explanation blue bibcodes open ADS page with paths to full text
Author name code: snik
ADS astronomy entries on 2022-09-14
author:"Snik, Frans"
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Title: XPipeline: Starlight subtraction at scale for MagAO-X
Authors: Long, Joseph D.; Males, Jared R.; Haffert, Sebastiaan Y.;
Close, Laird M.; Morzinski, Katie M.; Van Gorkom, Kyle; Lumbres,
Jennifer; Foster, Warren; Hedglen, Alexander; Kautz, Maggie; Rodack,
Alex; Schatz, Lauren; Miller, Kelsey; Doelman, David; Bos, Steven;
Kenworthy, Matthew A.; Snik, Frans; Otten, Gilles P. P. L.
2022arXiv220807354L Altcode:
MagAO-X is an extreme adaptive optics (ExAO) instrument for the
Magellan Clay 6.5-meter telescope at Las Campanas Observatory in
Chile. Its high spatial and temporal resolution can produce data
rates of 1 TB/hr or more, including all AO system telemetry and
science images. We describe the tools and architecture we use for
commanding, telemetry, and science data transmission and storage. The
high data volumes require a distributed approach to data processing,
and we have developed a pipeline that can scale from a single laptop
to dozens of HPC nodes. The same codebase can then be used for both
quick-look functionality at the telescope and for post-processing. We
present the software and infrastructure we have developed for ExAO
data post-processing, and illustrate their use with recently acquired
direct-imaging data.
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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.
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Title: ABORAS: polarimetric, 10cm/s RV observations of the Sun as
a star
Authors: Farret Jentink, Casper; Mortier, Annelies; Snik, Frans;
Dorval, Patrick; Thompson, Samantha J.; Navarro, Ramon; Naylor, Tim
2022arXiv220704804F Altcode:
We present a description of A dual-Beam pOlarimetric Robotic Aperture
for the Sun (ABORAS), to serve as a Solar input with a dedicated Stokes
V polarimeter for the HARPS3 high-resolution spectrograph. ABORAS has
three main science drivers: trying to understand the physics behind
stellar variability, tracking the long-term stability of HARPS3, and
serve as a benchmark for Earth-sized exoplanet detection with HARPS3
by injecting an Earth RV signal into the data. By design, ABORAS
will (together with the HARPS3 instrument) be able to measure 10cm/s
variations in RV of the integrated Solar disk and detect integrated
magnetic field levels at sub 1 Gauss level through circularly polarized
light.
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Title: L-band Integral Field Spectroscopy of the HR 8799 Planetary
System
Authors: Doelman, David S.; Stone, Jordan M.; Briesemeister, Zackery
W.; Skemer, Andrew J. I.; Barman, Travis; Brock, Laci S.; Hinz, Philip
M.; Bohn, Alexander; Kenworthy, Matthew; Haffert, Sebastiaan Y.; Snik,
Frans; Ertel, Steve; Leisenring, Jarron M.; Woodward, Charles E.;
Skrutskie, Michael F.
2022AJ....163..217D Altcode: 2022arXiv220308165D
Understanding the physical processes sculpting the appearance of
young gas-giant planets is complicated by degeneracies confounding
effective temperature, surface gravity, cloudiness, and chemistry. To
enable more detailed studies, spectroscopic observations covering
a wide range of wavelengths are required. Here we present the first
L-band spectroscopic observations of HR 8799 d and e and the first
low-resolution wide-bandwidth L-band spectroscopic measurements of HR
8799 c. These measurements were facilitated by an upgraded LMIRCam/ALES
instrument at the Large Binocular Telescope, together with a new
apodizing phase plate coronagraph. Our data are generally consistent
with previous photometric observations covering similar wavelengths,
yet there exists some tension with narrowband photometry for HR 8799
c. With the addition of our spectra, each of the three innermost
observed planets in the HR 8799 system has had its spectral energy
distribution measured with integral field spectroscopy covering ~0.9-4.1
μm. We combine these spectra with measurements from the literature and
fit synthetic model atmospheres. We demonstrate that the bolometric
luminosity of the planets is not sensitive to the choice of model
atmosphere used to interpolate between measurements and extrapolate
beyond them. Combining luminosity with age and mass constraints, we
show that the predictions of evolutionary models are narrowly peaked
for effective temperature, surface gravity, and planetary radius. By
holding these parameters at their predicted values, we show that more
flexible cloud models can provide good fits to the data while being
consistent with the expectations of evolutionary models.
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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.
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Title: Cryogenic characterization of the grating vector apodizing
phase plate coronagraph for the enhanced resolution imager and
spectrograph at the Very Large Telescope
Authors: Boehle, Anna; Doelman, David; Konrad, Björn S.; Snik,
Frans; Glauser, Adrian M.; Por, Emiel H.; Warriner, Nathaniel Z.; Shi,
Shuojia; Escuti, Michael J.; Kenworthy, Matthew A.; Quanz, Sascha P.
2021JATIS...7d5001B Altcode:
We present results on the laboratory characterization of the grating
vector apodizing phase plate (gvAPP) coronagraph that will be included
in the upcoming instrument enhanced resolution imager and spectrograph
(ERIS) at the VLT. ERIS will include a 1 to 5 μm adaptive-optics-fed
imager, NIX, that will greatly improve the capability of the VLT
to perform high-contrast imaging of exoplanets especially in the
3 to 5 μm wavelength range. The gvAPP, one of the coronagraphs in
the NIX suite, is a pupil plane coronagraph that uses a thin film
of patterned liquid crystals to create two images of a star with a
D-shaped dark hole on either side. The gvAPP is manufactured using
an innovative direct-write system that produces precise patterns of
liquid crystals. We utilized the upgraded infrared cryogenic test
bench run by the Exoplanets and Habitability Group at ETH Zurich to
measure the morphology of the gvAPP PSF and to test the accuracy of the
liquid crystal manufacturing technique in the lab for the first time
at contrast levels of ∼10<SUP> − 5</SUP>. We find that the gvAPP
can reach raw contrasts below ∼10<SUP> − 5</SUP> between ∼10 and
13 λ / D. This contrast upper limit translates to a writing accuracy
of the orientation of the liquid crystal's fast axis of better than 0.3
deg for the spatial frequencies corresponding to those separations. This
is a sufficient accuracy such that the gvAPP will not be the limiting
factor in achieving the required contrasts to image exoplanets.
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Title: First on-sky demonstration of spatial Linear Dark Field
Control with the vector-Apodizing Phase Plate at Subaru/SCExAO
Authors: Bos, S. P.; Miller, K. L.; Lozi, J.; Guyon, O.; Doelman,
D. S.; Vievard, S.; Sahoo, A.; Deo, V.; Jovanovic, N.; Martinache,
F.; Currie, T.; Snik, F.
2021A&A...653A..42B Altcode: 2021arXiv210606286B
Context. One of the key noise sources that currently limits
high-contrast imaging observations for exoplanet detection is
quasi-static speckles. Quasi-static speckles originate from slowly
evolving non-common path aberrations (NCPA). These NCPA are related
to the different optics encountered in the wavefront sensing path and
the science path, and they also exhibit a chromatic component due to
the difference in the wavelength between the science camera and the
main wavefront sensor. These speckles degrade the contrast in the
high-contrast region (or dark hole) generated by the coronagraph
and make the calibration in post-processing more challenging. <BR
/> Aims: The purpose of this work is to present a proof-of-concept
on-sky demonstration of spatial Linear Dark Field Control (LDFC). The
ultimate goal of LDFC is to stabilize the point spread function
by addressing NCPA using the science image as additional wavefront
sensor. <BR /> Methods: We combined spatial LDFC with the Asymmetric
Pupil vector-Apodizing Phase Plate (APvAPP) on the Subaru Coronagraphic
Extreme Adaptive Optics system at the Subaru Telescope. To allow for
rapid prototyping and easy interfacing with the instrument, LDFC was
implemented in Python. This limited the speed of the correction loop
to approximately 20 Hz. With the APvAPP, we derive a high-contrast
reference image to be utilized by LDFC. LDFC is then deployed on-sky
to stabilize the science image and maintain the high-contrast achieved
in the reference image. <BR /> Results: In this paper, we report the
results of the first successful proof-of-principle LDFC on-sky tests. We
present results from two types of cases: (1) correction of instrumental
errors and atmospheric residuals plus artificially induced static
aberrations introduced on the deformable mirror and (2) correction
of only atmospheric residuals and instrumental aberrations. When
introducing artificial static wavefront aberrations on the DM, we find
that LDFC can improve the raw contrast by a factor of 3-7 over the dark
hole. In these tests, the residual wavefront error decreased by ∼50
nm RMS, from ∼90 nm to ∼40 nm RMS. In the case with only residual
atmospheric wavefront errors and instrumental aberrations, we show that
LDFC is able to suppress evolving aberrations that have timescales
of < 0.1-0.4 Hz. We find that the power at 10<SUP>−2</SUP>
Hz is reduced by a factor of ∼20, 7, and 4 for spatial frequency
bins at 2.5, 5.5, and 8.5λ/D, respectively. <BR /> Conclusions: We
have identified multiplied challenges that have to be overcome before
LDFC can become an integral part of science observations. The results
presented in this work show that LDFC is a promising technique for
enabling the high-contrast imaging goals of the upcoming generation
of extremely large telescopes. <P />Based on data collected at Subaru
Telescope, which is operated by the National Astronomical Observatory
of Japan.
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Title: High-contrast observations of brown dwarf companion HR 2562
B with the vector Apodizing Phase Plate coronagraph
Authors: Sutlieff, Ben J.; Bohn, Alexander J.; Birkby, Jayne L.;
Kenworthy, Matthew A.; Morzinski, Katie M.; Doelman, David S.; Males,
Jared R.; Snik, Frans; Close, Laird M.; Hinz, Philip M.; Charbonneau,
David
2021MNRAS.506.3224S Altcode: 2021arXiv210614890S; 2021MNRAS.tmp.1644S
The vector Apodizing Phase Plate (vAPP) is a class of pupil plane
coronagraph that enables high-contrast imaging by modifying the Point
Spread Function (PSF) to create a dark hole of deep flux suppression
adjacent to the PSF core. Here, we recover the known brown dwarf HR
2562 B using a vAPP coronagraph, in conjunction with the Magellan
Adaptive Optics (MagAO) system, at a signal-to-noise of S/N = 3.04 in
the lesser studied L-band regime. The data contained a mix of field
and pupil-stabilized observations, hence we explored three different
processing techniques to extract the companion, including Flipped
Differential Imaging (FDI), a newly devised Principal Component
Analysis (PCA)-based method for vAPP data. Despite the partial
field-stabilization, the companion is recovered sufficiently to
measure a 3.94 $\mu\mathrm{ m}$ narrow-band contrast of (3.05 ± 1.00)
× 10<SUP>-4</SUP> ($\Delta \, {\rm m}_{3.94 \mu {\rm m}}$ = 8.79
± 0.36 mag). Combined with archival GPI and SPHERE observations,
our atmospheric modelling indicates a spectral type at the L/T
transition with mass M = 29 ± 15 M<SUB>Jup</SUB>, consistent with
literature results. However, effective temperature and surface
gravity vary significantly depending on the wavebands considered
(1200 ≤ T<SUB>eff</SUB>(K) ≤ 1700 and 4.0 ≤ log(g)(dex)
≤ 5.0), reflecting the challenges of modelling objects at the L/T
transition. Observations between 2.4 and 3.2 $\mu\mathrm{ m}$ will be
more effective in distinguishing cooler brown dwarfs due to the onset of
absorption bands in this region. We explain that instrumental scattered
light and wind-driven halo can be detrimental to FDI+PCA and thus must
be sufficiently mitigated to use this processing technique. We thus
demonstrate the potential of vAPP coronagraphs in the characterization
of high-contrast substellar companions, even in sub-optimal conditions,
and provide new complementary photometry of HR 2562 B.
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Title: The Young Suns Exoplanet Survey: imaging infant planets around
young, solar analogs
Authors: Kenworthy, Matthew; Bohn, Alexander; Ginski, Christian;
Reggiani, Maddalena; Meshkat, Tiffany; Mamajek, Eric; Pecaut, Mark;
Snik, Frans
2021EPSC...15...35K Altcode:
Within the Young Suns Exoplanet Survey (YSES) we are observing a
homogeneous sample of 70 solar-mass members of the approximately
16 Myr-old Lower Centaurus-Crux subgroup of the Scorpius-Centaurus
association to search for sub-stellar companions.High-contrast imaging
observations with VLT/SPHERE/IRDIS revealed (i) a shadowed transition
disk around Wray 15-788 that shows significant signs of ongoing planet
formation and (ii) one of the lowest-mass companions imaged to date:
YSES-2 b has a mass of 6.5 Jupiter masses and is orbiting its solar-mass
primary at a separation of 110 au. Most intriguing, though, was (iii)
the discovery of the first directly imaged multi-planet system around
a Sun-like star. The detection of two gas-giant companions of 14±3
and 6±1 Jupiter masses that are orbiting YSES-1 (TYC 8998-760-1)
at separations of 160 au and 320 au, respectively, provides important
implications for the outer architecture of planetary systems and the
underlying formation mechanisms.In addition to the SPHERE observations,
we identified further companions to our `Young Suns' outside the
instrument's field of view in the third early data release of the
Gaia mission. Based on parallaxes and proper motions provided in this
catalogue, we detected eight additional sub-stellar companions at
separations larger than 500 au amongst our sample.By combining Gaia
astrometry with the high-contrast imaging capabilities of SPHERE,
our survey will provide a complete census of wide-orbit sub-stellar
companions for a statistically highly significant sample of young,
solar analogues. From the current results we derived a preliminary
probability of 14.3±3.1% for our solar-type stars to host wide-orbit,
sub-stellar companions. As follow-up observations of 45 YSES targets are
still pending, this ratio can be interpreted as a lower limit, which is
tentatively indicating a higher companion yield than previous surveys.
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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.
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Title: The Santa Cruz Extreme AO Lab (SEAL): design and first light
Authors: Jensen-Clem, Rebecca; Dillon, Daren; Gerard, Benjamin; van
Kooten, M. A. M.; Fowler, J.; Kupke, Renate; Cetre, Sylvain; Sanchez,
Dominic; Hinz, Philip; Laguna, Cesar; Doelman, David; Snik, Frans
2021SPIE11823E..1DJ Altcode: 2021arXiv210903318J
The Santa Cruz Extreme AO Lab (SEAL) is a new visible-wavelength testbed
designed to advance the state of the art in wavefront control for high
contrast imaging on large, segmented, ground-based telescopes. SEAL
provides multiple options for simulating atmospheric turbulence,
including a custom spatial light modulator. A 37-segment deformable
mirror simulates the W. M. Keck Observatory segmented primary
mirror. The adaptive optics system consists of a woofer/tweeter DM
system, and four wavefront sensor arms: 1) a high-speed Shack-Hartmann
WFS, 2) a reflective pyramid WFS, 3) vector-Zernike mask, and 4) a Fast
Atmospheric SCC Technique demonstration arm. Finally, a science arm
preliminarily includes a classical Lyot-style coronagraph. SEAL's real
time control system is based on the CACAO package, and is designed to
support the efficient transfer of software between SEAL and the Keck
II AO system. In this paper, we present an overview of the design and
first light performance of SEAL.
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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.
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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.
