Magnetic fields and differential rotation in stars
Abstract
In a star with a magnetic field that is not symmetric about the rotation axis, nonuniform rotation in the electrically conducting stellar material shears the field and generates magnetic torques. This leads to a competition between the efforts of the magnetic stresses to remove nonuniformities in angular velocity, and those of the velocity field to bury and destroy magnetic flux. Illustrative calculations are presented for a compressible model in an idealized twodimensional geometry. They show how, with values of diffusion coefficients appropriate to a radiative envelope, the Lorentz stresses can rapidly establish a state of approximately uniform rotation for relatively modest field strengths. This is found to occur whether or not the field lines are anchored in an inner core region with prescribed angular velocity. The numerical model is extended to include the competition between angular momentum transport by the Lorentz stresses and the turbulent Reynolds stresses. An estimate is made of the field strength required to produce a state of approximately uniform rotation in a largely convective envelope, although all the discussion ignores the possibility of effective dynamo action in the region considered.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 1992
 DOI:
 10.1093/mnras/257.4.593
 Bibcode:
 1992MNRAS.257..593M
 Keywords:

 Angular Velocity;
 Rotating Plasmas;
 Stellar Magnetic Fields;
 Stellar Rotation;
 Angular Momentum;
 Diffusion Coefficient;
 Dynamo Theory;
 Stellar Envelopes;
 Astrophysics