Transport and mixing in the radiation zones of rotating stars II. Axisymmetric magnetic field

TL;DR

This paper enhances stellar radiation zone models by incorporating axisymmetric magnetic fields, accounting for their interaction with rotation, meridional circulation, and turbulence, to better understand chemical mixing and angular momentum transport.

Contribution

It introduces a self-consistent method to include magnetic fields in stellar mixing models, expanding variables in spherical functions for improved simulation accuracy.

Findings

Magnetic fields significantly influence angular momentum transport.

The model accounts for advection, diffusion, and shear effects on magnetic fields.

Equations are formulated for implementation in stellar structure codes.

Abstract

The purpose of this paper is to improve the modeling of the mixing of chemical elements that occurs in stellar radiation zones. In addition to the classical rotational mixing considered in our previous paper, which results of the combined action of the thermally-driven meridional circulation and of the turbulence generated by the shear of differential rotation, we include here the effect of an axisymmetric magnetic field in a self-consistent way. We treat the advection of the field by the meridional circulation, its Ohmic diffusion, and the production of its toroidal component through the shear of differential rotation. The Lorentz force is assumed not to exceed the centrifugal force; it acts on the baroclinic balance and therefore on the meridional flow, and it has a strong impact on the transport of angular momentum. All variables and governing equations are expanded in spherical or spherical vectorial functions, to arbitrary order: this yields a system of partial differential equations in time and in the radial coordinate, which is ready to be implemented in a stellar structure code.