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Title: Full characterization of the instrumental polarization effects
of the spectropolarimetric mode of SCExAO-CHARIS
Authors: Joost `t Hart, G. J.; van Holstein, Rob G.; Bos, Steven P.;
Ruigrok, Jasper; Snik, Frans; Lozi, Julien; Guyon, Olivier; Kudo,
Tomoyuki; Zhang, Jin; Jovanovic, Nemanja; Norris, Barnaby; Martinod,
Marc-Antoine; Groff, Tyler D.; Chilcote, Jeffrey; Currie, Thayne;
Tamura, Motohide; Vievard, Sébastien; Sahoo, Ananya; Deo, Vincent;
Ahn, Kyohoon; Martinache, Frantz; Kasdin, Jeremy
2021arXiv210804833J Altcode: 2021arXiv210804833H
SCExAO at the Subaru telescope is a visible and near-infrared
high-contrast imaging instrument employing extreme adaptive optics
and coronagraphy. The instrument feeds the near-infrared light (JHK)
to the integral-field spectrograph CHARIS. The spectropolarimetric
capability of CHARIS is enabled by a Wollaston prism and is unique
among high-contrast imagers. We present a detailed Mueller matrix
model describing the instrumental polarization effects of the complete
optical path, thus the telescope and instrument. From measurements with
the internal light source, we find that the image derotator (K-mirror)
produces strongly wavelength-dependent crosstalk, in the worst case
converting ~95% of the incident linear polarization to circularly
polarized light that cannot be measured. Observations of an unpolarized
star show that the magnitude of the instrumental polarization of the
telescope varies with wavelength between 0.5% and 1%, and that its angle
is exactly equal to the altitude angle of the telescope. Using physical
models of the fold mirror of the telescope, the half-wave plate, and
the derotator, we simultaneously fit the instrumental polarization
effects in the 22 wavelength bins. Over the full wavelength range,
our model currently reaches a total polarimetric accuracy between 0.08%
and 0.24% in the degree of linear polarization. We propose additional
calibration measurements to improve the polarimetric accuracy to
<0.1% and plan to integrate the complete Mueller matrix model
into the existing CHARIS post-processing pipeline. Our calibrations
of CHARIS' spectropolarimetric mode will enable unique quantitative
polarimetric studies of circumstellar disks and planetary and brown
dwarf companions.
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Title: Full characterization of the instrumental polarization effects
of the spectropolarimetric mode of SCExAO/CHARIS
Authors: 't Hart, Joost G. J.; van Holstein, Rob G.; Bos, Steven P.;
Ruigrok, Jasper; Snik, Frans; Lozi, Julien; Guyon, Olivier; Kudo,
Tomoyuki; Zhang, Jin; Jovanovic, Nemanja; Norris, Barnaby; Martinod,
Marc-Antoine; Groff, Tyler D.; Chilcote, Jeffrey; Currie, Thayne;
Tamura, Motohide; Vievard, Sébastien; Sahoo, Ananya; Deo, Vincent;
Ahn, Kyohoon; Martinache, Frantz; Kasdin, Jeremy
2021SPIE11833E..0OT Altcode: 2021SPIE11833E..0O'
SCExAO at the Subaru telescope is a visible and near-infrared
high-contrast imaging instrument employing extreme adaptive optics and
coronagraphy. The instrument feeds the near-infrared light (JHK) to the
integralfield spectrograph CHARIS. The spectropolarimetric capability of
CHARIS is enabled by a Wollaston prism and is unique among high-contrast
imagers. We present a detailed Mueller matrix model describing the
instrumental polarization effects of the complete optical path, thus
the telescope and instrument. From measurements with the internal light
source, we find that the image derotator (K-mirror) produces strongly
wavelength-dependent crosstalk, in the worst case converting ∼95%
of the incident linear polarization to circularly polarized light that
cannot be measured. Observations of an unpolarized star show that the
magnitude of the instrumental polarization of the telescope varies with
wavelength between 0.5% and 1%, and that its angle is exactly equal
to the altitude angle of the telescope. Using physical models of the
fold mirror of the telescope, the half-wave plate, and the derotator,
we simultaneously fit the instrumental polarization effects in the 22
wavelength bins. Over the full wavelength range, our model currently
reaches a total polarimetric accuracy between 0.08% and 0.24% in the
degree of linear polarization. We propose additional calibration
measurements to improve the polarimetric accuracy to <0.1%
and plan to integrate the complete Mueller matrix model into the
existing CHARIS post-processing pipeline. Our calibrations of CHARIS'
spectropolarimetric mode will enable unique quantitative polarimetric
studies of circumstellar disks and planetary and brown dwarf companions.
---------------------------------------------------------
Title: Pupil-Plane Phase Apodization
Authors: Kenworthy, Matthew A.; Codona, Johanan L.; Snik, Frans
2021hai3.book..377K Altcode: 2018arXiv180711242K
Phase apodization coronagraphs are implemented in a pupil plane
to create a dark hole in the science camera focal plane. They are
successfully created as "Apodizing Phase Plates" (APPs) using classical
optical manufacturing, and as "vector-APPs" using liquid-crystal
patterning with essentially achromatic performance. This type
of coronagraph currently delivers excellent broadband contrast
($\sim$10$^{-5}$) at small angular separations (few $\lambda/D$)
at ground-based telescopes, owing to their insensitivity to tip/tilt
errors.
---------------------------------------------------------
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 ($>96\%$) 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: The <SUP>13</SUP>CO-rich atmosphere of a young accreting
super-Jupiter
Authors: Zhang, Yapeng; Snellen, Ignas A. G.; Bohn, Alexander J.;
Mollière, Paul; Ginski, Christian; Hoeijmakers, H. Jens; Kenworthy,
Matthew A.; Mamajek, Eric E.; Meshkat, Tiffany; Reggiani, Maddalena;
Snik, Frans
2021Natur.595..370Z Altcode: 2021arXiv210706297Z
Isotope abundance ratios have an important role in astronomy
and planetary sciences, providing insights into the origin and
evolution of the Solar System, interstellar chemistry and stellar
nucleosynthesis<SUP>1,2</SUP>. In contrast to deuterium/hydrogen ratios,
carbon isotope ratios are found to be roughly constant (around 89)
in the Solar System<SUP>1,3</SUP>, but do vary on galactic scales
with a <SUP>12</SUP>C/<SUP>13</SUP>C isotopologue ratio of around 68
in the current local interstellar medium<SUP>4-6</SUP>. In molecular
clouds and protoplanetary disks, <SUP>12</SUP>CO/<SUP>13</SUP>CO
ratios can be altered by ice and gas partitioning<SUP>7</SUP>,
low-temperature isotopic ion-exchange reactions<SUP>8</SUP> and
isotope-selective photodissociation<SUP>9</SUP>. Here we report
observations of <SUP>13</SUP>CO in the atmosphere of the young,
accreting super-Jupiter TYC 8998-760-1 b, at a statistical significance
of more than six sigma. Marginalizing over the planet's atmospheric
temperature structure, chemical composition and spectral calibration
uncertainties suggests a <SUP>12</SUP>CO/<SUP>13</SUP>CO ratio of
31<SUB>−10</SUB><SUP>+17</SUP>?(90% confidence), a substantial
enrichment in <SUP>13</SUP>C with respect to the terrestrial standard
and the local interstellar value. As the current location of TYC
8998-760-1 b at greater than or equal to 160 astronomical units is far
beyond the CO snowline, we postulate that it accreted a substantial
fraction of its carbon from ices enriched in <SUP>13</SUP>C through
fractionation.
---------------------------------------------------------
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 > 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: 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: Discovery of a directly imaged planet to the young solar
analog YSES 2
Authors: Bohn, Alexander J.; Ginski, Christian; Kenworthy, Matthew A.;
Mamajek, Eric E.; Pecaut, Mark J.; Mugrauer, Markus; Vogt, Nikolaus;
Adam, Christian; Meshkat, Tiffany; Reggiani, Maddalena; Snik, Frans
2021A&A...648A..73B Altcode: 2021arXiv210408285B
Context. To understand the origin and formation pathway of wide-orbit
gas giant planets, it is necessary to expand the limited sample of these
objects. The mass of exoplanets derived with spectrophotometry, however,
varies strongly as a function of the age of the system and the mass
of the primary star. <BR /> Aims: By selecting stars with similar ages
and masses, the Young Suns Exoplanet Survey (YSES) aims to detect and
characterize planetary-mass companions to solar-type host stars in the
Scorpius-Centaurus association. <BR /> Methods: Our survey is carried
out with VLT/SPHERE with short exposure sequences on the order of 5
min per star per filter. The subtraction of the stellar point spread
function (PSF) is based on reference star differential imaging using
the other targets (with similar colors and magnitudes) in the survey
in combination with principal component analysis. Two astrometric
epochs that are separated by more than one year are used to confirm
co-moving companions by proper motion analysis. <BR /> Results: We
report the discovery of YSES 2b, a co-moving, planetary-mass companion
to the K1 star YSES 2 (TYC 8984-2245-1, 2MASS J11275535-6626046). The
primary has a Gaia EDR3 distance of 110 pc, and we derive a revised
mass of 1.1 M<SUB>⊙</SUB> and an age of approximately 14 Myr. We
detect the companion in two observing epochs southwest of the star
at a position angle of 205° and with a separation of ~1."05, which
translates to a minimum physical separation of 115 au at the distance
of the system. Photometric measurements in the H and K<SUB>s</SUB>
bands are indicative of a late L spectral type, similar to the
innermost planets around HR 8799. We derive a photometric planet
mass of 6.3<SUB>−0.9</SUB><SUP>+1.6</SUP> M<SUB>Jup</SUB> using
AMES-COND and AMES-dusty evolutionary models; this mass corresponds
to a mass ratio of q = (0.5 ± 0.1)% with the primary. This is the
lowest mass ratio of a direct imaging planet around a solar-type star
to date. We discuss potential formation mechanisms and find that
the current position of the planet is compatible with formation by
disk gravitational instability, but its mass is lower than expected
from numerical simulations. Formation via core accretion must have
occurred closer to the star, yet we do not find evidence that supports
the required outward migration, such as via scattering off another
undiscovered companion in the system. We can exclude additional
companions with masses greater than 13 M<SUB>Jup</SUB> in the full
field of view of the detector (0."15<ρ<5."50), at 0."5 we can
rule out further objects that are more massive than 6 M<SUB>Jup</SUB>,
and for projected separations ρ >2" we are sensitive to planets with
masses as low as 2 M<SUB>Jup</SUB>. <BR /> Conclusions: YSES 2b is an
ideal target for follow-up observations to further the understanding
of the physical and chemical formation mechanisms of wide-orbit Jovian
planets. The YSES strategy of short snapshot observations (≤5 min)
and PSF subtraction based on a large reference library proves to be
extremely efficient and should be considered for future direct imaging
surveys. <P />Data are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr">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/648/A73">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/648/A73</A>
<P />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), 0101.C-0341(A), and 106.20X2.001.
---------------------------------------------------------
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: VizieR Online Data Catalog: Discovery of the directly imaged
planet YSES 2b (Bohn+, 2021)
Authors: Bohn, A. J.; Ginski, C.; Kenworthy, M. A.; Mamajek, E. E.;
Pecaut, M. J.; Mugrauer, M.; Vogt, N.; Adam, C.; Meshkat, T.; Reggiani,
M.; Snik, F.
2021yCat..36480073B 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. Furthermore, the achieved
contrast performance that is presented in the paper is included in
this catalogue. <P />(6 data files).
---------------------------------------------------------
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 <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: Spatial linear dark field control on Subaru/SCExAO. Maintaining
high contrast with a vAPP coronagraph
Authors: Miller, K. L.; Bos, S. P.; Lozi, J.; Guyon, O.; Doelman,
D. S.; Vievard, S.; Sahoo, A.; Deo, V.; Jovanovic, N.; Martinache,
F.; Snik, F.; Currie, T.
2021A&A...646A.145M Altcode:
Context. One of the key challenges facing direct exoplanet imaging is
the continuous maintenance of the region of high contrast within which
light from the exoplanet can be detected above the stellar noise. In
high-contrast imaging systems, the dominant source of aberrations is the
residual wavefront error that arises due to non-common path aberrations
(NCPA) to which the primary adaptive optics (AO) system is inherently
blind. Slow variations in the NCPA generate quasi-static speckles in
the post-AO corrected coronagraphic image resulting in the degradation
of the high-contrast dark hole created by the coronagraph. <BR />
Aims: In this paper, we demonstrate spatial linear dark field control
(LDFC) with an asymmetric pupil vector apodizing phase plate (APvAPP)
coronagraph as a method to sense time-varying NCPA using the science
image as a secondary wavefront sensor (WFS) running behind the primary
AO system. By using the science image as a WFS, the NCPA to which
the primary AO system is blind can be measured with high sensitivity
and corrected, thereby suppressing the quasi-static speckles which
corrupt the high contrast within the dark hole. <BR /> Methods: On
the Subaru Coronagraphic Extreme Adaptive Optics instrument (SCExAO),
one of the coronagraphic modes is an APvAPP which generates two PSFs,
each with a 180° D-shaped dark hole with approximately 10<SUP>-4</SUP>
contrast at λ = 1550 nm. The APvAPP was utilized to first remove
the instrumental NCPA in the system and increase the high contrast
within the dark holes. Spatial LDFC was then operated in closed-loop to
maintain this high contrast in the presence of a temporally-correlated,
evolving phase aberration with a root-mean-square wavefront error of
80 nm. In the tests shown here, an internal laser source was used,
and the deformable mirror was used both to introduce random phase
aberrations into the system and to then correct them with LDFC in
closed-loop operation. <BR /> Results: The results presented here
demonstrate the ability of the APvAPP combined with spatial LDFC to
sense aberrations in the high amplitude regime (∼80 nm). With LDFC
operating in closed-loop, the dark hole is returned to its initial
contrast and then maintained in the presence of a temporally-evolving
phase aberration. We calculated the contrast in 1 λ/D spatial frequency
bins in both open-loop and closed-loop operation, and compared the
measured contrast in these two cases. This comparison shows that with
LDFC operating in closed-loop, there is a factor of ∼3x improvement
(approximately a half magnitude) in contrast across the full dark hole
extent from 2-10 λ/D. This improvement is maintained over the full
duration (10 000 iterations) of the injected temporally-correlated,
evolving phase aberration. <BR /> Conclusions: This work marks the
first deployment of spatial LDFC on an active high-contrast imaging
instrument. Our SCExAO testbed results show that the combination of
the APvAPP with LDFC provides a powerful new focal plane wavefront
sensing technique by which high-contrast imaging systems can maintain
high contrast during long observations. This conclusion is further
supported by a noise analysis of LDFC's performance with the APvAPP
in simulation. <P />Based on data collected at Subaru Telescope,
which is operated by the National Astronomical Observatory of Japan.
