Physics – Optics
Scientific paper
Jun 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007lyot.confe..50v&link_type=abstract
Proceedings of the conference In the Spirit of Bernard Lyot: The Direct Detection of Planets and Circumstellar Disks in the 21s
Physics
Optics
Scientific paper
Direct detection of exoplanets is one of the most challenging prospects for astronomical instrumentation today. The SPHERE1 instrument for the VLT (ESO) is currently under development to achieve this goal with very good performance. It aims at detecting exoplanets down to a few masses of Jupiter at distances as close as 0.1' to the central star with the use of extreme adaptive optics and coronagraphs. One of its science modules, the Infra-Red Dual Imaging Spectrograph (IRDIS), offers several observing modes. One of them is long slit spectroscopy with low (~40) or medium (~400) resolution that allows measuring the planets spectra once they have been detected by other instrumental configuration. The main problem is to extract a good spectrum of the planet from that of the star. We are facing many difficulties in this task. One of the main limitations is the speckle noise close to the star. Moreover, as we use a dispersive element, the chromatic dependence of the speckle patterns creates a modulation of the spectrum known as speckle chromatism. Finally, we are also facing problems linked to the use of a long slit: Airy patterns of the star modulating the spectrum, difficulty to preserve a continuous slope for the planet spectrum and slit efficiency. Several simulations have been performed using the SPHERE end-to-end simulation package based on CAOS in order to generate images as representative as possible to the one that will be delivered by IRDIS signal. We present here an analysis of the different noise sources and limitations, as well as their influence on the signal. As a result we will also present the current state of the data reduction process that is planned for the slit spectroscopy mode.
Boccaletti Anthony
Carbillet Marcel
Dohlen Kj.
Langlois Maud
Moutou Claire
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