26 July 2016 The ZIMPOL high contrast imaging polarimeter for SPHERE: polarimetric high contrast commissioning results
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Abstract
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.
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Ronald Roelfsema, Ronald Roelfsema, Andreas Bazzon, Andreas Bazzon, Hans Martin Schmid, Hans Martin Schmid, Johan Pragt, Johan Pragt, Alain Govaert, Alain Govaert, Daniel Gisler, Daniel Gisler, Carsten Dominik, Carsten Dominik, Andrea Baruffolo, Andrea Baruffolo, Jean-Luc Beuzit, Jean-Luc Beuzit, Anne Costille, Anne Costille, Kjetil Dohlen, Kjetil Dohlen, Mark Downing, Mark Downing, Eddy Elswijk, Eddy Elswijk, Menno de Haan, Menno de Haan, Norbert Hubin, Norbert Hubin, Markus Kasper, Markus Kasper, Christoph Keller, Christoph Keller, Jean-Louis Lizon, Jean-Louis Lizon, David Mouillet, David Mouillet, Alexey Pavlov, Alexey Pavlov, Pascal Puget, Pascal Puget, Bernardo Salasnich, Bernardo Salasnich, Jean-Francois Sauvage, Jean-Francois Sauvage, Francois Wildi, Francois Wildi, } "The ZIMPOL high contrast imaging polarimeter for SPHERE: polarimetric high contrast commissioning results", Proc. SPIE 9909, Adaptive Optics Systems V, 990927 (26 July 2016); doi: 10.1117/12.2231883; https://doi.org/10.1117/12.2231883
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