---------------------------------------------------------
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: Status of the SCExAO instrument: recent technology upgrades
and path to a system-level demonstrator for PSI
Authors: Lozi, Julien; Guyon, Olivier; Vievard, Sébastien; Sahoo,
Ananya; Deo, Vincent; Jovanovic, Nemanja; Norris, Barnaby; Martinod,
Marc-Antoine; Mazin, Ben; Walter, Alex; Fruitwala, Neelay; Steiger,
Sarah; Davis, Kristina; Tuthill, Peter; Kudo, Tomoyuki; Kawahara,
Hajime; Kotani, Takayuki; Ireland, Michael; Anagnos, Theodoros;
Schwab, Chrstian; Cvetojevic, Nick; Huby, Elsa; Lacour, Sylvestre;
Barjot, Kevin; Groff, Tyler D.; Chilcote, Jeffrey; Kasdin, Jeremy;
Martinache, Frantz; Laugier, Romain; N'Diaye, Mamadou; Knight, Justin;
Males, Jared; Bos, Steven; Snik, Frans; Doelman, David; Miller, Kelsey;
Bendek, Eduardo; Belikov, Ruslan; Pluzhnik, Eugene; Currie, Thayne;
Kuzuhara, Masayuki; Uyama, Taichi; Nishikawa, Jun; Murakami, Naoshi;
Hashimoto, Jun; Minowa, Yosuke; Clergeon, Christophe; Ono, Yoshito;
Takato, Naruhisa; Tamura, Motohide; Takami, Hideki; Hayashi, Masa
2020SPIE11448E..0NL Altcode:
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument
is a high-contrast imaging system installed at the 8-m Subaru Telescope
on Maunakea, Hawaii. Due to its unique evolving design, SCExAO is both
an instrument open for use by the international scientific community,
and a testbed validating new technologies, which are critical to
future high-contrast imagers on Giant Segmented Mirror Telescopes
(GSMTs). Through multiple international collaborations over the
years, SCExAO was able to test the most advanced technologies in
wavefront sensors, real-time control with GPUs, low-noise high frame
rate detectors in the visible and infrared, starlight suppression
techniques or photonics technologies. Tools and interfaces were put
in place to encourage collaborators to implement their own hardware
and algorithms, and test them on-site or remotely, in laboratory
conditions or on-sky. We are now commissioning broadband coronagraphs,
the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera
(MEC) for high-speed speckle control, as well as a C-RED ONE camera for
both polarization differential imaging and IR wavefront sensing. New
wavefront control algorithms are also being tested, such as predictive
control, multi-camera machine learning sensor fusion, and focal plane
wavefront control. We present the status of the SCExAO instrument,
with an emphasis on current collaborations and recent technology
demonstrations. We also describe upgrades planned for the next few
years, which will evolve SCExAO —and the whole suite of instruments
on the IR Nasmyth platform of the Subaru Telescope— to become a
system-level demonstrator of the Planetary Systems Imager (PSI),
the high-contrast instrument for the Thirty Meter Telescope (TMT).
---------------------------------------------------------
Title: New NIR spectro-polarimetric modes for the SCExAO instrument
Authors: Lozi, Julien; Guyon, Olivier; Kudo, Tomoyuki; Zhang, Jin;
Jovanovic, Nemanja; Norris, Barnaby; Martinod, Marc-Antoine; Groff,
Tyler D.; Chilcote, Jeffrey; Tamura, Motohide; Bos, Steven; Snik,
Frans; Vievard, Sébastien; Sahoo, Ananya; Deo, Vincent; Martinache,
Frantz; Kasdin, Jeremy
2020SPIE11448E..7CL Altcode:
Polarization Differential Imaging (PDI) is one of the most productive
modes of current high-contrast imagers. Dozens of new protoplanetary,
transition and debris disks were imaged recently for the first time,
helping us understand the processes of planet formation, and giving
clues on the mass of potential planets inside these disks, even if
they cannot be imaged directly. The Subaru Coronagraphic Extreme
Adaptive Optics (SCExAO) instrument is equipped with a fast visible
dual-camera polarimetric module, VAMPIRES, already producing valuable
scientific observations of protoplanetary disks and dust shells. In
addition, we recently commissioned two new polarimetric modules in
the infrared. The first one is a spectro-polarimetric mode using
the CHARIS Integral Field Spectrograph (IFS). A Wollaston prism was
added in front of the IFS, reducing the field-of-view to 2x1 arcsec to
accommodate for the imaging of both polarizations on the same detector
without sacrificing the spectral resolution of the instrument, in
any of its spectral modes. The second module, similar to VAMPIRES,
uses a low-noise high frame rate C-RED ONE camera combined with a
Ferroelectric Liquid Crystal (FLC) device to modulate and record
the polarization at high-speed, freezing effectively the atmospheric
speckles for higher precision. We present on-sky results of the new
polarimetric capabilities taken during the commissioning phase. In
addition, we show future capabilities that are already scheduled to
increase the performance of these modules, especially the addition of
non-redundant masks, as well as a polarimetric vector Apodizing Phase
Plate (vAPP) coronagraph.
---------------------------------------------------------
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: A Search for Polarized Thermal Emission from Directly Imaged
Exoplanets and Brown Dwarf Companions to Nearby Stars
Authors: Jensen-Clem, Rebecca; Millar-Blanchaer, Maxwell A.; van
Holstein, Rob G.; Mawet, Dimitri; Graham, James; Sengupta, Sujan;
Marley, Mark S.; Snik, Frans; Vigan, Arthur; Hinkley, Sasha; de
Boer, Jos; Girard, Julien H.; De Rosa, Robert J.; Bowler, Brendan
P.; Wiktorowicz, Sloane J.; Perrin, Marshall D.; Crepp, Justin R.;
Macintosh, Bruce
2020AJ....160..286J Altcode:
Aerosols in the atmospheres of cloudy gas giant exoplanets and brown
dwarfs scatter and polarize these objects' thermal emission. If such
an object has an oblate shape or nonuniform cloud distribution, the
net degree of linear polarization can show an increase ranging from
several tenths of a percent to a few percent. Modern high-contrast
imaging polarimeters are now poised to detect such low-polarization
signals, opening up a new window into the rotational velocities
and cloud properties of substellar companions to nearby stars. In
this paper, we present the results of a near-IR survey searching
for linearly polarized thermal emission from a sample of two
planetary-mass companions and five brown dwarf companions using GPI
and SPHERE-IRDIS. We probe the subpercent linear polarization regime
that typifies polarized free-floating brown dwarfs and place limits on
each object's degree of linear polarization. We relate our upper limits
on each target's degree of linear polarization to its rotation rate,
and place our results in the context of rotation rates measured using
high-resolution spectroscopy.
---------------------------------------------------------
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 (< 70%), high resolution (19 mas),
and high contrast (< 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: New concepts in vector-apodizing phase plate coronagraphy
Authors: Bos, Steven P.; Doelman, David S.; Miller, Kelsey L.;
Snik, Frans
2020SPIE11448E..3WB Altcode: 2020arXiv201200462B
The vector-Apodizing Phase Plate (vAPP) is a pupil-plane coronagraph
that manipulates phase to create darkholes in the stellar PSF. The
phase is induced on the circular polarization states through the
inherently achromatic geometric phase by spatially varying the fast axis
orientation of a half-wave liquid-crystal layer. The two polarized PSFs
can be separated, either by a quarter-wave plate (QWP) followed by a
polarizing beamsplitter (PBS) for broadband operation, or a polarization
sensitive grating (PSG) for narrowband or IFS operation. Here we
present new vAPP concepts that lift the restrictions of previous
designs and report on their performance. We demonstrated that the
QWP+PBS combination puts tight tolerances on the components to prevent
leakage of non-coronagraphic light into the dark-hole. We present a new
broadband design using an innovative two-stage patterned liquid-crystal
element system based on multi-color holography, alleviating the leakage
problem and relaxing manufacturing tolerances. Furthermore, we have
shown that focal-plane wavefront sensing (FPWFS) can be integrated
into the vAPP by an asymmetric pupil. However, such vAPPs suffer
from a reduced throughput and have only been demonstrated with a PSG
in narrowband operation. We present advanced designs that maintain
throughput and enable phase and amplitude wavefront sensing. We also
present broadband vAPP FPWFS designs and outline a broadband FPWFS
algorithm. Finally, previous dual-beam vAPP designs for sensitive
polarimetry with one-sided dark holes were very complex. We show new
dual-beam designs that significantly reduce the complexity.
---------------------------------------------------------
Title: Calibration of the instrumental polarization effects of
SCExAO-CHARIS' spectropolarimetric mode
Authors: van Holstein, Rob G.; Bos, Steven P.; Ruigrok, Jasper;
Lozi, Julien; Guyon, Olivier; Norris, Barnaby; Snik, Frans; Chilcote,
Jeffrey; Currie, Thayne; Groff, Tyler D.; 't Hart, Joost; Jovanovic,
Nemanja; Kasdin, Jeremy; Kudo, Tomoyuki; Martinache, Frantz; Mazin,
Ben; Sahoo, Ananya; Tamura, Motohide; Vievard, Sébastien; Walter,
Alex; Zhang, Jin
2020SPIE11447E..5BV Altcode: 2020arXiv201200475V
SCExAO at the Subaru telescope is a visible and near-infrared
high-contrast imaging instrument employing extreme adaptive optics
and coronagraphy. The instrument feeds the near-infrared light (JHK)
to the integral field spectrograph CHARIS. Recently, a Wollaston prism
was added to CHARIS' optical path, giving CHARIS a spectropolarimetric
capability that is unique among high-contrast imaging instruments. We
present a comprehensive and detailed Mueller matrix model describing the
instrumental polarization effects of the complete optical path, thus the
telescope and instrument, using measurements with the internal source
and observations of standard stars. The 22 wavelength bins of CHARIS
provide a unique opportunity to investigate in detail the wavelength
dependence of the instrumental polarization effects. We find that
the image derotator (K-mirror) produces strongly wavelength-dependent
crosstalk, in the worst case converting ~95% of the incident linear
polarization to circularly polarized light that cannot be measured. We
fit the crosstalk of the half-wave plate (HWP) for all wavelengths
with a simple two-parameter model of an achromatic HWP consisting
of a layer of quartz and a layer of MgF2. While the magnitude of
the telescope-induced polarization varies with wavelength, its angle
varies solely with the altitude angle of the telescope. We show initial
steps toward correcting on-sky data for the instrumental polarization
effects, with which we aim to achieve a polarimetric accuracy <0.1%
in the degree of linear polarization. Our calibrations of CHARIS'
spectropolarimetric mode enable unique quantitative polarimetric
studies of circumstellar disks and planetary and brown dwarf companions.
---------------------------------------------------------
Title: Validating advanced wavefront control techniques on the
SCExAO testbed/instrument
Authors: Guyon, Olivier; Lozi, Julien; Vievard, Sebastien; Belikov,
Ruslan; Bendek, Eduardo; Bos, Steven; Currie, Thayne; Deo, Vincent;
Fitzgerald, Michael; Gratadour, Damien; Groff, Tyler; Jovanovic,
Nemanja; Kawahara, Hajime; Kotani, Takayuki; Kudo, Tomoyuki; Lopez,
Coline; Ltaief, Hatem; Males, Jared; Martinache, Frantz; Martinod,
Marc-Antoine; Mazin, Benjamin A.; Miller, Kelsey; Norris, Barnaby;
Ndiaye, Mamadou; Pluzhnyk, Eugene; Sahoo, Ananya; Sevin, Arnaud;
Skaf, Nour; Snik, Frans; Tamura, Motohide; Wong, Alison
2020SPIE11448E..1ZG Altcode:
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) serves both
a science instrument in operation, and a prototyping platform for
integrating and validating advanced wavefront control techniques. It
provides a modular hardware and software environment optimized for
flexible prototyping, reducing the time from concept formulation to
on-sky operation and validation. This approach also enables external
research group to deploy and test new hardware and algorithms. The
hardware architecture allows for multiple subsystems to run
concurrently, sharing starlight by means of dichroics. The multiplexing
lends itself to running parallel experiments simultaneously, and
developing sensor fusion approaches for increased wavefront sensing
sensitivity and reliability. Thanks to a modular realtime control
software architecture designed around the CACAO package, users can
deploy WFS/C routines with full low-latency access to all cameras
data streams. Algorithms can easily be shared with other cacao-based
AO systems at Magellan (MagAO-X) and Keck. We highlight recent
achievements and ongoing activities that are particularly relevant
to the development of high contrast imaging instruments for future
large ground-based telescopes (ELT, TMT, GMT) and space telescopes
(HabEx, LUVOIR). These include predictive control and sensor fusion,
PSF reconstruction from AO telemetry, integrated coronagraph/WFS
development, focal plane speckle control with photon counting MKIDS
camera, and fiber interferometry. We also describe upcoming upgrades to
the WFS/C architecture: a new 64x64 actuator first stage DM, deployment
of a beam switcher for concurrent operation of SCExAO with other science
instruments, and the ULTIMATE upgrade including deployment of multiple
LGS WFSs and an adaptive secondary mirror.
---------------------------------------------------------
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: METIS high-contrast imaging: design and expected performance
(Erratum)
Authors: Carlomagno, Brunella; Delacroix, Christian; Absil, Olivier;
Cantalloube, Faustine; de Xivry, Gilles Orban; Pathak, Prashant; Agocs,
Tibor; Bertram, Thomas; Brandl, Bernhard; Burtscher, Leonard; Doelman,
David; Feldt, Markus; Glauser, Adrian; Hippler, Stefan; Kenworthy,
Matthew; Por, Emiel; Snik, Frans; Stuik, Remko; van Boekel, Roy
2020JATIS...6d9801C Altcode:
This erratum corrects the omission of authors and references from the
paper as it was originally published.
---------------------------------------------------------
Title: LOUPE: Spectropolarimetry in the Search for (Extra)Terrestrial
Life
Authors: Klindžić, Dora; Stam, Daphne; Snik, Frans; Pallichadath,
Vidhya; van Dijk, Chris; Esposito, Marco
2020EPSC...14..887K Altcode:
Since the discovery of the first planets orbiting other stars in the
1990"s, the field of exoplanetary study has come to understand that
Earth-like planets, i.e. rocky planets in the habitable zone, are more
common than previously thought. Astronomical spectropolarimetry will
hold the key in characterizing these exoplanets, including deriving
their atmospheric and surface properties from linearly polarized
light, such as the presence of oxygen, liquid water, continents,
oceans, clouds, vegetation, ice, deserts; and even their circularly
polarized biomarkers - signs of homochiral extraterrestrial life. But,
in order to recognize life in the Universe, we ought to first use
life on Earth as an observational benchmark.We present a novel
spectropolarimetric instrument design: LOUPE, the Lunar Observatory
for Unresolved Polarimetry of the Earth (Klindžić+, submitted),
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: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.Fig 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: Detection of polarization neutral points in observations of the
combined corona and sky during the 21 August 2017 total solar eclipse
Authors: Snik, Frans; Bos, Steven P.; Brackenhoff, Stefanie A.;
Doelman, David S.; Por, Emiel H.; Bettonvil, Felix; Rodenhuis, Michiel;
Vorobiev, Dmitry; Eshelman, Laura M.; Shaw, Joseph A.
2020ApOpt..59F..71S Altcode: 2020arXiv200712482S
We report the results of polarimetric observations of the total solar
eclipse of 21 August 2017 from Rexburg, Idaho (USA). We use three
synchronized DSLR cameras with polarization filters oriented at 0°,
60°, and 120° to provide high-dynamic-range RGB polarization images
of the corona and surrounding sky. We measure tangential coronal
polarization and vertical sky polarization, both as expected. These
observations provide detailed detections of polarization neutral points
above and below the eclipsed Sun where the coronal polarization is
canceled by the sky polarization. We name these special polarization
neutral points after Minnaert and Van de Hulst.
---------------------------------------------------------
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
> 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&F), can be used to measure and correct the IE/LWE. The
F&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&F can
correct a wide variety of LWE phase screens. Subsequently, F&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&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 > 90% and an VAR ⪅ 0.05. Furthermore, the
on-sky results show that F&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&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&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: VSTpol: the first large survey telescope for optical
polarimetry
Authors: Covino, S.; Smette, A.; Snik, F.
