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Title: Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star
Authors: Lanza, A. F
Pagano, I
Leto, G
Messina, S
Aigrain, S
Alonso, R
Auvergne, M
Baglin, A
Barge, P
Bonomo, A. S
Boumier, P
Collier Cameron, A
Comparato, M
Cutispoto, G
de Medeiros, J. R
Foing, B
Kaiser, A
Moutou, C
Parihar, P. S
Silva-Valio, A
Weiss, W. W
Keywords: Stars: Magnetic Fields;Stars: Late-Type;Stars: Activity;Stars: Rotation;Stars: Individual: CoRoT-Exo-2a;Planetary Systems
Issue Date: Jan-2009
Publisher: EDP Sciences
Citation: Astronomy and Astrophysics, Vol. 493, No. 1, pp. 193 - 200
Abstract: Context: The space experiment CoRoT has recently detected transits by a hot Jupiter across the disc of an active G7V star (CoRoT-Exo-2a) that can be considered as a good proxy for the Sun at an age of approximately 0.5 Gyr. Aims: We present a spot modelling of the optical variability of the star during 142 days of uninterrupted observations performed by CoRoT with unprecedented photometric precision. Methods: We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations, a good proxy for the optical flux variations of the Sun as a star. The best results in terms of mapping of the surface brightness inhomogeneities are obtained by means of maximum entropy regularized models. To model the light curve of CoRoT-Exo-2a, we take into account the photometric effects of both cool spots and solar-like faculae, adopting solar analogy. Results: Two active longitudes initially on opposite hemispheres are found on the photosphere of CoRoT-Exo-2a with a rotation period of 4.522 ± 0.024 days. Their separation changes by ≈80° during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than ~1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity ~1 percent lower than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 ± 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. We discuss the effects of solar-like faculae on our models, finding indications of a facular contribution to the optical flux variations of CoRoT-Exo-2a being significantly smaller than in the present Sun. Conclusions: The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed, based on solar analogy. A possible magnetic star-planet interaction is suggested by the cyclic variation of the spotted area. Alternatively, the 28.9-d cycle may be related to Rossby-type waves propagating in the subphotospheric layers of the star.
ISSN: 0004-6361
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