Recherche et étude de planètes autour des naines M

Abstract : In a decade of hunt for extrasolar planetary systems about 170 exoplanets have been found to orbit almost 150 stars. My thesis takes place in this new field of astrophysics by looking for planets around M dwarfs. These stars are very-low mass stars, and hence this work focuses on the caracterisation of the formation of planets depending on the host stars mass.

First, I describe the paradigm of the planetary formation, on one hand by giving the statistical properties of the already detected systems and, on the other hand with a description of the standard model. Next I review different methods for the detection of exoplanets, with a particular stress on the radial-velocities method, its advantages and drawbacks. It is this last method we use for our different research programmes. Afetr what, I describe our stars samples and the obtained precisions according to the used instruments. From these programmes I present a detection of a planet with the mass of Neptune orbiting a M dwarf as well as the identification of a star which displays a spot on its surface. These two results, presented in a concurrent way, allow me to explain how it is possible to descriminate the signal induced by an exoplanet from false detections.

Because in the case of sun-like stars a strong correlation is observed between the occurence of planets and the metal content of host stars, a part of my thesis is devoted to the study of the metallicity for M dwarfs.

Finally, the last part of my work aims to estimate the frequency of giant planets orbiting M dwarfs. This is done through a comparison of our gathered data with output from numerical simulations. The computed frequency is analysed to the light of our determination of M-dwarf metallicity.
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Xavier Bonfils. Recherche et étude de planètes autour des naines M. Astrophysique [astro-ph]. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00186322⟩

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