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

VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert

¹ Laboratoire d'Astrophysique de Marseille (UMR 6110), Technopole de Marseille-Étoile, 13388 Marseille Cedex 13, France e-mail: magali.deleuil@oamp.fr
² Instituto de Astrofísica de Canarias, C. via Lactea S/N, 38200 La Laguna, Spain
³ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁴ LESIA, CNRS UMR 8109, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon, France
⁵ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁶ School of Physics A28, University of Sydney, Australia
⁷ IAS, Université Paris XI, 91405 Orsay, France
⁸ School of Physics and Astronomy, University of St Andrews, UK
⁹ Institute of Planetary Research, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
¹⁰ Observatório Nacional, Rio de Janeiro, RJ, Brazil
¹¹ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹² Research and Scientific Support Department, European Space Agency, ESTEC, 2200 Noordwijk, The Netherlands
¹³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁴ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
¹⁵ Observatoire de la Côte d'Azur, Laboratoire Cassiopée, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
¹⁶ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
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: 16 July 2008
Accepted: 22 September 2008

Abstract

Context. The CoRoT space mission routinely provides high-precision photometric measurements of thousands of stars that have been continuously observed for months.

Aims. The discovery and characterization of the first very massive transiting planetary companion with a short orbital period is reported.

Methods. A series of 34 transits was detected in the CoRoT light curve of an F3V star, observed from May to October 2007 for 152 days. The radius was accurately determined and the mass derived for this new transiting, thanks to the combined analysis of the light curve and complementary ground-based observations: high-precision radial-velocity measurements, on-off photometry, and high signal-to-noise spectroscopic observations.

Results. CoRoT-Exo-3b  has a radius of 1.01 ± 0.07 R_Jup and transits around its F3-type primary every 4.26 days in a synchronous orbit. Its mass of 21.66 ± 1.0 M_Jup, density of 26.4 ± 5.6 g cm^-3, and surface gravity of logg = 4.72 clearly distinguish it from the regular close-in planet population, making it the most intriguing transiting substellar object discovered so far.

Conclusions. With the current data, the nature of CoRoT-Exo-3b is ambiguous, as it could either be a low-mass brown-dwarf or a member of a new class of “superplanets”. Its discovery may help constrain the evolution of close-in planets and brown-dwarfs better. Finally, CoRoT-Exo-3b confirms the trend that massive transiting giant planets (M ≥ 4 M_Jup) are found preferentially around more massive stars than the Sun.