  chromospheric longitudinal magnetograms. In addition, the VSM takes
  daily full-disk He I 1083 nm equivalent width observations. These
  parameter-grams are constructed from individual scans in declination
  of the projected solar image on the entrance slit with a relatively
  large field angle of over a half of a degree in the spectrograph. The
  calibration of the VSM longitudinal magnetic observations is reviewed,
  along with a comparison between the VSM mean field, sun-as-a-star,
  measurements with those by the Wilcox Solar Observatory. In addition,
  the making of synoptic maps derived from the VSM magnetograms is
  discussed, including the filling of data gaps in polar regions and
  the use of accompanying weight maps. VSM magnetograms and synoptic
  maps are available via the Internet at: http://solis.nso.edu/. This
  research was supported in part by the Office of Naval Research Grant
  N00014-91-J-1040. The National Solar Observatory is operated by AURA,
  Inc. under a cooperative agreement with the National Science Foundation.

---------------------------------------------------------
Title: Early Results from SOLIS
Authors: Harvey, J.; Giampapa, M.; Henney, C.; Keller, C.; Jones, H.
2004AAS...204.3701H    Altcode: 2004BAAS...36..708H
  SOLIS (Synoptic Optical Long-Term Investigations of the Sun)
  is a project that is replacing antiquated synoptic observing
  equipment at the National Solar Observatory. SOLIS consists of
  a suite of three instruments on an equatorial mount that will be
  installed on Kitt Peak in April 2004. The major SOLIS instrument
  is a vector spectromagnetograph (VSM) that maps magnetic fields
  across the full solar disk using a slit spectrograph and one arc
  sec pixels. Limited daily observations started at a temporary site
  in August, 2003 and include line-of-sight component magnetograms in
  the photosphere and chromosphere and, for the first time, full-disk
  vector magnetograms. At a medium scan speed ( ∼ 10 minutes for the
  full disk) noise is less than 1 Mx/cm<SUP>2</SUP>. This low noise,
  combined with negligible instrumental polarization and well resolved
  spectral line profiles, yields moderate resolution magnetograms of
  unprecedented quality. Observations show magnetic flux nearly everywhere
  in the photosphere from the disk center to the solar limb. Weak,
  intranetwork fields are now routinely observed and show a tendency to
  be of opposite polarity to the stronger surrounding fields. Diffuse
  fields surround decaying active regions and appear to be distinct from
  canopy fields. Vector magnetograms easily show the radial orientation
  of network fields, and the diffuse component surrounding decaying active
  regions. Near the disk center, the transverse magnetic fields of network
  elements change on a time scale of minutes. Detailed quantitative
  calibration of the observations is in progress. Good results have been
  obtained from the other SOLIS instruments: a full-disk filter imager at
  several narrow wavelengths and a double-pass grating spectrograph that
  provides high-accuracy line spectra of integrated sunlight. SOLIS data
  are freely available via the Internet and users are invited to submit
  observing time requests for special observations. The National Solar
  Observatory is operated by AURA, Inc. under a cooperative agreement
  with the National Science Foundation. Additional support for the
  development of SOLIS from NASA and ONR is gratefully acknowledged.

---------------------------------------------------------
Title: Innovative Information Technology for Space Weather Research
Authors: Wang, H.; Qu, M.; Shih, F.; Denker, C.; Gerbessiotis, A.;
   Lofdahl, M.; Rees, D.; Keller, C.
2004AAS...204.5209W    Altcode: 2004BAAS...36..755W
  Solar activity is closely related to the near earth environment --
  summarized descriptively as space weather. Changes in space weather
  have adverse effect on many aspects of life and systems on earth and in
  space. Real-time, high-quality data and data processing would be a key
  element to forecast space weather promptly and accurately. Recently,
  we obtained a funding from US National Science Foundation to apply
  innovative information technology for space weather prediction. <P />(1)
  We use the technologies of image processing and pattern recognition,
  such as image morphology segmentation, Support Vector Machines (SVMs),
  and neural networks to detect and characterize three important solar
  activities in real-time: filament eruptions, flares, and emerging flux
  regions (EFRs). Combining the real time detection with the recent
  statistical study on the relationship among filament eruptions,
  flares, EFRs, coronal mass ejections (CMEs), and geomagnetic storms,
  we are establishing real time report of solar events and automatic
  forecasting of earth directed CMEs and subsequent geomagnetic storms. <P
  />(2) We combine state-of-art parallel computing techniques with phase
  diverse speckle imaging techniques, to yield near real-time diffraction
  limited images with a cadence of approximately 10 sec. We utilize the
  multiplicity of parallel paradigms to optimize the calculation of phase
  diverse speckle imaging to improve calculation speed. With such data,
  we can monitor flare producing active regions continuously and carry
  out targeted studies of the evolution and flows in flare producing
  active regions. <P />(3) We are developing Web based software tools to
  post our processed data, events and forecasting in real time, and to
  be integrated with current solar activity and space weather prediction
  Web pages at BBSO. This will also be a part of Virtual Solar Observatory
  (VSO) being developed by the solar physics community. <P />This research
  is supported by NSF ITR program.

---------------------------------------------------------
Title: Evershed Flow of CO at Different Depths in a Sunspot Penumbra.
Authors: Clark, T. Alan; Plymate, C.; Bergman, M. W.; Keller, C. U.
2004AAS...204.3720C    Altcode: 2004BAAS...36..712C
  CO lines of different strengths near 4.7 microns have been used to
  observe Evershed flow of molecular gas in the penumbra of a large
  sunspot near to the solar limb. An adaptive optics system and IR
  camera on the main spectrograph of the McMath-Pierce Solar Telescope
  produced a sequence of diffraction-limited spectral-spatial images to
  0.8 arc-second resolution as the telescope was scanned across this
  sunspot. Dopplergrams constructed from this sequence for several
  of these CO lines have been used to outline the characteristics of
  this molecular flow as a function of depth within the penumbra. <P
  />Particularly noteworthy in these Dopplergrams is the change in
  pattern of high-speed outflow, from a radial direction deep in the
  penumbra from weak-line images, matching the structure in the continuum
  penumbral image, to a spiral pattern more closely resembling the
  appearance of penumbral structure at chromospheric heights. Typical
  weak-line flow speeds were a few km/s, significantly lower than those
  measured recently by Penn et al.,(2003) for weak CH lines at shorter
  wavelengths, which are postulated to originate in dark fibrils deeper
  in the penumbra. Strong CO-line images show lower flow speeds. Small
  regions of narrow inverse Evershed flow channels appear in these latter
  images near to the outer penumbral boundary. For all lines, the speed of
  the Evershed flow reaches a maximum just before this boundary and all
  flow appears to cease at or just beyond it. <P />Future Evershed flow
  investigations will include observations of other potentially useful
  spectral features within this spectral range such as weak OH lines,
  in addition to several atomic FeI and SiI lines whose high Zeeman
  sensitivity make them suitable for simultaneous penumbral magnetic
  field mapping. <P />Penn, M.J, et al., Ap.J. 590, L119, 2003.

---------------------------------------------------------
Title: Measurement Scale of the SOLIS Vector Spectromagnetograph
Authors: Jones, H. P.; Harvey, J. W.; Henney, C. J.; Keller, C. U.;
   Malanushenko, O. M.
2004AAS...204.3703J    Altcode: 2004BAAS...36Q.709J
  Longitudinal magnetograms obtained with the SOLIS Vector
  Spectromagnetograph (VSM) during a cross-calibration period are
  compared with similar data from the NASA/NSO Spectromagnetograph (SPM)
  at the NSO/Kitt Peak Vacuum Telescope as well as with SOHO/MDI and GONG
  magnetograms. The VSM began observations at the University of Arizona
  agricultural test site and collaborative observations were obtained
  with both the VSM and SPM from 2003 Aug 05 through 2003 Sep 21 when
  the SPM was officially retired. The VSM replaces the SPM and continues
  the 30-year NSO/Kitt Peak synoptic magnetogram record. Magnetograms
  are compared by equating histograms and, for selected examples, by
  pixel-by-pixel comparison of coregistered images. The VSM was not
  corrected for polarization crosstalk and was operated without fast
  guiding. Solar activity was at best moderate during this period. Over
  the range of observed fields, the VSM magnetograms show greatly
  improved sensitivity but are otherwise virtually identical with "raw"
  SPM magnetograms. GONG magnetograms are also closely comparable with
  the SPM while MDI flux values tend to be stronger by a factor of 1.2 -
  1.4. Dependence of the results on seeing will be discussed. Partial
  funding for this work was provided through Solar and Heliospheric
  Research Supporting Research and Technology grants from NASA's Office
  of Space Sciences.

---------------------------------------------------------
Title: Advanced Technology Solar Telescope: a progress report
Authors: Oschmann, Jim; Dalrymple, Nathan; Warner, Mark; Price, Ron;
   Hill, Frank; Hubbard, Rob; Rimmele, Thomas R.; Keller, Christoph U.;
   Keil, Stephen
2004SPIE.5171..160O    Altcode:
  The 4m ATST will be the most powerful solar telescope in the world,
  providing a unique scientific tool to study the Sun and other
  astronomical objects. The design and development phase for the Advance
  Technology Solar Telescope (ATST) is progressing. The conceptual design
  review (CoDR) for the ATST is scheduled for August 2003. We present a
  brief description of the science requirements of ATST, and remind the
  reader of some of the technical challenges of building a 4-m solar
  telescope. We will discuss some of the design strategies that will
  allow us to achieve the required performance specifications, present
  conceptual designs for the ATST, and summarize the results of trades
  we have made on our path to the CoDR. The thermal impacts to local,
  self-induced seeing with respect to some of our system level trades
  that have been completed will be discussed.

---------------------------------------------------------
Title: High-speed cameras and solar observing
Authors: Harvey, John; Keller, Christoph U.; Cole, Lonnie; Tucker,
   Roy; Jaksha, David
2004SPIE.5171..258H    Altcode:
  The National Solar Observatory operates two facilities with
  demanding needs for rapid image collection (i.e. &gt; television
  frame rates). The first is GONG, a global network of six identical
  small telescopes devoted to nearly continuous observations of the
  sun's surface vibrations in order to study its internal properties by
  helioseismology. The second, SOLIS, is a suite of three instruments
  that collects images and spectra of the sun needed to study the behavior
  of solar activity on time scales of minutes to decades. Five different
  types of cameras are installed in these instruments. High speed, high
  sensitivity, large dynamic range, and good photometric performance
  are key factors for cameras used to make measurements of subtle solar
  signals that pass through the noisy terrestrial atmosphere. A camera
  that combines all these characteristics is elusive. The combination
  of high speed and good photometric performance, when observing small
  intensity changes, is particularly hard to get in practice. High speed
  in large format CCD and hybrid FPA cameras is achieved by dividing the
  array into multiple channels that are read simultaneously. An unwanted
  result of this technique is cross talk between signal channels. It
  is of order 1 percent in the case of Silicon Mountain Design 1M60_20
  cameras (1k x 1k, 60 fps) and Rockwell Scientific Company HyViSI-1024
  cameras (1k x 256, 92 fps). Cross talk (and also successive-frame image
  retention) are particularly hard to deal with since they may exhibit
  non-linear characteristics that depend on illumination light level. We
  describe these and other phenomena, attempts to mitigate the effects,
  and results from solar observations.

---------------------------------------------------------
Title: Charge caching CMOS detector for polarimetry (C<SUP>3</SUP>Po)
Authors: Keller, Christoph U.
2004SPIE.5171..239K    Altcode:
  C<SUP>3</SUP>Po is a concept for a novel array detector concept that
  is optimized for highly sensitive and precise differential imaging
  such as needed for astrophysical polarimetry. Chopping between two
  or more independent image states (such as four linearly independent
  polarization states) can be performed at speeds in the kHz domain to
  provide virtually simultaneous images without the need to read out the
  array at kHz frame rates. This allows the technology to be applied
  to large arrays with precise, slow readouts. All independent image
  planes are observed with the same physical pixel on the detector, which
  renders normalized differences between image planes insensitive to the
  gain of individual pixels. The detector concept has 100% geometrical
  fill factor and a quantum efficiency approaching unity. The technology
  can be applied to silicon to cover the 200-1100 nm wavelength range,
  and to infrared-sensitive materials such as HgCdTe or InSb for the
  1-20 μm wavelength range. While the detector concept has a wide range
  of potential applications outside of astronomy, we focus here on its
  application to polarimetric observations of the Sun.

---------------------------------------------------------
Title: Mapping sodium distribution on the surface of Mercury
Authors: Potter, A.; Plymate, C.; Keller, C.; Killen, R.; Morgan, T.
2004cosp...35.1293P    Altcode: 2004cosp.meet.1293P
  The distribution of sodium emission over the surface of Mercury
  is non-uniform, and changes over time. These non-uniformities and
  time-dependent changes give clues to the processes that produce
  sodium. Photon-stimulated desorption may be the major sodium source
  process on Mercury, so the sodium density might be expected to maximize
  at the subsolar point. Another source process may be sputtering by
  solar particles that impact the surface at high latitudes in the polar
  cusps, producing sodium emissions at these locations. Variations in
  the geographic distribution of sodium-rich minerals might produce
  localized emissions that do not change position with time. Mapping the
  sodium emission is a difficult observational problem, since Mercury is
  seen either against the bright daytime sky, or against a dark sky at
  very high air masses. We have adapted an image stabilizer utilizing a
  piezoelectric driven tip-tilt correction mirror for daytime spectral
  imaging of Mercury. The image stabilizer was originally developed
  for solar observations at the McMath-Pierce solar telescope. Use of
  image stabilization results in a noticeable improvement in spatial
  resolution of our Mercury sodium images. A series of sodium images
  taken over an eight-day period show changes in which an emission peak
  in high southern latitudes disappears, and is replaced by an emission
  peak at high northern latitudes. Further systematic observations and
  improvements are planned for the image stabilizer system, as well
  as experimental observations with a low-order adaptive optics system
  incorporating a commercially available 37-actuator deformable mirror.

---------------------------------------------------------
Title: First Results from SOLIS
Authors: Harvey, J.; Giampapa, M.; Henney, C.; Jones, H.; Keller, C.
2003AGUFMSH42B0545H    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a
  project to replace antiquated synoptic observing equipment at the
  National Solar Observatory. SOLIS includes a suite of three instruments
  on an equatorial mount originally installed at a site in Tucson and will
  be moved to Kitt Peak before the end of 2003. The major SOLIS instrument
  is a vector spectromagnetograph that maps magnetic fields across the
  full solar disk using a slit spectrograph and one arc sec pixels. Daily
  observations include several line-of-sight component magnetograms in the
  photosphere and chromosphere and, for the first time, full-disk vector
  magnetograms. At a medium scan speed ( ∼10 minutes for the full disk)
  noise is less than 1 Mx/cm<SUP>2</SUP>. This low noise, combined with
  negligible instrumental polarization and well resolved spectral line
  profiles, yields moderate resolution magnetograms of unprecedented
  quality. Sample observations show magnetic flux nearly everywhere
  in the photosphere from the disk center to the solar limb. The flux
  is organized in large scale patterns that heretofore had been visible
  only in strong flux elements or after substantial spatial smearing. Good
  results have been obtained from the other SOLIS instruments: a full-disk
  filter imager at several narrow wavelengths and a grating spectrograph
  that provides high-accuracy line spectra of integrated sunlight. SOLIS
  data are freely available via the Internet and users may submit
  observing time requests for special observations. The National Solar
  Observatory is operated by AURA, Inc. under a cooperative agreement
  with the National Science Foundation. Additional support for the
  development of SOLIS from NASA and ONR is gratefully acknowledged.

