Astronomy & Astrophysics

Free access article

A&A 488, L43-L46 (2008)
DOI: 10.1051/0004-6361:200810246

Letter

Transiting exoplanets from the CoRoT space mission

IV. CoRoT-Exo-4b: a transiting planet in a 9.2 day synchronous orbit

S. Aigrain¹, A. Collier Cameron², M. Ollivier³, F. Pont¹, L. Jorda⁴, J. M. Almenara⁵, R. Alonso⁴, P. Barge⁴, P. Bordé³, F. Bouchy⁶, H. Deeg⁵, R. De la Reza⁷, M. Deleuil⁴, R. Dvorak⁸, A. Erikson⁹, M. Fridlund¹⁰, P. Gondoin¹⁰, M. Gillon¹¹, T. Guillot¹², A. Hatzes¹³, H. Lammer¹⁴, A. F. Lanza¹⁵, A. Léger³, A. Llebaria⁴, P. Magain¹⁶, T. Mazeh¹⁷, C. Moutou⁴, M. Paetzold¹⁸, C. Pinte¹, D. Queloz¹¹, H. Rauer^{9, 19}, D. Rouan²⁰, J. Schneider²¹, G. Wuchter¹³, and S. Zucker²²

¹ School of Physics, University of Exeter, Exeter, EX4 4QL, UK
e-mail: suz@astro.ex.ac.uk
² Sch. Physics & Astronomy, Univ. St Andrews, St Andrews, KY16 9SS, UK
³ IAS, Université Paris XI, 91405 Orsay, France
⁴ LAM, Université de Provence, 13388 Marseille, France
⁵ IAC, E-38205 La Laguna, Spain
⁶ IAP, Université Pierre & Marie Curie, 75014 Paris, France
⁷ ON/MCT, 20921-030, Rio de Janeiro, Brazil
⁸ IfA, University of Vienna, 1180 Vienna, Austria
⁹ Institute of Planetary Research, DLR, 12489 Berlin, Germany
¹⁰ RSSD, ESA/ESTEC, 2200 Noordwijk, The Netherlands
¹¹ Observatoire de Genève, 1290 Sauverny, Switzerland
¹² OCA, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
¹³ Thüringer Landessternwarte, 07778 Tautenburg, Germany
¹⁴ IWF, Austrian Academy of Sciences, 8042 Graz, Austria
¹⁵ INAF - Osservatorio Astrofisico di Catania, 95123 Catania, Italy
¹⁶ IAG, Université de Liège, Liège 1, Belgium
¹⁷ Sch. Physics & Astronomy, Tel Aviv Univ., Tel Aviv 69978, Israel
¹⁸ RIU, Universität zu Köln, 50931 Köln, Germany
¹⁹ ZAA, TU Berlin, 10623 Berlin, Germany
²⁰ LESIA, Observatoire de Paris, 92195 Meudon, France
²¹ LUTH, Observatoire de Paris, 92195 Meudon, France
²² Dept. Geophysics & Planetary Sciences, Tel Aviv Univ., Tel Aviv 69978, Israel

Received 22 May 2008 / Accepted 18 July 2008

Abstract
CoRoT, the first space-based transit search, provides ultra-high-precision light curves with continuous time-sampling over periods of up to 5 months. This allows the detection of transiting planets with relatively long periods, and the simultaneous study of the host star's photometric variability. In this Letter, we report the discovery of the transiting giant planet CoRoT-Exo-4b and use the CoRoT light curve to perform a detailed analysis of the transit and determine the stellar rotation period. The CoRoT light curve was pre-processed to remove outliers and correct for orbital residuals and artefacts due to hot pixels on the detector. After removing stellar variability about each transit, the transit light curve was analysed to determine the transit parameters. A discrete autocorrelation function method was used to derive the rotation period of the star from the out-of-transit light curve. We determine the periods of the planetary orbit and star's rotation of 9.20205 $\pm$ 0.00037 and 8.87 $\pm$ 1.12 days respectively, which is consistent with this being a synchronised system. We also derive the inclination, $i = 90.00_{\rm -0.085}^$ in degrees, the ratio of the orbital distance to the stellar radius, $a/R_{\rm s} = 17.36_^$ , and the planet-to-star radius ratio $R_{\rm p}/R_{\rm s}=0.1047_^$ . We discuss briefly the coincidence between the orbital period of the planet and the stellar rotation period and its possible implications for the system's migration and star-planet interaction history.

Key words: techniques: photometric -- stars: planetary systems -- stars: rotation

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