Quantitative X-ray spectroscopy of massive stars
  Radiative transfer in a clumped winds is used to describe X-ray emission line profiles observed in the XMM-Newton RGS spectrum of the OI star Zeta Puppis. It is shown that this X-ray spectrum can be explained as originating from a multi-temperature collisional plasma located in the wind acceleration zone. The X-rays are attenuated in the clumped stellar wind, which gives characteristic profiles to the emergent lines. We specifically study the N VII emission line in the spectrum of Zeta Pup. Long RGS exposures reveal that the N VII line profile is structured. On the basis of our Zeta Pup atmosphere model, we rule out the presence of N VII in the cool wind component. We suggest that the detailed N VII line structure is due to self-absorption in the hot plasma. Wind clumping also affects the transfer of ionizing radiation in high-mass X-ray binaries (HMXBs). We derive analytical formulae for the ionisation parameter in dependence on the parameters of wind clumping. 
L.M. Oskinova, W.-R. Hamann, A. Feldmeier (Potsdam University)