Non-dipolar magnetic fields in Ap stars

TL;DR

This paper investigates how initial magnetic fields in A stars evolve into stable, non-dipolar configurations, explaining observations of complex magnetic fields in Ap stars and extending to other non-convective stars.

Contribution

It presents simulations and analytic insights into the formation and stability of non-axisymmetric, twisted flux tube equilibria in stars.

Findings

Formation of stable, non-dipolar magnetic equilibria

Analytic relations between stability and field configuration

Relevance to observed magnetic fields in Ap stars

Abstract

An arbitrary initial magnetic field in an A star evolves into a stable equilibrium. Simulations are presented of the formation of non-axisymmetric equilibria consisting of twisted flux tubes meandering under the surface of the star, and analytic arguments are given relating the stability and form of these equilibria. These results may help to explain observations of Ap stars with very non-dipolar fields. This work is also applicable to other essentially non-convective stars such as white dwarfs and neutron stars.