Transiting exoplanets from the CoRoT space mission^⋆

XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet

¹ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
e-mail: magali.deleuil@oamp.fr
² IAG, Universidade de São Paulo, Brazil
³ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁴ Observatoire de Haute Provence, 04670 Saint Michel l’Observatoire, France
⁵ Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
⁶ Observatoire de la Côte d’ Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
⁷ Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK
⁸ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁹ LESIA, Obs de Paris, Place J. Janssen, 92195 Meudon Cedex, France
¹⁰ Institut d’astrophysique spatiale, Université Paris-Sud 11 & CNRS (UMR 8617), Bât. 121, 91405 Orsay, France
¹¹ Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
¹² Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
¹³ Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁴ Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain
¹⁵ University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
¹⁶ University of Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
¹⁷ Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778 Tautenburg, Germany
¹⁸ Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042 Graz, Austria
¹⁹ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
²⁰ Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel
²¹ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot ; 5 place Jules Janssen, 92195 Meudon, France

Received: 11 July 2011
Accepted: 27 September 2011

Abstract

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24  ±  0.23 M_Jup and a radius of 0.84  ±  0.04 R_Jup. With a mean density of 8.87  ±  1.10  g cm^-3, it is among the most compact planets known so far. Evolutionary models for the planet suggest a mass of heavy elements of the order of 800 M_⊕ if embedded in a central core, requiring a revision either of the planet formation models or both planet evolution and structure models. We note however that smaller amounts of heavy elements are expected by more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56.The star’s projected rotational velocity is vsini = 4.5  ±  1.0  km s^-1, corresponding to a spin period of 11.5  ±  3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving toward a triple synchronous state with equality of the orbital, planetary and stellar spin periods.