---------------------------------------------------------
Title: Linear Polarization Measurements of Chromospheric Emission
    Lines
Authors: Sheeley, N. R., Jr.; Keller, C. U.
2003ApJ...594.1085S    Altcode:
  We have used the Zurich Imaging Stokes Polarimeter (ZIMPOL I)
  with the McMath-Pierce 1.5 m main telescope on Kitt Peak to obtain
  linear polarization measurements of the off-limb chromosphere with a
  sensitivity better than 1×10<SUP>-5</SUP>. We found that the off-disk
  observations require a combination of good seeing (to show the emission
  lines) and a clean heliostat (to avoid contamination by scattered light
  from the Sun's disk). When these conditions were met, we obtained the
  following principal results:1. Sometimes self-reversed emission lines
  of neutral and singly ionized metals showed linear polarization caused
  by the transverse Zeeman effect or by instrumental cross talk from the
  longitudinal Zeeman effect in chromospheric magnetic fields. Otherwise,
  these lines tended to depolarize the scattered continuum radiation
  by amounts that ranged up to 0.2%.2. Lines previously known to show
  scattering polarization just inside the limb (such as the Na I λ5889 D2
  and the He I λ5876 D3 lines) showed even more polarization above the
  Sun's limb, with values approaching 0.7%.3. The O I triplet at λ7772,
  λ7774, and λ7775 showed a range of polarizations. The λ7775 line,
  whose maximum intrinsic polarizability, P<SUB>max</SUB>, is less than
  1%, revealed mainly Zeeman contributions from chromospheric magnetic
  fields. However, the more sensitive λ7772 (P<SUB>max</SUB>=19%) and
  λ7774 (P<SUB>max</SUB>=29%) lines had relatively strong scattering
  polarizations of approximately 0.3% in addition to their Zeeman
  polarizations. At times of good seeing, the polarization spectra
  resolve into fine structures that seem to be chromospheric spicules.

---------------------------------------------------------
Title: Calibration and Data Analysis for the SOLIS-VSM
Authors: Henney, C. J.; Harvey, J. W.; Keller, C. U.; Jones, H. P.;
   SOLIS Team
2003SPD....34.0303H    Altcode: 2003BAAS...35..808H
  The Vector Spectromagnetograph (VSM) instrument of the Synoptic
  Optical Long-term Investigations of the Sun (SOLIS) project will
  provide a unique 25-year record of synoptic solar observations with
  daily full-disk photospheric vector and high sensitivity longitudinal
  magnetograms. In addition, the VSM will produce daily full-disk
  chromospheric longitudinal magnetograms along with various He I 1083
  nm parameter images. The VSM is being prepared for installation at a
  temporary site in Tucson for a comparison period with observations from
  the Kitt Peak Vacuum Telescope (KPVT). After the cross-calibration
  period, the VSM will replace the KPVT spectromagnetograph at Kitt
  Peak. We outline the various VSM data products, with emphasis on the
  calibration and data reduction efforts. <P />The data transmission
  and storage resources are such that the reduction of VSM data will be
  performed at the observing site on Kitt Peak. Reduced data products
  will be transmitted via a DS3 link from Kitt Peak to the National Solar
  Observatory's digital archive in Tucson. During a typical observing day,
  three full-disk photospheric vector magnetograms will be available over
  the Internet in two stages: first, as a “quick-look” product within
  10 minutes of data acquisition, and then as a full Milne-Eddington
  (ME) inversion product within 12 hours of each observation. The
  quick-look parameters will include estimates of the magnetic field
  strength, azimuth and inclination based on Auer, Heasley, House (1977,
  Solar Physics 55, p. 47). The high-precision vector products will be
  determined with the High Altitude Observatory ME inversion technique
  implemented by Skumanich and Lites (1987, ApJ, 322, p.473). The
  flexible design of the VSM data handling system can incorporate
  future improvements under consideration (e.g., principal component
  analysis). <P />This research was supported in part by the Office of
  Naval Research Grant N00014-91-J-1040.

---------------------------------------------------------
Title: Advanced Technology Solar Telescope - Approach to a Four-meter
    Diffraction Limited Solar Telescope
Authors: Keil, S.; Rimmele, T.; Oschmann, J.; Warner, M.; Dalrymple,
   N.; Hubbard, R.; Price, R.; Goodrich, B.; Keller, C.; ATST Team
2003SPD....34.2019K    Altcode: 2003BAAS...35..847K
  The Advanced Technology Solar Telescope (ATST) is intended to be
  the next major step in ground based solar observatories. The ATST
  will provide a laboratory for ultra high resolution, polarimetric
  measurements of all layers of the solar atmosphere. Currently the
  project is preparing a conceptual design to fulfill this mission,
  including plans for the design, development, construction and operation
  of this facility. Given the nearly three-fold increase in aperture
  size over the largest existing solar facilities, our approach combines
  techniques from the newest solar facilities with lessons from recent
  nighttime telescope designs. This approach insures the ATST will meet
  the scientific goals that include diffraction-limited performance in
  the optical for high spatial resolution solar observations and very
  low scattered light to advance coronal observation capabilities. The
  current telescope design incorporates the latest active optics
  techniques, fast focal ratios for the primary optics, an open design
  for ventilation of locally produced seeing, an un-obscured off-axis
  pupil and a very high order adaptive optics system built into the
  telescope from the beginning. Examples of some of the current design
  concepts for the telescope structure, optics, thermal management,
  scattered light control, upgrade paths to multi-conjugate adaptive
  optics, software and facilities to support future potential upgrades
  and instrumentation are given along with some of the key challenges
  that lie ahead. <P />The National Solar Observatory is sponsored and
  supported by the National Science Foundation.

---------------------------------------------------------
Title: The SOLIS Vector-Spectromagnetograph (VSM)
Authors: Keller, C. U.; SOLIS Team
2003SPD....34.2023K    Altcode: 2003BAAS...35..848K
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is
  a suite of three innovative instruments that will greatly improve
  ground-based synoptic solar observations. The main instrument, the
  Vector Spectro-Magnetograph (VSM), is a compact, high-throughput
  vector-polarimeter with an active secondary mirror, an actively
  controlled grating spectrograph, and two high-speed cameras based on
  silicon-on-CMOS-multiplexer hybrid focal plane arrays. It measures
  the photospheric magnetic field strength and direction over the full
  solar disk within 15 minutes using two iron lines at 630 nm. It can
  also record the longitudinal magnetic flux in the chromosphere and
  coronal proxies derived from the HeI 1083 nm spectral line. <P />The
  VSM has just been assembled and is expected to see first light at
  a temporary site in Tucson before the end of May. We will present
  an overview of the instrument, describe its performance, and discuss
  first results. <P />SOLIS has been supported by a specific grant from
  NSF, NSO base funding, NASA/GSFC, and the ONR. The project has also
  received significant technical assistance from HAO and the Solar and
  Astrophysics Lab of Lockheed-Martin.

---------------------------------------------------------
Title: Site testing issues for the frequency agile solar
    radiotelescope (FASR)
Authors: Gary, Dale E.; Keller, Christoph U.
2003SPIE.4853..523G    Altcode:
  The Frequency Agile Solar Radiotelescope (FASR) will be a broadband
  synthesis-imaging array with 3-km or larger baselines, operating over
  a broad frequency range of 0.1-30 GHz. The instrument demands a site
  with low levels of Radio Frequency Interference (RFI) over this entire
  band. The site also must be large enough to accommodate the expected
  size of the array configuration and ideally would provide room to grow
  with future upgrades. The site must have a benign environment in which
  at least 100 separate elements will operate with little degradation
  and weather-related downtime. Several sites in the U.S. are being
  considered. We discuss what criteria are being used to assess the sites,
  and give some initial results of testing some of the sites.

---------------------------------------------------------
Title: Solar polarimetry close to the diffraction limit
Authors: Keller, Christoph U.
2003SPIE.4843..100K    Altcode:
  Much progress has been made during the last years in obtaining
  polarimetric observations of the Sun close to the diffraction
  limit. Here I summarize the problems one encounters when observing close
  to the diffraction limit of a large solar telescope, review techniques,
  present examples of recent observations, and discuss the need for
  further developments of instruments and image reconstruction techniques.

---------------------------------------------------------
Title: PEPSI spectro-polarimeter for the LBT
Authors: Strassmeier, Klaus G.; Hofmann, Axel; Woche, Manfred F.; Rice,
   John B.; Keller, Christoph U.; Piskunov, N. E.; Pallavicini, Roberto
2003SPIE.4843..180S    Altcode:
  PEPSI (Postham Echelle Polarimetric and Spectroscopic Instrument) is
  to use the unique feature of the LBT and its powerful double mirror
  configuration to provide high and extremely high spectral resolution
  full-Stokes four-vector spectra in the wavelength range 450-1100nm. For
  the given aperture of 8.4m in single mirror mode and 11.8m in double
  mirror mode, and at a spectral resolution of 40,000-300,000 as designed
  for the fiber-fed Echelle spectrograph, a polarimetric accuracy between
  10<SUP>-4</SUP> and 10<SUP>-2</SUP> can be reached for targets with
  visual magnitudes of up to 17th magnitude. A polarimetric accuracy
  better than 10<SUP>-4</SUP> can only be reached for either targets
  brighter than approximately 10th magnitude together wiht a substantial
  trade-off wiht the spectral resolution or with spectrum deconvolution
  techniques. At 10<SUP>-2</SUP>, however, we will be able to observe
  the brightest AGNs down to 17th magnitude.

---------------------------------------------------------
Title: SOLIS: an innovative suite of synoptic instruments
Authors: Keller, Christoph U.; Harvey, John W.; Giampapa, Mark S.
2003SPIE.4853..194K    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is
  a suite of three innovative instruments under construction that
  will greatly improve ground-based synoptic solar observations. The
  Vector Spectromagnetograph (VSM) is a compact, high-throughput
  vector-polarimeter with an active secondary mirror, an actively
  controlled grating spectrograph, and two high-speed cameras with
  silicon-on-CMOS-multiplexer hybrid focal plane arrays. It will measure
  the magnetic field strength and direction over the full solar disk
  within 15 minutes. The Full-Disk Patrol (FDP) takes full-disk solar
  intensity and Doppler images in various spectral lines and in the
  continuum at a high cadence through liquid-crystal tuned birefringent
  filters. The Integrated Sunlight Spectrometer (ISS) uses a fiber-fed
  spectrograph to measure minute changes of the Sun-as-a-star in
  many spectral lines. A high degree of automation and remote control
  provides fast user access to data and flexible interaction with the
  data-collection process. SOLIS is currently in the final assembly
  phase and will become operational early in 2003.

---------------------------------------------------------
Title: Design and development of the Advanced Technology Solar
    Telescope (ATST)
Authors: Keil, Stephen L.; Rimmele, Thomas; Keller, Christoph U.;
   Hill, Frank; Radick, Richard R.; Oschmann, Jacobus M.; Warner, Mark;
   Dalrymple, Nathan E.; Briggs, John; Hegwer, Steven L.; Ren, Dauxing
2003SPIE.4853..240K    Altcode:
  High-resolution studies of the Sun's magnetic fields are needed for
  a better understanding of solar magnetic fields and the fundamental
  processes responsible for solar variability. The generation of magnetic
  fields through dynamo processes, the amplification of fields through
  the interaction with plasma flows, and the destruction of fields
  are still poorly understood. There is still incomplete insight as
  to what physical mechanisms are responsible for heating the corona,
  what causes variations in the radiative output of the Sun, and what
  mechanisms trigger flares and coronal mass ejections. Progress in
  answering these critical questions requires study of the interaction
  of the magnetic field and convection with a resolution sufficient to
  observe scales fundamental to these processes. The 4m aperture Advanced
  Technology Solar Telescope (ATST) will be a unique scientific tool,
  with excellent angular resolution, a large wavelength range, and low
  scattered light. With its integrated adaptive optics, the ATST will
  achieve a spatial resolution nearly 10 times better than any existing
  solar telescope. Building a large aperture telescope for viewing the
  sun presents many challenges, some of the more difficult being: · Heat
  control and rejection · Contamination and scattered light control ·
  Control of telescope and instrument polarization · Site selection
  This talk will present a short summary of the scientific questions
  driving the ATST design, the design challenges faced by the ATST, and
  the current status of the developing design and siting considerations

---------------------------------------------------------
Title: Low-cost solar adaptive optics in the infrared
Authors: Keller, Christoph U.; Plymate, Claude; Ammons, S. M.
2003SPIE.4853..351K    Altcode:
  We have developed a low-cost adaptive optics system for solar
  observations in the infrared between 1 and 28 μm with the 1.5-m
  McMath-Pierce solar telescope. The 37-actuator membrane mirror and a
  fast tip-tilt mirror are controlled by a PC running Linux RedHat 7.1
  that analyzes images from a 256 by 256 pixel, 1 kHz frame rate CCD
  camera. The total hardware cost is less than $25,000, and the system
  provides diffraction-limited performance under median seeing conditions
  above 2.3 μm. The single Pentium III processor provides enough
  computing power to analyze the 200 subapertures of the Shack-Hartmann
  wavefront sensor in real time. We describe the hardware and software
  implementations and show results from the first tests at the telescope.

---------------------------------------------------------
Title: Technical challenges of the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Keil, Stephen L.; Keller, Christoph
   U.; Hill, Frank; Briggs, John; Dalrymple, Nathan E.; Goodrich, Bret
   D.; Hegwer, Steven L.; Hubbard, Rob; Oschmann, Jacobus M.; Radick,
   Richard R.; Ren, Deqing; Wagner, Jeremy; Wampler, Stephen; Warner, Mark
2003SPIE.4837...94R    Altcode:
  The 4m Advance Technology Solar Telescope (ATST) will be the most
  powerful solar telescope in the world, providing a unique scientific
  tool to study the Sun and possibly other astronomical objects, such
  as solar system planets. We briefly summarize the science drivers and
  observational requirements of ATST. The main focus of this paper is on
  the many technical challenges involved in designing a large aperture
  solar telescope. The ATST project has entered the design and development
  phase. Development of a 4-m solar telescope presents many technical
  challenges. Most existing high-resolution solar telescopes are designed
  as vacuum telescopes to avoid internal seeing caused by the solar heat
  load. The large aperture drives the ATST to an open-air design, similar
  to night-time telescope designs, and makes thermal control of optics
  and telescope structure a paramount consideration. A heat stop must
  reject most of the energy (13 kW) at prime focus without introducing
  internal seeing. To achieve diffraction-limited observations at visible
  and infrared wavelengths, ATST will have a high order (order 1000
  DoF) adaptive optics system using solar granulation as the wavefront
  sensing target. Coronal observations require occulting in prime focus,
  a Lyot stop and contamination control of the primary. An initial set of
  instruments will be designed as integral part of the telescope. First
  telescope design and instrument concepts will be presented.

---------------------------------------------------------
Title: Design and development of the Advanced Technology Solar
    Telescope
Authors: Keil, S.; Rimmele, T.; Keller, C.; ATST Team
2003AN....324..303K    Altcode:
  Led by the National Solar Observatory, plans have been made to design
  and to develop the Advanced Technology Solar Telescope (ATST). The ATST
  will be a 4-m general-purpose solar telescope equipped with adaptive
  optics and versatile post-focus instrumentation. Its main aim will be
  to achieve an angular resolution of 0.03 arcsec (20 km on the solar
  surface). The project and the telescope design are briefly described.

---------------------------------------------------------
Title: Polarimetry with the ATST (Invited review)
Authors: Keller, C. U.
2003ASPC..286...31K    Altcode: 2003ctmf.conf...31K
  No abstract at ADS

---------------------------------------------------------
Title: Solar observing facilities
Authors: Fleck, B.; Keller, C. U.
2003dysu.book..403F    Altcode:
  An overview is given of current and planned ground-based solar
  telescopes and instruments, balloon-borne and suborbital solar
  telescopes, and solar and heliospheric space missions. These observing
  facilities operate in all areas of solar physics, from the solar
  interior to interplanetary space and from regimes of high energy to
  observations requiring high resolution. The next generation of solar
  telescopes and instruments promise us the ability to investigate solar
  processes on their fundamental scales, whether sub-arc second or global
  in nature.