2020vstb.conf...20C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: First Images of the Protoplanetary Disk around PDS 201
Authors: Wagner, Kevin; Stone, Jordan; Dong, Ruobing; Ertel, Steve;
Apai, Daniel; Doelman, David; Bohn, Alexander; Najita, Joan; Brittain,
Sean; Kenworthy, Matthew; Keppler, Miriam; Webster, Ryan; Mailhot,
Emily; Snik, Frans
2020AJ....159..252W Altcode: 2020arXiv200406157W
Scattered light imaging has revealed nearly a dozen circumstellar disks
around young Herbig Ae/Be stars—enabling studies of structures in the
upper disk layers as potential signs of ongoing planet formation. We
present the first images of the disk around the variable Herbig Ae star
PDS 201 (V* V351 Ori) and an analysis of the images and spectral energy
distribution through 3D Monte Carlo radiative transfer simulations
and forward modeling. The disk is detected in three data sets with
the Large Binocular Telescope Interferometer/Large Binocular Telescope
mid-infrared camera at the Large Binocular Telescope, including direct
observations in the Ks and L' filters, and an L' observation with the
360° vector apodizing phase plate coronagraph. The scattered light
disk extends to a very large radius of ∼250 au, which places it among
the largest of such disks. Exterior to the disk, we establish detection
limits on substellar companions down to ∼5 M<SUB>Jup</SUB> at ≳1"5
(≳500 au), assuming the Baraffe et al. models. The images show a
radial gap extending to ∼0"4 (∼140 au at a distance of 340 pc)
that is also evident in the spectral energy distribution. The large
gap is a possible signpost of multiple high-mass giant planets at
orbital distances (∼60-100 au) that are unusually massive and widely
separated compared to those of planet populations previously inferred
from protoplanetary disk substructures.
---------------------------------------------------------
Title: Detection of Polarization due to Cloud Bands in the Nearby
Luhman 16 Brown Dwarf Binary
Authors: Millar-Blanchaer, Maxwell A.; Girard, Julien H.; Karalidi,
Theodora; Marley, Mark S.; van Holstein, Rob G.; Sengupta, Sujan;
Mawet, Dimitri; Kataria, Tiffany; Snik, Frans; de Boer, Jos;
Jensen-Clem, Rebecca; Vigan, Arthur; Hinkley, Sasha
2020ApJ...894...42M Altcode:
Brown dwarfs exhibit patchy or spatially varying banded cloud
structures that are inferred through photometric and spectroscopic
variability modeling techniques. However, these methods are insensitive
to rotationally invariant structures, such as the bands seen in
Jupiter. Here, we present H-band Very Large Telescope/NaCo linear
polarization measurements of the nearby Luhman 16 L/T transition
binary, which suggest that Luhman 16A exhibits constant longitudinal
cloud bands. The instrument was operated in pupil tracking mode,
allowing us to unambiguously distinguish between a small astrophysical
polarization and the ∼2% instrumental linear polarization. We measure
the degree and angle of linear polarization of Luhman 16A and B to be
p<SUB>A</SUB> = 0.031% ± 0.004% and ψ<SUB>A</SUB> = -32° ± 4°, and
p<SUB>B</SUB> = 0.010% ± 0.004% and ${\psi }_{B}={73}_{-11}^{+13\circ}
$ , respectively. Using known physical parameters of the system, we
demonstrate that an oblate homogeneous atmosphere cannot account for
the polarization measured in Luhman 16A, but could be responsible for
that of the B component. Through a nonexhaustive search of banded cloud
morphologies, we demonstrate a two-banded scenario that can achieve
a degree of linear polarization of p = 0.03% and conclude that the
measured polarization of the A component must be predominantly due to
cloud banding. For Luhman 16B, either oblateness or cloud banding could
be the dominant source of the measured polarization. The misaligned
polarization angles of the two binary components tentatively suggest
spin-orbit misalignment. These measurements provide new evidence for
the prevalence of cloud banding in brown dwarfs while at the same
time demonstrating a new method—complementary to photometric and
spectroscopic variability methods—for characterizing the cloud
morphologies of substellar objects without signs of variability.
---------------------------------------------------------
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: Minimizing the Polarization Leakage of Geometric-phase
Coronagraphs with Multiple Grating Pattern Combinations
Authors: Doelman, David S.; Por, Emiel H.; Ruane, Garreth; Escuti,
Michael J.; Snik, Frans
2020PASP..132d5002D Altcode: 2020arXiv200205622D
The design of liquid-crystal diffractive phase plate coronagraphs
for ground-based and space-based high-contrast imaging systems is
limited by the trade-off between spectral bandwidth and polarization
leakage. We demonstrate that by combining phase patterns with
a polarization grating (PG) pattern directly followed by one or
several separate PGs, we can suppress the polarization leakage
terms by additional orders of magnitude by diffracting them out of
the beam. Using two PGs composed of a single-layer liquid crystal
structure in the lab, we demonstrate a leakage suppression of more
than an order of magnitude over a bandwidth of 133 nm centered around
532 nm. At this center wavelength we measure a leakage suppression
of three orders of magnitude. Furthermore, simulations indicate that
a combination of two multi-layered liquid-crystal PGs can suppress
leakage to <10<SUP>-5</SUP> for 1-2.5 μm and <10<SUP>-10</SUP>
for 650-800 nm. We introduce multi-grating solutions with three or more
gratings that can be designed to have no separation of the two circular
polarization states, and offer even deeper suppression of polarization
leakage. We present simulations of a triple-grating solution that
has <10<SUP>-10</SUP> leakage on the first Airy ring from 450
to 800 nm. We apply the double-grating concept to the Vector-vortex
coronagraph of charge 4, and demonstrate in the lab that polarization
leakage no longer limits the on-axis suppression for ground-based
contrast levels. Lastly, we report on the successful installation and
first-light results of a double-grating vector Apodizing Phase Plate
pupil-plane coronagraph installed at the Large Binocular Telescope. We
discuss the implications of these new coronagraph architectures for
high-contrast imaging systems on the ground and in space.
---------------------------------------------------------
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: 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: New NIR spectro-polarimetric modes for the SCExAO instrument
Authors: Lozi, J.; Guyon, O.; Jovanovic, N.; Norris, B.; Groff, T.;
Chilcote, J.; Kasdin, N.; Kudo, T.; Tamura, M.; Zhang, J.; Bos,
S.; Snik, F.; Doelman, D.; Vievard, S.; Sahoo, A.; Currie, T.;
Martinache, F.
2020AAS...23516107L Altcode:
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument
is a high-contrast imaging system installed at Subaru. It is equipped
with a fast visible dual-camera polarimetric module, VAMPIRES,
already producing valuable observations of protoplanetary disks
and dust shells. We present two new polarimetric modules that were
recently implemented,. using the NIR light from y- to K-band and
Wollaston prisms. The fast polarization module, similarly to VAMPIRES,
uses a fast IR camera that can run at kilohertz frame rates, and a
Ferroelectric Liquid Crystal (FLC) device modulating the polarization
in a synchronized way with the acquisition. This allows to freeze
atmospheric speckles and to calibrate more precisely the degree of
polarization of the target, as already demonstrated by VAMPIRES. For
the second module, we perform spectro-polarimetric measurements
at a slower rate, using the CHARIS Integral Field Spectrograph
(IFS). The field-of-view is reduced by a factor 2 in one direction
to 2x1 arcsec, to accommodate for the imaging of both polarizations
on the same detector without sacrificing the spectral resolution of
the instrument. This is the first demonstration of a high-contrast
spectro-polarimeter using an IFS. This mode is now available for
open-use. We present on-sky results of the new polarimetric capabilities
taken during the commissioning phase, on strongly polarized targets.
---------------------------------------------------------
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 (> 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: Circular Spectropolarimetric Sensing of Vegetation in the
Field: Possibilities for the Remote Detection of Extraterrestrial Life
Authors: Patty, C. H. Lucas; Loes ten Kate, Inge; Buma, Wybren Jan;
van Spanning, Rob J. M.; Steinbach, Gábor; Ariese, Freek; Snik, Frans
2019AsBio..19.1221P Altcode: 2019arXiv190205859P
Homochirality is a generic and unique property of all biochemical
life, and the fractional circular polarization of light it induces
therefore constitutes a potentially unambiguous biosignature. However,
while high-quality circular polarimetric spectra can be easily and
quickly obtained in the laboratory, accurate measurements in the
field are much more challenging due to large changes in illumination
and target movement. In this study, we measured various targets in
the field, up to distances of a few kilometers, using the dedicated
circular spectropolarimeter TreePol. We show how photosynthetic life
can readily be distinguished from abiotic matter. We underline the
potential of circular polarization signals as a remotely accessible
means to characterize and monitor terrestrial vegetation, for example,
for agriculture and forestry. In addition, we discuss the potential of
circular polarization for the remote detection of extraterrestrial life.
---------------------------------------------------------
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: 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: Standardized spectral and radiometric calibration of consumer
cameras
Authors: Burggraaff, Olivier; Schmidt, Norbert; Zamorano, Jaime; Pauly,
Klaas; Pascual, Sergio; Tapia, Carlos; Spyrakos, Evangelos; Snik, Frans
2019OExpr..2719075B Altcode: 2019arXiv190604155B
Consumer cameras, particularly onboard smartphones and UAVs, are now
commonly used as scientific instruments. However, their data processing
pipelines are not optimized for quantitative radiometry and their
calibration is more complex than that of scientific cameras. The lack
of a standardized calibration methodology limits the interoperability
between devices and, in the ever-changing market, ultimately the
lifespan of projects using them. We present a standardized methodology
and database (SPECTACLE) for spectral and radiometric calibrations
of consumer cameras, including linearity, bias variations, read-out
noise, dark current, ISO speed and gain, flat-field, and RGB spectral
response. This includes golden standard ground-truth methods and
do-it-yourself methods suitable for non-experts. Applying this
methodology to seven popular cameras, we found high linearity in RAW
but not JPEG data, inter-pixel gain variations >400% correlated with
large-scale bias and read-out noise patterns, non-trivial ISO speed
normalization functions, flat-field correction factors varying by up
to 2.79 over the field of view, and both similarities and differences
in spectral response. Moreover, these results differed wildly between
camera models, highlighting the importance of standardization and a
centralized database.
---------------------------------------------------------
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° <
ϕ < 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: Simultaneous phase and amplitude aberration sensing with a
liquid-crystal vector-Zernike phase mask
Authors: Doelman, David S.; Fagginger Auer, Fedde; Escuti, Michael J.;
Snik, Frans
2019OptL...44...17D Altcode: 2018arXiv181108805D
We present an enhanced version of the Zernike wavefront sensor,
that simultaneously measures phase and amplitude aberrations. The
'vector-Zernike' wavefront sensor consists of a patterned liquid-crystal
mask, which imposes $\pm \pi/2$ phase on the point spread function core
through the achromatic geometric phase acting with opposite sign on
opposite circular polarizations. After splitting circular polarization,
the ensuing pupil intensity images are used to reconstruct the phase and
the amplitude of the incoming wavefront. We demonstrate reconstruction
of the complex wavefront with monochromatic lab measurements and show
in simulation the high accuracy and sensitivity over a bandwidth up
to $100\%$
---------------------------------------------------------
Title: The SCExAO High Contrast Imaging Platform: Current and
Upcoming Capabilities
Authors: Guyon, Olivier; Lozi, Julien; Vievard, Sébastien; Sahoo,
Ananya; Jovanovic, Nemanja; Currie, Thayne; Pathak, Prashant;
Martinache, Frantz; Kudo, Tomoyuki; Tamura, Motohide; Singh,
Garima; Clergeon, Christophe; Minowa, Yosuke; Ono, Yoshito; Mieda,
Etsuko; Mazin, Benjamin; Walter, Alexander; Cvetojevic, Nick; Lacour,
Sylvestre; Huby, Elsa; Norris, Barnaby; Wong, Alison; Ireland, Michael;
Schwab, Christian; Feger, Tobias; Tuthill, Peter; Lagadec, Tiphaine;
Groff, Tyler; Chilcote, Jeff; Brandt, Timothy; Hall, Don; Goebel,
Sean; Snik, Frans; Doelman, David; Bos, Steven; Kawahara, Hajime;
Kotani, Takayuki; Mawet, Dimitri; Belikov, Ruslan; Bendek, Eduardo;
Sevin, Arnaud; Gratadour, Damien; Ltaief, Hatem; Males, Jared; Jin,
Zhang; Murakami, Naoshi; Knight, Justin; Kasdin, Jeremy
2019AAS...23310403G Altcode:
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system,
currently in science operation on the Subaru Telescope, combines high
performance wavefront control and starlight suppression to image
exoplanets and disks. In addition to its flagship science cameras,
CHARIS (near-IR spectro-imaging) and VAMPIRES (visible polarimetric
imaging), new capabilities are being deployed, including advanced small
inner working angle coronagraphy, high frame rate low noise imaging,
near-IR polarimetric imaging, interferometric imaging/nulling and high
resolution diffraction-limited spectroscopy. A significant part of
SCExAO's development and performance improvements is realized through
wavefront control algorithms (focal plane wavefront control, sensor
fusion, predictive control, multi-star WFC) implemented through
the cacao software package and enabled by advances in detector
technologies (photon counting with MKIDs camera) and modern computer
hardware. Further improvements are also expected from the use of
real-time WFS telemetry to enhance removal of residual starlight in
post-processing. Much of SCExAO's development activities are aimed at
direct imaging of giant planets in reflected light with current large
telescopes, and imaging/spectroscopy of habitable planets with future
giant segmented mirror telescopes.
---------------------------------------------------------
Title: HiCIBaS: A precursor mission for high contrast imaging
balloon systems
Authors: Marchis, F.; Thibault, S.; Côté, O.; Brousseau, D.; Allain,
G.; Lord, M. P.; Ouellet, M.; Patel, D.; Vallée, C.; Belikov, R.;
Bendek, E.; Blain, C.; Bradley, C.; Doelman, D.; Daigle, O.; Doyon,
R.; Grandmont, F. J.; Helmbrecht, M.; Kenworthy, M.; Lafrenière,
D.; Marois, C.; Montminy, S.; Snik, F.; de Jonge, C.; Vasisht, G.;
Veran, J. P.; Vincent, P.
2018AGUFM.P41C3747M Altcode:
Even though space-based astronomical observations provides valuable
data in optical regimes that are not possible on ground, they are still
scarce and difficult to plan because of the high cost that is involved
with space-based instrumentation. Flying scientific instruments
aboard sub-orbital balloons can be achieve at a fraction of the
cost. HiCIBaS, the High-Contrast Imaging Balloon System, provides a
platform to develop instrumentation and imaging techniques for future
balloon-borne high-contrast coronagraph to detect and characterize
extrasolar planets. <P />HiCIBaS consists of an off-the-shelf
14-inch Schmidt-Cassegrain telescope, a custom Nasmyth mount and
a high-contrast instrument. The optical payload will be flown at
an altitude of 36 km aboard a pointed multi-instrument gondola
(CARMEN) provided by CNES using CSA's Stratos program from Timmins,
Ontario (Canada). High-contrast imaging becomes interesting at this
altitude because there is only 1% of the atmosphere left to induce
wavefront error. The gondola can be stabilized in azimuth to ±1 deg,
so the front-end optics include two cameras used for a coarse pointing
system. The telescope mount can rotate to ±20 degrees in azimuth and
from -20 degrees to +60 degrees in elevation. The optical payload
consists of two instruments, a pyramidal-style low-order wavefront
sensor (LOWFS) and a coronagraphic wavefront sensor (CWS). Both the
telescope mount and the optical bench were designed by the HiCIBaS team
in collaboration with OMP Inc, science EMCCD's were provided by Nüvü
Caméras and the segmented deformable mirror was provided by Iris AO
Inc. <P />HiCIBaS launch is scheduled between August 13<SUP>th</SUP>
and August 25<SUP>th</SUP>, just after 23h00 local time. The mission
will be in two parts, a night and an early-day phase. During the night
phase Cappella will be used to record data on atmospheric turbulence
and test the new technology used on this first flight. During the day,
the objective will mainly be to obtain data on the luminosity of the
background compared to Polaris, the second target star.
