Etude de l' environnements circumstellaire d'étoiles de la séquence principale

The study of circumstellar environments of Main Sequence stars concerns most of stars; it is moreover closely related to the studies of star and planetary system formation. However, the faintness of these circumstellar media makes the observations very difficult. Therefore, they require a very high sensitivity, together with high angular resolution. On the one hand, l have studied the applicability and the efficiency of some observational techniques for this study. In particular, this led me to discuss the theoretical and actual capabilities of stellar coronography coupIed with adaptive optics, and that of infrared and optical interferometry. On the other hand, l have participated in the study of circumstellar environments with new observations. First, the spectroscopy allowed to improve the analysis of the gazeous component of the disk around beta Pictoris. Secondly, l tried to image the light scattered by the dust around this star and around other candidates, in coronography with adaptive optics. Finally, the observations are interpreted to improve our knowledge of the circumstellar matter distribution, together with its chemical and physical properties. This information is compared to other recent results, and considered in the frame of the evolution from the remnants of the protostellar nebula to the observed system.