# Studying the presence of magnetic fields in a sample of high-mass X-ray binaries

## TL;DR

This study investigates magnetic fields in high-mass X-ray binaries, including Cyg X-1, using spectropolarimetric observations to detect weak magnetic fields on stellar surfaces.

## Contribution

It presents new spectropolarimetric measurements of Cyg X-1 and other high-mass X-ray binaries, expanding understanding of magnetic fields in such systems.

## Key findings

- Detection of weak longitudinal magnetic fields in Cyg X-1.
- First spectropolarimetric measurements of additional high-mass X-ray binaries.
- Confirmation of magnetic field presence in high-mass X-ray binary systems.

## Abstract

Previous circular polarization observations obtained with the ESO FOcal Reducer low dispersion spectrograpgh at the VLT in 2007-2008 revealed the presence of a weak longitudinal magnetic field on the surface of the optical component of the X-ray binary Cyg X-1, which contains a black hole and an O9.7Iab supergiant on a 5.6d orbit. In this contribution we report on recently acquired FORS2 spectropolarimetric observations of Cyg X-1 along with measurements of a few additional high-mass X-ray binaries.