The nearby magnetic cool DZ white dwarf PM J08186-3110

TL;DR

This study analyzes a nearby cool magnetic DZ white dwarf, revealing a 92 kG magnetic field, variable heavy element abundances, and indicating that about 40% of similar white dwarfs below 7000 K are magnetic.

Contribution

It provides detailed spectroscopic and spectropolarimetric analysis of PM J08186-3110, highlighting magnetic field strength, abundance variations, and the prevalence of magnetism in cool DZ white dwarfs.

Findings

Magnetic field of 92 kG detected in the white dwarf.

Heavy element abundances vary over a decade.

Approximately 40% of cool DZ white dwarfs are magnetic.

Abstract

We present an analysis of photometric, spectroscopic and spectropolarimetric data of the nearby, cool, magnetic DZ white dwarf PM J08186-3110. High dispersion spectra show the presence of Zeeman splitted spectral lines due to the presence of a surface average magnetic field of 92 kG. The strong magnesium and calcium lines show extended wings shaped by interactions with neutral helium in a dense, cool helium-rich atmosphere. We found that the abundance of heavy elements varied between spectra taken ten years apart but we could not establish a time-scale for these variations; such variations may be linked to surface abundance variations in the magnetized atmosphere. Finally, we show that volume limited samples reveal that about 40% of DZ white dwarfs with effective temperatures below 7000 K are magnetic.