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Résumé:

Gaia will provide a three-dimensional map of our Galaxy, with unprecedented positional and radial velocity measurements for about one per cent of the Galactic stellar population. Combined with astrophysical information derived from spectroscopy and photometry for each star, this will lead to a detailed understanding of Êthe formation, and dynamical and chemical evolution of our Galaxy. Other scientific products include extra-solar planets, minor bodies in the solar system, or distant quasars. The contribution of Gaia to stellar physics is less publicized, although very significant.Ê I show here a number of illustrative examples. For example, we will have access to very precise HR diagrams with very large sample of stars allowing extensive tests of fine effects in stellar evolution. Accurate parameters (esp. luminosities, and masses) will allow the independent determination of surface gravities, the characterization of non-LTE effects, and the derivation of more accurate chemical abundances. We will be able to quantify transport processes in various populations of stars, and shed new light on abundance anomalies. In addition, the preparation of Gaia induces a very large effort devoted to homogenize the stellar parameters of a great number of reference stars, and the development of performant tools designed to automatically extract parameters from tremendous amounts of spectra.