---------------------------------------------------------
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 (< 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 > 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 < 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: 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: A unique infrared spectropolarimetric unit for CRIRES+
Authors: Piskunov, Nikolai; Stempels, Eric; Lavail, Alexis; Escuti,
Michael; Snik, Frans; Dolgopolov, Andrey; Rozel, Milan; Durandet,
Candice; Hatzes, Artie; Bristow, Paul; Brucalassi, Anna; Cumani,
Claudio; Dorn, Reinhold J.; Haimerl, Andreas; Heiter, Ulrike;
Hinterschuster, Renate; Follert, Roman; Ives, Derek; Jung, Yves;
Kerber, Florian; Klein, Barbara; Lizon, Jean-Louis; Marquart, Thomas;
Molina-Conde, Ignacio; Pasquini, Luca; Paufique, Jérôme; Oliva,
Ernesto; Reiners, Ansgar; Seemann, Ulf; Stegmeier, Jörg; Tordo,
Sebastien; Valenti, Elena
2018SPIE10702E..34P Altcode:
High-resolution infrared spectropolarimetry has many science
applications in astrophysics. One of them is measuring weak magnetic
fields using the Zeeman effect. Infrared domain is particularly
advantageous as Zeeman splitting of spectral lines is proportional
to the square of the wavelength while the intrinsic width of the
line cores increases only linearly. Important science cases include
detection and monitoring of global magnetic fields on solar-type
stars, study of the magnetic field evolution from stellar formation
to the final stages of the stellar life with massive stellar winds,
and the dynamo mechanism operation across the boundary between fully-
and partially-convective stars. CRIRES+ (the CRIRES upgrade project)
includes a novel spectropolarimetric unit (SPU) based on polar-
ization gratings. The novel design allows to perform beam-splitting
very early in the optical path, directly after the tertiary mirror
of the telescope (the ESO Very Large Telescope, VLT), minimizing
instrumental polariza- tion. The new SPU performs polarization
beam-splitting in the near-infrared while keeping the telescope beam
mostly unchanged in the optical domain, making it compatible with the
adaptive optics system of the CRIRES+ instrument. The SPU consists
of four beam-splitters optimized for measuring circular and linear
polarization of spectral lines in YJ and HK bands. The SPU can perform
beam switching allowing to correct for throughput in each beam and for
variations in detector pixel sensitivity. Other new features of CRIRES+,
such as substantially increased wavelength coverage, stability and
advanced data reduction pipeline will further enhance the sensitivity
of the polarimetric mode. The combination of the SPU, CRIRES+ and the
VLT is a unique facility for making major progress in understanding
stellar activity. In this article we present the design of the SPU,
laboratory measurements of individual components and of the whole unit
as well as the performance prediction for the operation at the VLT.
---------------------------------------------------------
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: A review of high contrast imaging modes for METIS
Authors: Kenworthy, Matthew A.; Absil, Olivier; Carlomagno, Brunella;
Agócs, Tibor; Por, Emiel H.; Bos, Steven; Brandl, Bernhard; Snik,
Frans
2018SPIE10702E..A3K Altcode:
The Mid-infrared E-ELT Imager and Spectrograph (METIS) for the European
Extremely Large Telescope (E- ELT) consists of diffraction-limited
imagers that cover 3 to 14 microns with medium resolution (R 5000)
long slit spectroscopy, and an integral field spectrograph for
high spectral resolution spectroscopy (R 100,000) over the L and M
bands. We present our approach for high contrast imaging with METIS,
covering diffraction suppression with coronagraphs, the removal of
residual aberrations using QACITS1, 2 and Phase Sorting Interferometry
(PSI),3 and simulations demonstrating the expected contrast.
---------------------------------------------------------
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: Analysis of the polarimetric performance of the HARPS3
Cassegrain adaptor unit
Authors: Dorval, Patrick; Snik, Frans; Piskunov, Nikolai; Navarro,
Ramon; Kragt, Jan; ter Horst, Rik; Kunst, Peter; Snellen, Ignas;
Naylor, Tim; Thompson, Samantha
2018SPIE10702E..6BD Altcode:
The third version of the High Accuracy Radial velocity Planet Searcher
(HARPS3) instrument is built for a ten-year programme aimed at achieving
10 cm/sec radial velocity precision on nearby stars to search for
Earth-like planets. HARPS3 will be commissioned on the to-be-roboticized
2.54-m Isaac Newton Telescope at La Palma in 2021. One of the main
changes compared to its predecessors is the novel dual-beam Cassegrain
focus, featuring a stabilised beam feed into the HARPS3 spectrograph
and an insertable polarimetric sub-unit. This polarimetric sub-unit
enables HARPS3 to directly measure stellar activity signatures,
which can be useful for correcting activity-induced radial velocity
jitter in the search for Earth-like planets. The sub-unit consists
of superachromatic polymer quarter- and half-wave retarders for
circular and linear polarizations respectively, designed to suppress
polarized fringing, and a novel polarimetric beam splitter based
on a wire-grid design, separating the two polarimetric beams by 30
mm and feeding two separate science fibers. The dual-beam exchange
implementation in combination with the extreme stability of the HARPS3
spectrograph enables a polarimetric sensitivity of 10<SUP>-5</SUP>
on bright stars. One of the main challenges of such a system is in the
characterization of instrumental polarization effects which limit the
polarimetric accuracy of the polarimetric observing mode. By design
and characterization of this subsystem and by pre-emptively mitigating
possible noise sources, we can minimize the noise characteristics of
the polarization sub-unit to allow for precise observations. In this
paper we report on the design, realization, assembly, alignment, and
testing of the polarimetric unit to be installed in the Cassegrain
Adaptor Unit of the HARPS3 spectrograph
---------------------------------------------------------
Title: Fully broadband vAPP coronagraphs enabling polarimetric high
contrast imaging
Authors: Bos, Steven P.; Doelman, David S.; de Boer, Jos; Por, Emiel
H.; Norris, Barnaby; Escuti, Michael J.; Snik, Frans
2018SPIE10706E..5MB Altcode: 2018arXiv181109775B
We present designs for fully achromatic vector Apodizing Phase
Plate (vAPP) coronagraphs, that implement low polarization leakage
solutions and achromatic beam-splitting, enabling observations in
broadband filters. The vAPP is a pupil plane optic, inducing the phase
through the inherently achromatic geometric phase. We discuss various
implementations of the broadband vAPP and set requirements on all the
components of the broadband vAPP coronagraph to ensure that the leakage
terms do not limit a raw contrast of 10<SUP>-5</SUP>. Furthermore, we
discuss superachromatic QWPs based of liquid crystals or quartz/MgF2
combinations, and several polarizer choices. As the implementation
of the (broadband) vAPP coronagraph is fully based on polarization
techniques, it can easily be extended to furnish polarimetry by adding
another QWP before the coronagraph optic, which further enhances
the contrast between the star and a polarized companion in reflected
light. We outline several polarimetric vAPP system designs that could
be easily implemented in existing instruments, e.g. SPHERE and SCExAO.
---------------------------------------------------------
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 (> 70%), high
resolution (19 mas), and high contrast (< 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: The hunt for Sirius Ab: comparison of algorithmic sky and
PSF estimation performance in deep coronagraphic thermal-IR high
contrast imaging
Authors: Long, Joseph D.; Males, Jared R.; Morzinski, Katie M.; Close,
Laird M.; Snik, Frans; Kenworthy, Matthew A.; Otten, Gilles P. P. L.;
Monnier, John; Tolls, Volker; Weinberger, Alycia
2018SPIE10703E..2TL Altcode: 2018arXiv180704361L
Despite promising astrometric signals, to date there has been no
success in direct imaging of a hypothesized third member of the Sirius
system. Using the Clio instrument and MagAO adaptive optics system on
the Magellan Clay 6.5 m telescope, we have obtained extensive imagery of
Sirius through a vector apodizing phase plate (vAPP) coronagraph in a
narrowband filter at 3.9 microns. The vAPP coronagraph and MagAO allow
us to be sensitive to planets much less massive than the limits set
by previous non-detections. However, analysis of these data presents
challenges due to the target's brightness and unique characteristics
of the instrument. We present a comparison of dimensionality reduction
techniques to construct background illumination maps for the whole
detector using the areas of the detector that are not dominated
by starlight. Additionally, we describe a procedure for sub-pixel
alignment of vAPP data using a physical-optics-based model of the
coronagraphic PSF.
---------------------------------------------------------
Title: Focal plane wavefront sensing and control strategies for
high-contrast imaging on the MagAO-X instrument
Authors: Miller, Kelsey; Males, Jared R.; Guyon, Olivier; Close,
Laird M.; Doelman, David; Snik, Frans; Por, Emiel; Wilby, Michael J.;
Bohlman, Chris; Lumbres, Jennifer; Van Gorkom, Kyle; Kautz, Maggie;
Rodack, Alexander; Knight, Justin; Jovanovic, Nemanja; Morzinski,
Katie; Schatz, Lauren
2018SPIE10703E..1TM Altcode: 2018arXiv180704381M
The Magellan extreme adaptive optics (MagAO-X) instrument is a
new extreme adaptive optics (ExAO) system designed for operation
in the visible to near-IR which will deliver high contrast-imaging
capabilities. The main AO system will be driven by a pyramid wavefront
sensor (PyWFS); however, to mitigate the impact of quasi-static
and non-common path (NCP) aberrations, focal plane wavefront sensing
(FPWFS) in the form of low-order wavefront sensing (LOWFS) and spatial
linear dark field control (LDFC) will be employed behind a vector
apodizing phase plate (vAPP) coronagraph using rejected starlight at an
intermediate focal plane. These techniques will allow for continuous
high-contrast imaging performance at the raw contrast level delivered
by the vAPP coronagraph ( 6 x 10<SUP>-5</SUP>). We present simulation
results for LOWFS and spatial LDFC with a vAPP coronagraph, as well
as laboratory results for both algorithms implemented with a vAPP
coronagraph at the University of Arizona Extreme Wavefront Control Lab.
---------------------------------------------------------
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: Modeling coronagraphic extreme wavefront control systems for
high contrast imaging in ground and space telescope missions
Authors: Lumbres, Jennifer; Males, Jared; Douglas, Ewan; Close, Laird;
Guyon, Olivier; Cahoy, Kerri; Carlton, Ashley; Clark, Jim; Doelman,
David; Feinberg, Lee; Knight, Justin; Marlow, Weston; Miller, Kelsey;
Morzinski, Katie; Por, Emiel; Rodack, Alexander; Schatz, Lauren;
Snik, Frans; Van Gorkom, Kyle; Wilby, Michael
2018SPIE10703E..4ZL Altcode: 2018arXiv180704729L
The challenges of high contrast imaging (HCI) for detecting exoplanets
for both ground and space applications can be met with extreme adaptive
optics (ExAO), a high-order adaptive optics system that performs
wavefront sensing (WFS) and correction at high speed. We describe 2
ExAO optical system designs, one each for ground- based telescopes
and space-based missions, and examine them using the angular spectrum
Fresnel propagation module within the Physical Optics Propagation in
Python (POPPY) package. We present an end-to-end (E2E) simulation
of the MagAO-X instrument, an ExAO system capable of delivering
6x10<SUP>-5</SUP> visible-light raw contrast for static, noncommon
path aberrations without atmosphere. We present an E2E simulation of
a laser guidestar (LGS) companion spacecraft testbed demonstration,
which uses a remote beacon to increase the signal available for WFS
and control of the primary aperture segments of a future large space
telescope, providing of order 10 factor improvement for relaxing
observatory stability requirements.
---------------------------------------------------------
Title: Cryogenic characterization of the grating vector APP
coronagraph for the upcoming ERIS instrument at the VLT
Authors: Boehle, Anna; Glauser, Adrian M.; Kenworthy, Matthew A.;
Snik, Frans; Doelman, David; Quanz, Sascha P.; Meyer, Michael R.
2018SPIE10702E..3YB Altcode:
We present results from a cryogenic characterization of the grating
vector Apodizing Phase Plate (gvAPP) coro- nagraph that will be
used in the upcoming instrument ERIS (Enhanced Resolution Imager and
Spectrograph) at the VLT. ERIS consists of a 1-5 μm imager (NIX) and
a 1 2.5 μm integral field spectrograph (SPIFFIER), both fed by the
Adaptive Optics Facility of UT4 to yield diffraction-limited spatial
resolution. A gvAPP coronagraph will be included in the NIX imager to
enable high-contrast imaging observations, which will be particularly
powerful for the direct imaging of exoplanets at L and M bands ( 3-5
μm) and will compliment the current capabilities of VLT/SPHERE and
surpass the capabilities of VLT/NACO. We utilize the near-infrared test
bench of the Star and Planet Formation group at ETH Zurich to measure
key properties of the gvAPP coronagraph at its operating wavelengths
and under the vacuum/cryogenic ( 70 K) conditions of the future ERIS
instrument.
---------------------------------------------------------
Title: SCExAO, an instrument with a dual purpose: perform cutting-edge
science and develop new technologies
Authors: Lozi, Julien; Guyon, Olivier; Jovanovic, Nemanja; Goebel,
Sean; Pathak, Prashant; Skaf, Nour; Sahoo, Ananya; Norris, Barnaby;
Martinache, Frantz; N'Diaye, Mamadou; Mazin, Ben; Walter, Alex B.;
Tuthill, Peter; Kudo, Tomoyuki; Kawahara, Hajime; Kotani, Takayuki;
Ireland, Michael; Cvetojevic, Nick; Huby, Elsa; Lacour, Sylvestre;
Vievard, Sébastien; Groff, Tyler D.; Chilcote, Jeffrey K.; Kasdin,
Jeremy; Knight, Justin; Snik, Frans; Doelman, David; Minowa, Yosuke;
Clergeon, Christophe; Takato, Naruhisa; Tamura, Motohide; Currie,
Thayne; Takami, Hideki; Hayashi, Masa
2018SPIE10703E..59L Altcode: 2018arXiv180908301L
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument
is an extremely modular high- contrast instrument installed on the
Subaru telescope in Hawaii. SCExAO has a dual purpose. Its position
in the northern hemisphere on a 8-meter telescope makes it a prime
instrument for the detection and characterization of exoplanets and
stellar environments over a large portion of the sky. In addition,
SCExAO's unique design makes it the ideal instrument to test
innovative technologies and algorithms quickly in a laboratory setup
and subsequently deploy them on-sky. SCExAO benefits from a first
stage of wavefront correction with the facility adaptive optics AO188,
and splits the 600-2400 nm spectrum towards a variety of modules,
in visible and near infrared, optimized for a large range of science
cases. The integral field spectrograph CHARIS, with its J, H or K-band
high-resolution mode or its broadband low-resolution mode, makes SCExAO
a prime instrument for exoplanet detection and characterization. Here we
report on the recent developments and scientific results of the SCExAO
instrument. Recent upgrades were performed on a number of modules,
like the visible polarimetric module VAMPIRES, the high-performance
infrared coronagraphs, various wavefront control algorithms, as well as
the real-time controller of AO188. The newest addition is the 20k-pixel
Microwave Kinetic Inductance Detector (MKIDS) Exoplanet Camera (MEC)
that will allow for previously unexplored science and technology
developments. MEC, coupled with novel photon-counting speckle control,
brings SCExAO closer to the final design of future high-contrast
instruments optimized for Giant Segmented Mirror Telescopes (GSMTs).
---------------------------------------------------------
Title: A precursor mission to high contrast imaging balloon system
Authors: Côté, Olivier; Allain, Guillaume; Brousseau, Denis; Lord,
Marie-Pier; Ouahbi, Samy; Ouellet, Mireille; Patel, Deven; Thibault,
Simon; Vallée, Cédric; Belikov, Ruslan; Bendek, Eduardo; Blain,
Célia; Bradley, Collin; Daigle, Olivier; de Jong, Chris; Doelman,
David; Doyon, René; Grandmont, Frédéric; Helmbrecht, Michael;
Kenworthy, Matthew; Lafrenière, David; Marchis, Frank; Marois,
Christian; Montminy, Steeve; Snik, Frans; Vasisht, Gautam; Véran,
Jean-Pierre; Vincent, Philippe
2018SPIE10702E..48C Altcode:
The HiCIBaS (High-Contrast Imaging Balloon System) project aims at
launching a balloon borne telescope up to 36km to test high contrast
imaging equipment and algorithms. The payload consists of a off
the shelf 14-inch telescope with a custom-built Alt-Az mount. This
telescope provides lights to two sensors, a pyramidal low order wave
front sensor, and a coronagraphic wavefront sensor. Since the payload
will reach its cruise altitude at about midnight mission, two target
stars have been designated for observations, Capella as the night
target, and Polaris as the early morning target. Data will be collected
mainly on the magnitude of atmospheric and gondola's turbulences,
the luminosity of the background. The whole system is already built
and ready to ship to Timmins for the launch in mid-August 2018.
