The action of inexorable meridional circulation on a stellar magnetic field

Results for the behavior over time of an initial magnetic field in the presence of prescribed meridional circulation within a rotating upper-main-sequence star are presented. Various model flows are studied, and it is found that the presence of mass motions leads to a more rapid depletion of the magnetic flux which emerges from the stellar surface than for the situation when mass motions are absent. It is also shown that, for the circulation models studied here, the e-folding time of decay is not a reliable measure of the decay rate of the surface magnetic field. Tentative agreement between the results for the particular model flows presented and some observations reported in the literature lends support to the theoretical prediction that rotationally driven circulation in the radiative region of single nonmagnetic upper-main-sequence stars is double-cell in structure. Further, it is found that the magnetic intensity increases deep within the star when certain circulation patterns are present.