Magnetic fields at the surface of a few early-type stars have been directly
detected. These fields have magnitudes between a few hundred G up to a few kG.
In one case, evidence of magnetic braking has been found. We investigate the
effects of magnetic braking on the evolution of rotating (υini=200 km s−1) 10 M⊙ stellar models at solar metallicity during
the main-sequence (MS) phase. The magnetic braking process is included in our
stellar models according to the formalism deduced from 2D MHD simulations of
magnetic wind confinement by ud-Doula and co-workers. Various assumptions are
made regarding both the magnitude of the magnetic field and of the efficiency
of the angular momentum transport mechanisms in the stellar interior. When
magnetic braking occurs in models with differential rotation, a strong and
rapid mixing is obtained at the surface accompanied by a rapid decrease in the
surface velocity. Such a process might account for some MS stars showing strong
mixing and low surface velocities. When solid-body rotation is imposed in the
interior, the star is slowed down so rapidly that surface enrichments are
smaller than in similar models with no magnetic braking. In both kinds of
models (differentially or uniformly rotating), magnetic braking due to a field
of a few 100 G significantly reduces the angular momentum of the core during
the MS phase. This reduction is much greater in solid-body rotating models.Comment: 4 pages, 4 figures, accepted for publication as a Letter in Astronomy
and Astrophysic