---------------------------------------------------------
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: VST: The First Large Survey Telescope for Optical Polarimetry
Authors: Smette, Alain; Bagnulo, Stefano; Snik, Frans; Cox, Nick;
Hainaut, Olivier; Hutsemekers, Damien; Magalhaes, Antonio Mario
2018vels.confE..44S Altcode:
Replacing the unused ADC by a polarizing filter would transform the
VST into the first large polarimetric optical survey telescope,
without affecting the current capabilities of the VST+OmegaCAM
system. <P />Scientific cases include: mapping the Milky-Way and
Magellanic clouds magnetic fields, surveys of quasar polarization,
identification and variability of polarized brown dwarfs, polarimetric
characterization and mapping of solar-system objects (incl. the moon,
comets, and asteroids), detection of polarized signal around the L4
and L5 Lagrange points, a census of magnetic white dwarfs and Herbig
Ae/Be stars, etc. <P />The design of the VST limits the technical
implementation for the polarimetric unit to a single-beam system:
therefore, we will develop data-driven calibration methods to achieve a
sub-percent polarimetric accuracy. <P />The proposed implementation is
of low cost and requires no major development, as polarizing filters
of the needed size are readily available. In particular, it does not
require major modification neither of VST, nor of OmegaCAM. In fact,
the currently offered capabilities of the VST+OmegaCAM are preserved
as the polarizing filter can be removed from the optical beam. Would
this project be accepted, efforts will be needed on the design of
the polarimeter unit to optimize accuracy and execution times, on
the design of the calibration plan, and on the extension of the data
reduction pipeline to extract the polarization signals.
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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.
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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: Spectropolarimetry for earth observations: a novel method
for characterization of aerosols and clouds
Authors: Van der Togt, Oana; Verlaan, Ad; Moddemeijer, Kees; Smit,
Martijn; Rietjens, Jeroen; Hasekamp, Otto P.; Stam, Daphne; Snik,
Frans; van Harten, Gerard
2017SPIE10564E..1SV Altcode:
Aerosols affect Earth's energy level by scattering and absorbing
radiation and by changing the properties of clouds. Such effects
influence the precipitation patterns and lead to modifications of
the global circulation systems that constitute Earth's climate. The
aerosol effects on our climate cannot be at full scale estimated
due to the insufficient knowledge of their properties at a global
scale. Achieving global measurement coverage requires an instrument
with a large instantaneous field of view that can perform polarization
measurements with high accuracy, typically better than 0.1%. Developing
such an instrument can be considered as the most important challenge in
polarimetric aerosol remote sensing. Using a novel technique to measure
polarization, we have designed an instrument for a low-Earth orbit,
e.g. International Space Station, that can simultaneously characterize
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° viewing angle. In this article we present the instrument's
optical design concept.
---------------------------------------------------------
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: Polarimetric Imaging Of Protoplanetary Disks From The Optical
To Sub-Mm
Authors: De Boer, Jos; Ménard, F.; Pinte, C.; van der Plas, G.;
Snik, F.
2017ques.workE...5D Altcode:
To learn how planets form from the smallest building blocks within
protoplanetary disks, we first need to know how dust grains grow from
micron to mm sizes. Polarimetry across the spectrum has proven to
be sensitive to grain properties like dust size distribution and
composition and thus can be used to characterize the scattering
grains. However, polarization measured with radio interferometric
arrays is rarely studied in concert with optical polarimetry. Our
team has successfully calibrated the NIR polarimetric imaging mode
of VLT/SPHERE, hence upgrading the instrument from a high-contrast
imager to a robust tool for quantitative characterization. In this
presentation, we will discuss which lessons can be learned by comparing
polarimetry in the optical and sub-mm and explore for which science
cases both techniques can complement each other. When we combine the
polarimetric capabilities of the most advanced optical high-contrast
imagers (e.g., Gemini GPI or VLT SPHERE) with that of ALMA we will
be able to study the spatial distribution of an extensive range of
different grains, which allows us to take an essential step towards
a deeper understanding of planet formation.
---------------------------------------------------------
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 <=
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: Patterned liquid-crystal optics for broadband coronagraphy
and wavefront sensing
Authors: Doelman, David S.; Snik, Frans; Warriner, Nathaniel Z.;
Escuti, Michael J.
2017SPIE10400E..0UD Altcode: 2017arXiv170909897D
The direct-write technology for liquid-crystal patterns allows for
manufacturing of extreme geometric phase patterned coronagraphs
that are inherently broadband, e.g. the vector Apodizing Phase Plate
(vAPP). We present on-sky data of a double-grating vAPP operating from
2-5 μm with a 360-degree dark hole and a decreased leakage term of
∼ 10<SUP>-4</SUP> . We report a new liquid-crystal design used in
a grating-vAPP for SCExAO that operates from 1-2.5μm. Furthermore,
we present wavelength-selective vAPPs that work at specific wavelength
ranges and transmit light unapodized at other wavelengths. Lastly,
we present geometric phase patterns for advanced implementations of
WFS (e.g. Zernike-type) that are enabled only by this liquid-crystal
technology.
---------------------------------------------------------
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: Investigating circular patterns in linear polarization
observations of Venus
Authors: Mahapatra, Gourav; Stam, Daphne; Rossi, Loic; Rodenhuis,
Michiel; Snik, Frans
2017EGUGA..1915926M Altcode:
ESA's Venus Express mission has revealed our neighbouring planet
to be a highly dynamic world, with ever-changing cloud properties
and structures, wind speeds that increase in time, and variable
concentrations of atmospheric trace gases such as SO2. The SPICAV-IR
instrument on Venus Express has provided us with close-up linear
polarization data of sunlight reflected by Venus's clouds and hazes,
that allows a characterisation of their composition and particle
sizes. Here, we analyse linear polarization data of the planet at
a distance, obtained with the Extreme Polarimeter (ExPo) on the
William Herschel Telescope on La Palma. These spatially resolved,
high-accuracy polarization observations of Venus show faint circular
patterns centered on the sub-solar point that are absent in the flux
observations. So far, careful analyses have ruled out instrumental
effects which leaves us to wonder about atmospheric properties as
the cause of the circular patterns. Using numerical simulations of
the flux and polarization of sunlight that is reflected by Venus,
we have investigated the relation between the observed patterns and
several atmospheric properties, such as variations in particle sizes,
composition, density and altitude. We discuss the plausibility of the
possible causes in the view of the current knowledge of the composition
and dynamical processes in Venus's atmosphere.
---------------------------------------------------------
Title: Circular spectropolarimetric sensing of chiral photosystems
in decaying leaves
Authors: Patty, C. H. Lucas; Visser, Luuk J. J.; Ariese, Freek; Buma,
Wybren Jan; Sparks, William B.; van Spanning, Rob J. M.; Röling,
Wilfred F. M.; Snik, Frans
2017JQSRT.189..303P Altcode: 2017arXiv170101297P
Circular polarization spectroscopy has proven to be an indispensable
tool in photosynthesis research and (bio)molecular research in
general. Oxygenic photosystems typically display an asymmetric
Cotton effect around the chlorophyll absorbance maximum with a signal
≤ 1 % . In vegetation, these signals are the direct result of the
chirality of the supramolecular aggregates. The circular polarization
is thus directly influenced by the composition and architecture of the
photosynthetic macrodomains, and is thereby linked to photosynthetic
functioning. Although ordinarily measured only on a molecular level,
we have developed a new spectropolarimetric instrument, TreePol, that
allows for both laboratory and in-the-field measurements. Through
spectral multiplexing, TreePol is capable of fast measurements
with a sensitivity of ∼ 1 *10<SUP>-4</SUP> and is therefore
suitable of non-destructively probing the molecular architecture
of whole plant leaves. We have measured the chiroptical evolution
of Hedera helix leaves for a period of 22 days. Spectrally resolved
circular polarization measurements (450-900 nm) on whole leaves in
transmission exhibit a strong decrease in the polarization signal over
time after plucking, which we accredit to the deterioration of chiral
macro-aggregates. Chlorophyll a levels measured over the same period by
means of UV-vis absorption and fluorescence spectroscopy showed a much
smaller decrease. With these results we are able to distinguish healthy
from deteriorating leaves. Hereby we indicate the potency of circular
polarization spectroscopy on whole and intact leaves as a nondestructive
tool for structural and plant stress assessment. Additionally, we
underline the establishment of circular polarization signals as remotely
accessible means of detecting the presence of extraterrestrial life.
---------------------------------------------------------
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: 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: 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: HARPS3 for a roboticized Isaac Newton Telescope
Authors: Thompson, Samantha J.; Queloz, Didier; Baraffe, Isabelle;
Brake, Martyn; Dolgopolov, Andrey; Fisher, Martin; Fleury, Michel;
Geelhoed, Joost; Hall, Richard; González Hernández, Jonay I.; ter
Horst, Rik; Kragt, Jan; Navarro, Ramón; Naylor, Tim; Pepe, Francesco;
Piskunov, Nikolai; Rebolo, Rafael; Sander, Louis; Ségransan, Damien;
Seneta, Eugene; Sing, David; Snellen, Ignas; Snik, Frans; Spronck,
Julien; Stempels, Eric; Sun, Xiaowei; Santana Tschudi, Samuel;
Young, John
2016SPIE.9908E..6FT Altcode: 2016arXiv160804611T
We present a description of a new instrument development, HARPS3,
planned to be installed on an upgraded and roboticized Isaac Newton
Telescope by end-2018. HARPS3 will be a high resolution (R≃115,000)
echelle spectrograph with a wavelength range from 380-690 nm. It is
being built as part of the Terra Hunting Experiment - a future 10-
year radial velocity measurement programme to discover Earth-like
exoplanets. The instrument design is based on the successful
HARPS spectrograph on the 3.6m ESO telescope and HARPS-N on the
TNG telescope. The main changes to the design in HARPS3 will be: a
customised fibre adapter at the Cassegrain focus providing a stabilised
beam feed and on-sky fibre diameter ≍1:4 arcsec, the implementation of
a new continuous ow cryostat to keep the CCD temperature very stable,
detailed characterisation of the HARPS3 CCD to map the effective pixel
positions and thus provide an improved accuracy wavelength solution,
an optimised integrated polarimeter and the instrument integrated into
a robotic operation. The robotic operation will optimise our programme
which requires our target stars to be measured on a nightly basis. We
present an overview of the entire project, including a description of
our anticipated robotic operation.
---------------------------------------------------------
Title: OCTOCAM: a fast multi-channel imager and spectrograph proposed
for the Gemini Observatory
Authors: de Ugarte Postigo, A.; Roming, P.; Thöne, C. C.; van der
Horst, A. J.; Pope, S.; García Vargas, M. L.; Sánchez-Blanco, E.;
Maldonado Medina, M.; Content, R.; Snik, F.; Killough, R.; Winters,
G.; Persson, K.; Jeffers, S.; Riva, A.; Bianco, A.; Zanutta, A.
2016SPIE.9908E..40D Altcode:
OCTOCAM has been proposed to the Gemini Observatory as a workhorse
imager and spectrograph that will fulfill the needs of a large number of
research areas in the 2020s. It is based on the use of high-efficiency
dichroics to divide the incoming light in eight different channels, four
optical and four infrared, each optimized for its wavelength range. In
its imaging mode, it will observe a field of 3'x3' simultaneously in g,
r, i, z, Y, J, H, and KS bands. It will obtain long-slit spectroscopy
covering the range from 3700 to 23500 Å with a resolution of 4000 and
a slit length of 3 arcminutes. To avoid slit losses, the instrument
it will be equipped with an atmospheric dispersion corrector for
the complete spectral range. Thanks to the use of state of the art
detectors, OCTOCAM will allow high time-resolution observations and
will have negligible overheads in classical observing modes. It will
be equipped with a unique integral field unit that will observe in
the complete spectral range with an on-sky coverage of 9.7"x6.8",
composed of 17 slitlets, 0.4" wide each. Finally, a state-of-the-art
polarimetric unit will allow us to obtain simultaneous full Stokes
spectropolarimetry of the range between 3700 and 22000 Å.
---------------------------------------------------------
Title: High-contrast imaging with METIS
Authors: Kenworthy, Matthew A.; Absil, Olivier; Agócs, Tibor; Pantin,
Eric; Quanz, Sascha; Stuik, Remko; Snik, Frans; Brandl, Bernhard
2016SPIE.9908E..A6K Altcode:
The Mid-infrared E-ELT Imager and Spectrograph (METIS) for the European
Extremely Large Telescope (E-ELT) consists of diffraction-limited
imagers that cover 3 to 14 microns with medium resolution (R 5000)
long slit spectroscopy, and an integral field spectrograph for high
spectral resolution spectroscopy (R 100,000) over the L and M bands. One
of the science cases that METIS addresses is the characterization of
faint circumstellar material and exoplanet companions through imaging
and spectroscopy. We present our approach for high contrast imaging
with METIS, covering diffraction suppression with coronagraphs,
the removal of slowly changing optical aberrations with focal plane
wavefront sensing, interferometric imaging with sparse aperture masks,
and observing strategies for both the imagers and IFU image slicers.
---------------------------------------------------------
Title: The path to visible extreme adaptive optics with MagAO-2K
and MagAO-X
Authors: Males, Jared R.; Close, Laird M.; Guyon, Olivier; Morzinski,
Katie M.; Hinz, Philip; Esposito, Simone; Pinna, Enrico; Xompero,
Marco; Briguglio, Runa; Riccardi, Armando; Puglisi, Alfio; Mazin,
Ben; Ireland, Michael J.; Weinberger, Alycia; Conrad, Al; Kenworthy,
Matthew; Snik, Frans; Otten, Gilles; Jovanovic, Nemanja; Lozi, Julien
2016SPIE.9909E..52M Altcode:
The next generation of extremely large telescopes (ELTs) have the
potential to image habitable rocky planets, if suitably optimized. This
will require the development of fast high order "extreme" adaptive
optics systems for the ELTs. Located near the excellent site of the
future GMT, the Magellan AO system (MagAO) is an ideal on-sky testbed
for high contrast imaging development. Here we discuss planned
upgrades to MagAO. These include improvements in WFS sampling
(enabling correction of more modes) and an increase in speed to
2000 Hz, as well as an H2RG detector upgrade for the Clio infrared
camera. This NSF funded project, MagAO-2K, is planned to be on-sky in
November 2016 and will significantly improve the performance of MagAO
at short wavelengths. Finally, we describe MagAO-X, a visible-wavelength
extreme-AO "afterburner" system under development. MagAO-X will deliver
Strehl ratios of over 80% in the optical and is optimized for visible
light coronagraphy.
