HARPS spectropolarimetry of O and B-type stars

Our knowledge of the presence and strengths of magnetic fields in massive O- and B-type stars remains very poor. Recent observations indicate that the presence of a magnetic field is responsible for a wide range of phenomena that are observed in massive stars at different wavelengths, such as chemical peculiarity, excess emission in UV-wind lines and periodic UV wind-line variability, unusual X-ray emission, and cyclic variability in Ha and in He II lambda 4686 angstrom. However, it is difficult to establish relationships involving multiwavelength diagnostics, because the strengths and the geometry of the magnetic fields that have been detected differ from one star to another. This paper presents new measurements of magnetic fields in a number of O- and B-type stars of various classifications, observed with HARPS in spectropolarimetric mode.