Doppler search for exoplanet candidates and binary stars in a CoRoT field using a multi-fiber spectrograph^*

I. Global analysis and first results

¹ Laboratoire d'Astrophysique de Marseille, BP 8, 13376 Marseille Cedex 12, Université de Provence, CNRS (UMR 6110) and CNES, France e-mail: benoit.loeillet@oamp.fr
² Institut d'Astrophysique de Paris, CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
³ GEPI/CNRS UMR 8111, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁴ Observatoire de la Côte d'Azur, Dpt. Cassiopée, CNRS-UMR 6202, BP 4229, 06304 Nice Cedex 04, France
⁵ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁶ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 26 January 2007
Accepted: 26 November 2007

Abstract

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.