Transiting exoplanets from the CoRoT space mission ^*

VIII. CoRoT-7b: the first super-Earth with measured radius

¹ Institut d'Astrophysique Spatiale, UMR 8617 CNRS, Bât. 121, Université Paris-Sud, 91405 Orsay, France e-mail: alain.leger@ias.fr
² LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France e-mail: daniel.rouan@obspm.fr
³ LUTH, UMR 8102 CNRS, Observatoire de Paris-Meudon, 5 place J. Janssen, 92195 Meudon, France
⁴ Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS, Technopôle de Marseille- Etoile, 13388 Marseille Cedex 13, France
⁵ Research and Scientific Support Department, European Space Agency, ESTEC, 2200 Noordwijk, The Netherlands
⁶ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁷ Instituto de Astrofísica de Canarias, C. via Lactea , 38200 La Laguna, Spain
⁸ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁹ Observatoire de Haute Provence, USR 2207 CNRS, OAMP, 04870 St. Michel l'Observatoire, France
¹⁰ Institute of Planetary Research, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
¹¹ Rheinisches Institut für Umweltforschung, Universität zu Köln, Abt. Planetenforschung, Aachener Str. 209, 50931 Köln, Germany

¹² Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹³ Instituto de Astronomia, Geofisica e Ciências Atmosféricas, USP, Sao Paulo, Brazil
¹⁴ Observatoire de la Côte d'Azur, Laboratoire Cassiopée, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
¹⁵ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
¹⁶ Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, 2 rue de la Houssiniére, 44322 NANTES Cedex 03, France
¹⁷ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
¹⁸ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁹ School of Physics and Astronomy, R. and B. Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
²⁰ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²¹ Laboratoire d'Astronomie de Lille, Université de Lille 1, 1 impasse de l'Observatoire, 59000 Lille, France
²² Centre National d'Etudes Spatiales, 2 place Maurice Quentin 75039 Paris Cedex 01, France
²³ Institute of Robotics and Mechatronics, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
²⁴ Centre Spatial de Liège, ULG Science Park, av. du Pré-Aly, 4031, Angleur-Liège, Belgique
²⁵ Ingenieurbüro Ulmer, Im Technologiepark 1, 15236 Frankfurt/Oder, Germany

Received: 23 February 2009
Accepted: 28 July 2009

Abstract

Aims. We report the discovery of very shallow (), periodic dips in the light curve of an active  G9V star observed by the CoRoT  satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion.

Methods. We used CoRoT  colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT  light curve to derive parameters of the companion.

Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40´´or triple systems are almost excluded with a  risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 day and a radius of  R_Earth. Analysis of preliminary radial velocity data yields an upper limit of 21 M_Earth  for the companion mass, supporting the finding.

Conclusions. CoRoT-7b  is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b  remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800–2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived.