DYNAMICS OF THE ENVELOPES OF BE STARS IN THE EQUATORIAL PLANE .2. THE INFLUENCE OF A WEAK MAGNETIC-FIELD ON THE AZIMUTHAL MOTION OF A SLOWLY EXPANDING WIND

We have investigated how a weak radial magnetic field (B0 approximately 10 G) influences the dynamics in the equatorial plane of the envelopes of Be stars. We calculate the distributions of the azimuthal velocity and the azimuthal magnetic field for models with various mass-loss rates, radial velocity distributions, and strengths of the radial component of the magnetic field at the surface of the star. Our investigation has shown that, in a slowly expanding envelope, a weak magnetic field can influence the rotational velocity distribution quite effectively by transferring angular momentum from the magnetic field to the material. The radial component of the magnetic force is negligible for the strength of the magnetic field considered. But the centrifugal force is enhanced as the result of the increase of rotational velocity. For some cases the centrifugal force is so large that it can counterbalance gravity.