Spin-down and reduced mass loss in early-type stars with large-scale magnetic fields

TL;DR

This study models how large-scale magnetic fields in early-type stars influence their spin-down and mass loss, revealing significant effects on stellar evolution and chemical mixing across different metallicities.

Contribution

It provides a comprehensive, open-source grid of stellar models incorporating magnetic braking and chemical mixing effects for the first time.

Findings

Magnetic fields prevent quasi-chemically homogeneous evolution.

Magnetic braking leads to slowly-rotating, nitrogen-enriched stars.

Differences in models significantly affect stellar evolution predictions.

Abstract

Magnetism can greatly impact the evolution of stars. In some stars with OBA spectral types there is direct evidence via the Zeeman effect for stable, large-scale magnetospheres, which lead to the spin-down of the stellar surface and reduced mass loss. So far, a comprehensive grid of stellar structure and evolution models accounting for these effects was lacking. For this reason, we computed and studied models with two magnetic braking and two chemical mixing schemes in three metallicity environments with the MESA software instrument. We find notable differences between the subgrids, which affects the model predictions and thus the detailed characterisation of stars. We are able to quantify the impact of magnetic fields in terms of preventing quasi-chemically homogeneous evolution and producing slowly-rotating, nitrogen-enriched ("Group 2") stars. Our model grid is fully open access and open source.