| Massive stars represent a crucial stellar class for the galactic environment evolution. In spite of their low number, their large mass loss rate during all the stages of their rapid evolution and the subsequent energy injection have a deep impact on the interstellar medium, even at long distances. The origin of this mass loss is closely related to their intense radiation, which generates a fast and sometimes dense wind. Recent instrumental progress revealed the deeply inhomogeneous and variable behaviour of these winds, exhibiting stochastic and even periodic phenomena. This implies the existence of competing phenomena able to modify and modulate the radiative wind, namely the stellar rotation, the presence of non-radial pulsations (NRP) or magnetic fields. This thesis results from a collaboration between the astrophysics group of the Universite de Montreal and the long baseline interferometry group of the Observatoire de la Cote d'Azur. I first present the problem of instabilities exhibited by LBVs (Luminous Blue Variables) with the study of the emblematic star P Cygni. After having developed the context of its eruptive manifestation from an observational point of view, I present the results of observations carried out with an experimental adaptive optics operating in the visible at the Observatoire de Haute-Provence (OHP). Then I study the problems of the periodic features detected in O stars and certain WR stars in order to detect magnetic fields. This study is based on observations carried out with the spectropolarimeter CASPEC of the 3.6m telescope of La Silla (ESO/Chile). I finally describe the prospective work undertaken on an interferometric technique using polarimetry called SPIN (Spectro-Polarimetric INterferometry). The use of SPIN can bring a complementary information simultaneously locating and quantifying the mass loss close to the star. I stress particularly on the detection and the characterization of magnetic fields using the SPIN technique in circular polarization. |
