Thèse d’Alizée Duthu : L’étude de l’influence du champ magnétique sur l’évolution stellaire

The influence of the magnetic field on the stellar evolutions has still to be determined, particularly for the transition from the asymptotic giant branch (AGB) to planetary ne- bulae (PN) for intermediate and solar mass stars, and the transition from red supergiant (RSG) to supernova (SN) or Wolf Rayet (WR) for massive stars. The magnetic field plays likely an important role in the mass loss process, and the star morphology changes from a spherical to an asymmetric object with outflows. During my thesis, I studied the circum- stellar envelope of Betelgeuse, an RSG. I used the radio telescope IRAM-30m, to make a spectral survey at 1,3 and 3 mm. We detect only 7 species hence revealing that Betelgeuse is chemically young. However we detect for the first time the SiO maser, which will make possible to estimate the magnetic field in the envelope of this star. The second part of my thesis was to estimate the intensity of the magnetic field for a sample of AGBs and PNe using the CN radical sensitive to the Zeeman effect. The intensity of the magnetic field along the line of sight (Bl os) is estimated between -7.5 and 14.2 mG. Comparing with pre- vious studies at all wavelengths, we can conclude that the magnetic field decreases in 1/r with r the distance to the star. For the star IRC+10216, Blos is estimated for several posi- tions of the envelope between -7.2 and 9.5 mG : Blos is not homogeneous and aligned in the CSE.