Planet detection with SPHERE and EPICS

In the last fifteen years a large amount (more than 500) of extrasolar planets has been found. However, until now the great majority of them has been discovered exploiting indirect techniques like e.g. the radial velocity method (that gives, actually, the most important contribution), the transit method, the microlensing method and others. Direct imaging of extrasolar planets would be very important to sample the external parts of the extrasolar systems where the most important indirect methods (e.g. radial velocity) are not able to get until now, and to test the model on the formation of the planetary systems. However, direct imaging of extrasolar planets is very difficult because of the great luminosity contrast ( 10−6÷−7 for a giant planet and 10−9 for an Earth-like planet) and the small separation (few tenths of arcsec for a planet at 10 AU at some tens of pc) between the companion object and the central star. Until now just a few extrasolar planets have been imaged around stellar or substellar (brown dwarfs) objects. In the near future, some instruments like SPHERE (that will operate at ESO VLT) promise to be able to largely improve the number of planets that will be found through direct imaging. These instruments to work properly, however, we should be able to strongly reduce the impact of the speckle noise. To this aim, various differential imaging methods have been developed in these years like e.g. the Spectral Differential Imaging (that exploits the spectral characteristics of the searched planets), the Angular Differential Imaging (that exploits the rotation of the Field of View to subtract the static speckle pattern) and the Spectral Deconvolution (that exploits the spectral characteristics of the speckle pattern itself). All these methods have been tested during the simulations that we performed on the SPHERE IFS performances with some modifications to adapt them to the characteristics of the instrument (see Section 3.2). The results of these simulations confirm that, using the SPHERE IFS instrument in association with differential imaging techniques, we will be able to get luminosity contrasts between the companion object and the central star of the order of some 10−7 at separations of less than 1 arcsec. Moreover, from our simulations, it seems that spectral deconvolution can get slightly better contrasts with respect to the spectral differential imaging method. An example of possible data analysis on real data is given in Chapter 2 where I present the results of the analysis performed on data from the NACO Large Program. In Section 3.3 I then present the results of an analysis made to test the astrometric potential of SPHERE IFS exploiting, in particular, the characteristics of the speckle pattern. It results that these methods should allow an astrometric precision better than 1 mas. In Section 3.4 I then present a possible pipeline developed for the IFS data reduction with the aim to find and characterize eventual companion objects. A further development in the field of direct imaging of extrasolar planets should be reached with EPICS, which is an instrument designed to work at the future ESO European Extremely Large Telescope (E-ELT). It is at present in the post Phase A. In Chapter 4 I present the results of a laboratory experiment aimed to test the possible advantages in using an apodizer in place of a traditional pupil mask. It resulted that, probably due to the presence of ghosts, we are not able to strongly reduce the cross-talk using an apodizer but however its level is well below the requested values. Finally in the same Chapter I present the preliminary opto-mechanical design of the IFS that will be part of EPICS. This design has been presented at the Phase A meeting of the instrument.