Analysis of the X-ray emission of OB stars II: B stars

Abstract

Abstract This paper is the second part of an investigation into the mechanism for the origin of X-rays in early-type stars. Archival X-ray observations of 25 B stars, obtained by the XMM-Newton satellite, are analysed. We check two hypotheses on the origin of X-ray emission: the Magnetically Confined Wind Shock Model (MCWS) and Pollock’s paradigm. For all studied stars, the mean ratio of the half widths at half maximum to the terminal velocities appears to be R ≈ 0.15 − 0.20 in contradiction to Pollock’s hypothesis that R ≈ 0.5 . We checked three possible consequences of the MCWS model: correlations between the hardness of the X-ray spectra for B stars and terminal wind velocities, mass loss rates and magnetic fields. It was shown that such correlations are marginal or even absent both for magnetic and non-magnetic B stars.