Research Note

Transiting exoplanets from the CoRoT space mission

XXI. CoRoT-19b: a low density planet orbiting an old inactive F9V-star^⋆

¹ Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
e-mail: guenther@tls-tautenburg.de
² Institut d’Astrophysique de Paris, UPMC-CNRS, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
³ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁴ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
⁵ Observatoire de Haute-Provence, Université Aix-Marseille & CNRS, 04870 St. Michel l’Observatoire, 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, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
¹⁰ Institut d’Astrophysique Spatiale, Université Paris-Sud 11, 91405 Orsay, France
¹¹ Institute of Planetary Research, German Aerospace Centre, Rutherfordstraße 2, 12489 Berlin, Germany
¹² Centre for Astronomy and Astrophysics, TU Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
¹³ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot ; 5 place Jules Janssen, 92195 Meudon, France
¹⁴ Rheinisches Institut für Umweltforschung an der Universiät zu Köln, Aachener Straße 209, 50931 Köln, Germany
¹⁵ Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
¹⁶ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁷ University of Vienna, Institute of Astronomy, Türkenschanzstraße 17, 1180 Vienna, Austria
¹⁸ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo, Brazil
¹⁹ University of Liège, Allée du 6 août 17, S. Tilman, Liège 1, Belgium
²⁰ Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042 Graz, Austria
²¹ Dpto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
²² Georg-August-Universität, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
²³ Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark

Received: 14 July 2011
Accepted: 24 November 2011

Abstract

Context. Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. These measurements indicate that planets of similar mass can have very different radii. For low-density planets, it is generally assumed that they are inflated owing to their proximity to the host-star. To determine the causes of this inflation, it is necessary to obtain a statistically significant sample of planets with precisely measured masses and radii.

Aims. The CoRoT space mission allows us to achieve a very high photometric accuracy. By combining CoRoT data with high-precision radial velocity measurements, we derive precise planetary radii and masses. We report the discovery of CoRoT-19b, a gas-giant planet transiting an old, inactive F9V-type star with a period of four days.

Methods. After excluding alternative physical configurations mimicking a planetary transit signal, we determine the radius and mass of the planet by combining CoRoT photometry with high-resolution spectroscopy obtained with the echelle spectrographs SOPHIE, HARPS, FIES, and SANDIFORD. To improve the precision of its ephemeris and the epoch, we observed additional transits with the TRAPPIST and Euler telescopes. Using HARPS spectra obtained during the transit, we then determine the projected angle between the spin of the star and the orbit of the planet.

Results. We find that the host star of CoRoT-19b is an inactive F9V-type star close to the end of its main-sequence life. The host star has a mass M_∗ = 1.21  ±  0.05  M_⊙ and radius R_∗ = 1.65  ±  0.04 R_⊙. The planet has a mass of M_P = 1.11  ±  0.06 M_Jup and radius of R_P = 1.29  ±  0.03 R_Jup. The resulting bulk density is only ρ = 0.71  ±  0.06 g cm^-3, which is much lower than that for Jupiter.

Conclusions. The exoplanet CoRoT-19b is an example of a giant planet of almost the same mass as Jupiter but a  ≈30% larger radius.