Dynamo Action in the Presence of an Imposed Magnetic Field, Astron

Published online later Key words Editorial notes instruction for authors The persistent magnetic elds of Ap stars are generally thought to be of primordial origin, but dynamo generation of magnetic elds may offer alternative possibilities. Deep within the interiors of such stars, vigorous core convection likely couples with rotation to yield magnetic dynamo action, generating strong magnetic elds. Recent numerical models sug-gest that a primordial eld remaining from the star's formation may possess a highly twisted toroidal shape in the radiative envelope. We have used detailed 3-D simulations to study the interaction of such a magnetic eld with a dynamo generated within the core of a 2 solar mass A-type star. Dynamo action realized under these circumstances is much more vigorous than in the absence of a fossil eld in the radiative envelope, yielding magnetic eld strengths (of order 100 kG) much higher than their equipartition values relative to the convective velocities. We examine the generation of these elds, as well as their effect on the complex dynamics of the convective core