Recherche et caracterisation des exoplanetes de type super-Terres – super-Terres

The field of exoplanet research has became very intensive since the discovery of the first such systems in 1995. This field is driven by three main motivations: 1) characterising and understanding the planetary populations in our Galaxy; 2) understanding the formation of evolution of planetary systems; 3) the search for and study of Earth-like planets in habitable zone of a star. In the exoplanet field, the search for low-mass exoplanets (Neptune and super-Earth like exoplanets) is motivated by efforts to understand 1) their formation and evolution mechanisms and, by analogy, to gain an improved understanding of the formation of our own Solar System; 2) their frequency of occurrence in comparison with giant exoplanets. The transiting low-mass exoplanets (only one known up to day) makes them extremely precious targets since a direct measurement of their mass, radius and mean density can be obtained. Furthermore transiting exoplanets orbiting bright stars offer the possibility to drill their atmosphere by transmission spectroscopy during the transit. Such informations bring new constraints for theoretical studies on planet structure and composition. The goal of our proposal is to put significant and intensive efforts in the detection, characterization and studies of low-mass exoplanets (Neptune and super-Earth like exoplanets) which are considered today as prime objectives in exoplanet field and a step towards the Earth-like exoplanets. Our aims are to push the limit of detection in radial velocity and photometric technics and to explore the new domain of the long-period low-mass exoplanets (inside the habitable zone of their star). Our objectives may be described in 4 specific work-packages : 1- Search for long-period low-mass exoplanets with HARPS (3.6-m ESO). The HARPS Guarantee Time Observation (GTO) program will be close in march 2009. We want to keep the lead on this program in close collaboration with Geneva Observatory and we will apply for a new ESO large program to focus and enlarge the research for low-mass exoplanets. The observation over a time scale of up to 8 years will allow us the unique possibility of discovery of long period (0.3 – 3 years) Neptune-like exoplanets around bright solar-type stars (only 1 known up to day). 2- Optimization of SOPHIE spectrograph (1.93-m OHP) to reach the 1-2 m/s precision for close-in low-mass exoplanets. The main limitation of SOPHIE (3-5 m/s) comes from the old Cassegrain Fiber Adapter (used for ELODIE spectrograph) an more specifically to the guiding and centering system on the fiber entrance. The change of the guiding camera and guiding software will permit us a significant gain in radial velocity accuracy in order to have the capability to detect close-in low-mass exoplanets orbiting bright solar-type stars. Our objective is to reach the same level of Doppler accuracy than HARPS in order that SOPHIE becomes the unique instrument in the North hemisphere enable to conduct an efficient search for low-mass exoplanets (including transiting exoplanets). 3 - Characterization of the Neptune-like CoRoT exoplanets candidates. The space CoRoT mission is just starting and conducted, thanks to complementary ground-based observations with SOPHIE and HARPS, to the discovery of 2 new hot-Jupiters. Our goal is to put significant effort to focus on the Neptune-like CoRoT exoplanets candidates. The aim is to optimize and reinforce the follow-up strategy in order to reveal and to characterize the low-mass and small-size exoplanets detected by CoRoT. 4- Monitor the stellar activity and follow-up the low-mass transiting exoplanet with the automatic photometric telescope ROSACE. Precise photometric monitoring of exoplanetary systems is indeed needed: 1) to search for the signature of planets transiting in front of the star; 2) to measure the photometric variability of the candidate exoplanet host star to establish whether observed Doppler variations are caused by stellar activity or by planetary reflex motion; 3) for the timing monitoring of transiting exoplanets discovered so far including the CoRoT transiting systems to put in obviousness possible low-mass companions and to catch for a second or third transit event in case of non confirmed long period candidates for which CoRoT observed only one or two transit events. Our goal is to adapt and upgrade the automatic telescope ROSACE based on OHP in order to carry out systematic precise photometric monitoring of low-mass exoplanets.