Rotation and Magnetism in Massive Stars

TL;DR

This paper explores the effects of rotation and magnetic fields on massive star evolution, incorporating magnetic dynamo models into stellar evolution codes and comparing their predictions with observations of stellar populations and white dwarf magnetic fields.

Contribution

It introduces a modified stellar evolution model that includes magnetic field evolution driven by dynamo processes, enhancing understanding of magnetic effects in stellar evolution.

Findings

Magnetic fields can significantly influence stellar rotation and chemical mixing.

Dynamo-generated magnetic fields may explain the strong magnetism observed in white dwarfs.

Inclusion of magnetic fields alters predicted stellar population characteristics.

Abstract

Rotation has a number of important effects on the evolution of stars. It decreases the surface gravity, causes enhanced mass loss and leads to surface abundance anomalies of various chemical isotopes. We have adapted the Cambridge stellar evolution code to incorporate a number of different physical models for rotation. We compare detailed grids of stellar evolution models along with simulated stellar populations to identify the key differences between them. Models of rotationally-driven dynamos in stellar radiative zones have suggested that magnetohydrodynamic transport of angular momentum and chemical composition can dominate over the otherwise purely hydrodynamic processes. We have adapted our purely hydrodynamic model to include the evolution of the magnetic field. We consider what effects this has on our populations of rotating stars and how these relate to observational data. Strong magnetic fields are also observed at the end of the stellar lifetime. The surface magnetic field strength of white dwarfs is observed to vary from very little up to 10^9G. We look at how the strongest magnetic fields in white dwarfs may be generated by dynamo action during the common envelope phase of strongly interacting binary stars.