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We quantitatively investigate the extent of wind absorption signatures in theX-ray grating spectra of all non-magnetic, effectively single O stars in theChandra archive via line profile fitting. Under the usual assumption of aspherically symmetric wind with embedded shocks, we confirm previous claimsthat some objects show little or no wind absorption. However, many otherobjects do show asymmetric and blue shifted line profiles, indicative of windabsorption. For these stars, we are able to derive wind mass-loss rates fromthe ensemble of line profiles, and find values lower by an average factor of 3than those predicted by current theoretical models, and consistent with H-alphaif clumping factors of f_cl ~ 20 are assumed. The same profile fittingindicates an onset radius of X-rays typically at r ~ 1.5 R_star, and terminalvelocities for the X-ray emitting wind component that are consistent with thatof the bulk wind. We explore the likelihood that the stars in the sample thatdo not show significant wind absorption signatures in their line profiles haveat least some X-ray emission that arises from colliding wind shocks with aclose binary companion. The one clear exception is zeta Oph, a weak-wind starthat appears to simply have a very low mass-loss rate. We also reanalyse theresults from the canonical O supergiant zeta Pup, using a solar-metallicitywind opacity model and find Mdot = 1.8 \times 10^{-6} M_sun/yr, consistent withrecent multi-wavelength determinations.

Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive