Discovery of magnetic fields in five DC white dwarfs

TL;DR

This study reports the discovery of magnetic fields in five DC white dwarfs, nearly doubling the known sample, using broadband filter polarimetry to better understand magnetic evolution in aging white dwarfs.

Contribution

It presents new detections of magnetic fields in five DC white dwarfs, expanding the sample and aiding the understanding of magnetic field evolution in old white dwarfs.

Findings

Discovered magnetic fields in five DC white dwarfs

Almost doubled the known magnetic DC white dwarf sample

Used broadband filter polarimetry for detection

Abstract

About half of white dwarfs (WDs) evolve to the DC state as they cool; the others become DQ or (temporarily?) DZ WDs. The recent magnetic survey of the local 20 pc volume has established a high frequency of magnetic fields among WDs older than 2-3 Gyr, demonstrating that in low- and average-mass WDs, the effects of magnetism become more common as they age, and the fields on average become stronger. However, the available statistics of WDs older than about 5 Gyr do not clearly establish how fields evolve beyond this age. We are carrying out a survey to clarify the occurrence of magnetism in DC-type WDs in order to better understand this late evolution. We use broadband filter polarimetry, arguably the most efficient way to detect magnetic fields in featureless WDs via continuum circular polarization. Here we report the discovery of a magnetic field in five DC WDs (of 23 observed), almost doubling the total sample of known magnetic WDs belonging to the DC spectral class.