Transiting exoplanets from the CoRoT  space mission ^⋆

XIX. CoRoT-23b: a dense hot Jupiter on an eccentric orbit

¹ LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
e-mail: daniel.rouan@obspm.fr
² Instituto de Astrofisica de Canarias, 38205, La Laguna, Tenerife, Spain
³ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁴ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁵ Research and Scientic Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁶ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
⁷ Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
⁸ Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK
⁹ Institut d’Astrophysique Spatiale, Université Paris XI, 91405 Orsay, France
¹⁰ Observatoire de Haute Provence, 04670 Saint Michel l’Observatoire, France
¹¹ Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
¹² University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
¹³ IAG, Universidade de Sao Paulo, Brazil
¹⁴ Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778 Tautenburg, Germany
¹⁵ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
¹⁶ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
¹⁷ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931, Germany
¹⁸ University of Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
¹⁹ Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042 Graz, Austria
²⁰ Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain

Received: 19 August 2011
Accepted: 3 October 2011

Abstract

We report the detection of CoRoT-23b, a hot Jupiter transiting in front of its host star with a period of 3.6314  ±  0.0001 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite, combined with spectroscopic radial velocity (RV) measurements. A photometric search for possible background eclipsing binaries conducted at CFHT and OGS concluded with a very low risk of false positives. The usual techniques of combining RV and transit data simultaneously were used to derive stellar and planetary parameters. The planet has a mass of M_p = 2.8 ± 0.3 M_Jup, a radius of R_pl= 1.05  ±  0.13R_Jup, a density of  ≈ 3 g cm^-3. RV data also clearly reveal a nonzero eccentricity of e = 0.16 ± 0.02. The planet orbits a mature G0 main sequence star of V = 15.5 mag, with a mass M_⋆ = 1.14  ±  0.08 M_⊙, a radius R _⋆ = 1. 61 ±  0.18 R_⊙  and quasi-solarabundances. The age of the system is evaluated to be 7 Gyr, not far from the transition to subgiant, in agreement with the rather large stellar radius. The two features of a significant eccentricity of the orbit and of a fairly high density are fairly uncommon for a hot Jupiter. The high density is, however, consistent with a model of contraction of a planet at this mass, given the age of the system. On the other hand, at such an age, circularization is expected to be completed. In fact, we show that for this planetary mass and orbital distance, any initial eccentricity should not totally vanish after 7 Gyr, as long as the tidal quality factor Q_p is more than a few 10⁵, a value that is the lower bound of the usually expected range. Even if CoRoT-23b  features a density and an eccentricity that are atypical of a hot Jupiter, it is thus not an enigmatic object.