Astérosismologie des étoiles de type solaire, avec ou sans planètes, abondance des éléments et phénomènes de transport

Since several decades, the observations of stellar oscillations and the search for exoplanets were developed in parallel, using the same instruments and similar methods: the radial velocity method, from ground-based instruments like SOPHIE in OHP and HARPS in La Silla, Chile, and the photometric method, basically from space instruments, like CoRoT and Kepler. The interest of doing asteroseismic studies of exoplanets host stars appeared from the beginning of these observations. The characterization of planets needs a good knowledge of the central star, particularly of its global parameters like its mass, radius, effective temperature. The study of the differences between stars with or without detected planets may bring information for a better understanding of the formation of planetary systems. It is well known, for example, that the stars which possess planets have on the average larger metallicities than those without detected planets. The very large number of exoplanets or candidates exoplanets detected by the space experiment Kepler, needs automatic procedures to extract the basic parameters of the central stars from studies of their oscillations. However, precise asteroseismic studies of well chosen stars are still important for a better precision of the results, and also to test the other procedures. During this thesis, we chose to perform precise studies of three central stars of planetary systems: (i) HD 52265, the only CoRoT main target with planets, observed continuously during several months with a very good precision;(ii) 94~Cet, a central star of planetary system whose spectroscopic parameters are close to those of  Virginis, a star without planets, well studied in the past by other authors. 94 Cet has been observed with the HARPS spectrograph in La Silla Observatory; and (iii) 51 Pegasi,"mythic" star, host of the first exoplanet ever detected, in 1995, by Michel Mayor and Didier Queloz, and that has been observed with the spectrograph SOPHIE in the Haute Provence Observatory. In all cases, we have compared the observed frequencies and their combinations, with those computed for models obtained with the Toulouse-Geneva Evolution Code. Oscillation frequencies were computed using the code PULSE, from Montreal. Various physical aspects were tested, in particular atomic diffusion including radiative accelerations on heavy elements. We obtained interesting results for these three stars, in different ways. In the three cases we deduced the external parameters and some information on their internal structure. In the case of HD 52265, we could check results of two different automatic codes. The case of 51 Peg was, however, more difficult to treat than the others due to the precision on the observations was not as good as we expected. This work presented both and observational and modeling aspects. It represents a somewhat complete approach of asteroseismology and its techniques.

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