---------------------------------------------------------
Title: Science Objectives and Technical Challenges of the Advanced
    Technology Solar Telescope (Invited review)
Authors: Rimmele, T.; Keil, S. L.; Keller, C.; Hill, F.; Penn, M.;
   Goodrich, B.; Hegwer, S.; Hubbard, R.; Oschmann, J.; Warner, M.;
   Dalrymple, N.; Radick, R.; Atst Team
2003ASPC..286....3R    Altcode: 2003ctmf.conf....3R
  No abstract at ADS

---------------------------------------------------------
Title: Polarimetry with the Advanced Technology Solar Telescope
Authors: Keller, C. U.
2003ASPC..307...23K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The SOLIS Vector-Spectromagnetograph
Authors: Keller, C. U.; Harvey, J. W.; Solis Team
2003ASPC..307...13K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Helicity and the SOLIS Vector-Spectromagnetograph
Authors: Keller, Christoph U.; Harvey, John W.; Henney, Carl J.;
   Jones, Harrison P.
2003IAUJD...3E..18K    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun)
  is a suite of three innovative instruments that greatly improve
  ground-based synoptic solar observations. The main instrument the
  Vector Spectro-Magnetograph (VSM) is a compact high-throughput
  vector-polarimeter that measures the magnetic field strength and
  direction over the full solar disk within 15 minutes. Helicity can
  be directly calculated from the full-disk vector field data provided
  by the Stokes inversion of the observed polarized line profiles. We
  present an anlysis of the difficulties and problems that one faces
  when interpreting the the helicity derived from VSM data.

---------------------------------------------------------
Title: Data analysis for the SOLIS Vector Spectromagnetograph
Authors: Jones, Harrison P.; Harvey, John W.; Henney, Carl J.; Hill,
   Frank; Keller, Christoph U.
2002ESASP.505...15J    Altcode: 2002solm.conf...15J; 2002IAUCo.188...15J
  The National Solar Observatory's SOLIS Vector Spectromagnetograph, which
  will produce three or more full-disk maps of the Sun's photospheric
  vector magnetic field every day for at least one solar magnetic cycle,
  is in the final stages of assembly. Initial observations, including
  cross-calibration with the current NASA/NSO spectromagnetograph (SPM),
  will soon be carried out at a test site in Tucson. This paper discusses
  data analysis techniques for reducing the raw data, calculation of
  line-of-sight magnetograms, and both quick-look and high-precision
  inference of vector fields from Stokes spectral profiles. Existing
  SPM algorithms, suitably modified to accommodate the cameras, scanning
  pattern, and polarization calibration optics for the VSM, will be used
  to "clean" the raw data and to process line-of-sight magnetograms. A
  recent version of the High Altitude Observatory Milne-Eddington (HAO-ME)
  inversion code will be used for high-precision vector fields.

---------------------------------------------------------
Title: Spectroscopic Detection of the 3.934 Micron Line of Si IX in
    the Solar Corona
Authors: Judge, P. G.; Tomczyk, S.; Livingston, W. C.; Keller, C. U.;
   Penn, M. J.
2002ApJ...576L.157J    Altcode:
  We report the detection of the
  2s<SUP>2</SUP>2p<SUP>2</SUP><SUP>3</SUP>P<SUB>1--&gt;0</SUB> line of
  Si IX using the McMath-Pierce telescope on Kitt Peak. Observations
  were made of the solar disk and at various heights above the limb
  between 2002 May 13 and 17, under nonideal sky conditions, using the
  13.5 m vertical spectrograph and an InSb single-diode detector. We
  report a new rest wavelength for the line and discuss its potential
  use as a diagnostic of coronal magnetic fields using ground-based
  telescopes. Our observations give λ<SUB>rest</SUB>=3.93434+/-0.00007
  μm, consistent with earlier less accurate values, but it places the
  blue wing of the line under a strong telluric N<SUB>2</SUB>O line. In
  the active regions observed, the line's intensity is comparable to or
  larger than predicted in earlier work for the quiet Sun.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Keller, C. U.; Rimmele, T. R.; Hill, F.; Keil, S. L.;
   Oschmann, J. M.; ATST Team
2002AN....323..294K    Altcode:
  The Advanced Technology Solar Telescope is the largest solar optical
  facility currently under development. The National Solar Observatory
  and its partners have just started the design and development phase
  with first light being planned for late this decade. The 4-m telescope
  will provide an angular resolution down to 0.025 arcsec, a large photon
  flux for precise magnetic and velocity field measurements, and access
  to a broad set of diagnostics from 0.3 to 28 mu m. We summarize the
  currently envisioned scientific capabilities of the telescope and its
  suite of instruments along with a glimpse at some of the early concepts.

---------------------------------------------------------
Title: Spatial mapping of the Hanle and Zeeman effects on the Sun
Authors: Stenflo, J. O.; Gandorfer, A.; Holzreuter, R.; Gisler, D.;
   Keller, C. U.; Bianda, M.
2002A&A...389..314S    Altcode:
  Spatial mapping of the Hanle and Zeeman effects on the Sun has been done
  for the first time, through Stokes vector imaging with a narrow-band
  (0.2 Å) universal filter. It is shown how the polarization signatures
  of the Hanle and Zeeman effects can be cleanly distinguished from each
  other by comparing the Stokes images recorded at different, specially
  selected wavelengths within the Na I D<SUB>2</SUB>-D<SUB>1</SUB>
  line system. Examples of the polarization signatures of sunspots,
  faculae, the supergranulation network, and large-scale canopy fields
  are shown. The most striking result of our observations is that the
  scattering polarization has an extremely intermittent structure rather
  than being a simple function of limb distance. These intermittent
  scattering polarization signals are cospatial with the facular
  and supergranulation network seen both in intensity and circular
  polarization. The observed pattern can be explained in terms of magnetic
  enhancement of the scattering polarization in the network and/or Hanle
  depolarization of the scattering polarization outside the network. Since
  however no magnetic fields are seen in circular polarization outside the
  network, the relative absence of linear scattering polarization there
  may be explained by Hanle depolarization only if the volume filling,
  depolarizing magnetic field has mixed polarities on a subarcsec scale
  that is not resolved.

---------------------------------------------------------
Title: Preliminary tests of a low-cost solar infrared adaptive
    optics system
Authors: Ammons, S. M.; Keller, C. U.
2002AAS...200.5610A    Altcode: 2002BAAS...34..736A
  Images produced by the National Solar Observatory's McMath-Pierce
  telescope on Kitt Peak, the largest solar telescope in the world,
  have been at the mercy of atmospheric turbulence for decades. Work
  is currently underway to install a low-cost adaptive optics system
  with the goal of correction in the infrared for a total hardware cost
  of \$25k. As a preliminary step, a slow AO system was constructed in
  the lab to demonstrate the feasibility of the low-cost approach. The
  design is a simple feedback loop that reads the wavefront shape with a
  Hartmann wavefront sensor and makes corrections through a micromachined
  membrane deformable mirror. A computer calculates the voltages to apply
  to the 37-actuator mirror based on the wavefront information. The
  system operates at 1 Hz and is able to correct a distorted laser
  wavefront within several cycles. This test paves the way to deploy a
  faster version of this system that runs at 500 Hz. Funded by NSF.

---------------------------------------------------------
Title: Stokes Inversion Techniques for the SOLIS-VSM
Authors: Henney, C. J.; Keller, C. U.; Jones, H. P.; SOLIS Team
2002AAS...200.5514H    Altcode: 2002BAAS...34Q.734H
  The Vector Spectromagnetograph (VSM) instrument of the Synoptic Optical
  Long-term Investigations of the Sun (SOLIS) project will begin operation
  in 2002 and provide a 25 year record of synoptic solar observations. The
  50-cm aperture VSM will provide daily full-disk photospheric vector
  and high sensitivity longitudinal magnetograms. In addition, the VSM
  will produce daily full-disk chormospheric longitudinal magnetograms,
  along with 1083 nm equivalent width images. Current data transmission
  and storage resources are such that the reduction of VSM data will be
  performed at the observing site on Kitt Peak. Reduced data products
  will be transmitted via a DS3 link from Kitt Peak to the National
  Solar Observatory's digital archive in Tucson. During a typical
  observing day, three full-disk photospheric vector magnetograms will
  be available over the web in two stages: first, as a “quick-look”
  product within 10 minutes of data acquisition, and then as a full
  Milne-Eddington (ME) inversion product within 24 hours of each
  observation. The quick-look parameters will include estimates of
  the magnetic field strength, azimuth and inclination based on Auer,
  Heasley, House (1977, Solar Physics 55, p. 47). The high-precision
  vector products will be determined with the High Altitude Observatory
  ME inversion technique implemented by Skumanich and Lites (1987, ApJ,
  322, p.473). The flexible design of the VSM data handling system can
  incorporate future improvements under consideration (e.g., principal
  component analysis). However, since the original Stokes profiles
  observed will not be archived, a retrospective reduction of VSM data
  will not be possible. Quick-look and full ME inversion results are
  compared using simulated VSM Stokes profile data based on Kitt Peak
  Vacuum Telescope magnetograms. This research was supported in part by
  the Office of Naval Research Grant N00014-91-J-1040.

---------------------------------------------------------
Title: Observational Signatures of a Solar Small-Scale Global Dynamo
Authors: Keller, C. U.; Stein, R. F.; Nordlund, A.
2002AAS...200.8908K    Altcode: 2002BAAS...34..792K
  There is ample theoretical and observational evidence for the existence
  of a dynamo operating in the solar convection zone that produces
  small-scale, weak magnetic fields. The next generation of solar
  telescopes such as the 4-m Advanced Technology Solar Telescope and
  the 1.5-m GREGOR will be able to provide observational data on these
  magnetic fields. In order to guide the development of instruments and
  observational procedures to investigate these small-scale magnetic
  fields, we have calculated polarized spectral line profiles from
  numerical simulations of a small-scale global dynamo and analyzed
  them as if they were actual observations of the Sun. The simulated
  observations include realistic noise, spatial smearing from a partially
  correcting AO system, and spectral smearing and scattered light from a
  spectrograph. We identify the unique signatures of these magnetic fields
  and relate them to the physical conditions in the numerical simulations.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.;
   Oschmann, J. M.; Warner, M.; Dalrymple, N. E.; ATST Team
2002AAS...200.3408R    Altcode: 2002BAAS...34..691R
  The 4m aperture Advance Technology Solar Telescope (ATST) will be the
  most powerful solar telescope in the world and a unique scientific tool
  to study the Sun and other astronomical objects, such as planets. The
  ATST will replace major existing national solar facilities at the end
  of this decade. The ATST project has entered the design and development
  phase. We present an overview of the ATST science drivers and discuss
  preliminary design concepts and technical challenges. The ATST science
  goals lead to the following general requirements for the ATST facility:
  - Diffraction limited angular resolution in the visible and infrared
  to study fundamental astrophysical processes with unprecedented
  resolution enabling verification of model predictions. - A high photon
  flux for accurate measurements of physical parameters throughout
  the solar atmosphere, such as magnetic strength and direction,
  temperature and velocity. - Access to a new diagnostics at relatively
  unexplored infrared wavelength. - Low scattered light to enable
  coronal observations. - Low instrumental polarization for accurate
  measurements of magnetic fields. Development of a 4m solar telescope
  presents many technical challenges. The large aperture drives the ATST
  to an open-air design and makes thermal control of optics and telescope
  structure a paramount consideration. To achieve diffraction-limited
  observations at visible and infrared wavelength ATST will have a high
  order solar adaptive optics system. Coronal observations require,
  occulting in prime focus, a Lyot stop and contamination control of the
  primary. An initial set of instruments will be designed as integral
  part of the telescope. Preliminary telescope and instrument concepts
  will be discussed.

---------------------------------------------------------
Title: Instrumentation for astrophysical spectropolarimetry
Authors: Keller, Christoph U.
2002apsp.conf..303K    Altcode:
  Astronomical spectropolarimetry is performed from the X-ray to
  the radio regimes of the electromagnetic spectrum. The following
  chapter deals with instruments and their components that are used
  in the wavelength range from 300 nm to 20 μm. After introducing
  the terminology and formalisms that are used in the context of
  astronomical spectropolarimeters, I discuss the most widely used
  optical components. These include crystal and sheet polarizers, fixed
  monochromatic and achromatic retarders, and variable retarders such
  as liquid crystals and photoelastic modulators. Since polarimetric
  measurements are often limited by systematic errors rather than
  statistical errors due to photon noise, I deal with these instrumentally
  induced errors in detail. Among these errors, I discuss instrumental
  polarization of various kinds and chromatic and angle of incidence
  errors of optical components. I close with a few examples of successful,
  modern night-time and solar spectropolarimeter.

---------------------------------------------------------
Title: The ionosphere of Titan
Authors: Cravens, T.; Vann, J.; Clark, J.; Yu, J.; Keller, C.
2002cosp...34E.399C    Altcode: 2002cosp.meetE.399C
  Titan has an atmosphere consisting mainly of molecular nitrogen and
  methane. Solar extreme ultraviolet and x-ray radiation and energetic
  electrons from SaturnSs magnetosphere interact with the upper atmosphere
  producing an ionosphere. We will review our current understanding of
  TitanSs ionosphere. We will emphasize recent models of the horizontal
  and vertical ion density structure. The ionospheric chemistry is quite
  complex and a large number of hydrocarbon ion species are present. The
  ion chemistry operating in the ionosphere will be reviewed. The
  ionosphere acts as an obstacle to the external magnetospheric flow
  and this will also be briefly discussed.

---------------------------------------------------------
Title: 1000 years of climate change
Authors: Keller, C.
2002cosp...34E1791K    Altcode: 2002cosp.meetE1791K
  Solar activity has been observed to vary on decadal and centennial time
  scales. Recent evidence (Bond, 2002) points to a major semi-periodic
  variation of approximately 1,500 yrs. For this reason, and because high
  resolution proxy records are limited to the past thousand years or so,
  assessing the role of the sun's variability on climate change over
  this time f ame has received much attention. A pressingr application
  of these assessments is the attempt to separate the role of the sun
  from that of various anthropogenic forcings in the past century and
  a half. This separation is complicated by the possible existence
  of natural variability other than solar, and by the fact that the
  time-dependence of solar and anthropogenic forcings is very similar
  over the past hundred years or so. It has been generally assumed that
  solar forcing is direct, i.e. changes in sun's irradiance. However,
  evidence has been put forth suggesting that there exist various
  additional indirect forcings that could be as large as or even exceed
  direct forcing (modulation of cosmic ray - induced cloudiness, UV-
  induced stratospheric ozone change s, or oscillator -driven changes in
  the Pacific Ocean). Were such forcings to be large, they could account
  for nearly all 20th Century warming, relegating anthropogenic effects
  to a minor role. Determination of climate change over the last thousand
  years offers perhaps the best way to assess the magnitude of total
  solar forcing, thus allowing its comparison with that of anthropogenic
  sources. Perhaps the best proxy records for climate variation in the
  past 1,000 yrs have been variations in temperat ure sensitive tree
  rings (Briffa and Osborne, 2002). A paucity of such records in the
  Southern Hemisphere has largely limited climate change determinations
  to the subtropical NH. Two problems with tree rings are that the
  rings respond to temperature differently with the age of the tree,
  and record largely the warm, growing season only. It appears that
  both these problems have been adequately solved although caution is
  warranted. A promising adjunct to tree rings is actual measurement of
  temperatures in boreholes. Inversion of such records gives low frequency
  temperatures that are potentially more accurate than any proxy- derived
  ones. All these records give a fairly consistent picture of at least
  one major warming and cooling extreme (Medieval Warming Period (MWP) and
  Little Ice Age (LIA). Many modeling efforts using direct solar forcing
  have been done. These typically employ proxy data (sunspot number and
  variations in Be-10 and C -14 calibrated by satellite observations) for
  changes in solar forcing, and give the same general picture-- that of
  a substantial warming 1,000 yrs ago (MWP) followed by cooling that was
  particularly marked in the late 17th and early 19th centuries (LIA). The
  resulting amplitude of temperature change between MWP and LIA agrees
  well with paleo-temperature reconstructions and suggests that solar
  forcing alone is inadequate to account for more than about half the
  20th century warming (Lean et al 1995, Crowley and Lowry 2000). Since
  these quantitatively reproduce climate variations in the past 1000
  years, the role of indirect solar forcing is inferred to be small but
  may be important (Lean and Rind 2001). Gerard Bond, Bernd Kromer,
  Juerg Beer, Raimund Muscheler, Michael N. Evans, William Showers,
  Sharon Hoffmann, Rusty Lotti-Bond, Irka Hajdas, and Georges Bonani,
  (2001) Persistent Solar Influence on North Atlantic Climate During the
  Holocene,Science 294: 2130-2136 Briffa and Osborne, (2002) Blowing Hot
  and Cold, Science 295, 2227-2228. Lean, J., Beer, J., and Bradley, R.,
  (1995) Reconstruction of solar irradiance since 1610: Implications
  for climate change, Geophys. Res. Lett.., 22, 3195-3198. Crowley ,T.,
  (2000) Causes of climate change over the past 1000 years, Science,289,
  270- 277. Lean and Rind, (2001), Earth's Response to a Variable Sun,
  Science, 292, 234-236.