---------------------------------------------------------
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: Modelling the circular polarisation of Earth-like exoplanets:
constraints on detecting homochirality
Authors: Hogenboom, Michael; Stam, Daphne; Rossi, Loic; Snik, Frans
2016EGUGA..18.4721H Altcode:
The circular polarisation of light is a property of electromagnetic
radiation from which extensive information can be extracted. It is
oft-neglected due to its small signal relative to linear polarisation
and the need for advanced instrumentation in measuring it. Additionally,
numerical modelling is complex as the full Stokes vector must always be
computed. Circular polarisation is commonly induced through the multiple
scattering of light by aerosols te{hansen} and multiple reflections of
light by rough surfaces te{circplanets}. Most interestingly, distinctive
spectral circular polarimetric behaviour is exhibited by light reflected
by organisms due to the homochiral molecular structure of all known
organisms te{chiralbailey}. Especially fascinating is the unique
circular polarimetric behaviour of light reflected by photosynthesising
organisms at the absorption wavelength of the chlorophyll pigment
te{circpolchar}. This presents the previously unexplored possibility
of circular polarimetry as a method for identifying and characterising
the presence of organisms, a method which could be applied in the
hunt for extraterrestrial life. To date, few telescopes exist that
measure circular polarisation and none that have been deployed in
space. Observations of the circular polarisation reflected by other
planets in the solar system have been made with ground-based telescopes,
with significant results te{circplanets}. However, none of these
observations have been made at the phase angles at which exoplanets
will be observed. Also, none have been made of the Earth, which is
the logical starting point for the study of biologically induced
circular polarisation signals. This introduces the need for numerical
modelling to determine the extent to which circular polarisation is
present in light reflected by exoplanets or the Earth. In this study,
we model the multiple scattering and reflection of light using the
doubling-adding method te{dehaan}. We will present circular polarisation
signals for both spatially resolved and spatially unresolved planets,
using various atmospheric and surface properties and across a range of
phase angles. As a test, the calculated degree of circular polarisation
resulting from the multiple scattering of light in an atmosphere with
varying properties was compared with results presented by Kawata
te{circatmos} and was found to be in agreement. Initial modelling
of the atmospheric scattering of light by a planetary disk has
shown a presence of degree of circular polarisation in the order
of 10<SUP>-4</SUP>. This represents a static case with one cloudy
hemisphere, one cloudless hemisphere and a Lambertian surface. Results
containing varied patchy cloud patterns shall also be presented in a
bid to reflect the random nature of planetary cloud cover. We will also
present the calculated degree of circular polarisation of planets with
various cloud coverage and a circularly polarising surface in order
to discover the influence of organisms on the numerical results. {1}
{hansen} J. E. {Hansen} and L. D. {Travis}. {Light scattering in
planetary atmospheres}. {Space Science Reviews}, 16:527-610, October
1974. {circplanets} J. C. {Kemp} and R. D. {Wolstencroft}. {Circular
Polarization: Jupiter and Other Planets}. {Nature}, 232:165-168, July
1971. {chiralbailey} J. {Bailey}. {Circular Polarization and the Origin
of Biomolecular Homochirality}. In G. {Lemarchand} and K. {Meech},
editors, {Bioastronomy 99}, volume 213 of {Astronomical Society of
the Pacific Conference Series}, 2000. {circpolchar} L. {Nagdimunov},
L. {Kolokolova}, and D. {Mackowski}. {Characterization and remote
sensing of biological particles using circular polarization}. {Journal
of Quantitative Spectroscopy and Radiative Transfer}, 131:59-65,
December 2013. dehaan} J. F. {de Haan}, P. B. {Bosma}, and
J. W. {Hovenier}. {The adding method for multiple scattering
calculations of polarized light}. {Astronomy and Astrophysics},
183:371-391, September 1987. {circatmos} Y. {Kawata}. {Circular
polarization of sunlight reflected by planetary atmospheres}. {Icarus},
33:217-232, January 1978.
---------------------------------------------------------
Title: Preliminary design of the full-Stokes UV and visible
spectropolarimeter for UVMag/Arago
Authors: Pertenais, Martin; Neiner, Coralie; Parès, Laurent; Petit,
Pascal; Snik, Frans; van Harten, Gerard
2015IAUS..305..168P Altcode: 2015arXiv150200856P
The UVMag consortium proposed the space mission project Arago to ESA
at its M4 call. Arago is dedicated to the study of the dynamic 3D
environment of stars and planets. This space mission will be equipped
with a high-resolution spectropolarimeter working from 119 to 888
nm. A preliminary optical design of the whole instrument has been
prepared and is presented here. The design consists of the telescope,
the instrument itself, and the focusing optics. Considering not only
the scientific requirements, but also the cost and size constraints
to fit an M-size mission, the telescope has a 1.3 m diameter primary
mirror and is a classical Cassegrain-type telescope that allows a
polarization-free focus. The polarimeter is placed at this Cassegrain
focus. This is the key element of the mission and the most challenging
one to be designed. The main challenge lies in the huge spectral range
offered by the instrument; the polarimeter has to deliver the full
Stokes vector with a high precision from the FUV (119 nm) to the NIR
(888 nm). The polarimeter module is then followed by a high-resolution
echelle-spectrometer achieving a resolution of 35000 in the visible
range and 25000 in the UV. The two channels are separated after the
echelle grating, allowing specific cross-dispersion and focusing
optics for the UV and the visible ranges. Considering the large field
of view and the high numerical aperture, the focusing optics for both
the UV and the visible channels is a Three-Mirror-Anastigmatic (TMA)
telescope, needed to focus the various wavelengths and many orders
onto the detectors.
---------------------------------------------------------
Title: Instrumemtation
Authors: Keller, Christoph U.; Snik, Frans; Harrington, David M.;
Packham, Chris
2015psps.book...35K Altcode:
No abstract at ADS
---------------------------------------------------------
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: Performance characterization of a broadband vector Apodizing
Phase Plate coronagraph
Authors: Otten, Gilles P. P. L.; Snik, Frans; Kenworthy, Matthew A.;
Miskiewicz, Matthew N.; Escuti, Michael J.
2014OExpr..2230287O Altcode: 2014arXiv1412.0660O
One of the main challenges for the direct imaging of planets around
nearby stars is the suppression of the diffracted halo from the primary
star. Coronagraphs are angular filters that suppress this diffracted
halo. The Apodizing Phase Plate coronagraph modifies the pupil-plane
phase with an anti-symmetric pattern to suppress diffraction over
a 180 degree region from 2 to 7 {\lambda}/D and achieves a mean raw
contrast of 10^-4 in this area, independent of the tip-tilt stability
of the system. Current APP coronagraphs implemented using classical
phase techniques are limited in bandwidth and suppression region
geometry (i.e. only on 1 side of the star). In this paper, we show the
vector-APP (vAPP) whose phase pattern is implemented by the orientation
of patterned liquid crystals. Beam-splitting according to circular
polarization states produces two, complementary PSFs with dark holes on
either side. We have developed a prototype vAPP that consists of a stack
of 3 twisting liquid crystal layers with a bandwidth of 500-900 nm. We
characterize the properties of this device using reconstructions of the
pupil-plane pattern, and of the ensuing PSF structures. By imaging the
pupil between crossed and parallel polarizers we reconstruct the fast
axis pattern, transmission, and retardance of the vAPP, and use this as
input for a PSF model. This model includes aberrations of the laboratory
set-up, and matches the measured PSF, which shows a raw contrast of
10^-3.8 between 2 and 7 {\lambda}/D in a 135 degree wedge. The vAPP
coronagraph is relatively easy to manufacture and can be implemented
together with a broadband quarter-wave plate and Wollaston prism in a
pupil wheel in high-contrast imaging instruments. The manufacturing
techniques permit the application of phase patterns with deeper
contrasts inside the dark holes and enables unprecedented spectral
bandwidths for phase-manipulation coronagraphy.
---------------------------------------------------------
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: Combining vector-phase coronagraphy with dual-beam polarimetry
Authors: Snik, Frans; Otten, Gilles; Kenworthy, Matthew; Mawet,
Dimitri; Escuti, Michael
2014SPIE.9147E..7US Altcode:
Utilizing the so-called vector phase of polarized light, both
focal-plane coronagraphs (e.g. the Vector Vortex Coronagraph) and
pupil-plane coronagraphs (e.g. the vector Apodizing Phase Plate) are
powerful components for high-contrast imaging. These coronagraphs can
be built and optimized with polarization techniques and liquid crystal
technology, that enable patterning at the micron level and furnish
broad-band performance. The contrast between the residual starlight and
the (polarized) reflected light off exoplanets can be further bridged by
incorporating sensitive, dual-beam imaging polarimetry. As vector-phase
coronagraphs use polarizers to enhance their performance, we introduce
optimally integrated solutions that combine advanced coronagraphy and
polarimetry. For both the VVC and the vAPP we present polarization
beam-splitting concepts, with polarization analyzers either behind
or in front of the coronagraphic optics. We discuss design solutions
for the implementation of polarization optics, and set the stage for
a trade-off between the improvement of coronagraphic and polarimetric
performance and the ensuing degradation on the high-contrast imaging
performance due to wavefront errors.
---------------------------------------------------------
Title: UVMag: Space UV and visible spectropolarimetry
Authors: Pertenais, Martin; Neiner, Coralie; Parès, Laurent P.;
Petit, Pascal; Snik, Frans; van Harten, Gerard
2014SPIE.9144E..3BP Altcode: 2014arXiv1406.4378P
UVMag is a project of a space mission equipped with a high-resolution
spectropolarimeter working in the UV and visible range. This M-size
mission will be proposed to ESA at its M4 call. The main goal of UVMag
is to measure the magnetic fields, winds and environment of all types of
stars to reach a better understanding of stellar formation and evolution
and of the impact of stellar environment on the surrounding planets. The
groundbreaking combination of UV and visible spectropolarimetric
observations will allow the scientists to study the stellar surface
and its environment simultaneously. The instrumental challenge for
this mission is to design a high-resolution space spectropolarimeter
measuring the full- Stokes vector of the observed star in a huge
spectral domain from 117 nm to 870 nm. This spectral range is the main
difficulty because of the dispersion of the optical elements and of
birefringence issues in the FUV. As the instrument will be launched
into space, the polarimetric module has to be robust and therefore use
if possible only static elements. This article presents the different
design possibilities for the polarimeter at this point of the project.
---------------------------------------------------------
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 -->
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: Successes and challenges of the APP Coronagraph
Authors: Kenworthy, Matthew A.; Quanz, Sascha; Otten, Gilles; Meshkat,
Tiffany; Codona, Johanan; Snik, Frans; Meyer, Michael E.; Kasper,
Markus; Girard, Julien
2014IAUS..299...40K Altcode:
The Apodizing Phase Plate (APP) coronagraph has been used to image
the exoplanet β Pictoris b and the protoplanet candidate around
HD 100546, and is currently in use in surveys with NaCo at the
VLT. Its success is due to its tolerance to tip-tilt pointing errors
in current AO systems, which degrade the performance of nearly all
other coronagraphs. Currently the sensitivity of the APP is limited
by non-common path errors in the science camera systems and by its
chromatic behaviour. We present the achromatized Vector APP coronagraph
and address how we will measure and minimise non-common path errors
with Focal Plane Wavefront Sensing algorithms.
---------------------------------------------------------
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: 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: 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: The polarimeters for HARPS and X-shooter
Authors: Snik, F.; Harpspol Team; X-Shooter-Pol Team
2013ASPC..470..401S Altcode:
Spectropolarimetry enables observations of stellar magnetic fields and
circumstellar asymmetries, e.g. in disks and supernova explosions. To
furnish better diagnostics of such stellar physics, we designed and
commissioned a polarimetric unit at the successful HARPS spectrograph
at ESO's 3.6-m telescope at La Silla. We present the design and
performance of HARPSpol, and show some first science results. The
most striking achievement of HARPSpol is its capability to measure
stellar magnetic fields as small as 0.1 G. Finally, we give a sneak
preview of the polarimeter we are currently designing for X-shooter
at the VLT. It contains a novel type of polarimetric modulator that
is able to efficiently measure all the Stokes parameters over the huge
wavelength range of 300-2500 nm.
---------------------------------------------------------
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: 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 (<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: Innovative technology for optical and infrared astronomy
Authors: Cunningham, Colin R.; Evans, Christopher J.; Molster, Frank;
Kendrew, Sarah; Kenworthy, Matthew A.; Snik, Frans
2012SPIE.8450E..31C Altcode: 2012arXiv1207.4892C
Advances in astronomy are often enabled by adoption of new
technology. In some instances this is where the technology has been
invented specifically for astronomy, but more usually it is adopted from
another scientific or industrial area of application. The adoption of
new technology typically occurs via one of two processes. The more
usual is incremental progress by a series of small improvements,
but occasionally this process is disruptive, where a new technology
completely replaces an older one. One of the activities of the OPTICON
Key Technology Network over the past few years has been a technology
forecasting exercise. Here we report on a recent event which focused on
the more radical, potentially disruptive technologies for ground-based,
optical and infrared astronomy.
---------------------------------------------------------
Title: Design of a full-Stokes polarimeter for VLT/X-shooter
Authors: Snik, Frans; van Harten, Gerard; Navarro, Ramon; Groot,
Paul; Kaper, Lex; de Wijn, Alfred
2012SPIE.8446E..25S Altcode: 2012arXiv1207.2965S
X-shooter is one of the most popular instruments at the VLT, offering
instantaneous spectroscopy from 300 to 2500 nm. We present the design
of a single polarimetric unit at the polarization-free Cassegrain focus
that serves all three spectrograph arms of X-shooter. It consists of
a calcite Savart plate as a polarizing beam-splitter and a rotatable
crystal retarder stack as a "polychromatic modulator". Since even
"superachromatic" wave plates have a wavelength range that is too
limited for X-shooter, this novel modulator is designed to offer
close-to-optimal polarimetric efficiencies for all Stokes parameters
at all wavelengths. We analyze the modulator design in terms of its
polarimetric performance, its temperature sensitivity, and its polarized
fringes. Furthermore, we present the optical design of the polarimetric
unit. The X-shooter polarimeter will furnish a myriad of science cases:
from measuring stellar magnetic fields (e.g., Ap stars, white dwarfs,
massive stars) to determining asymmetric structures around young stars
and in supernova explosions.
---------------------------------------------------------
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: Modeling the instrumental polarization of the VLT and E-ELT
telescopes with the M&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&m's code, an error budget
and performance simulator for polarimetric systems. In this study
we present the realistic Mueller matrices calculated with M&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: The vector-APP: a broadband apodizing phase plate that yields
complementary PSFs
Authors: Snik, Frans; Otten, Gilles; Kenworthy, Matthew; Miskiewicz,
Matthew; Escuti, Michael; Packham, Christopher; Codona, Johanan
2012SPIE.8450E..0MS Altcode: 2012arXiv1207.2970S
The apodizing phase plate (APP) is a solid-state pupil optic that
clears out a D-shaped area next to the core of the ensuing PSF. To
make the APP more efficient for high-contrast imaging, its bandwidth
should be as large as possible, and the location of the D-shaped area
should be easily swapped to the other side of the PSF. We present the
design of a broadband APP that yields two PSFs that have the opposite
sides cleared out. Both properties are enabled by a half-wave liquid
crystal layer, for which the local fast axis orientation over the pupil
is forced to follow the required phase structure. For each of the two
circular polarization states, the required phase apodization is thus
obtained, and, moreover, the PSFs after a quarter-wave plate and a
polarizing beam-splitter are complementary due to the antisymmetric
nature of the phase apodization. The device can be achromatized
in the same way as half-wave plates of the Pancharatnam type or by
layering self-aligning twisted liquid crystals to form a monolithic
film called a multi-twist retarder. As the VAPP introduces a known
phase diversity between the two PSFs, they may be used directly for
wavefront sensing. By applying an additional quarter-wave plate in
front, the device also acts as a regular polarizing beam-splitter,
which therefore furnishes high-contrast polarimetric imaging. If the
PSF core is not saturated, the polarimetric dual-beam correction can
also be applied to polarized circumstellar structure. The prototype
results show the viability of the vector-APP concept.
