Observational properties of magnetic white dwarfs

TL;DR

This paper reviews the observational properties of magnetic white dwarfs, discussing their magnetic fields, binary systems, and planetary debris, to understand their origins and evolution.

Contribution

It synthesizes current knowledge on magnetic white dwarfs, highlighting the lack of known systems with strong magnetic fields in binaries and exploring planetary signatures.

Findings

No known magnetic white dwarfs with >3MG in detached binaries.

Magnetic white dwarfs may originate from stellar coalescence.

Planetary debris around white dwarfs provides clues to planetary system formation.

Abstract

There are no known examples of magnetic white dwarfs with fields larger than about 3MG paired with a non-degenerate companion in detached binary systems. The suggestion is that highly magnetic, isolated white dwarfs may originate from stars that coalesce during common envelope evolution while those stars that emerge from a common envelope on a close orbit may evolve into double degenerate systems consisting of two white dwarfs, one or both magnetic. The presence of planets or planetary debris around white dwarfs is also a new and exciting area of research that may give us important clues on the formation of first and second generation planetary systems, since these place unique signatures in the spectra of white dwarfs.