The rotation of early-type magnetic stars

In a star with a magnetic field that is strictly symmetrical about the rotation axis, direct magnetic transport of angular momentum in a radiative envelope occurs along but not across field lines. Significant mutual coupling of different field lines will, however, occur if there is some penetration of the field into the outer regions of the strongly viscous convective core. Some numerical examples show how an initially arbitrary rotation field can thus be converted into one of near-uniform rotation. If the field distribution is non-axisymmetric, as in the oblique rotator, non-uniform rotation generates magnetic torques which in general do interchange angular momentum between different flux tubes. Calculations for a cylindrical model with quite small dissipative coefficients illustrate how a moderately strong field will again quickly establish near-uniform rotation. (author)