---------------------------------------------------------
Title: Polarization Modulation for Solar Vector-Polarimeters using
    Ferroelectric Liquid Crystals
Authors: Pifer, R.; Keller, C.
2001AGUSM..SP51B05P    Altcode:
  Polarization modulation for solar vector polarimetry can be performed
  in various ways. Ferroelectric liquid crystals (FLC) have the advantage
  of allowing modulation frequencies of up to several kHz, therefore
  avoiding spurious signals due to seeing. A new modulation scheme using
  two FLC modulators was designed for the SOLIS Vector-Spectromagnetograph
  (VSM). Here we present experimental confirmation of this modulation
  scheme from a laboratory setup using a fast CCD camera running at
  300 frames per second. Furthermore, we also show measurements from a
  circular polarization modulator that operates at 854 nm but uses one
  FLC built for 630 nm. This provides a means to cover a large wavelength
  range with a single, chromatic FLC modulator.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope -- Science Goals and
    Instrument Description.
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.
2001AGUSM..SH31D08R    Altcode:
  High-resolution studies of the Sun's magnetic fields are needed for
  a better understanding of solar magnetic fields and the fundamental
  processes responsible for solar variability. The generation of magnetic
  fields through dynamo processes, the amplification of fields through
  the interaction with plasma flows, and the destruction of fields are
  still poorly understood. There is still incomplete insight as to what
  physical mechanisms are responsible for heating the corona, what causes
  variations in the radiative output of the Sun, and what mechanisms
  trigger flares and coronal mass ejections. Progress in answering
  these critical questions requires study of the interaction of the
  magnetic field and convection with a resolution sufficient to observe
  physical scales fundamental to these processes. The 4m aperture ATST
  will be a unique scientific tool, with excellent angular resolution,
  a large wavelength range, and low scattered light. With its integrated
  adaptive optics, the ATST will achieve a spatial resolution nearly 10
  times better than any existing solar telescope. The ATST will provide:
  <P />Unprecedented angular resolution of 0.03 arcsec in the visible and
  0.08 arcsec at 1.6 microns to enable us to clearly resolve and study the
  fundamental astrophysical processes on their intrinsic scales and to
  verify model predictions. A high photon flux for accurate and precise
  measurements of physical parameters, such as magnetic field strength
  and direction, temperature and velocity, on the short time scales
  involved. Access to a broad set of diagnostics, from visible to thermal
  infrared wavelengths. Low scattered light observations and coronagraphic
  capabilities in the infrared, allowing measurements of coronal magnetic
  fields. The ATST has been highly ranked by the latest Decadal Survey
  of Astronomy and Astrophysics and the NAS/NRC study of ground-based
  solar astronomy. A large part of the solar community will participate
  in the design and development of the ATST. A strawman telescope design,
  design challenges and instrument concepts will be discussed. Examples
  of recent high resolution observations with adaptive optics, that
  demonstrate the potential of this new technology will be shown.

---------------------------------------------------------
Title: Influence of magnetic fields on the coherence effects in the
    Na I D<SUB>1</SUB> and D<SUB>2</SUB> lines
Authors: Stenflo, J. O.; Gandorfer, A.; Wenzler, T.; Keller, C. U.
2001A&A...367.1033S    Altcode:
  To clarify the physical nature of the enigmatic scattering
  polarization in the Na i D<SUB>1</SUB> and D<SUB>2</SUB> line cores
  we have explored their behavior with full Stokes vector polarimetry
  in regions with varying degree of magnetic activity near the solar
  limb. These observations represent the first time that ZIMPOL II,
  the second generation of our CCD based imaging polarimeter systems,
  has been used for a scientific program. With ZIMPOL II the four Stokes
  images can be demodulated and recorded with a single CCD sensor such
  that the resulting images of the fractional polarization Q/I, U/I,
  and V/I are entirely free from spurious features due to seeing or
  flat-field effects. The polarization in the cores of the lines, in
  particular in D<SUB>2</SUB>, exhibits dramatic and unexpected spatial
  variations in both Q/I and U/I, including polarization self-reversals
  of the D<SUB>2</SUB> Q/I core peak. As the fluctuations in the Q,
  U, and V parameters appear to be relatively uncorrelated, we have
  parametrized the profiles and made scatter plots of the extracted
  parameters. Comparison with synthetic scatter plots based on different
  theoretical models suggests that the polarization signals in the cores
  of the D<SUB>2</SUB> and D<SUB>1</SUB> lines have different physical
  origins: While the D<SUB>1</SUB> core is likely to be governed by
  ground-state atomic polarization, the D<SUB>2</SUB> core is dominated by
  the alignment of the excited state and by effects of partial frequency
  redistribution.

---------------------------------------------------------
Title: The SOLIS Vector-Spectromagnetograph (VSM)
Authors: Keller, C. U.; Solis Team
2001ASPC..236...16K    Altcode: 2001aspt.conf...16K
  No abstract at ADS

---------------------------------------------------------
Title: High Resolution Polarimetry and the Need for a Large-Aperture
    Solar Telescope
Authors: Keller, C. U.
2001ASPC..236..389K    Altcode: 2001aspt.conf..389K
  No abstract at ADS

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Keller, C. U.; Atst Team
2001ASPC..236..597K    Altcode: 2001aspt.conf..597K
  No abstract at ADS

---------------------------------------------------------
Title: Solar Chromospheric Magnetic Fields
Authors: Keller, C. U.
2001ASPC..248...61K    Altcode: 2001mfah.conf...61K
  No abstract at ADS

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope: Science Goals and
    Instrument Description
Authors: Rimmele, T.; Keller, C.; Keil, S.; Hill, F.; Atst Team
2001AGM....18S1006R    Altcode:
  High-resolution studies of the Sun's magnetic fields are needed for
  a better understanding of solar magnetic fields and the fundamental
  processes responsible for solar variability. For example, the
  generation of magnetic fields through dynamo processes is still poorly
  understood. There is still incomplete insight as to what physical
  mechanisms are responsible for heating the corona, what causes
  variations in the radiative output of the Sun. Progress in answering
  these critical questions requires study of the interaction of the
  magnetic field and convection with a resolution sufficient to observe
  scales fundamental to these processes. The 4m aperture ATST will be
  a unique scientific tool, which will provide unprecedented angular
  resolution, high photon flux, access to a broad set of diagnostics,
  from visible to thermal infrared wavelengths, and low scattered light
  observations and coronagraphic capabilities in the infrared. Development
  of a 4-m solar telescope presents several technical challenges. The
  large heat flux makes thermal control of optics and telescope structure
  a paramount consideration. To achieve diffraction-limited performance,
  a powerful solar adaptive optics system is required. Low scattered
  light is essential for observing the corona but also to accurately
  measure the physical properties of small structures in, for example,
  sunspots. Contamination control of the primary and secondary mirrors
  must therefore be addressed. An initial set of instruments will be
  designed as integral part of the telescope during the upcoming design
  and development phase. A strawman telescope design and instrument
  concepts will be discussed.

---------------------------------------------------------
Title: The Advanced Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Keller, C.; Hill, F.
2000AAS...197.1710K    Altcode: 2000BAAS...32.1433K
  The planned Advanced Technology Solar Telescope (ATST) will be a 4-m
  aperture general-purpose solar telescope with integrated adaptive
  optics and versatile post focus instrumentation. The ATST will achieve
  an angular resolution of 0.03 arcsec (20 km on the solar surface)
  in the visible, which is almost an order of magnitude better than
  what is achieved with current solar telescopes. This will make it
  possible to resolve the fundamental astrophysical hydrodynamic and
  magnetohydrodynamic processes and structures in the solar atmosphere
  such as the building blocks of solar magnetic fields that are believed
  to be responsible for solar irradiance variations and the heating of the
  outer solar atmosphere. The ATST will cover the wavelength range from
  0.35 to 35 ?m and minimize scattered light. The initial set of post
  focus instruments will exploit the unique capabilities of the ATST to
  study magnetic fields at the highest spatial resolution in the visible
  and near-infrared parts of the spectrum. The ATST was highly recommended
  by the recent Decadal Study. A proposal for a four-year Design and
  Development phase has just been submitted to the NSF. Construction is
  expected to start in FY2005. The National Solar Observatory is operated
  by the Associated Universities for Research in Astronomy and is funded
  by the National Science Foundation under a cooperative agreement.

---------------------------------------------------------
Title: Results from a revisit to the K<SUB>2V</SUB> bright points
Authors: Sivaraman, K. R.; Gupta, S. S.; Livingston, W. C.; Damé,
   L.; Kalkofen, W.; Keller, C. U.; Smartt, R.; Hasan, S. S.
2000A&A...363..279S    Altcode:
  We have used pairs of temporally simultaneous CaII K-line
  spectroheliograms and magnetic area scans to search for spatial
  correlation between the CaII K<SUB>2V</SUB> bright points in the
  interior of the network and corresponding magnetic elements. We find
  that about 60% of the K<SUB>2V</SUB> bright points spatially coincide
  with magnetic elements of flux density &gt; 4 Mx cm<SUP>-2</SUP>. About
  25% of the K<SUB>2V</SUB> bright points with equally enhanced emission
  lie over bipole elements where the fields are &gt; 4 Mx cm<SUP>-2</SUP>
  for both polarity elements which merge and presumably cancel and
  result in low fields. The rest, 15%, of the bright points coincide
  with areas of fields &lt; 4 Mx cm<SUP>-2</SUP> which is the noise
  level set by us for the magnetic scans. When magnetic elements of
  opposite polarity merge and form bipoles, the associated K<SUB>2V</SUB>
  bright points show excess emission. Although such excess emission is a
  magnetic-field-driven phenomenon, the measured value of the field at the
  site of the bipole is typically low, and these cases would therefore be
  excluded in the count of coincidences of excess emission with excess
  magnetic fields. In our opinion, these cases of excess emission at
  the sites of the bipoles, as well as at the sites of fields &gt;
  4 Mx cm<SUP>-2</SUP>, are both instances of magnetic-field-related
  emissions. If the former are not taken into account as coincidences,
  the correlation will drop down and this might be interpreted as not an
  obvious correlation. Our present results, taking into account the low
  fields of merging bipoles, establish the association of K<SUB>2V</SUB>
  bright points with magnetic elements.

---------------------------------------------------------
Title: New Initiatives for Synoptic Observations
Authors: Keller, C. U.
2000JApA...21..127K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: New Results from the Flare Genesis Experiment
Authors: Rust, D. M.; Bernasconi, P. N.; Eaton, H. A.; Keller, C.;
   Murphy, G. A.; Schmieder, B.
2000SPD....31.0302R    Altcode: 2000BAAS...32..834R
  From January 10 to 27, 2000, the Flare Genesis solar telescope
  observed the Sun while suspended from a balloon in the stratosphere
  above Antarctica. The goal of the mission was to acquire long time
  series of high-resolution images and vector magnetograms of the
  solar photosphere and chromosphere. Images were obtained in the
  magnetically sensitive Ca I line at 6122 Angstroms and at H-alpha
  (6563 Angstroms). The FGE data were obtained in the context of Max
  Millennium Observing Campaign #004, the objective of which was to study
  the “Genesis of Solar Flares and Active Filaments/Sigmoids." Flare
  Genesis obtained about 26,000 usable images on the 8 targeted active
  regions. A preliminary examination reveals a good sequence on an
  emerging flux region and data on the M1 flare on January 22, as well
  as a number of sequences on active filaments. We will present the
  results of our first analysis efforts. Flare Genesis was supported
  by NASA grants NAG5-4955, NAG5-5139, and NAG5-8331 and by NSF grant
  OPP-9615073. The Air Force Office of Scientific Research and the
  Ballistic Missile Defense Organization supported early development of
  the Flare Genesis Experiment.

---------------------------------------------------------
Title: Evolution of small-scale magnetic fields from combined adaptive
    optics and phase-diverse speckle imaging
Authors: Keller, C. U.; Rimmele, T. R.; Paxman, R. G.; Seldin, J. H.;
   Carrara, D.; Gleichman, K.
2000SPD....31.0301K    Altcode: 2000BAAS...32..833K
  We have obtained movies of the photospheric magnetic field at a
  sustained resolution of 0.2 arcsec by combining the adaptive optics
  system at the Dunn Solar Telescope with the Zurich Imaging Polarimeter I
  (ZIMPOL) and processing the data with Phase-Diverse Speckle Imaging and
  speckle deconvolution. The adaptive optics was correcting the low-order
  aberrations with an update rate of about 1.5 kHz and fed a narrow-band
  channel through the Universal Birefringent Filter in the wing of the CaI
  610.3 nm line and two white-light channels that were used to obtain one
  in-focus and one out-of-focus image for the phase-diversity processing,
  which removes the remaining aberrations. All three channels were
  equipped with ZIMPOL I cameras running simultaneously at 5 frames
  per second. The narrow-band intensity and magnetogram images were
  reconstructed using speckle deconvolution. This combined attack to
  obtain the best magnetogram movies of the solar surface was very
  successful and led to spectacular time sequences with a consistent
  spatial resolution of better than 0.2 arcsec. We will present the
  first scientific results on the evolution of the small-scale magnetic
  fields in an active region. This work was supported by the National
  Science Foundation.

---------------------------------------------------------
Title: Center-to-limb variation of the enigmatic Na bt I D_1 and
    D_2 polarization profiles
Authors: Stenflo, J. O.; Gandorfer, A.; Keller, C. U.
2000A&A...355..781S    Altcode:
  The remarkable polarization structure of the Na i D_1 and D_2 lines
  that is due to coherent scattering has remained an enigma, since it has
  not yet been possible to find an explanation that is consistent with
  both current understanding of quantum mechanics and the astrophysical
  properties of the Sun's atmosphere. To guide future theoretical efforts
  we have here explored the detailed center-to-limb variation of the
  linearly polarized profiles in non-magnetic regions. In particular we
  find that the unexplained narrow polarization peaks in the Doppler
  cores of the two lines become even more pronounced with respect to
  the relative profile shape as we move away from the limb towards the
  center of the solar disk.

---------------------------------------------------------
Title: Anomalous polarization effects due to coherent scattering on
    the Sun
Authors: Stenflo, J. O.; Keller, C. U.; Gandorfer, A.
2000A&A...355..789S    Altcode:
  The richly structured linearly polarized spectrum that is produced
  by coherent scattering in the Sun's atmosphere contains a number of
  spectral features for which no explanation has been found within the
  standard scattering theory. According to this quantum-mechanical
  framework, the intrinsic polarizability of a given line should be
  determined by the total angular momentum quantum numbers of the
  atomic levels involved in the scattering transition (which may be
  resonant or fluorescent). Well defined polarization peaks have been
  observed in many lines, which according to these theoretical concepts
  should be intrinsically unpolarizable. A possible explanation for
  these anomalous spectral structures could be that the initial ground
  state of the scattering transition becomes polarized by an optical
  pumping process. However, such an explanation is contradicted by
  other observations, since it seems to require that much of the solar
  atmosphere must be filled with extremely weak magnetic fields (&lt;~
  10 mG). We have searched through the whole visible solar spectrum
  for lines with the quantum numbers that should normally make them
  unpolarizable, and have carried out a systematic observing program
  for the most prominent of these lines. Here we report on the observed
  properties of the polarized line profiles of these lines and explain
  in what respect their behaviors are anomalous and cannot be understood
  within current conceptual frameworks.

