CHANDRA DETECTION OF DOPPLER SHIFTED X-RAY LINE PROFILES FROM THE WIND OF ζ PUPPIS (O4f)

We report on a 67 ks HETG observation of the optically brightest early O-star, ζ Pup (O4 f). Many resolved X-ray lines are seen in the spectra over a wavelength range of 5 to 25 Å. Chandra has sufficient spectral resolution to study the velocity structure of isolated X-ray line profiles, and to distinguish the individual forbidden, intercombination, and resonance (fir) emission lines in several He-like ions even where the individual components are strongly Doppler broadened. In contrast with X-ray line profiles in other hot stars, ζ Pup shows blue-shifted and skewed line profiles, providing the clearest and most direct evidence that the X-ray sources are embedded in the stellar wind. The broader the line, the greater the blueward centroid shift tends to be. The N VII line at 24.78 Å is a special case, showing a flat-topped profile. This indicates it is formed in regions beyond most of the wind attenuation. The sensitivity of the He-like ion fir lines to a strong UV radiation field is used to derive the radial distances at which lines of S XV, Si XIII, Mg XI, Ne IX, and O VII originate. The formation radii correspond well with continuum optical depth unity at the wavelength of each line complex, indicating that the X-ray line emission is distributed throughout the stellar wind. However, the S XV emission lines form deeper in the wind than expected from standard wind shock models. Subject headings: X-rays: stars — stars: individual (ζ Pup) — stars: early-type — stars: winds, outflows — stars: mass-loss — line: profiles