1 Department of Physics and Astronomy, Science and Technology, Aarhus University2 Rheinisches Institut für Umweltforschung an der Universität zu Köln, Germany3 McDonald Observatory, The University of Texas at Austin, Austin, Texas, 78712, USA4 Institute of Planetary Research, German Aerospace Center, Berlin, Germany5 Research and Scientific Support Department, ESTEC/ESA, Noordwijk, The Netherlands6 Laboratoire d'Astrophysique de Marseille, France7 Institute of Planetary Research, German Aerospace Center, Germany8 Department of Physics, Oxford, OX1 3RH, UK9 Observatoire de la Côte d Azur, Laboratoire Cassiopée, France10 LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, France11 Institut d'Astrophysique Spatiale, Université Paris-Sud 11, France12 Observatoire de Haute-Provence, Université d'Aix-Marseille & CNRS, 04670, Saint-Michel l'Observatoire, France13 Institut d'Astrophysique Spatiale, Université Paris-Sud 11, CNRS (UMR 8617), Bât. 121, 91405, Orsay, France14 Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain15 University of Vienna, Institute of Astronomy, Vienna, Austria16 Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany17 IAG, Universidade de Sao Paulo, Brazil18 University of Liège, Liège 1, Belgium19 Observatoire de la Côte d Azur, Laboratoire Cassiopée, BP 4229, 06304, Nice Cedex 4, France20 Thüringer Landessternwarte, Sternwarte 5, Tautenburg, Germany21 Space Research Institute, Austrian Academy of Science, Graz, Austria22 School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel23 School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 69978, Tel Aviv, Israel24 LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, Meudon, France25 Department of Physics and Astronomy, Science and Technology, Aarhus University
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 M1/3 − 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∗/k2∗ ≤ 107.