---------------------------------------------------------
Title: 5,000 by 5,000 Spatial by 15,000 Spectral Resolution Elements:
    First Astronomical Observations with a Novel 3-D Detector
Authors: Keller, C. U.
2000ASPC..195..495K    Altcode: 2000iutd.conf..495K
  No abstract at ADS

---------------------------------------------------------
Title: Deconvolution of narrowband solar images using aberrations
    estimated from phase-diverse imagery
Authors: Seldin, John H.; Paxman, Richard G.; Carrara, David A.;
   Keller, Christoph U.; Rimmele, Thomas R.
1999SPIE.3815..155S    Altcode:
  Phase-Diverse Speckle (PDS) is a short-exposure data- collection and
  processing technique that blends phase- diversity and speckle-imaging
  concepts. PDS has been successfully used for solar astronomy to achieve
  near diffraction-limited resolution in ground-based imaging of solar
  granulation. Variants of PDS that involve narrow-band, spectroscopic,
  and polarimetric data provide more information observations. We
  present results from processing data collected with the 76-cm Richard
  B. Dunn Solar Telescope (DST) on Sacramento Peak, NM. Three-channel
  data sets consisting of a pair of phase-diverse images of the solar
  continuum and a narrow-band image were collected over spans of 15 - 20
  minutes. Point-spread functions that are estimated from the PDS data are
  used in a multi-frame deconvolution algorithm to correct the narrow-band
  imagery. The data were processed into a number of time series. A rare,
  short-lived continuum bright point with a peak intensity at a factor
  of 2.1 above the mean intensity in the continuum was observed in one
  such sequence. The field of view spans multiple isoplanatic patches,
  and strategies for processing these large fields were developed. We will
  discuss these methods along with other techniques that were explored
  for accelerating the processing. Finally, we show the first PDS
  reconstruction of adaptive-optics (AO) compensated solar granulation
  taken at the DST. As expected, we find that these data are less
  aberrated and, thus, the use of AO in future experiments is planned.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
    features. XV. Evershed flow in cool, weak penumbral fields
Authors: Rüedi, I.; Solanki, S. K.; Keller, C. U.
1999A&A...348L..37R    Altcode:
  Observations of Ti I lines at 2.2 mu m show that the Evershed flow takes
  place in cool, almost horizontal channels with a low magnetic field
  strength (~ 500-900 G) that does not appear to change significantly
  across the penumbra. This property might allow an outward directed
  siphon flow to exist along such cool flux tubes.

---------------------------------------------------------
Title: Evolution of Protoplanetary Accretion Disks including Chemistry
    and Transport Processes
Authors: Duschl, W. J.; Gail, H. -P.; Keller, C.; Tscharnuter, W. M.
1999AGAb...15...22D    Altcode: 1999AGM....15..B14D
  According to our current understanding, planetary systems form in
  protostellar accretion disks. At late stages of the star formation
  process, conditions become favourable for the dust component in
  the disk to agglomerate first into km-sized planetesimals and by a
  complicated hierarchy of further growth process into planets. The
  simulation of the structure and evolution of protoplanetary accretion
  disks are a necessary prerequisite for understanding the formation
  of planetary systems. An important topic in this context is the study
  of the chemistry of gas and dust, the mineralogical and petrological
  properties of the dust, and of radial and vertical transport processes
  in the disc, since this determines the temporal evolution and radial
  distribution of the composition of the disk material, from which the
  planetary system bodies are formed. The construction of hydrodynamic
  evolution models including chemical and transport processes is
  part of a project within the SFB 359 "Reactive Flows, Diffusion, and
  Transport" at Heidelberg University. The present state of this project
  and the future plans are briefly discussed. As a special result, we
  discuss the chemistry and structure of a stationary disk model, which
  combines self-consistently chemical equilibrium calculations for the
  gas phase and the mineral assemblage in the disk with the complete
  set of equations for the radial and vertical disk structure in the
  1+1 dimensional approximation. Convection and radiative transfer is
  included in the model calculation. We briefly discuss the mineral
  composition predicted by this model with (i) results of earlier
  condensation calculations, and (ii) the mineral assemblage observed
  for primitive meteorites.

---------------------------------------------------------
Title: Optimum Apodization for Speckle Imaging of Extended Sources
Authors: Keller, C.
1999ASPC..183..342K    Altcode: 1999hrsp.conf..342K
  No abstract at ADS

---------------------------------------------------------
Title: The Advanced Solar Telescope: I. Science Goals
Authors: Keller, C.
1999ASPC..183..169K    Altcode: 1999hrsp.conf..169K
  No abstract at ADS

---------------------------------------------------------
Title: Phase-Diversity Data Sets and Processing Strategies
Authors: Paxman, R.; Seldin, J.; Keller, C.
1999ASPC..183..311P    Altcode: 1999hrsp.conf..311P
  No abstract at ADS

---------------------------------------------------------
Title: Scattering polarization in the chromosphere
Authors: Keller, C. U.; Sheeley, N. R., Jr.
1999ASSL..243...17K    Altcode: 1999sopo.conf...17K
  No abstract at ADS

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. XIV. TI
    i and the cool components of sunspots
Authors: Rueedi, I.; Solanki, S. K.; Keller, C. U.; Frutiger, C.
1998A&A...338.1089R    Altcode:
  The first systematic observations of sunspot umbrae using the lines
  of the Ti Ii multiplet at 2.2 mu m are presented. Their diagnostic
  capabilities are investigated, developed and used to investigate the
  magnetic and velocity structure of a sunspot. These lines are most
  sensitive to cool plasma. In addition, they are extremely Zeeman
  sensitive. We find that a sunspot is composed of two distinct cool
  magnetic components. One of them is fairly vertical, has a large
  magnetic field strength and is associated with the central (umbral)
  part of the sunspot. The other component is strongest near the outer
  boundary of the spot (penumbra), is much more inclined, has a very
  low magnetic field strength and shows the signature of the Evershed
  effect. In contrast to the smooth transition of field strength from
  the darkest part of the umbra to the outer penumbral boundary usually
  visible in observations carried out in other spectral lines, the Ti
  Ii lines exhibit a sharp transition between the two magnetic components.

---------------------------------------------------------
Title: SOLIS: a modern facility for synoptic solar observations
Authors: Keller, Christoph U.
1998SPIE.3352..732K    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a suite
  of instruments that will modernize and greatly improve synoptic solar
  observations carried out by the National Solar Observatory. It will
  provide fundamental data necessary to understand the solar activity
  cycle, sudden energy releases in the solar atmosphere, and solar
  spectral irradiance changes. State-of-the-art instrumentation and data
  collection techniques will be employed to enhance both the quality
  and quantity of data. A high degree of automation and remote control
  will provide faster user access to data and flexible interaction
  with the data- collection process. The instruments include a vector
  spectromagnetograph that will measure the magnetic field strength and
  direction over the full solar disk in 15 minutes, a full disk patrol
  delivering digital images in various spectral lines at a high cadence,
  and a Sun-as-a- star precision spectrometer to measure changes in many
  spectral lines.

---------------------------------------------------------
Title: SOLIS: A Modern Facility for Synoptic Solar Observations
Authors: Keller, C. U.
1998STIN...9946076K    Altcode:
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a suite
  of instruments that will modernize and greatly improve synoptic solar
  observations carried out by the National Solar Observatory. It will
  provide fundamental data necessary to understand the solar activity
  cycle, sudden energy releases in the solar atmosphere, and solar
  spectral irradiance changes. State-of-the-art instrumentation and data
  collection techniques will be employed to enhance both the quality
  and quantity of data. A high degree of automation and remote control
  will provide faster user access to data and flexible interaction
  with the data-collection process. The instruments include a vector
  spectromagnetograph that will measure the magnetic field strength and
  direction over the full solar disk in 15 minutes, a full disk patrol
  delivering digital images in various spectral lines at a high cadence,
  and a Sun-as-a-star precision spectrometer to measure changes in many
  spectral lines.

---------------------------------------------------------
Title: Complex magnetic fields in an active region
Authors: Bernasconi, P. N.; Keller, C. U.; Solanki, S. K.; Stenflo,
   J. O.
1998A&A...329..704B    Altcode:
  High-resolution observations of the full Stokes vector in Fe\sc i
  spectral lines around 5250 Angstroms obtained at the Swedish Vacuum
  Solar Telescope on La Palma with the ZIMPOL I Stokes polarimeter in a
  complex active region reveal the presence of anomalously shaped Stokes
  profiles indicating the coexistence of at least two magnetic components
  within the same spatial resolution element. These Stokes profiles have
  been analyzed with an inversion code based on a 3-component atmospheric
  model with two magnetic and one field-free component. The fits to
  the observations in a magnetic region that resembles a small penumbra
  reveal the presence of a horizontal magnetic field component with an
  average field strength of /line{B}=840 G, a mean filling factor of
  /lineα=0.12, and an average temperature /line{T}=5400 K at log {tau_
  {5000}}=-1.5 embedded in the main “penumbral” magnetic field that
  has /line{B}=1500 G, /lineα=0.56, and /line{T}=4900 K. The horizontal
  component exhibits a mean outflow of 2.7 km s(-1) which is mainly due
  to the Evershed flow. In a region where there are strong downflows up
  to 7 km s(-1) , we infer the possible presence of a shock front whose
  height changes along the slit. The height variation can be explained by
  a change of the gas pressure at the base of the photosphere below the
  shock front as proposed by Thomas &amp; Montesinos (1991). Small plages
  with field strengths below 900 G have been observed in the vicinity
  of some pores. Finally, we present a puzzling field structure at the
  boundary between two adjacent pores. Ambiguous results suggest that
  although the inversion code is able to successfully invert even very
  complex Stokes profiles, we are far from a complete description of the
  field structure in complex magnetic regions. We warn that magnetograms
  and fits to data involving only a single magnetic component may hide
  the true complexity of the magnetic structure in at least some parts
  of active regions.

---------------------------------------------------------
Title: SOLIS --- A Modern Facility for Synoptic Solar Observations
Authors: Keller, C. U.; Nso Staff
1998ASPC..154..636K    Altcode: 1998csss...10..636K
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is
  a proposed suite of instruments that will modernize and greatly
  improve synoptic solar observations carried out by the National Solar
  Observatory. The primary scientific goal is to provide fundamental data
  necessary to understand the solar activity cycle, sudden energy releases
  in the solar atmosphere, and solar spectral irradiance changes. An
  operational goal is to produce real-time and near real-time data for
  forecasting space weather, and to augment the scientific yield from
  space missions such as SOHO and TRACE, and ground-based projects
  including RISE and GONG. State-of-the-art instrumentation and data
  collection techniques will be employed to enhance both the quality
  and quantity of data. A high degree of automation and remote control
  will provide faster user access to data and flexible interaction
  with the data-collection process. The instruments include a vector
  spectromagnetograph that will measure the magnetic field strength and
  direction over the full solar disk in 15 minutes, a full disk patrol
  delivering digital images in various spectral lines at a high cadence,
  a coronal emission line imager and photometer that will provide
  photometric and velocity images in at least five spectral lines,
  and a Sun-as-a-star precision spectrometer to measure changes in many
  spectral lines.

---------------------------------------------------------
Title: SOLIS Instrumentation Aspects
Authors: Keller, C. U.; NSO Staff
1998ASPC..140..539K    Altcode: 1998ssp..conf..539K
  No abstract at ADS

---------------------------------------------------------
Title: Population number inversion in disk-impinging-clumps
Authors: Fiebig, D.; Els, S. G.; Keller, C.
1998AGAb...14...22F    Altcode: 1998AGM....14..B27F
  The model of accretion disk-impinging-clumps is numerically investigated
  with respect to the occurrence of a population number inversion between
  the J_{K_{-1} {K_{+1}} = 6<SUB>16</SUB>, 5<SUB>23</SUB> ortho-{H_2O}
  rotational levels. Former studies (Fiebig 1997) have shown that the
  collision of small, dense clumps onto the protostellar accretion disk
  around the deeply embedded YSO in L 1287 can account for the appearence
  of the associated position-velocity structure of identified 22 GHz
  {H_2O} masers. Recently another source was found which indicates a very
  similar structure (Torrelles et al. 1998). Since the origin of the
  22 GHz {H_2O} maser emission is assigned to shock heated disk-clump
  collisions, a 2-D radiative transfer code was developed to calculate
  the population numbers of water molecules in the interaction region
  of a single collision event. Starting from the results obtained by
  a 2-D SPH-Code (Keller &amp; Fiebig \ this conference) the spatial
  distribution of gas and dust temperature, density, and velocity
  were adopted as boundary conditions. Since dust was found to be the
  dominant cooling agent (Els &amp; Fiebig \ this conference), the
  radiative transfer between water molecules could be decoupled from
  the heating/cooling processes incorporated into the SPH-Code. The 2-D
  radiative transfer code makes use of a modified short characteristics
  method, considers Rayleigh scattering, and is usual ly run for a number
  of 60 rotational levels covering corresponding levels temperatures up
  to 2600 K. The computational results clearly show the occurrence of
  compact regions of population number inversion to be identified with
  observable 22 GHz {H_2O} maser emission.

---------------------------------------------------------
Title: Differential Hanle effect and the spatial variation of
    turbulent magnetic fields on the Sun
Authors: Stenflo, J. O.; Keller, C. U.; Gandorfer, A.
1998A&A...329..319S    Altcode:
  While diagnostic techniques based on the ordinary Zeeman effect
  (e.g. magnetograms) are almost “blind” to a turbulent magnetic field
  with mixed magnetic polarities within the spatial resolution element,
  the Hanle effect is sensitive to this domain of solar magnetism. We
  present observational evidence that the turbulent magnetic field that
  fills the 99\ts%\ of the volume between the kG flux tubes in quiet
  solar regions does not have a unique field-strength distribution,
  but the rms turbulent field strength can vary by an order of magnitude
  from one solar location to the next. The varying Hanle depolarization
  in combinations of spectral lines with different sensitivities to the
  Hanle effect is conspicuously evident from direct visual inspection
  of the spectra. To quantify these variations we have extracted the
  polarization amplitudes for a selection of spectral lines observed in 8
  different solar regions with different turbulent field strengths, and
  then applied an inversion technique to find the field strengths and
  calibrate the selected lines. The inversion gives stable solutions
  for the turbulent field strengths, in the range 4--40\ts G, but
  the field-strength scale is presently very uncertain. The inversion
  exercise has helped to expose a number of problem areas which need to be
  attended to before the differential Hanle effect can become a standard,
  reliable diagnostic tool. One major problem is the extraction of the
  line polarization when the contributions from the line and continuum
  are of the same order of magnitude, which is the usual case. For
  exploratory purposes we have applied a heuristic, statistical approach
  to deal with this problem here.

---------------------------------------------------------
Title: The USAF Improved Solar Observing Optical Network (ISOON)
    and its Impact on Solar Synoptic Data Bases
Authors: Neidig, D.; Wiborg, P.; Confer, M.; Haas, B.; Dunn, R.;
   Balasubramaniam, K. S.; Gullixson, C.; Craig, D.; Kaufman, M.; Hull,
   W.; McGraw, R.; Henry, T.; Rentschler, R.; Keller, C.; Jones, H.;
   Coulter, R.; Gregory, S.; Schimming, R.; Smaga, B.
1998ASPC..140..519N    Altcode: 1998ssp..conf..519N
  No abstract at ADS

---------------------------------------------------------
Title: The Procyon campaign: Observations from Kitt Peak
Authors: Pilachowski, C. A.; Barden, S.; Hill, F.; Harvey, J. W.;
   Keller, C. U.; Giampapa, M. S.
1998IAUS..185..319P    Altcode:
  Time series spectra of the F5IV star Procyon (alpha CMi) were obtained
  at the Kitt Peak National Observatory during a 35-night observing run
  in January-February 1997. The observations were obtained as part of an
  international collaboration to detect and study acoustic oscillations
  in solar-type stars. Spectra covered the wavelength range from 4000
  to 5300 AA , with a resolving power of approximately 3500 (1.3 AA
  resolution). The sampling rate was one observation per minute, and
  the typical S/N ratio per observation is in excess of 1000. At the
  time of writing, we have obtained over 10,000 spectra. The spectra
  will be analyzed to identify any periodic signals due to acoustic
  oscillations in Procyon. In addition to measuring the equivalent widths
  of the three Balmer lines (Kjeldsen et al. 1995) covered by our spectra
  (Hβ, Hγ, and Hdelta) we will also examine the spectra for variations
  in the average metal line strength. Preliminary power spectra will
  be presented.

