# Examining O and WR star winds with X-rays

### Lida Oskinova, Wolf-Rainer Hamann, and Achim Feldmeier

Universität Potsdam, Institut für Physik, Astrophysik

The X-ray spectra of O stars show characteristic emission-line profiles. Their shape results from the attenuation of the X-ray emission by the inhomogenous wind material, and can be reproduced by adequate models. The wind absorption in Wolf-Rayet type stars is at least order of magnitude higher than in O-type stars. This high wind absorption was suggested to explain the lack of X-ray emission from WC-type stars. Winds of WN stars are less opaque for X-ray than winds of WC stars. Some putatively single WN stars are detected in X-rays, while others are not. It is presently unclear whether wind absorption alone can account for the different levels of X-ray emission observed in WR stars. - The profile of the N\,{\sc vii} resonance line in the X-ray spectrum of $\zeta$ Puppis shows a self-absorption feature, indicating that the hot X-ray emitting plasma is optically thick.