X-ray Emission Line Profile Modeling of O stars: Fitting a   Spherically-Symmetric Analytic Wind-Shock Model to the Chandra Spectrum of   zeta Puppis
  X-ray emission line profiles provide the most direct insight into the dynamics and spatial distribution of the hot, X-ray-emitting plasma above the surfaces of OB stars. The O supergiant zeta Puppis shows broad, blueshifted, and asymmetric line profiles, generally consistent with the wind-shock picture. We model the profiles of eight lines in the Chandra HETGS spectrum of this prototypical hot star. The fitted lines indicate that the plasma is distributed throughout the wind starting close to the photosphere, that there is significantly less attenuation of the X-rays by the overlying wind than is generally supposed, and that there is not a strong trend in wind absorption with wavelength. 
Roban H. Kramer, David H. Cohen, Stanley P. Owocki