---------------------------------------------------------
Title: Asteroseismology from equivalent widths: a test of the sun
Authors: Keller, C. U.; Harvey, J. W.; Barden, S. C.; Giampapa, M. S.;
   Hill, F.; Pilachowski, C. A.
1998IAUS..185..375K    Altcode:
  Kjeldsen et al. (1995) reported a probable detection of solar-like,
  low-amplitude, p-mode oscillations of eta Bootes using equivalent
  width measurements from low-resolution spectra of the hydrogen Balmer
  lines. We tested the usefulness of this technique using observations of
  the Sun in integrated light. Despite the very high signal-to-noise ratio
  of the data stretching over six continuous days, no solar oscillation
  signal was found so far in the equivalent width of Hβ. Spatially
  resolved observations of the Hβ equivalent width at solar disk center
  reveal that the oscillation signal is suppressed in the wings of Hβ
  as compared to the continuum. Extrapolation of the oscillation signal
  seen in the spatially resolved data suggests an amplitude of about
  1ppm for integrated light measurements, which is about a factor of
  5 lower than expected from simple theoretical arguments. We explore
  other methods to deduce an oscillation signal from all spectral lines
  simultaneously. cont has: Deng, L. et al.; auths fixed below

---------------------------------------------------------
Title: Center-to-limb variation of the second solar spectrum.
Authors: Stenflo, J. O.; Bianda, M.; Keller, C. U.; Solanki, S. K.
1997A&A...322..985S    Altcode:
  The linear polarization that is caused by scattering processes in the
  solar atmosphere has been refered to as the "second solar spectrum",
  since it is structurally as rich as the ordinary intensity spectrum
  but quite different in appearance and information contents. One
  of the most used and theoretically best understood lines in the
  second solar spectrum is the SrI 4607Å line, which has served as a
  diagnostic tool for determinations of spatially unresolved, turbulent
  magnetic fields via the Hanle effect. Here we present the detailed
  center-to-limb variation of the scattering polarization in this line
  for a number of new data sets obtained both with an electrooptical
  modulation system (ZIMPOL) and a non-modulating beam splitter system
  (at IRSOL, Locarno), to provide improved observational constraints for
  theoretical modelling. The amplitude and width of the polarization
  profile, the amount of continuum polarization, as well as the depth
  and width of the intensity profile have been evaluated and carefully
  corrected for spectral broadening and stray light. While there is
  generally good agreement between the five data sets, some systematic
  differences are shown to be of solar rather than instrumental origin,
  most likely due to spatially varying Hanle depolarization across the
  solar disk. A number of other spectral lines have been observed with
  the ZIMPOL system at two different limb distances (μ=0.1 and 0.2) to
  allow us to compare the steepness of the center-to-limb variation of
  their polarization amplitudes. The steepest variation is exhibited by
  the continuum polarization, which declines by approximately a factor of
  6 when going the 15 arcsec distance from μ=0.1 to μ=0.2. The spectral
  lines with the steepest center-to-limb variation are molecular lines,
  the CaII infrared triplet, and Hα. In contrast the SrI 4607 and BaII
  4554Å lines have only moderately steeper center-to-limb variations
  than that of an ideal, purely dipole-scattering atmosphere, for
  which the polarization ratio between μ=0.1 and μ=0.2 is 1.38. These
  center-to-limb variations may be used to constrain temperature-density
  models of the upper photosphere and chromosphere.

---------------------------------------------------------
Title: ISOON: The Improved Solar Observing Optical Network
Authors: Neidig, D.; Confer, M.; Wiborg, P.; Dunn, R.; Balasubramaniam,
   K. S.; Frederick, R.; Kutzman, R.; Soli, R.; Keller, C.; Gullixson,
   C.; Alios, Inter
1997SPD....28.0224N    Altcode: 1997BAAS...29..897N
  Efforts are under way to replace the existing SOON system, which was
  designed in the 1970s, with a new system (ISOON) based on a fully
  tunable narrow-band filter and CCD detector. ISOON would feature
  autonomous, rapid-cadence solar imaging and remote operation at four
  sites, and would transmit solar images in near real time to central
  facilities at Falcon AFB and Boulder CO, for use in space weather
  forecasting. The ISOON technical approach is to retain the front
  end of the existing SOON telescope, but replace the optical bench,
  birefringent filter, and spectrograph with a dual Fabry-Perot filter
  system and secondary optics contained in a single pod. ISOON data
  products will include full-disk H-alpha, continuum, and line-of-sight
  magnetograms on 1-arcsecond pixels. High- resolution images (limited
  field, 0.3-arcsecond pixels) would be available via a future upgrade
  in the secondary optics. ISOON will also be capable of acquiring
  vector magnetic field images via a software upgrade to be added at a
  future time.

---------------------------------------------------------
Title: The second solar spectrum. A new window for diagnostics of
    the Sun.
Authors: Stenflo, J. O.; Keller, C. U.
1997A&A...321..927S    Altcode:
  The Sun's radiation becomes linearly polarized by coherent scattering
  processes in the solar atmosphere. With a novel polarimetry system
  that achieves a precision of 10^-5^ in the degree of polarization, the
  previously largely unexplored territory of scattering physics on the Sun
  is now fully accessible. The observations reveal a polarized spectrum
  that looks very different as compared with the ordinary, unpolarized
  solar spectrum but has an astounding wealth of spectral structures. It
  is therefore refered to as the "second solar spectrum". In the present
  paper we show how the second solar spectrum is governed by different
  physical processes, which provide new diagnostic opportunities and tools
  that are complementary to those of the ordinary intensity spectrum. We
  illustrate the effects of quantum interferences and hyperfine structure,
  isotope abundances, partial frequency redistribution, molecular
  contributions, and magnetic canopies. Also shown are polarization
  features, for which the underlying physics has not yet been identified.

---------------------------------------------------------
Title: Chromospheric Events in the Quiet Network
Authors: Keller, C.; Bastian, T.; Benz, A.; Krucker, S.
1997SPD....28.1304K    Altcode: 1997BAAS...29..917K
  Time sequences of a quiet network region close to disk center have
  been simultaneously recorded with the VLA, various instruments on SOHO,
  and the solar telescopes on Kitt Peak. The analysis of the Hα spectra
  obtained at the McMath-Pierce telescope revealed down-flows with
  apparent velocities of more than 2.5 km/s associated with magnetic
  field structures in the quiet network. During such events, the Hα
  spectra show a pronounced asymmetry. The photospheric magnetic field was
  determined from rapid scans in three iron lines with the Zurich Imaging
  Stokes Polarimeter. Up- and down-flow velocity excursions outside of
  magnetic field regions are compatible with chromospheric waves. We
  describe the properties of these events as seen in the observations
  of the visible part of the spectrum and their signatures at radio
  and UV wavelengths. The final goal of this study is the construction
  of a time-dependent 3-D picture of the quiet solar atmosphere and the
  understanding of the dynamical coupling of photospheric magnetic fields
  with the chromosphere and the corona.

---------------------------------------------------------
Title: Observations of the quiet Sun's magnetic field.
Authors: Grossmann-Doerth, U.; Keller, C. U.; Schuessler, M.
1996A&A...315..610G    Altcode:
  The profiles of Stokes I and V of FeI 5247A, CrI 5247A, FeI 5250.2A and
  Fe I 5250.6A have been measured in the quiet photosphere with ZIMPOL,
  a new polarimeter, with very low noise level. The spatial resolution
  element of about 1Mm was essentially determined by seeing. In about
  15% of the observed area, the signal-to-noise ratio was sufficiently
  large to determine the strength of the magnetic field and to derive
  various properties of the Stokes V profiles (asymmetries, zero-crossing
  shift and thermal line ratio). Our results show that, at least in this
  fraction of area, the magnetic field in the quiet Sun is dominated by
  strong flux concentrations which must be rather small. The data on the
  Stokes V properties provide observational constraints for theoretical
  models of flux concentrations.

---------------------------------------------------------
Title: Concept for a miniature solar magnetograph
Authors: Keller, Christoph U.; Harvey, John W.
1996SPIE.2804...14K    Altcode:
  We present a novel concept for a solar magnetograph that uses a
  photo-refractive crystal to reflect and focus the light from the wings
  of many spectral lines onto a camera. The crystal acts simultaneously as
  multiple, narrow-band filters and as an off-axis telescope. Polarization
  measurements are performed close to the final focus. Since this approach
  uses the light from many spectral lines simultaneously, the required
  telescope aperture is substantially reduced and exposure times can be
  so short that accurate tracking is not necessary. Such a concept is
  particularly attractive for NASA's Minimum Solar Mission where very
  compact, light-weight instruments are required.

---------------------------------------------------------
Title: Time series restoration from ground-based solar observations
Authors: Seldin, John H.; Paxman, Richard G.; Keller, Christoph U.
1996SPIE.2804..166S    Altcode:
  Many processes of interest in the solar atmosphere have spatial scales
  of much less than one second of arc. If the processes are related to
  magnetic fields, the relevant scales are even smaller. Noticeable
  evolutions of solar features occur on time-scales of less than a
  minute if a spatial resolution of better than one second of arc is
  reached. It is, therefore, of great interest to recover time-series
  imagery with near diffraction-limited spatial resolution and good
  temporal resolution on a consistent basis and over extended periods of
  time using ground-based techniques. Phase diversity is a post-collection
  technique for restoring fine-resolution detail when imaging in the
  presence of phase aberrations such as atmospheric turbulence. Incident
  energy is split into two channels: one is collected at the conventional
  focal plane, the other is intentionally defocussed a known amount
  and collected by a second detector array. Phase-diverse speckle is an
  extension of phase diversity whereby a time sequence of short-exposure
  image pairs is collected. The maximum-likelihood estimate of a common
  object and a set of phase aberrations is performed jointly using
  all images. A phase-diverse speckle set of images of a plage region
  was collected over a span of 13.5 minutes using the 76-cm Vacuum
  Tower Telescope at the National Solar Observatory on Sacramento
  Peak. A phase- diverse pair of broad-band images at 6563 angstroms
  was collected along a third, narrow-band image in the wing of H-
  (alpha) . A set of restorations was made into a movie depicting the
  highly dynamic photosphere at scales below 0.3 arcsec. We conclude that
  the combination of fine spatial and temporal resolution achieved with
  phase-diverse speckle opens a new window to the study of the dynamics
  of the solar atmosphere from ground-based observatories.

---------------------------------------------------------
Title: Flare Genesis Experiment
Authors: Murphy, Graham A.; Rust, David M.; Strohbehn, Kim; Eaton,
   Harry A.; Keil, Stephen L.; Keller, Christoph U.; Wiborg, P. H.
1996SPIE.2804..141M    Altcode:
  In January 1996, the Flare Genesis Experiment was carried for 19
  days by a 29.4 M cu. ft helium-filled balloon in the stratosphere
  above Antarctica, during which over 14000 images of the Sun were
  recorded. Long-duration ballooning provides a relatively inexpensive
  means to observe the Sun under near-space conditions and to develop
  instrumentation and techniques that will be used on future solar space
  missions. The purpose of the flight was to improve understanding of
  the mechanisms involved in many different types of solar activity,
  particularly flares and solar filament eruptions. Achieving this goal
  demanded the development of a platform for an 80-cm F/1.5 optical
  telescope that would be stable to 10 arcseconds. In addition, we
  developed an image motion compensation system capable of holding the
  Sun's image to better than the system's 0.2 arcsecond diffraction
  limit. Other key elements on board included a lithium-niobate
  Fabry-Perot etalon filter to provide a tunable 0.016-nm bandpass over
  a wide wavelength range, a fast 1534 X 1024-pixel Kodak CCD camera,
  and 180 GBytes of on-board storage. There was also a system for
  sending commands and receiving telemetry and a high-speed downlink
  for sending images during periods when the payload was in line of
  sight of the ground station. On- board computers provided a command
  and control system capable of near-autonomous operation. During most
  of the flight, contact with the payload was sporadic, so operation
  was primarily under autonomous control.

---------------------------------------------------------
Title: Evaluation of Phase-Diversity Techniques for Solar-Image
    Restoration
Authors: Paxman, Richard G.; Seldin, John H.; Loefdahl, Mats G.;
   Scharmer, Goeran B.; Keller, Christoph U.
1996ApJ...466.1087P    Altcode:
  Phase-diversity techniques provide a novel observational method for
  overcoming the effects of turbulence and instrument-induced aberrations
  in ground-based astronomy. Two implementations of phase-diversity
  techniques that differ with regard to noise model, estimator,
  optimization algorithm, method of regularization, and treatment of edge
  effects are described. Reconstructions of solar granulation derived
  by applying these two implementations to common data sets are shown to
  yield nearly identical images. For both implementations, reconstructions
  from phase-diverse speckle data (involving multiple realizations of
  turbulence) are shown to be superior to those derived from conventional
  phase-diversity data (involving a single realization). Phase-diverse
  speckle reconstructions are shown to achieve near diffraction-limited
  resolution and are validated by internal and external consistency tests,
  including a comparison with a reconstruction using a well-accepted
  speckle-imaging method.

---------------------------------------------------------
Title: Imaging Coronal Emission Lines under High Sky-Background
    Conditions
Authors: Keller, C. U.; Smartt, R. N.
1996SoPh..166..311K    Altcode:
  We have obtained images in solar coronal emission lines under high
  sky-background conditions by making precise differential measurements
  between the coronal emission line and the near-by continuum, which is
  primarily due to scattered light from the solar disk. Chopping between
  the two wavelengths was performed at 100 kHz to avoid artifacts from
  fast-flying dust particles and other aerosols, and also from seeing
  effects. The differential signal was detected with a novel CCD camera
  that demodulates signals up to 100 kHz. These preliminary observations
  show coronal emission at the 0.2% level of the scattered-light
  background and pave the way to efficient and precise imaging of coronal
  emission features under less than ideal `coronal-sky' conditions.

---------------------------------------------------------
Title: The Flare Genesis Experiment
Authors: Rust, D. M.; Murphy, G. A.; Strohbehn, K.; Keil, S. L.;
   Keller, C. U.
1996AAS...188.6705R    Altcode: 1996BAAS...28Q.934R
  The goal of the Flare Genesis Experiment is to make solar observations
  at the highest practicable resolution in order to improve understanding
  of the mechanisms involved in many different types of solar activity,
  particularly flares and solar filament eruptions. Achieving this goal
  demanded the development of a balloon-borne platform for an 80-cm F/1.5
  optical telescope that could maintain 10 arcsec pointing stability. The
  first flight of the Flare Genesis Experiment took place in January
  1996. In the stratosphere, 37 km above Antarctica, for more than 19
  days, the Flare Genesis telescope pointed at the Sun with the planned
  stability. While the primary science objective, to measure the vector
  magnetic fields using two liquid crystal polarization modulators, was
  not achieved on this flight, 18,000 continuum images were obtained. They
  demonstrate that the major engineering challenges for such a flight
  were overcome. In addition, we developed an image motion compensation
  system capable of limiting the motion of the Sun's image on the focal
  plane to less than the system's 0.2 arcsec diffraction limit. Other key
  elements on board included a lithium-niobate Fabry-Perot etalon filter
  to provide a tunable 0.016-nm bandpass over a wide wavelength range,
  a 1538 x 1024- pixel CCD camera and 100 GBytes of on-board storage. We
  will describe the payload design and how the instruments performed. We
  will discuss how the constraints of long duration Antarctic ballooning
  guided the final design and impacted the results. Two more flights
  are planned before the next solar maximum. Such long-duration balloon
  flights provide a relatively inexpensive means to observe the Sun at
  the highest resolution and to develop instrumentation and techniques
  for future space missions.

