Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6^⋆

A. F. Lanza¹, A. S. Bonomo^1,2, I. Pagano¹, G. Leto¹, S. Messina¹, G. Cutispoto¹, C. Moutou², S. Aigrain³, R. Alonso⁴, P. Barge², M. Deleuil², M. Fridlund⁵, A. Silva-Valio⁶, M. Auvergne⁷, A. Baglin⁷ and A. Collier Cameron⁸

¹ INAF - Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy
e-mail: nuccio.lanza@oact.inaf.it
² Laboratoire d’Astrophysique de Marseille (UMR 6110), Technopole de Château-Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
³ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁴ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁵ Research and Scientific Support Department, European Space Agency, Keplerlaan 1, 2200AG, Noordwijk, The Netherlands
⁶ CRAAM, Mackenzie University, rua de Consolação 896, 01302-907 São Paulo, Brazil
⁷ LESIA, CNRS UMR 8109, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon, France
⁸ School of Physics and Astronomy, University of St. Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland, UK

Received: 21 June 2010
Accepted: 16 September 2010

Abstract

Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days.

Aims. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction.

Methods. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of  ~140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts.

Results. Individual active regions have lifetimes up to 30−40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of ΔΩ/Ω = 0.12 ± 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by  ~200° with the probability of a chance occurrence being smaller than 1 percent.

Conclusions. Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force.