Wind Signatures in the X-ray Emission Line Pro¯les of the Late

X-ray line pro¯le analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line pro¯les provide information about the velocity distribu-tion of the hot plasma, while the wavelength-dependent attenuation across a line pro¯le provides information about the absorption to the hot plasma, thus pro-viding a strong constraint on its physical location. In this paper we apply several analysis techniques to the emission lines in the Chandra HETGS spectrum of the late-O supergiant Ori (O9.7 Ib), including the ¯tting of a simple line-pro¯le model. We show that there is distinct evidence for blue shifts and pro¯le asym-metry, as well as broadening in the X-ray emission lines of Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for Ori are very similar to those for the earlier O star, Pup, which we have previously shown to be well-¯t by the same wind-shock line-pro¯le model. The more sub-tle e®ects on the line-pro¯le morphologies in Ori, as compared to Pup, are consistent with the somewhat lower density wind in this later O supergiant. In the context of the recent reanalysis of the helium-like line intensity ratios in this star, and also in light of recent work questioning the accepted mass-loss rates in OB stars, these new results indicate that the X-ray emission from Ori ca