Stellar magnetism through the polarized eyes of the FORS1 instrument

TL;DR

This paper reviews and reanalyzes a decade of stellar magnetic field data from the FORS1 instrument, developing a new semi-automatic method to improve detection reliability and providing a comprehensive catalog of measurements.

Contribution

It introduces a semi-automatic procedure for magnetic field detection, critically assesses previous measurements, and offers a revised understanding of stellar magnetic incidence.

Findings

Developed a self-consistent magnetic field detection method.

Produced a catalog of approximately 1000 magnetic field measurements.

Suggested revisions to the incidence rates of stellar magnetic fields.

Abstract

During the last decade, the FORS1 instrument of the ESO Very Large Telescope has been used to obtain low resolution circular polarized spectra for about 500 stars, with the aim of measuring their mean longitudinal magnetic fields. Magnetic field estimates were obtained by different authors, using different software tools. Several interesting detections were obtained at a 3 sigma level; some of them were eventually confirmed by follow-up investigations, some of them were not. This raises issues about the reliability of the stated uncertainties of some of the published field values. To investigate these problems, we have developed a semi-automatic procedure for magnetic field determination, which includes self-consistent checks for field detection reliability. We have applied our procedure to the full content of single star ("fast mode") circular spectropolarimetric measurements of the FORS1 archive, and explored the details and interagreement of various methods for data reduction. We have finally produced a catalogue of FORS1 longitudinal field measurements which includes about 1000 entries. Here we critically review the previously published FORS1 measurements, and, based on our results, we suggest that the incidence of the magnetic field in various classes of stars should be revised.