* Astronomy

Members Login
Post Info TOPIC: CoRoT-Exo-2a


L

Posts: 131433
Date:
CoRoT-Exo-2a
Permalink  
 


Title: Magnetic activity in the photosphere of CoRoT-Exo-2a
Active longitudes and short-term spot cycle in a young Sun-like star
Authors: A. F. Lanza, I. Pagano1,G.Leto, S. Messina, S. Aigrain, R. Alonso, M. Auvergne, A. Baglin, P.Barge, A. S. Bonomo, P. Boumier, A. Collier Cameron, M.Comparato, G. Cutispoto, J.R.DeMedeiros, B.Foing, A. Kaiser, C. Moutou, P.S.Parihar, A. Silva-Valio, and W. W. Weiss

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 regularised 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.

Read more (PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star
Authors: A. F. Lanza, I. Pagano, G. Leto, S. Messina, S. Aigrain, R. Alonso, M. Auvergne, A. Baglin, P. Barge, A. S. Bonomo, P. Boumier, A. Collier Cameron, M. Comparato, G. Cutispoto, J. R. De Medeiros, B. Foing, A. Kaiser, C. Moutou, P. S. Parihar, A. V. R. Silva, W. W. Weiss

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. 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. We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations. To model the light curve of CoRoT-Exo-2a, we take into account both the photometric effects of cool spots as well as those of solar-like faculae, adopting solar analogy. 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 approximately 80 degrees during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than about 1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity about 1 percent smaller than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 $\pm$ 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed on the basis of 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.

Read more (166kb, PDF)

__________________


L

Posts: 131433
Date:
RE: CoRoT-Exo-2b
Permalink  
 


Title: Transiting exoplanets from the CoRoT space mission III. The spectroscopic transit of CoRoT-Exo-2b with SOPHIE and HARPS
Authors: F. Bouchy, D. Queloz, M. Deleuil, B. Loeillet, A.P. Hatzes, S. Aigrain, R. Alonso, M. Auvergne, A. Baglin, P. Barge, W. Benz, P. Bordé, H.J. Deeg, R. De la Reza, R. Dvorak, A. Erikson, M. Fridlund, P. Gondoin, T. Guillot, G. Hébrard, L. Jorda, H. Lammer, A. Léger, A. Llebaria, P. Magain, M. Mayor, C. Moutou, M. Ollivier, M. Pätzold, F. Pepe, F. Pont, H. Rauer, D. Rouan, J. Schneider, A.H.M.J. Triaud, S. Udry, G. Wuchterl

We report on the spectroscopic transit of the massive hot-Jupiter CoRoT-Exo-2b observed with the high-precision spectrographs SOPHIE and HARPS. By modelling the radial velocity anomaly occurring during the transit due to the Rossiter-McLaughlin (RM) effect, we determine the sky-projected angle between the stellar spin and the planetary orbital axis to be close to zero lambda=7.2±4.5 deg, and we secure the planetary nature of CoRoT-Exo-2b. We discuss the influence of the stellar activity on the RM modelling. Spectral analysis of the parent star from HARPS spectra are presented.

Read more (28kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Transiting exoplanets from the CoRoT space mission II. CoRoT-Exo-2b: A transiting planet around an active G star
Authors: R. Alonso, M. Auvergne, A. Baglin, M. Ollivier, C. Moutou, D. Rouan, H.J. Deeg, S. Aigrain, J.M. Almenara, M. Barbieri, P. Barge, W. Benz, P. Bordé, F. Bouchy, R. De la Reza, M. Deleuil, R. Dvorak, A. Erikson, M. Fridlund, M. Gillon, P. Gondoin, T. Guillot, A. Hatzes, G. Hébrard, P. Kabath, L. Jorda, H. Lammer, A. Léger, A. Llebaria, B. Loeillet, P. Magain, M. Mayor, T. Mazeh, M. Pätzold, F. Pepe, F. Pont, D. Queloz, H. Rauer, A. Shporer, J. Schneider, B. Stecklum, S. Udry, G. Wuchterl

Context. The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ~12000 stars in the galactic plane. An analysis of the raw data identifies the most promising candidates and triggers the ground-based follow-up.
Aims. We report on the discovery of the transiting planet CoRoT-Exo-2b, with a period of 1.743 days, and characterise its main parameters.
Methods. We filter the CoRoT raw light curve of cosmic impacts, orbital residuals, and low frequency signals from the star. The folded light curve of 78 transits is fitted to a model to obtain the main parameters. Radial velocity data obtained with the SOPHIE, CORALIE and HARPS spectrographs are combined to characterise the system. The 2.5 min binned phase-folded light curve is affected by the effect of successive occultations of stellar active regions by the planet, and the dispersion in the out of transit part reaches a level of 1.09x10-4 in flux units.
Results. We derive a radius for the planet of 1.465±0.029 R_Jup and a mass of 3.31±0.16 M_Jup, corresponding to a density of 1.31±0.04 g/cm^3. The large radius of CoRoT-Exo-2b cannot be explained by current models of evolution of irradiated planets.

Read more (99kb, PDF)

__________________
«First  <  1 2 | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard