Convective Core Dynamos of A–type Stars in the Presence of Fossil Magnetic Fields

Abstract

The persistent magnetic fields of Ap stars are generally thought to be of primordial origin, but dynamo generation of magnetic fields 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 fields. Recent numerical models suggest that a primordial field remaining from the star's formation may possess a highly twisted toroidal shape in the radiative interior. We have used detailed 3‐D simulations to study the interaction of such a magnetic field 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 field in the radiative envelope, yielding magnetic field strengths (of order 100 kG) much higher than their equipartition values relative to the convective velocities. We examine the generation of these fields, as well as their effect on the complex dynamics of the convective core.