Polarimetry of planets and planetary systems provide unique information on physics and chemistry of planetary atmospheres. We have built a new instrument, GREGOR Planet Polarimeter (GPP), which includes fast polarimetric modulation, high-rate readout CCD, and adaptive optics. It operates at the solar telescope GREGOR on Tenerife, Canary Islands, and it benefits from the possibility to calibrate the entire optical train after the secondary mirror. Here we present the instrument design, performance tests, and first scientific data. This research is supported by the ERC Advanced Grant HotMol.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation VLT instrument aimed at the direct detection of exo-planets. It has received its first light in May 2014. ZIMPOL (Zurich Imaging Polarimeter) is the imaging polarimeter subsystem of the SPHERE instrument. It's capable of both high accuracy and high sensitivity polarimetry but can also be used as a classical imager. It is located behind an extreme AO system and a stellar coronagraph. ZIMPOL operates at visible wavelengths which is best suited to detect the very faint reflected and hence polarized visible light from extra solar planets. During the SPHERE fourth commissioning period (October 2014) we have made deep coronagraphic observations of the bright star alpha Gru (mR = 1.75) to assess the high contrast polarimetric performance of SPHERE-ZIMPOL. We have integrated on the target for a total time of about 45 minutes during the meridian transit in the Very Broad Band filter (600 - 900 nm) with a classical Lyot coronagraph with 3 λ/D radius focal mask. We reduce the data by a combination of Polarized Background subtraction, Polarimetric Differential Imaging (PDI) and Angular Differential Imaging (ADI). We reach contrasts of 10-6 and 10-7 at a radial distances of respectively 7 and 14 lambda/D from the PSF core. At these radial distances we are respectively a factor of 10 and 2 above the photon noise limit. We discuss our results by considering the temporal and spatial speckle behavior close to the PSF core in combination with low order polarimetric aberrations.
The Hokupa’a-85 curvature adaptive optics system components have been adapted to create a new AO-corrected
coud´e instrument at the 3.67m Advanced Electro-Optical System (AEOS) telescope. This new AO-corrected
optical path is designed to deliver an f/40 diffraction-limited focus at wavelengths longer than 800nm. A new
EMCCD-based dual-beam imaging polarimeter called InnoPOL has been designed and is presently being installed
behind this corrected f/40 beam. The InnoPOL system is a flexible platform for optimizing polarimetric
performance using commercial solutions and for testing modulation strategies. The system is designed as a
technology test and demonstration platform as the coud´e path is built using off-the-shelf components wherever
possible. Models of the polarimetric performance after AO correction show that polarization modulation at rates
as slow as 200Hz can cause speckle correlations in brightness and focal plane location sufficient enough to change
the speckle suppression behavior of the modulators. These models are also verified by initial EMCCD scoring
camera data at AEOS. Substantial instrument trades and development efforts are explored between instrument
performance parameters and various polarimetric noise sources.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a new instrument for the VLT aimed at the direct
detection of exo-planets. It has received its first light in May 2014. ZIMPOL (Zurich Imaging Polarimeter) is the
imaging polarimeter subsystem of the SPHERE instrument. It's capable of both high accuracy and high sensitivity
polarimetry but can also be used as a classical imager. It is located behind an extreme AO system and a stellar
coronagraph. ZIMPOL operates at visible wavelengths (600-900 nm) which is best suited to detect the very faint
reflected and hence polarized visible light from extra solar planets. It has an instantaneous Field of View of 3 x 3 arcsec2
(extendable to 8 arcsec diameter) with an angular resolution of 14 mili-arcsec. We discuss the results that are obtained
from the full SPHERE-ZIMPOL system testing. In particular the optical, polarimetric and high contrast performance.
Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity
polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating
camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is
routinely used at IRSOL, Locarno. The fast modulation allows to “freeze” intensity variations due to seeing,
and to achieve a polarimetric sensitivity below 10-5 if the photon statistics is large enough. In October 2013
the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for
a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration
unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical
path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by
the authors for the first time in this occasion.
SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. SPHERE commissioning is foreseen in 2013 on the VLT. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light (600-900 nm) from extrasolar planets. It is located behind an extreme AO system (SAXO) and a stellar coronagraph. We present the first high contrast polarimetric results obtained for the fully integrated SPHERE-ZIMPOL system. We have measured the polarimetric high contrast performance of several coronagraphs: a Classical Lyot on substrate, a suspended Classical Lyot and two 4 Quadrant Phase Mask coronagraphs. We describe the impact of crucial system parameters – Adaptive Optics, Coronagraphy and Polarimetry - on the contrast performance.
The imaging polarimeter ZIMPOL is one of three focal plane instruments of the SPHERE / VLT planet finder. ZIMPOL
measures the linear polarization based on a fast modulation – demodulation principle using a charge-shifting technique
on a masked CCD for separating the photons with opposite polarization direction. This paper describes the on-chip
demodulation and the different detector read-out modes which are implemented for the ZIMPOL polarimeter. Test
results are presented which allow an evaluation of the performance of the ZIMPOL CCD detectors. The achievable
polarization efficiency is close to expectation and the charge trap correction with the two-phase demodulation mode
works well. Other detector effects like bias level variations and read-out patterns can be corrected in the data reduction
process. The tests demonstrate that the demodulating CCDs fulfill the requirements for the SPHERE project.
