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Stellar wind variations during the X-ray high and low states of Cygnus X-1

Gies, D. R. and Bolton, C. T. and Blake, R. M. and Caballero-Nieves, S. M. and Crenshaw, D. M. and Hadrava, P. and Herrero, A. and Hillwig, T. C. and Howell, S. B. and Huang, W. and Kaper, L. and Koubský, P. and McSwain, M. V. (2008) Stellar wind variations during the X-ray high and low states of Cygnus X-1. Astrophysical Journal, 678 (2). pp. 1237-1247. ISSN 0004-637X.

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We present results from Hubble Space Telescope ultraviolet spectroscopy of the massive X-ray and black hole binary system, HD 226868 = Cyg X-1. The spectra were obtained at both orbital conjunction phases in 2002 and 2003, when the system was in the X-ray high/soft state. The UV stellar wind lines suffer large reductions in absorption strength when the black hole is in the foreground due to the X-ray ionization of the wind ions. We constructed model UV wind line profiles assuming that X-ray ionization occurs everywhere in the wind except the zone where the supergiant blocks the X-ray flux. The good match between the observed and model profiles indicates that the wind ionization extends to near the hemisphere of the supergiant facing the X-ray source. We also present contemporaneous spectroscopy of the Hα emission that forms in the high-density gas at the base of the supergiant's wind and the He II λ4686 emission that originates in the dense, focused wind gas between the stars. The Hα emission strength is generally lower in the high/soft state than in the low/hard state, but the He II λ4686 emission is relatively constant between X-ray states. The results suggest that mass transfer in Cyg X-1 is dominated by the focused wind flow that peaks along the axis joining the stars, and that the stellar wind contribution from the remainder of the hemisphere facing the X-ray source is shut down by X-ray photoionization effects (in both X-ray states).

Item Type:Article
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Crenshaw, D. M.0000-0002-6465-3639
Howell, S. B.0000-0002-2532-2853
Additional Information:© 2008 The American Astronomical Society. Received 2007 June 14; accepted 2008 January 27. We thank the staffs of the David Dunlap Observatory, Kitt Peak National Observatory, Dominion Astrophysical Observatory, Ondrˇejov Observatory, and the Space Telescope Science Institute (STScI ) for their support in obtaining these observations. The KPNO spectra supporting the second HST run were obtained with the assistance of participants in the NOAO Teacher Leaders in Research Based Science Education program, including Joan Kadaras (Westford Academy, Westford, MA), Steve Harness (Kingsburg Joint Union High School, Kingsburg, CA), Elba Sepulveda (CROEM, Mayaguez, PR), and Dwight Taylor (Goldenview Middle School, Anchorage, AK). We also thank Saku Vrtilek and Bram Boroson for helpful comments, and we are especially grateful to an anonymous referee whose report was pivotal to our discussion of the results. Support for HST proposal number GO-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 X-ray results were provided by the ASM/RXTE teams at MIT and at the RXTE SOF and GOF at NASA’s GSFC. The IUE data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. C. T. B.’s research is partially supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant. P. H.’s research is funded under grant projects GACˇ R 202/06/0041 and LC06014. A. H. thanks the Spanish MEC for support under project AYA 2007-67456-C02-01. This work was also supported by the National Science Foundation under grants AST-0205297, AST-0506573, and AST-0606861. Institutional support has been provided from the GSU College of Arts and Sciences and from the Research Program Enhancement fund of the Board of Regents of the University System of Georgia, administered through the GSU Office of the Vice President for Research. We are grateful for all this support.
Funding AgencyGrant Number
Space Telescope Science InstituteUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)GACR 202/06/0041
Natural Sciences and Engineering Research Council of Canada (NSERC)LC06014
Ministerio de Educación y Ciencia (MEC)AYA 2007-67456-C02-01
Subject Keywords:binaries: spectroscopic; stars: early-type; stars: individual (HD 226868, Cygnus X-1); stars: winds, outflows; X-rays: binaries
Issue or Number:2
Record Number:CaltechAUTHORS:GIEapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13846
Deposited By: Tony Diaz
Deposited On:14 Jul 2009 21:10
Last Modified:03 Oct 2019 00:45

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