Doppler search for exoplanet candidates and binary stars in a CoRoT field using a multi-fiber spectrograph - I. Global analysis and first results

Context. The discovery of the short-period giant exoplanet population, the so-called hot Jupiter population, and their link to brown dwarfs and low-mass stars challenges the conventional view of planet formation and evolution. Aims. We took advantage of the multi-fiber facilities GIRAFFE and UVES/FLAMES (VLT) to perform the first large radial velocity survey using a multi-fiber spectrograph to detect planetary, brown-dwarf candidates and binary stars. Methods. We observed 816 stars during 5 consecutive half-nights. These stars were selected within one of the exoplanet fields of the space mission CoRoT. Results. We computed the radial velocities of these stars and showed that a systematic error floor of 30 m s -1 was reached over 5 consecutive nights with the GIRAFFE instrument. Over the whole sample the Doppler measurements allowed us to identify a sample of 50 binaries, 9 active or blended binary stars, 5 unsolved cases, 14 exoplanets and brown-dwarf candidates. Further higher precision Doppler measurements are now necessary to confirm and better characterize these candidates. Conclusions. This study demonstrates the efficiency of a multi-fiber approach for large radial-velocity surveys in search for exoplanets as well as the follow-up of transiting exoplanet candidates. The spectroscopic characterization of the large stellar population is an interesting by-product of such missions as the CoRoT space mission.