Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341021c&link_type=abstract
American Astronomical Society, AAS Meeting #213, #410.21; Bulletin of the American Astronomical Society, Vol. 41, p.214
Astronomy and Astrophysics
Astronomy
Scientific paper
We present continued results of high resolution ultraviolet spectroscopy from Hubble Space Telescope of the massive X-ray binary HD 226868 = Cyg X-1 which consists of an O supergiant with a black hole (BH) companion. The spectra were used in conjunction with International Ultraviolet Explorer and ground-based optical spectra to determine Teff and log g of the O9.7 Iab supergiant. Using non-LTE, line blanketed, plane parallel TLUSTY models, we obtain an approximate temperature of Teff 26 ±1 kK and gravity of log g = 2.8 ± 0.25 dex for the supergiant, both lower than in previous studies. We fit a spectral energy distribution for this temperature and gravity to the UV, optical and IR fluxes to determine the angular size and extinction towards the binary. The angular size we used to constrain the lower mass limits of each of the components as a function of distance following the argument proposed by Paczynski (1974). Our results agree with a distance <2; kpc and masses ranging from 18-32 solar masses for the supergiant and 8-16 solar masses for the BH, slightly lower values than in previous estimates (Ziólkowski 2005).
Cabllero-Nieves Saida M.
Gies Douglas R.
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