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R. H. Kramer, J. E. Reed, D. H. Cohen (Swarthmore College), S. P. Owocki (Bartol Research Institute, Univ. of Delaware)
With the high spectral resolution afforded by the Chandra spectrometers, it is now possible to observe directly the Doppler shift of a wind outflow in X-ray emission lines from hot stars. This provides an important and relatively unambiguous diagnostic for addressing the decades-old mystery of X-ray production in such stars. We have developed a broadly applicable general model of wind-based X-ray line emission in an expanding medium, which we apply to new Chandra HETGS spectra of several hot stars. This model includes both continuum and line opacity, as well as velocity- and density-gradient effects. In this paper, we report on the properties of the model and the results of fits to the prototypical O supergiant, zeta Pup, as well as several other OB stars. Only in some cases can these high-resolution Chandra spectra be explained in the context of the standard wind-shock paradigm.
This work was supported by NASA grant NAG5-10088 and by the Delware Space Grant Consortium.