Magnetic dynamos in white dwarfs -- II. Relating magnetism and pollution

TL;DR

This paper explores how a rotation and crystallization driven dynamo could explain the observed increase in magnetism and pollution in old white dwarfs, linking core crystallization, rotation, and magnetic field generation.

Contribution

It proposes a unified dynamo mechanism driven by rotation and crystallization to explain magnetism and pollution in old white dwarfs, supported by observational data.

Findings

Polluted magnetic white dwarfs are consistent with crystallizing cores.

Increased rotational velocities are linked to planetary accretion.

The dynamo mechanism explains the occurrence of magnetic fields in old white dwarfs.

Abstract

We investigate whether the recently suggested rotation and crystallization driven dynamo can explain the apparent increase of magnetism in old metal polluted white dwarfs. We find that the effective temperature distribution of polluted magnetic white dwarfs is in agreement with most/all of them having a crystallizing core and increased rotational velocities are expected due to accretion of planetary material which is evidenced by the metal absorption lines. We conclude that a rotation and crystallization driven dynamo offers not only an explanation for the different occurrence rates of strongly magnetic white dwarfs in close binaries, but also for the high incidence of weaker magnetic fields in old metal polluted white dwarfs.