Weak magnetic fields in white dwarfs and their direct progenitors?

TL;DR

This study re-analyzed polarimetric data of white dwarfs and related stars, finding that previous magnetic field detections were unconfirmed, but about 10% of white dwarfs exhibit weak magnetic fields at the kilogauss level.

Contribution

The paper provides a careful re-analysis of polarimetric data, clarifying the presence of weak magnetic fields in white dwarfs and challenging prior detections in related stars.

Findings

Previous magnetic field detections in subdwarfs and central stars were not confirmed.

Approximately 10% of white dwarfs have magnetic fields at the kilogauss level.

Proper calibration is crucial to avoid spurious signals in polarimetric measurements.

Abstract

We have carried out a re-analysis of polarimetric data of central stars of planetary nebulae, hot subdwarfs, and white dwarfs taken with FORS1 (FOcal Reducer and low dispersion Spectrograph) on the VLT (Very Large Telescope), and added a large number of new observations in order to increase the sample. A careful analysis of the observations using only one wavelength calibration for the polarimetrically analysed spectra and for all positions of the retarder plate of the spectrograph is crucial in order to avoid spurious signals. We find that the previous detections of magnetic fields in subdwarfs and central stars could not be confirmed while about 10% of the observed white dwarfs have magnetic fields at the kilogauss level.