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Imaging & Characterizing Giant Planets

Nowadays, more than 700 exoplanets have been discovered using various planet hunting techniques, initially around main-sequence solar-type stars (Udry & Santos 2007). All these techniques (radial velocity, transit, micro-lensing, imaging and astrometry) are very complementary in terms of constraints on the exoplanet physical properties, properties of the stellar targets explored and of the circumstellar environment probed around the stars. The direct imaging technique is unique for the study of long-periods exoplanets (located at more than 5 AU) opening a complete new window to study the outer part of exoplanetary systems, the characterization of their non-irradiated atmospheres and the connection with the presence of circumstellar disk. In that context, my research interest is the detection and the characterization of giant planets to broaden our understanding of their formation processes, their physical and chemical properties as well as their connection with their environment in terms of architecture and dynamical stability. My field of research can therefore be declined according to four main domains: direct imaging of giant planets and brown dwarfs, the characterization of their physics, the properties of their stellar hosts, finally the scientific preparation of future intrumentation such as SPHERE at VLT or the E-ELT.

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Figure: VLT/NaCo Ks-band ADI image of the young exoplanets detected around the stars Beta Pictoris (A6V, 12 Myr, 19.3pc, Bpic association). This very faint environment is revealed after a very careful subtraction of the much brighter stellar halo. Right, Composite image of the young circumstellar disks around AU Mic (12 Myr, M1V, 9.9pc, Bpic group), Beta Pictoris and HD61005 (G8V, 30 Myr, 35.3pc, Argus association).

Giant Planets and Brown Dwarf companions are faint and located close to their bright stellar host. Consequently, a dedicated instrumentation is then needed to simply image them with a high contrast (10-4 to 10-9) and a high angular resolution (at the subarcsecond level). For large ground-based telescopes, the turbulence limits the resolution of the astronomical images and the use of Adaptive Optics (AO) systems is required to compensate for the wavefront distorsions. Such systems are presently used at the the Keck Observatory, the Subaru Telescope, the Gemini North and South Telescopes as well as the VLT. During my PhD thesis, I had the chance to get involved into the NACO instrument, composed of NAOS (Nasmyth Adaptive Optics System) and the near-IR camera CONICA. NACO is actually installed at the 8.2m-UT4 of the ESO VLT Paranal Observatory. I was particularly interested in studying the AO system performances and limitations. This experience was followed by a 4-years fellowhip et the ESO Very Large Telescope. For these years, I could develop my field of expertise for the imaging and the characterization of very low mass companions to nearby stars.