ZIMPOL is an imaging polarimeter for the high-contrast SPHERE/VLT "planet finder" instrument using fast
polarization modulation and demodulating CCD detectors. The polarimetric performance of the ZIMPOL instrument
depends on the polarimetric alignment and quality of the polarization components. This paper gives an overview on the
polarimetric concept and the calibration plan of ZIMPOL. We discuss in particular the alignment of the polarimetric
calibration components and the polarimetric properties of the ferro-electric liquid crystal (FLC) modulator package used
in ZIMPOL. Our measurements demonstrate the good broad-band performance of the modulator. Faint targets, like
extra-solar planets, require mainly a high polarimetric efficiency while for detailed studies of bright targets a good
characterization of the modulator package is essential. Therefore we quantify in detail the wavelength dependence of the
polarimetric efficiency and the cross-talk effects which have to be taken into account in the calibration and data
reduction process of high S/N measurements.
ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to
detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an
extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT early 2013.
ZIMPOL is currently integrated in the SPHERE system and in testing phase.
We describe the alignment strategy and the results of the ZIMPOL system and the related alignment of ZIMPOL into
SPHERE by the aid of an alignment unit. The field selecting tip/tilt mirror alignment and it’s requirement for
perpendicularity to the two detectors is described. The test setup of the polarimetric components is described.
SPHERE is an instrument designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF,
Observatoire de Genève, ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the
direct detection from extra-solar planets. The instrument will search for direct light from old planets with orbital periods
of several months to several years as we know them from our solar system. These are planets which are in or close to the
habitable zone. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO
SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from
extrasolar planets. The search for reflected light from extra-solar planets is very demanding because the signal decreases
rapidly with the orbital separation. For a Jupiter-sized object and a separation of 1 AU the planet/star contrast to be
achieved is on the order of 10-8 for a successful detection. This is much more demanding than the direct imaging of
young self-luminous planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph.
SPHERE is foreseen to have first light at the VLT at the end of 2012. ZIMPOL is currently in the subsystem testing
phase. We describe the results of verification and performance testing done at the NOVA-ASTRON lab. We will give an
overview of the system noise performance, the polarimetric accuracy and the high contrast testing. For the high contrast
testing we will describe the impact of crucial system parameters on the contrast performance. SPHERE is an instrument
designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève,
ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to
detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an
extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of
2011. ZIMPOL is currently in the manufacturing, integration and testing phase. We describe the optical, polarimetric,
mechanical, thermal and electronic design as well as the design trade offs. Specifically emphasized is the optical quality
of the key performance component: the Ferro-electric Liquid Crystal polarization modulator (FLC). Furthermore, we
describe the ZIMPOL test setup and the first test results on the achieved polarimetric sensitivity and accuracy. These
results will give first indications for the expected overall high contrast system performance. SPHERE is an instrument
designed and built by a consortium consisting of LAOG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève,
ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
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.
Extreme adaptive optics (XAO) systems are highly specialized systems
to achieve very high Strehl numbers on comparatively small fields of
view, e.g. for high-contrast applications like planet finding. We
present a study of an XAO system using a pyramid wavefront sensor
on telescopes of 8m aperture diameter and above. We used standard
(CAOS) and custom numerical simulation tools to examine the influence
of the number of basis functions in a modal correction model,
the control loop frequency of the XAO system, and atmospheric
conditions.
We present results from a phase A study supported by ESO for a VLT instrument for the search and investigation of extrasolar planets.
The envisaged CHEOPS (CHaracterizing Extrasolar planets by Opto-infrared Polarization and Spectroscopy) instrument consists of an extreme AO system, a spectroscopic integral field unit and an imaging polarimeter. This paper describes the conceptual design of the imaging polarimeter which is based on the ZIMPOL (Zurich IMaging POLarimeter) technique using a fast polarization modulator combined with a demodulating CCD camera. ZIMPOL is capable of detecting polarization signals on the order of p=0.001% as demonstrated in solar applications. We discuss the planned implementation of ZIMPOL within the CHEOPS instrument, in particular the design of the polarization modulator. Further we describe strategies to minimize the instrumental effects and to enhance the overall measuring efficiency in order to achieve the very demanding science goals.
The design of an achromatic polarisation modulator is presented. The modulator is based on a combination of three electrically switchable non-achromatic ferroelectric liquid crystal retarders. The design follows the idea by Pancharatnam who first introduced suitable achromatic combinations of crystal retarders. We combined three ferroelectric liquid crystal retarders to create an electrically switchable achromatic halfwave plate which can be used in the
spectral range from 400 nm to 750 nm. Different designs are theoretically modeled and compared under the aspects of their individual response to temperature fluctuations and useful wavelength range. First results of laboratory tests are presented to experimentally evaluate the feasibility of the concept.
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