AAS 203rd Meeting, January 2004
Session 81 Black Holes
Poster, Wednesday, January 7, 2004, 9:20am-6:30pm, Grand Hall

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[81.06] Wind Accretion and State Transitions in the Black Hole Binary Cyg X-1

D. R. Gies (Georgia State Univ.), C. T. Bolton (Univ. Toronto), R. Fender (Univ. Amsterdam), A. Herrero (Inst. Astrofisica de Canarias), T. C. Hillwig (Georgia State Univ.), L. Kaper (Univ. Amsterdam), M. V. McSwain (Georgia State Univ.), J. Thomson (Univ. Toronto), D. J. Wallace (NASA GSFC), P. J. Wiita (Georgia State Univ.)

The black hole binary, Cyg X-1, is generally observed in one of two long duration X-ray states: a low flux, hard spectrum state (most common) and a high flux, soft spectrum state (rare). Models predict that the high/ soft state corresponds to a high mass transfer phase in the binary, and since the X-ray source is fueled by accretion from the stellar wind of the supergiant companion, the simple expectation is that the high/soft state results from an increased wind mass loss rate. Alternatively, a decrease in the wind mass loss rate could result in a more ionized and slower wind in the vicinity of the black hole, which would then be more easily accreted by the black hole. The best test of these hypotheses is to observe the UV P Cygni lines of the supergiant that are formed in its wind outflow. We recently used HST/STIS to obtain the first high resolution UV spectra of the system while it resided in the unusual high soft states in 2002 and 2003. Here we present our results on the orbital variations in the P Cygni wind lines that show dramatically how the X-ray source ionizes the wind.

Support for this work (HST Proposal Number 9840) was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

The author(s) of this abstract have provided an email address for comments about the abstract: gies@chara.gsu.edu

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