Magnetic fields in central stars of planetary nebulae?

TL;DR

This study used spectropolarimetric observations to investigate magnetic fields in central stars of planetary nebulae, finding no evidence of fields stronger than a few hundred Gauss, thus questioning their role in nebula shape asymmetries.

Contribution

The paper provides new spectropolarimetric measurements for six central stars of planetary nebulae, expanding the observational data and clarifying previous contradictory results regarding stellar magnetic fields.

Findings

No significant magnetic fields detected in the sample.

Measurement errors are around 150-300 G.

Previous detections may have been due to calibration issues.

Abstract

Most of the planetary nebulae (PN) have bipolar or other non-spherically symmetric shapes. The presence of a magnetic field in the central star may be the reason for this lack of symmetry, but observational works published in the literature have so far reported contradictory results. We try to correlate the presence of a magnetic field with the departures from the spherical geometry of the envelopes of planetary nebulae. We determine the magnetic field from spectropolarimetric observations of ten central stars of planetary nebulae. The results of the analysis of the observations of four stars was previously presented and discussed in the literature, while the observations of six stars, plus additional measurements for a star previously observed, are presented here for the first time. All our determinations of magnetic field in the central planetary nebulae are consistent with null results. Our field measurements have a typical error bar of 150-300 G. Previous spurious field detections obtained with FORS were probably due to the use of different wavelength calibration solutions for frames obtained at different position angles of the retarder waveplate. Currently, there is no observational evidence for the presence of magnetic fields with a strength of the order of hundreds Gauss or higher in the central stars of planetary nebulae.