AAS 207th Meeting, 8-12 January 2006
Session 182 Stellar Winds, Circumstellar Matter, and Activity
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[182.22] Wind Signatures in the X-ray Emission Line Profiles of the O Supergiant zeta Orionis

K. Grizzard (St. John's College), D. H. Cohen (Swarthmore College), M. A. Leutenegger (Columbia University), C. Reed (Swarthmore College), R. H. Kramer (Columbia University), S. P. Owocki (University of Delaware)

The profiles of X-ray emission lines from several hot stars are resolved by the Chandra grating spectrometers. These profile shapes provide information about the kinematics of the hot plasma around these stars and, via signatures of continuum attenuation, also provide information about the overlying cold stellar wind. We present a quantitative analysis of roughly one dozen emission lines in the Chandra HETGS spectrum of zeta Ori (O 9.7 Ib), and analyze the results in the context of the line-force instability shock model. The distribution in velocity space of the emission, along with the separate helium-like line ratio results, are consistent with the wind-shock scenario. But, although there is statistically significant evidence for some wind attenuation, the degree of wind attenuation is a factor of five to ten less than what would be expected in the context of a smooth, spherically symmetric wind and the UV-derived wind mass-loss rate. These results are consistent with those derived from the X-ray emission line profiles of the hotter O star, zeta Pup, and also with recent, independent evidence from UV spectroscopy, that O star mass-loss rates have been overestimated.

We acknowledge support from NASA contract NAS8-03060 and from the National Science Foundation, through their REU program at the Keck Northeast Astronomy Consortium, via contract AST-0353997.

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