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

Details Wind Accretion and State Transitions in the Black Hole Binary Cyg X-1 Wind Accretion and State Transitions in the Black Hole Binary Cyg X-1

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9840g&link_type=abstract

HST Proposal ID #9840

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Hst Proposal Id #9840 Hot Stars

Scientific paper

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 ever high resolution UV spectra of the system while it resided in the unusual high/soft state. Cyg X-1 has now returned to the low/hard state, and here we propose to revisit Cyg X-1 and complete our investigation of the wind - X-ray state connection. The study will determine {1} the mass loss rate and the dynamical {density and velocity} structure of the wind of the supergiant star in both X-ray states, and {2} how the X-ray source ionizes the wind. These spectra will be useful for other investigations and will form an important resource for the entire research community.

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