  We report on a 67 ks HETG observation of the optically brightest early
O-star, Zeta Pup (O4 f). Many resolved X-ray lines are seen in the spectra over
a wavelength range of 5 to 25 A. 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, Zeta 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 A 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.