---------------------------------------------------------
Title: Asteroseismology via equivalent widths - tests on Procyon,
    Eta Bootis, and Alpha Trianguli.
Authors: Harvey, J. W.; Pilachowski, C.; Barden, S.; Giampapa, M.;
   Keller, C. U.; Hill, F.
1996BAAS...28..917H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Second Solar Spectrum
Authors: Keller, C. U.; Stenflo, J. O.
1996AAS...188.5704K    Altcode: 1996BAAS...28..912K
  The Sun's radiation becomes linearly polarized by coherent scattering
  processes in the solar atmosphere. With a novel imaging polarimeter
  (Zurich Imaging Stokes Polarimeter I) that achieves a precision of
  10(-5) in the degree of polarization, the previously largely unexplored
  territory of scattering physics on the Sun is now fully accessible. The
  observations reveal a polarized spectrum that looks very different from
  the ordinary, unpolarized solar spectrum but has an astounding wealth
  of spectral structures from atoms as well as molecules. This second
  solar spectrum will be used as a new source of information to learn
  more about atomic physics, abundances and isotope ratios, radiative
  transfer physics, solar magnetic fields, and the thermodynamics of
  the solar atmosphere.

---------------------------------------------------------
Title: Asteroseismology via Equivalent Widths -- Tests on Procyon,
    Eta Bootes, and Alpha Triangulum
Authors: Harvey, J.; Pilachowski, C.; Barden, S.; Giampapa, M.;
   Keller, C.; Hill, F.
1996AAS...188.5903H    Altcode: 1996BAAS...28S.917H
  Recently, Kjeldsen et al. reported a probable detection of solar-like
  low-amplitude p-mode oscillations of Eta Bootes using equivalent
  width measurements from low-resolution spectra of the H Balmer
  lines. This technique has the potential to provide stellar oscillation
  measurements good enough to allow the asteroseismic inference of stellar
  structure. Here we report on the preliminary analysis of data from three
  observing runs with the Kitt Peak Coude Feed and 2.1-m telescope in
  November 1995 (Alpha Triangulum), February 1996 (Procyon), and March
  1996 (Eta Bootes). These runs are being used to develop observing
  and data reduction techniques, such as a synchronized timing system
  to maintain evenly spaced temporal samples, a continuous unshuttered
  CCD readout to increase the duty cycle of the observations, and a
  simulation of the probability of a detection as a function of observing
  run length. We observed the region around the H beta, gamma, and delta
  lines with a spectral dispersion of about 0.4 Angstroms per pixel,
  extracted equivalent widths, and performed time series analysis. The
  temporal spectrum of Alpha Triangulum contains a significant peak near
  the theoretical prediction, however, we do not yet know the origin of
  this peak.

---------------------------------------------------------
Title: SOLIS - A Modern Facility for Synoptic Solar Observations
Authors: Harvey, J.; Keller, C.; November, L.; NSO Staff
1996AAS...188.6703H    Altcode: 1996BAAS...28..934H
  SOLIS (Synoptic Optical Long-term Investigations of the Sun) is
  a proposed suite of instruments that will modernize and greatly
  improve synoptic solar observations carried out by the National
  Solar Observatory on behalf the solar and solar-terrestrial physics
  communities. The primary scientific goal is to provide fundamental data
  necessary to understand the solar activity cycle, sudden energy releases
  in the solar atmosphere, and solar spectral irradiance changes. An
  operational goal is to produce real-time and near real-time data
  for forecasting space weather, and to augment the scientific yield
  from space mission such as SOHO and TRACE, and ground-based projects
  including RISE and GONG. State-of-the-art instrumentation and data
  collection techniques will be employed to enhance both the quality
  and quantity of data. A high degree of automation and remote control
  will provide faster user access to data and flexible interaction
  with the data-collection process. The instruments include a vector
  spectromagnetograph that will measure the magnetic field strength and
  direction over the full solar disk in 15 minutes, a full disk patrol
  delivering digital images in various spectral lines at a high cadence,
  a coronal emission line imager and photometer that will provide
  photometric and velocity images in at least five spectral lines,
  and a Sun-as-a-star precision spectrometer to measure changes in
  many spectral lines. The choice of sites for the instruments depends
  on potential partnerships with other observatories and the level of
  funding that can be obtained. The goal is to place the instruments at
  sites with large amounts of sunshine and coronal observing conditions
  as appropriate. The SOLIS proposal is currently under review by the
  National Science Foundation.

---------------------------------------------------------
Title: NIM-2 -- A Near Infrared Imaging Vector Magnetograph
Authors: Rabin, D.; Keller, C.; Jaksha, D.
1996AAS...188.6706R    Altcode: 1996BAAS...28R.934R
  NIM-1 is a spectrograph-based Stokes polarimeter for measuring the
  strength and orientation of magnetic fields in the solar photosphere
  using two Zeeman-sensitive Fe I lines (g = 3 and g_geff = 1.53) near
  1565 nm. NIM-2, now under construction, also uses these spectral
  lines but is based on a high-resolution Fabry-Perot etalon. NIM-2
  will eliminate the image scanning and consequent spatial distortions
  of NIM-1 and will be compact and light enough to serve as a prototype
  for balloon or space instruments. The Queensgate etalon will provide a
  spectral resolving power of 10(5) over a 1-nm free spectral range. The
  initial detector will be the 256(2) InSb array shared with NIM-1, but
  NIM-2 is designed to accommodate a 512(2) or 1024(2) “Aladdin” InSb
  array. The data system, also shared with NIM-1, is being upgraded to
  handle the faster switching speed ( ~ 8 ms) of improved liquid-crystal
  variable retarders. NOAO is operated for the NSF by the Association of
  Universities for Research in Astronomy. Near-infrared magnetometry at
  NSO is supported by the the NASA Space Physics Division through the
  SR&amp;T program in solar physics.

---------------------------------------------------------
Title: Measurement of the full Stokes vector of He I 10830 Å
Authors: Rüedi, I.; Keller, C. U.; Solanki, S. K.
1996SoPh..164..265R    Altcode:
  First observations of the full Stokes vector in the upper chromosphere
  are presented. The He I 10830 Å line, which has been shown to give
  reliable measurements of the line-of-sight component of the magnetic
  field vector, has been used for this purpose. It is shown that the
  difference between the appearance of chromospheric and photospheric
  magnetic structures observed close to the solar limb is largely
  due to the difference in height to which they refer and projection
  effects. The observations do suggest, however, that the magnetic field
  above sunspot penumbrae is somewhat more vertical in the chromosphere
  than in the photosphere.

---------------------------------------------------------
Title: Recent Progress in Imaging Polarimetry
Authors: Keller, C. U.
1996SoPh..164..243K    Altcode:
  Recent instrumental developments in imaging polarimetry allow array
  detectors to reach a polarimetric sensitivity of 1 × 10<SUP>−4</SUP>
  of the intensity. New instrumental effects appear at these levels of
  sensitivity and generate spurious polarization signals with amplitudes
  of up to 5 × 10<SUP>−4</SUP>. Here I discuss these effects and
  present methods to avoid them. Polarized spectra with an rms noise of
  6 × 10<SUP>−6</SUP> may then be obtained. Furthermore a method is
  brought to the reader's attention that allows polarization measurements
  at the 1 × 10<SUP>−4</SUP> level with regular array detectors,
  e.g. in the near-infrared.

---------------------------------------------------------
Title: Balloon-Borne Polarimetry
Authors: Rust, D. M.; Murphy, G.; Strohbehn, K.; Keller, C. U.
1996SoPh..164..403R    Altcode:
  For about two weeks in 1995, the balloon-borne Flare Genesis
  Experiment will continuously observe the Sun well above the turbulent,
  image-blurring layers of the Earth's atmosphere. The polarization-free
  80 cm telescope will supply images to a liquid-crystal based vector
  magnetograph, which will measure magnetic features at a resolution
  of 0.2 arcsec. An electrically tunable lithium-niobate Fabry-Perot
  provides a spectral resolution of about 0.015 nm. In a follow-up
  series of Antarctic balloon flights, the Flare Genesis Experiment
  (FGE) will provide unprecedented details about sunspots, flares,
  magnetic elements, filaments, and the quiet solar atmosphere.

---------------------------------------------------------
Title: Direct measurements of flux tube inclinations in solar plages.
Authors: Bernasconi, P. N.; Keller, C. U.; Povel, H. P.; Stenflo, J. O.
1995A&A...302..533B    Altcode:
  Observations of the full Stokes vector in three spectral lines
  indicate that flux tubes in solar plages have an average inclination
  in the photosphere of 14^o^ with respect to the local vertical. Most
  flux tubes are inclined in the eastwards direction, i.e., opposite
  to the solar rotation. We have recorded the Stokes vector of the
  FeI 5247.1A, FeI 5250.2A, and FeI 5250.7A lines in nine different
  plages with the polarization-free 20cm Zeiss coronagraph at the Arosa
  Astrophysical Observatory of ETH Zuerich. The telescope has been
  modified for solar disk observations. The chosen spectral lines are
  particularly sensitive to magnetic field strength and temperature. To
  determine the field strength and geometry of the flux tubes in the
  observed plages we use an inversion code that numerically solves the
  radiative transfer equations and derives the emergent Stokes profiles
  for one-dimensional model atmospheres consisting of a flux tube and
  its surrounding non-magnetic atmosphere. Our results confirm earlier
  indirect estimates of the inclination of the magnetic fields in plages.

---------------------------------------------------------
Title: Handling of huge multispectral image data volumes from a
    spectral hole burning device (SHBD)
Authors: Graff, Werner; Rosselet, Armel C.; Wild, Urs P.; Gschwind,
   Rudolf; Keller, Christoph U.
1995SPIE.2480..445G    Altcode:
  We use chlorin-doped polymer films at low temperatures as the
  primary imaging detector. Based on the principles of persistent
  spectral hole burning, this system is capable of storing spatial and
  spectral information simultaneously in one exposure with extremely high
  resolution. The sun as an extended light source has been imaged onto
  the film. The information recorded amounts to tens of GBytes. This data
  volume is read out by scanning the frequency of a tunable dye laser and
  reading the images with a digital CCD camera. For acquisition, archival,
  processing, and visualization, we use MUSIC (MUlti processor System with
  Intelligent Communication), a single instruction multiple data parallel
  processor system equipped with the necessary I/O facilities. The huge
  amount of data requires the developemnt of sophisticated algorithms to
  efficiently calibrate the data and to extract useful and new information
  for solar physics.

---------------------------------------------------------
Title: Speckle spectrography of extended objects.
Authors: Keller, C. U.; Johannesson, A.
1995A&AS..110..565K    Altcode:
  We present a method to obtain diffraction limited spectrograms of
  extended sources from a series of ground-based slit-spectrograms. The
  method is a combination of speckle deconvolution (Keller &amp; von
  der Luehe 1992) and a rapid spectrograph scanning scheme (Johannesson
  et al. 1992). The slit of a spectrograph is scanned over the solar
  surface while simultaneous slit-jaw images and spectrograms are
  recorded. The exposure time is short with respect to seeing-induced
  variations. A Knox-Thompson speckle reconstruction scheme is applied
  to the slit jaw images. From the individual slit-jaw images and their
  speckle reconstruction the instantaneous point spread function can
  be determined for any location. The spectrograms are reconstructed
  by inverting a matrix that describes the action of the point-spread
  function on the spectrograms. The final product is a three-dimensional
  cube formed by the two spatial coordinates and the wavelength. In
  the spatial domain the data is nearly diffraction limited while the
  spectral resolution is not affected by the reconstruction. The method
  is applied to observations of the quiet solar granulation.

---------------------------------------------------------
Title: Weak Magnetic Fields in the Network
Authors: Keller, C. U.; Harvey, J. W.
1995SPD....26..206K    Altcode: 1995BAAS...27..952K
  No abstract at ADS

---------------------------------------------------------
Title: The spectral hole-burning device: a 3-dimensional photon
    detector.
Authors: Keller, C. U.; Gschwind, R.; Renn, A.; Rosselet, A.; Wild,
   U. P.
1995A&AS..109..383K    Altcode:
  We present the principles of a new device that combines a
  high-resolution spectrometer (0.001nm spectral resolution, 10nm
  bandwidth) with maximum efficiency, a large detector (pixel size
  1μm by 1μm, overall size 2cm by 2cm), and a very high density data
  storage device (up to 400TB) in a single optical device. This device
  is based on persistent spectral hole-burning in a dye-doped polymer at
  temperatures of a few K. It is called a Spectral Hole-Burning Device
  (SHBD) in analogy to Charge Coupled Devices (CCD). A SHBD can be
  thought of as a color film with extremely high spectral resolution:
  it records the intensity in the visible or the near-infrared according
  to the two-dimensional position and the wavelength. Therefore it is a
  3-dimensional photon detector. We show first results from laboratory
  measurements that prove the feasibility of a SHBD.

---------------------------------------------------------
Title: Visible and near-infrared polarimetry with LEST.
Authors: Keller, C. U.; Bernasconi, P. N.; Egger, U.; Povel, H. P.;
   Steiner, P.; Stenflo, J. O.
1995LFTR...59.....K    Altcode:
  This document describes the LEST vector polarimeters for the visible
  and the near-infrared part of the solar spectrum. After some general
  remarks on precise polarimetry with large telescopes, the authors
  present the specifications based on scientific reasons and some
  general design considerations. The proposed instrument design for the
  visible is based on the ZIMPOL II concept. They present two different
  concepts for vector polarimetry in the near infrared. One is based
  on a beam-splitter system combined with liquid crystal modulators,
  while the other is based on the same modulator package as used in the
  visible and optical demodulation in the final focus.

---------------------------------------------------------
Title: Infrared Capabilities of the Large Earth-Based Solar Telescope
    (LEST)
Authors: Keller, C. U.
1995itsa.conf..215K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Lest Detector and Data Acquisition System - Part One -
    Specifications
Authors: Collados, M.; Keller, C. U.; Steiner, P.
1995lest.rept....1C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Visible and Near Infrared Polarimetry with lest
Authors: Keller, C. U.; Bernasconi, P. N.; Egger, U.; Powel, H. P.;
   Steiner, P.; Stenflo, J. O.
1995lest.rept....1K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: LEST detector and data acquisition systems.
Authors: Collados, M.; Keller, C. U.; Steiner, P.
1995LFTR...61.....C    Altcode:
  Contents: 1. Specifications (M. Collados, C. U. Keller,
  P. Steiner). 2. Design considerations for the data acquisition system
  (P. Steiner).

---------------------------------------------------------
Title: First light for an astronomical 3-D photon detector.
Authors: Keller, C. U.; Graff, W.; Rosselet, A.; Gschwind, R.; Wild,
   U. P.
1994A&A...289L..41K    Altcode:
  Spectroscopic studies of extended astronomical sources at optical
  wavelengths are hampered by the two-dimensional nature of current
  photon detectors. Most photons of interest are not utilized because a
  spectrometer must scan in the spatial or spectral domain. We present
  the first solar spectrum recorded with a three-dimensional, highly
  wavelength-sensitive photon detector based on a dye-doped polymer film
  at 1.6K. The achieved spectral resolution is comparable to the best
  solar spectra obtained with a Fourier transform spectrometer. Our
  experiment paves the way for a photon detector that improves the
  efficiency of spectroscopy of extended sources by orders of magnitudes.

