Transiting exoplanets from the CoRoT space mission^⋆

XXIII. CoRoT-21b: a doomed large Jupiter around a faint subgiant star

¹ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
e-mail: Martin.Paetzold@uni-koeln.de
² McDonald Observatory, The University of Texas at Austin, Austin, Texas 78712, USA
³ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁴ Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁵ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁶ Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK
⁷ Observatoire de la Côte d Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
⁸ LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁹ Institut d’Astrophysique Spatiale, Université Paris-Sud 11, CNRS (UMR 8617), Bât. 121, 91405 Orsay, France
¹⁰ Observatoire de Haute-Provence, Université d’Aix-Marseille & CNRS, 04670 Saint-Michel l’Observatoire, France
¹¹ Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹² Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
¹³ University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
¹⁴ IAG, Universidade de Sao Paulo, Brazil
¹⁵ University of Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
¹⁶ Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778 Tautenburg, Germany
¹⁷ Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042 Graz, Austria
¹⁸ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
¹⁹ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
²⁰ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
²¹ Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain
²² Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²³ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
²⁴ Georg-August-Universität, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Received: 9 November 2011
Accepted: 2 July 2012

Abstract

CoRoT-21, a F8IV star of magnitude V = 16 mag, was observed by the space telescope CoRoT during the Long Run 01 (LRa01) in the first winter field (constellation Monoceros) from October 2007 to March 2008. Transits were discovered during the light curve processing. Radial velocity follow-up observations, however, were performed mainly by the 10-m Keck telescope in January 2010. The companion CoRoT-21b is a Jupiter-like planet of 2.26 ± 0.33 Jupiter masses and 1.30 ± 0.14 Jupiter radii in an circular orbit of semi-major axis 0.0417 ± 0.0011 AU and an orbital period of 2.72474 ± 0.00014 days. The planetary bulk density is (1.36    ±    0.48) × 10³   kg   m^-3, very similar to the bulk density of Jupiter, and follows an M^1/3 − R relation like Jupiter. The F8IV star is a sub-giant star of 1.29 ± 0.09 solar masses and 1.95 ± 0.2 solar radii. The star and the planet exchange extremetidal forces that will lead to orbital decay and extreme spin-up of the stellar rotation within 800 Myr if the stellar dissipation is Q_∗/k_2∗ ≤ 10⁷.