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.
Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most
challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the
planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design
of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and
at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through
their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and
expected performance of the SPHERE instrument.
The Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument for the VLT is designed for
discovering and studying new extra-solar giant planets orbiting nearby stars by direct imaging. In this paper, we describe
the philosophy behind the SPHERE baseline data processing sequences dealing with calibration observations, and how
these can affect the reduction of subsequent calibrations and scientific data. Additionally, we present the result of our
detector simulations and the first tests of data reduction recipe prototypes.
We present a method based on Mueller calculus to calibrate linear polarimetric observations. The key advantages
of the proposed way of calibration are: (1) that it can be implemented in a data reduction pipeline, (2) that it is possible
to do accurate polarimetry also for telescopes/instruments with polarimetric non-friendly architecture (e.g. Nasmyth
instruments) and (3) that the proposed strategy is much less time consuming than standard calibration procedures. The
telescope/instrument will polarimetrically be described by a train of Mueller matrices. The components of these matrices
are dependent on wavelength, incident angle of the incoming light and surface properties.
The result is, that an observer gets the polarimetrically calibrated data from a reduction pipeline. The data will be
corrected for the telescope/instrumental polarisation off-set and with the position angle of polarisation rotated into sky
coordinates. Up to now these two calibration steps were mostly performed with the help of dedicated and time consuming
night-time calibration measurements of polarisation standard stars.
We summarize here an experimental frame combination pipeline we developed for ultra high-contrast imaging with
systems like the upcoming VLT SPHERE instrument. The pipeline combines strategies from the Drizzle technique, the
Spitzer IRACproc package, and homegrown codes, to combine image sets that may include a rotating field of view and
arbitrary shifts between frames. The pipeline is meant to be robust at dealing with data that may contain non-ideal
effects like sub-pixel pointing errors, missing data points, non-symmetrical noise sources, arbitrary geometric distortions,
and rapidly changing point spread functions. We summarize in this document individual steps and strategies, as well as
results from preliminary tests and simulations.
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.