AbstractSince the discovery of HD209458b, the first planet which transits its star, more quantitative information about these objects (the so-called Pegasides) can be inferred. For example, Charbonneau et al. (2002) derived the first constraint on the atmospheric composition of this Pegaside, which static atmospheric models have difficulties to explain. These planets, very close to their parent star, should be in synchronous rotation, implying strong day-to-night temperature contrasts and vigourous atmospheric dynamics. In this framework, we developed a radiative model for the atmosphere of extrasolar giant planets. In addition to modeling the atmosphere in which the incoming stellar flux is averaged over the whole disk of the planet, we introduced a uniform rotation of the atmosphere which can mimick a constant zonal wind. This model was applied to the planet HD209458b. We calculated a mean thermal structure as well as the associated chemical composition. We confirmed the importance of the absorption by alkali metals in the energetic balance of the Pegasides and studied the flux absorption profile in their atmosphere, which is crucial for evolutionary models. When zonal winds are introduced, the temperature contrasts can explain the composition constrained by the observations of Charbonneau et al. (2002), pertaining to the whole limb of the planet. More generally, we studied the role of various parameters such as the distance to the star and the wind velocity. We could in particular characterize the differences in the spectra with respect to the distance and the uniformization of temperatures whith increasing wind velocity.
Keywords : extrasolar planets -- radiative transfer -- HD209458b .
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