The Primary orbit and the absorption-lines of HDE-226868 (Cygnus X-1)

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Title: The Primary orbit and the absorption-lines of HDE-226868 (Cygnus X-1)
Author: Ninkov, Zoran; Walker, Gordon; Yang, Stephenson
Abstract: From Reticon spectra of ~1 A resolution taken between 1980 and 1984, the radial velocity curve of HDE 226868 is found to be characteristic of a single-line spectroscopic binary with K = 75.0 +/- 1.0 km s^-1 and e=0.0. Combining historical velocities from the literature with our own data and applying a period-folding analysis, a period of 5.59964 +/- 0.00001 days is found. These values agree well with those published by Gies and Bolton in 1982, v sin i is estimated tob e 94.3 +/- 5 km s^-1 from CFHT Reticon spectra taken at 0.1 A resolution. Assuming that the rotation of the primary is synchronized to the orbital revolution of the secondary gives a primary to secondary mass between 1.5 and 2.3. An absolute magnitude of -6.5 +/- 0.2 is derived from the equivalent width of Hy (1.5 +/- 0.1 A) and the 1985 calibration of Walker and Millward which is consistent with the spectral classification of 09.7 Iab. Assuming 20 M_ as a reasonable estimate for the mass of the primary implies a mass of 10 +/- 1 M_ for the secondary. The equivalent width of Hy and HB are 20% larger at zero phase (X-ray minimum) of the 294 day X-ray period. A variation in the outflow rate from the primary could produce variations in both the Balmer-line equivalent widths and the X-ray flux (Refer to PDF file for exact formulas).
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Date: 1987-10-01

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