---------------------------------------------------------
Title: Compact and robust method for full Stokes spectropolarimetry
Authors: Sparks, William; Germer, Thomas A.; MacKenty, John W.;
Snik, Frans
2012ApOpt..51.5495S Altcode: 2012arXiv1206.7106S
We present an approach to spectropolarimetry which requires neither
moving parts nor time dependent modulation, and which offers the
prospect of achieving high sensitivity. The technique applies equally
well, in principle, in the optical, UV or IR. The concept, which is one
of those generically known as channeled polarimetry, is to encode the
polarization information at each wavelength along the spatial dimension
of a 2D data array using static, robust optical components. A single
two-dimensional data frame contains the full polarization information
and can be configured to measure either two or all of the Stokes
polarization parameters. By acquiring full polarimetric information in a
single observation, we simplify polarimetry of transient sources and in
situations where the instrument and target are in relative motion. The
robustness and simplicity of the approach, coupled to its potential
for high sensitivity, and applicability over a wide wavelength range,
is likely to prove useful for applications in challenging environments
such as space.
---------------------------------------------------------
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
& 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 &
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
& 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: 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: 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: Polarimetry at Current and Future Ground-based Telescopes
for Detection and Characterization of Exoplanets
Authors: Snik, F.
2011AGUFM.P14C..07S Altcode:
Reflected light off exoplanets is generally linearly polarized. This
offers a unique possibility to distinguish this light from the
halo of unpolarized starlight, which is many orders of magnitude
brighter. Polarimetry is therefore a powerful method that enables
direct imaging of exoplanets. Moreover, the spectral dependence of the
degree of polarization of the reflected starlight contains unambiguous
information on the exoplanetary atmosphere and surface. Polarimetry
is therefore also a very promising future technique for exoplanet
characterization. This contribution reviews polarimetric instrumentation
at current 4-10 m ground-based telescopes that is particularly suited
for exoplanet research. Furthermore, it provides an outlook for
exoplanet polarimetry with 30-40 m extremely large telescopes.
---------------------------------------------------------
Title: SPEX: a multi-angle Spectropolarimeter for Planetary
EXploration
Authors: Smit, J. M.; Hasekamp, O. P.; Rietjens, J.; Stam, D.; Snik,
F.; Van Harten, G.; Verlaan, A.; Voors, R.; Moon, S.; Wielinga, K.
2011AGUFM.P11F1635S Altcode:
We present SPEX, the Spectropolarimeter for Planetary Exploration, which
is a compact, robust and low-mass multi-viewing angle spectropolarimeter
designed to operate from an orbiting satellite platform. Its purpose
is to simultaneously measure, with high accuracy, the radiance and the
state (degree and angle) of linear polarization of sunlight that has
been scattered in a planetary atmosphere or reflected by a planetary
surface. 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 results in a
modulation of the radiance spectrum in both amplitude and phase by the
degree and angle of the linear polarization spectrum, respectively. The
polarization optics consists of an achromatic quarter-wave retarder, an
a-thermal multiple-order retarder, and a polarizing beam splitter. Such
a configuration is implemented for a range of viewin directions, which
allows sampling the full scattering phase function of each ground
pixel under investigation, while orbiting the planetary body. The
present design of SPEX is tuned to a Mars mission, as a payload on a
satellite in a low orbit. However, the concept is perfectly applicable
for Earth remote sensing from an orbiting platform like ISS or a
dedicated mission, for which we are developing a breadboard. A similar
concepts is under study for a mission to the Jovian system including the
Galilean Moons. We will show first test results obtained with recently
developed prototype of the SPEX instrument, demonstrating excellent
performance and overall behavior as compared with design parameters
and SPEX instrument simulator. In addition, we present results of
multi-angle spectropolarimetric measurements of the Earth's atmosphere
from the ground in conjunction with one of AERONET's sun photometers.
---------------------------------------------------------
Title: Astronomical Applications for “Radial Polarimetry”
Authors: Snik, F.
2011ASPC..449...21S Altcode:
Many objects on the sky exhibit a centrosymmetric polarization pattern,
particularly in cases involving single scattering around a central
source. Utilizing a novel liquid crystal device (the “theta cell”)
that transforms the coordinate system of linear polarization in an
image plane from Cartesian to polar, the observation of centrosymmetric
polarization patterns can be improved: instead of measuring Stokes Q and
U on the sky, one only needs to measure Stokes Q' in the new instrument
coordinate system. This reduces the effective exposure time by a factor
of two and simplifies the polarization modulator design. According to
the manufacturer's specifications and to measurements in the lab, the
liquid crystal device can be applied in the visible and NIR wavelength
range. Astronomical science cases for a“radial polarimeter” include
exoplanet detection, imaging of circumstellar disks, reflection
nebulae and light echos, characterization of planetary atmospheres
and diagnostics of the solar K-corona. The first astronomical
instrument that utilizes a theta cell for radial polarimetry is the
S<SUP>5</SUP>T (Small Synoptic Second Solar Spectrum Telescope),
which accurately measures scattering polarization signals near the
limb of the sun. These observations are crucial for understanding
the nature and origin of weak, turbulent magnetic fields in the solar
photosphere and elsewhere in the universe. A “radial polarimeter”
observing a slightly defocused point source performs one-shot full
linear polarimetry. With a theta cell in a pupil plane, a beam's linear
polarization properties (e.g. for calibration purposes) can be fully
controlled through pupil masking.
---------------------------------------------------------
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: M&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 & Snik, in 2009, we have developed the M&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&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: 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: 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: 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: 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: 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 < 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 Irkutsk Barium filter for narrow-band wide-field
high-resolution solar images at the Dutch Open Telescope
Authors: Hammerschlag, Robert H.; Skomorovsky, Valery I.; Bettonvil,
Felix C. M.; Kushtal, Galina I.; Olshevsky, Vyacheslav L.; Rutten,
Robert J.; Jägers, Aswin P. L.; Sliepen, Guus; Snik, Frans
2010SPIE.7735E..85H Altcode: 2010SPIE.7735E.265H
A wide-field birefringent filter for the barium II line at 455.4nm is
developed in Irkutsk. The Barium line is excellent for Doppler-shift
measurements because of low thermal line-broadening and steep
flanks of the line profile. The filter width is 0.008nm and the
filter is tunable over 0.4nm through the whole line and far enough
in the neighboring regions. A fast tuning system with servomotor is
developed at the Dutch Open Telescope (DOT). Observations are done
in speckle mode with 10 images per second and Keller-VonDerLühe
reconstruction using synchronous images of a nearby bluecontinuum
channel at 450.5nm. Simultaneous observation of several line positions,
typically 3 or 5, are made with this combination of fast tuning and
speckle. All polarizers are birefringent prisms which largely reduced
the light loss compared to polarizing sheets. The advantage of this
filter over Fabry-Perot filters is its wide field due to a large
permitted entrance angle and no need of polishing extremely precise
surfaces. The BaII observations at the DOT occur simultaneously with
those of a fast-tunable birefringent H-alpha filter. This gives the
unique possibility of simultaneous speckle-reconstructed observations
of velocities in photosphere (BaII) and chromosphere (H-alpha).
---------------------------------------------------------
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: 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: 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: Astronomical Polarimetry : new concepts, new instruments,
new measurements & observations
Authors: Snik, F.
2009PhDT.......489S Altcode:
All astronomical sources are polarized to some degree. Polarimetry
is therefore a powerful astronomical technique. It furnishes unique
diagnostics of e.g. magnetic fields and scattering media. This thesis
presents new polarimetric concepts, instruments, and measurements
targeting astronomical science questions. The first part of the
thesis describes three novel polarimetric concepts. -A dedicated
passive liquid crystal device known as a theta cell is introduced
to enable one-shot observations of astronomical targets exhibiting
a centrosymmetric polarization pattern. -A new passive measurement
concept for broad-band linear polarization is introduced. It is
based on a sinusoidal modulation of the spectrum, and is particularly
suitable for instruments for which classical spatial and/or temporal
polarization modulation is unfavorable. -Calibration of polarimetric
instruments is usually limited by non-ideal effects of the calibration
optics themselves. A mathematical frame-work based on Fourier analysis
is introduced to tackle various non-ideal effects in polarimetric
calibration. The second part of the thesis presents the designs and
first results of three very different astronomical polarimeters. -The
ultra-stable high-resolution HARPS spectrograph is successfully upgraded
with a dual-beam polarimetric module. It furnishes direct observations
of magnetic fields on stars. -The Small Synoptic Second Solar Spectrum
Telescope (S5T) is designed to accurately monitor the variation of
weak, turbulent magnetic fields on the Sun during a solar cycle. Such
measurements are crucial for the understanding of local dynamo action
in the solar photosphere. The prototype shows the feasibility of the
instrument concept. -The Spectropolarimeter for Planetary EXpolaration
(SPEX) is designed to study a planet's or moon's atmosphere from
orbit. The additional information from the polarization measurement of
scattered sunlight allows for determination of microphysical properties
of atmospheric aerosols. The third part of the thesis presents new
polarimetric measurements and observations. -A precise ellipsometer was
constructed to measure the polarization properties of various optical
components. The instrument was employed to measure the complete Mueller
matrix of an aluminum mirror at various durations after evaporation. It
is concluded that the aluminum oxide layer has a significant effect
on the polarization properties, which is constant in time after a
day from evaporation. -Next, an aluminized mirror was contaminated
with dust. This also has a significant effect on the measured Mueller
matrix, for which a linear model is presented as a function of dust
absorption. -Observations of solar scattering polarization at high
spatial resolution were obtained with the Hinode space telescope. A
significant difference of ~10% in scattering polarization was detected
between granules and intergranules, which constrains models of quiet
Sun magnetoconvection.
---------------------------------------------------------
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: 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: 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: Astronomical Applications for "Radial Polarimetry"
Authors: Snik, Frans
2009arXiv0903.2734S Altcode:
Many objects on the sky exhibit a centrosymmetric polarization pattern,
particularly in cases involving single scattering around a central
source. Utilizing a novel liquid crystal device (the “theta cell”)
that transforms the coordinate system of linear polarization in an
image plane from Cartesian to polar, the observation of centrosymmetric
polarization patterns can be improved: instead of measuring Stokes Q and
U on the sky, one only needs to measure Stokes Q' in the new instrument
coordinate system. This reduces the effective exposure time by a factor
of two and simplifies the polarization modulator design. According
to the manufacturer's specifications and to measurements in the
lab, the liquid crystal device can be applied in the visible and NIR
wavelength range. Astronomical science cases for a“radial polarimeter”
include exoplanet detection, imaging of circumstellar disks, reflection
nebulae and light echos, characterization of planetary atmospheres and
diagnostics of the solar K-corona. The first astronomical instrument
that utilizes a theta cell for radial polarimetry is the S5T (Small
Synoptic Second Solar Spectrum Telescope), which accurately measures
scattering polarization signals near the limb of the sun. These
observations are crucial for understanding the nature and origin of
weak, turbulent magnetic fields in the solar photosphere and elsewhere
in the universe. A “radial polarimeter” observing a slightly defocused
point source performs one-shot full linear polarimetry. With a theta
cell in a pupil plane, a beam's linear polarization properties (e.g. for
calibration purposes) can be fully controlled through pupil masking.
---------------------------------------------------------
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: Astronomical polarimetry: New concepts; new instruments;
new measurements & observations
Authors: Snik, Frans
2009PhDT.......584S 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: 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: 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: 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.
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Title: Calibration strategies for instrumental polarization at the
10 <SUP>-5</SUP> level
Authors: Snik, Frans
2006SPIE.6269E..5PS Altcode: 2006SPIE.6269E.182S
Many current instrumental developments for both solar and nighttime
telescopes are directed at measuring the polarization state of the
incoming light in addition to determining its spatial, temporal and/or
spectral properties. Such polarimeters need to be sensitive down to a
polarization degree of the order of 10 <SUP>-5</SUP> e.g. to employ the
full range of diagnostics to accurately measure solar magnetic fields
or to enable direct imaging of extrasolar planetary systems. At the low
polarization degree of these observations, it is crucial to accurately
know the polarization properties of the instrument itself. Since
instrumental polarization is inevitable for any telescopic configuration
with oblique reflections or refractions, it is always necessary to
cope with it by means of calibration in combination with (limited)
forward modeling. I present general strategies based on discrete
Fourier analysis for the calibration of instrumental polarization
to enable astronomical (spectro-)polarimetry at the 10 <SUP>-5</SUP>
level. The technique only assumes the presence of a freely rotatable
polarizer and (quarter) wave plate to create known input polarization
states. The Fourier components of the observed output polarization
contain information about the full instrumental polarization, as well
as about non-ideal effects in the calibration elements, polarized
input to the calibration unit and non-linear response of the detector.
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Title: GISOT: a giant solar telescope
Authors: Hammerschlag, Robert H.; von der Lühe, Oskar F.; Bettonvil,
Felix C.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..491H Altcode:
A concept is presented for an extremely large high-resolution solar
telescope with an aperture of 11 m and diffraction limited for visual
wavelengths. The structure of GISOT will be transparent to wind and
placed on a transparent stiff tower. For efficient wind flushing,
all optics, including the primary mirror, will be located above
the elevation axis. The aperture will be of the order of 11 m, not
rotatively symmetrical, but of an elongated shape with dimensions
11 x 4 m. It consists of a central on-axis 4 m mirror with on both
sides 3 pieces of 2 m mirrors. The optical layout will be kept simple
to guarantee quality and minimize stray light. A Coudé room for
instruments is planned below the telescope. The telescope will not
be housed in a dome-like construction, which interferes with the open
principle. Instead the telescope will be protected by a foldable tent
construction with a diameter of the order of 30 m, which doesn"t form
any obstruction during observations, but can withstand the severe
weather circumstances on mountain sites. Because of the nature of
the solar scene, extremely high resolution in only one dimension is
sufficient to solve many exciting problems in solar physics and in
this respect the concept of GISOT is very promising.
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Title: DOT++: the Dutch Open Telescope with 1.4-m aperture
Authors: Bettonvil, Felix C.; Hammerschlag, Robert H.; Sütterlin,
Peter; Rutten, Robert J.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..362B Altcode:
The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is
a revolutionary open solar telescope, on an excellent site, on top
of a transparent steel tower, and uses natural air flow to minimize
local seeing. The aim is long-duration high-resolution imaging with
a multi-wavelength camera system. In order to achieve this, the DOT
is equipped with a diffraction limited imaging system and uses the
speckle reconstruction technique for removing the remaining atmospheric
turbulence. The DOT optical system is simple and consists currently of
a 0.45m/F4.44 parabolic mirror and a 10x enlargement lens system. We
present our plans to increase the aperture of the DOT from 0.45m to
1.4m. The mirror support and telescope top shall be redesigned, but
telescope, tower, multi-wavelength camera system and speckle system
remain intact. The new optical design permits user selectable choice
between angular resolution and field size, as well as transversal pupil
shift introducing the possibility to use obstruction free apertures up
to 65cm. The design will include a low order AO system, which improves
the speckle S/N substantially during moderate seeing conditions.
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Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
K.; de Wijn, A. G.
2004IAUS..223..597R Altcode: 2005IAUS..223..597R
The Dutch Open Telescope (DOT) on La Palma is an innovative solar
telescope combining open telescope structure and an open support tower
with a multi-wavelength imaging assembly and with synchronous speckle
cameras to generate high-resolution movies which sample different
layers of the solar atmosphere simultaneously and co-spatially at high
resolution over long durations. The DOT test and development phase is
nearly concluded. The installation of an advanced speckle processor
enables full science utilization including "Open-DOT" time allocation
to the international community. Co-pointing with spectropolarimeters
at other Canary Island telescopes and with TRACE furnishes valuable
Solar-B precursor capabilities.