---------------------------------------------------------
Title: Two-dimensional polarimeter with a charge-coupled-device
    image sensor and a piezoelastic modulator
Authors: Povel, H. P.; Keller, C. U.; Yadigaroglu, I. -A.
1994ApOpt..33.4254P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the strength of solar intra-network fields.
Authors: Keller, C. U.; Deubner, F. -L.; Egger, U.; Fleck, B.; Povel,
   H. P.
1994A&A...286..626K    Altcode:
  The combination of the German Vacuum Tower Telescope and the prototype
  of ZIMPOL I (Zuerich Imaging Stokes Polarimeter I), a novel, very
  sensitive imaging polarimeter, has resulted in the first spectra
  of solar intra-network (IN) fields in circular polarization. The
  sensitivity in terms of flux density is 0.7 Mx/cm^2^. While magnetic
  fields in solar spots, pores, plages, and in the network have
  predominantly kG field strengths, the magnetic field strength of
  the IN flux is a controversial subject due to the absence of direct
  measurements. We first summarize the current ideas on IN fields and
  examine previous arguments for their field strength. Our measurements
  of the magnetic line ratio formed between the amplitudes of the Stokes
  V profiles of Fe I 5247.1 A and Fe I 5250.2 A are consistent with a
  field strength well below 1 kG. Since the sensitivity of the magnetic
  line ratio becomes low for small field strengths, we can only set an
  upper limit on the field strength of IN fields of 500 G at the level
  of line formation with a probability of 68% and an upper limit of 1
  kG with a probability of 95%. We emphasize that these are the first
  observations of a magnetic line ratio of unity near disk center.

---------------------------------------------------------
Title: Application of multiframe iterative blind deconvolution for
    diverse astronomical imaging
Authors: Christou, Julian C.; Hege, E. Keith; Jefferies, Stuart M.;
   Keller, Christoph U.
1994SPIE.2200..433C    Altcode: 1994aisi.conf..433C
  We present applications of a recently developed iterative blind
  deconvolution algorithm to both simulated and real data. The
  applications demonstrate the algorithm's performance for a wide range
  of astronomical imaging. We demonstrate the effectiveness of using
  multiple observations of the same object convolved with different
  point spread functions. We also show the extension of the algorithm
  to phase retrieval when the object Fourier amplitude is available.

---------------------------------------------------------
Title: Speckle techniques for spectroscopic observations
Authors: Keller, C. U.
1994ASIC..433...43K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Direct Measurements of Fluxtube Inclinations in Plages
Authors: Bernasconi, Pietro N.; Keller, Christoph U.; Stenflo, Jan Olof
1994ASPC...68..131B    Altcode: 1994sare.conf..131B
  No abstract at ADS

---------------------------------------------------------
Title: High spatial resolution observations of solar magnetic fields
Authors: Keller, C. U.
1994smf..conf..325K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Some aspects of polarimetry with LEST
Authors: Keller, C. U.
1994ASIC..433...37K    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: Small-Scale Structure in Active Regions (Invited)
Authors: Keller, C.
1993ASPC...46....3K    Altcode: 1993IAUCo.141....3K; 1993mvfs.conf....3K
  No abstract at ADS

---------------------------------------------------------
Title: Resolution of magnetic flux tubes on the Sun
Authors: Keller, C. U.
1992Natur.359..307K    Altcode:
  MAGNETIC flux at the surface of the Sun is predominantly concentrated
  in discrete areas with kilogauss field strengths<SUP>1</SUP>. Except
  for sunspots, these areas are too small to have been resolved
  by conventional observations. These magnetic flux tubes are an
  essential part of the physics of the activity and heating of the
  outer atmosphere of the Sun and other late-type stars<SUP>2</SUP>, but
  although their average properties have been studied in considerable
  detail<SUP>3,4</SUP>, direct observations of them have been lacking
  because of turbulence in the Earth's atmosphere, which limits
  resolution to ~400 km. Using a newly developed technique of speckle
  inter-ferometry<SUP>5</SUP>, we have obtained simultaneous direct
  observations of the white-light and magnetic field signature of flux
  tubes. Individual flux tubes are seen, with resolved diameters of
  ~200 km and continuum brightness contrast of at least +30%. Magnetic
  features larger than 300 km in size tend, however, to be darker than
  their surroundings.

---------------------------------------------------------
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: 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: Zurich Imaging Stokes Polarimeter Zimpol-I - Design Review
Authors: Keller, C. U.; Aebersold, F.; Egger, U.; Povel, H. P.;
   Steiner, P.; Stenflo, J. O.
1992lest.rept....1K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: GAP: yet another image processing system for solar
    observations.
Authors: Keller, C. U.
1992lest.rept....3K    Altcode:
  GAP is a versatile, interactive image processing system for analyzing
  solar observations, in particular extended time sequences, and for
  preparing publication quality figures. It consists of an interpreter
  that is based on a language with a control flow similar to PASCAL
  and C. The interpreter may be accessed from a command line editor and
  from user-supplied functions, procedures, and command scripts. GAP is
  easily expandable via external FORTRAN programs that are linked to
  the GAP interface routines. The current version of GAP runs on VAX,
  DECstation, Sun, and Apollo computers. Versions for MS-DOS and OS/2
  are in preparation.

---------------------------------------------------------
Title: High resolution observation of solar magnetic fields
Authors: Keller, Christoph Ulrich
1992PhDT.......203K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Zürich Imaging Stokes Polarimeter - ZIMPOL I. Design review.
Authors: Keller, C. U.; Aebersold, F.; Egger, U.; Povel, H. P.;
   Steiner, P.; Stenflo, J. O.
1992LFTR...53.....K    Altcode:
  This document describes the design of ZIMPOL I, the first Zürich
  Imaging Stokes Polarimeter. This solar vector polarimeter will mainly
  be used for observations of the solar magnetic field at high spatial
  and/or spectral resolution. A brief overview of ZIMPOL I is given
  in the preface. The scientific requirements are then specified in
  detail. They lead to an instrument concept which consists of several
  parts: the optical system, the camera system, the real-time image
  processing system, and the graphical user interface. Data reduction
  and analysis of observations recorded with this polarimeter are also
  dealt with in detail. Prototypes of the modulator package and the CCD
  camera have been tested at various observatories. Results from these
  tests are presented and discussed.

---------------------------------------------------------
Title: Demodulation of all four Stokes parameters with a single CCD -
    ZIMPOL II. Conceptual design.
Authors: Stenflo, J. O.; Keller, C. U.; Povel, H. P.
1992LFTR...54.....S    Altcode:
  It is shown how it is possible to simultaneously record images of
  all four Stokes parameters with a single CCD detector chip when
  fast (50 kHz), piezoelastic modulation of the polarization state
  is used. As the four image planes use the identical pixels of the
  CCD, all gain-table or flat-field effects vanish when forming the
  fractional polarization images. For each group of four pixel rows,
  one row collects the photons, while the other three are used for fast
  buffer storage. There are no light losses caused by masking of the pixel
  rows used for buffer storage, sinced a microlens array collects all the
  photons and directs them to the unmasked pixel rows. The efficiency of
  the system for simultaneous recording of all four Stokes parameters
  is six times greater than that of ZIMPOL I, the first generation of
  the Zürich Imaging Stokes Polarimeter, since no beam splitter with
  three separate CCD cameras is needed and no significant light losses
  occur at the masked pixel rows. The theoretically possible efficiency
  limit is thereby practically reached. The system is planned to be
  developed as ZIMPOL II, the second generation of the Zürich Imaging
  Stokes Polarimeter.

---------------------------------------------------------
Title: Round table discussion.
Authors: Darvann, T. A.; Keller, C. U.
1992lest.rept..131D    Altcode:
  The discussion session was divided into two parts: 1) Image processing
  software requirements for the future LEST, and 2) strategies at the
  present time to increase the collaboration and communication on image
  processing software within the solar community, and for the successful
  achievement of point 1.

---------------------------------------------------------
Title: Multicolor Continuum Analysis of the Solar Granulation in
    Quiet and Active Regions
Authors: Keller, C. U.; Koutchmy, S.
1991ApJ...379..751K    Altcode:
  A set of narrow-band filtergrams of the solar photosphere recorded in
  three widely separated true continuum windows and in Mg I b1 with a
  spatial resolution of about 0.5 arcsec is analyzed. The influence of
  small-scale magnetic fields on the granulation is studied by comparing
  various statistical parameters in selected active and quiet regions,
  and the temperature stratification of faculae at the level of continuum
  formation is investigated. In active regions there exist more points
  with enhanced continuum intensity as compared with quiet regions, and
  there is more power at small spatial scales in active regions, whereas
  more power exists at large scales in quiet regions. Quiet regions
  near and far away from a large sunspot do not show any significant
  difference. It is concluded that changes in the granular pattern near
  sunspots are caused by the small-scale magnetic fields often found near
  sunspots. Faculae, identified by their brightness in the Mg I b1 wing,
  show an enhanced continuum intensity and a reduced ratio between the
  blue and the red continuum, which is consistent with current flux
  tube models.

---------------------------------------------------------
Title: Fine-Scale Magnetic Field in a Sunspot Penumbra and Adjacent
    Photosphere
Authors: Frank, Z. A.; Scharmer, G. B.; Keller, C.; Lundstedt, H.
1991BAAS...23.1052F    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Two-dimensional polarimeter with CCD image sensors and
    piezo-elastic modulators.
Authors: Povel, H. P.; Keller, C. U.; Stenflo, J. O.
1991sopo.work..100P    Altcode:
  A new type of polarimeter for application in solar physics is described,
  which combines fast polarization modulation and high spatial resolution
  using piezoelastic modulators and charge coupled device (CCD) image
  sensors. The problem of incompatibility between the slow read-out of
  CCD sensors and fast modulation has been solved. First two-dimensional
  Stokes Q and V images, free from gain-table noise, and with an rms
  noise level of about 10<SUP>-3</SUP> have been obtained.

---------------------------------------------------------
Title: High spatial resolution polarimetry using filtergrams.
Authors: Keller, C. U.
1991sopo.work..124K    Altcode:
  Using tunable filters at the Sacramento Peak Vacuum Tower
  Telescope Stokes V images of various solar magnetic features have
  been observed. Simultaneous recording of left and right circular
  polarization leads to high spatial resolution magnetograms. Various
  instrumental effects of these observations are discussed in detail.

---------------------------------------------------------
Title: Inversion of Stokes V profiles: The structure of solar magnetic
    fluxtubes and its dependence on the filling factor.
Authors: Keller, C. U.; Solanki, S. K.; Stenflo, J. O.; Zayer, I.
1991sopo.work..387K    Altcode:
  The authors present results from an inversion procedure that derive the
  temperature stratification, the turbulent velocity, and the magnetic
  field strength of the photospheric layers of magnetic fluxtubes from
  observed Stokes V spectra near disk center. In a first step the
  inversion has been applied to 10 Fe I and Fe II Stokes V profiles
  of a plage and a network region to obtain reliable models of the
  fluxtubes. In a second step the dependence of the fluxtube structure
  on the filling factor has been studied with spectra of 3 Fe I lines
  from 23 different regions based on the models derived in the first step.

---------------------------------------------------------
Title: Dependence of the properties of solar magnetic flux tubes on
    filling factor. II - Results of an inversion approach
Authors: Zayer, I.; Stenflo, J. O.; Keller, C. U.; Solanki, S. K.
1990A&A...239..356Z    Altcode:
  The dependence of the properties of solar magnetic elements on the
  magnetic filling factor is studied using Stokes V spectra of three
  lines observed near the center of the solar disk. The inversion
  technique developed by Keller et al. (1990) is applied to three
  neighboring spectral lines, and the average temperature difference,
  the magnetic field strength, and the nonstationary velocity in the
  relevant line-forming layers are quantitatively determined. Quantitative
  evidence is provided for the dependence of the temperature within
  flux tubes on the amount of magnetic flux. The flux tubes are found
  to become cooler and their field strengths, at a given optical depth,
  to become larger as the filling factor increases. The presence of
  kilogauss field strengths within flux tubes is reconfirmed.

---------------------------------------------------------
Title: Solar magnetic field strength determinations from high spatial
    resolution filtergrams
Authors: Keller, C. U.; Stenflo, J. O.; Solanki, S. K.; Tarbell,
   T. D.; Title, A. M.
1990A&A...236..250K    Altcode:
  Circularly polarized images with high spatial resolution (better than 1
  arcsec) of a solar active region, obtained with a tunable filter in the
  wings of Fe I 5247.1 A and Fe I 5250.2 A, have been analyzed in terms of
  the magnetic line ratio technique introduced by Stenflo (1973). Whenever
  a measurable amount of polarization is present, the distribution of
  the observed magnetic-line ratio is compatible with a unique value,
  which is randomly blurred by noise due to the photon statistics,
  the CCD camera, and atmospheric distortions. There is no need for a
  distribution of field strengths to explain the observed distribution of
  the magnetic line ratio. Consequently, the observations are compatible
  with a unique magnetic field strength in solar small-scale magnetic
  elements of about 1000 G at the level of line formation. For a thin
  flux tube, this corresponds to a field strength of approximately 2000
  G at the level of continuum formation, which is in excellent agreement
  with previous field strength determinations from low spatial resolution
  spectra (4-10 arcsec).

---------------------------------------------------------
Title: Structure of solar magnetic fluxtubes from the inversion of
    Stokes spectra at disk center
Authors: Keller, C. U.; Steiner, O.; Stenflo, J. O.; Solanki, S. K.
1990A&A...233..583K    Altcode:
  The paper presents an inversion procedure that derives the temperature
  stratification, the turbulent velocity, and the magnetic field strength
  of the photospheric layers of small-scale magnetic fields from observed
  Stokes V spectra and the continuum intensity. The inversion is based
  on the determination of a small number of model flux parameters by a
  nonlinear least squares fitting algorithm. The minimization of the sum
  of the squared differences between observed and synthetic observables
  makes it possible to determine the temperature stratification and the
  magnetic field strength.

---------------------------------------------------------
Title: Empirical Photospheric Fluxtube Models from Inversion of
    Stokes V Data
Authors: Keller, C. U.
1990IAUS..138..121K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Restoration of distorted images as a variational problem:
    a dynamic programming approach
Authors: Keller, C. U.
1989hsrs.conf..208K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: High resolution photographic Stokes polarimetry of small
    scale magnetic flux (poster)
Authors: Keller, C. U.; Koutchmy, S.
1989hsrs.conf..443K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Properties of solar magnetic fluxtubes from only two spectral
    lines
Authors: Solanki, S. K.; Keller, C.; Stenflo, J. O.
1987A&A...188..183S    Altcode:
  A method for the determination of the magnetic field strength,
  velocity, and temperatures inside solar flux tubes, in addition to
  their inclinations and filling factors, is presented which requires
  only the Stokes V and Q profiles of the Fe I 5250.2 A and Fe I 5247.1
  A spectral lines. Application of the procedure to spectra of the two
  lines obtained at various distances from the solar limb shows that
  considerable velocity broadening is required at all positions on the
  disk in order to reproduce the polarimeter data. The center to limb
  variation of the 5250/5247 Stokes V and Q line ratios is found to
  contain little information on the height variation of the magnetic
  field in the context of one-dimensional models.

---------------------------------------------------------
Title: Comet Rudnicki (1966e)
Authors: Nielsen, A. V.; Milet, B.; Pereyra, Z. M.; Keller; Rodriguez,
   J. J.; Mintz, B.
1967IAUC.1987....2N    Altcode:
  Dr. Axel V. Nielsen, Ole Romer Observatory, points out that at its
  descending node Comet Rudnicki passes very near the orbit of the
  earth. Its heliocentric distance would then be 1.02 AU. He suggests
  the possibility of observing meteors associated with the comet on about
  1967 June 7. Further precise positions have been reported as follows:
  1966 UT R.A. (1950) Decl. Mag. Observer Nov. 16.81487 1 13 14.71 -
  6 54 55.1 Milet 16.82318 1 13 12.28 - 6 55 08.3 " Dec. 1.03499 0 06
  33.99 -11 24 24.3 9.0 Pereyra 1.04892 0 06 29.72 -11 24 35.6 9.0 "
  4.06458 23 50 37.02 -12 12 58.6 Mintz 4.08542 23 50 30.51 -12 13 14.7
  " 5.01250 23 45 31.56 -12 27 10.9 " Milet (Nice Observatory). Pereyra
  (Cordoba Observatory). Measurer: Keller. Computer: Rodriguez. Mintz
  (U.S. Naval Observatory, Washington). Measured on ADAMM.