Measurements and Analysis of Helium-like Triplet Ratios in the X-Ray Spectra of O-Type Stars

We discuss new methods of measuring and interpreting the forbidden-to-intercombination line ratios of helium-like triplets in the X-ray spectra of O-type stars, including accounting for the spatial distribution of the X-ray-emitting plasma and using the detailed photospheric UV spectrum. Measurements are made for four O stars using archival Chandra HETGS data. We assume an X-ray-emitting plasma spatially distributed in the wind above some minimum radius R sub(0)- We find minimum radii of formation typically in the range of 1.25 < R sub(0)/R sub(*) < 1.67, which is consistent with results obtained independently from line profile fits. We find no evidence for anomalously low f/i ratios, and we do not require the existence of X-ray-emitting plasmas at radii that are too small to generate sufficiently strong shocks.