Letter to the Editor

Transiting exoplanets from the CoRoT space mission^*,**

II. CoRoT-Exo-2b: a transiting planet around an active G star

¹ Laboratoire d'Astrophysique de Marseille, UMR 6110, CNRS/Université de Provence, Traverse du Siphon, 13376 Marseille, France e-mail: [email protected]
² LESIA, CNRS UMR 8109, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon, France
³ IAS, Université Paris XI, 91405 Orsay, France
⁴ Instituto de Astrofísica de Canarias, 38205 La Laguna, Spain
⁵ School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK
⁶ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁷ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁸ Observatório Nacional, Rio de Janeiro, RJ, Brazil
⁹ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹⁰ Institute of Planetary Research, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
¹¹ Research and Scientific Support Department, European Space Agency, ESTEC, 2200 Noordwijk, The Netherlands
¹² Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
¹³ Observatoire de la Côte d'Azur, Laboratoire Cassiopée, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
¹⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁶ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
¹⁷ School of Physics and Astronomy, R. and B. Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
¹⁸ Rheinisches Institut für Umweltforschung, Universität zu Köln, Abt. Planetenforschung, Aachener Str. 209, 50931 Köln, Germany
¹⁹ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²⁰ LUTH, Observatoire de Paris-Meudon, 5 place J. Janssen, 92195 Meudon, France

Received: 21 January 2008
Accepted: 27 February 2008

Abstract

Context. The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ~12 000 stars in the galactic plane. An analysis of the raw data identifies the most promising candidates and triggers the ground-based follow-up.

Aims. We report on the discovery of the transiting planet CoRoT-Exo-2b, with a period of 1.743 days, and characterize its main parameters.

Methods. We filter the CoRoT raw light curve of cosmic impacts, orbital residuals, and low frequency signals from the star. The folded light curve of 78 transits is fitted to a model to obtain the main parameters. Radial velocity data obtained with the SOPHIE, CORALIE and HARPS spectrographs are combined to characterize the system. The 2.5 min binned phase-folded light curve is affected by the effect of sucessive occultations of stellar active regions by the planet, and the dispersion in the out of transit part reaches a level of 1.0910^-4 in flux units.

Results. We derive a radius for the planet of 1.465 ± 0.029 R_Jup and a mass of 3.31 ± 0.16 M_Jup, corresponding to a density of 1.31 ± 0.04 g/cm³. The large radius of CoRoT-Exo-2b cannot be explained by current models of evolution of irradiated planets.