Identification of Cygnus X-1 with HDE 226868

@article{Bolton1972IdentificationOC,
  title={Identification of Cygnus X-1 with HDE 226868},
  author={Charles T. Bolton},
  journal={Nature},
  year={1972},
  volume={235},
  pages={271-273}
}
THE ninth magnitude BOIb star HDE 226868 is closely coincident with the position of Cygnus X-1 and its associated variable radio source1. Dolan2 has pointed out that Cyg X-1 appears to be a two component X-ray source. One component has a synchrotron spectrum, and the other has a thermal (or bremsstrahlung) spectrum. The latter component varies on a time scale of days in a way that suggests it is being eclipsed. Therefore I decided to take photographic spectra of HDE 226868 to look for velocity… 
Periodic light variations in HDE 226868 (Cyg X-1).
The positional coincidence of the ninth magnitude B01b supergiant HDE 226868 with the radio counterpart of Cyg X-1 (refs. 1, 2) and the radial velocity variations in the single-lined spectrum of this
Discovery of Two Types of X-Ray Dips in Cygnus X-1
We observed Cyg X-1 with RXTE continuously over its 5.6 day binary orbit. The source was found to be in the hard state throughout the observation. Many intensity dips were detected in the X-ray light
THE TRIGONOMETRIC PARALLAX OF CYGNUS X-1
We report a direct and accurate measurement of the distance to the X-ray binary Cygnus X-1, which contains the first black hole to be discovered. The distance of 1.86+0.12− 0.11 kpc was obtained from
Orbital, precessional and flaring variability of Cygnus X-1
We present the results of a 2.5-yr multiwavelength monitoring programme of Cygnus X-l, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular,
Variability of the Hα emission of Cygnus X-1 and its connection with the soft X-ray radiation
High-resolution Hα monitoring of Cyg X-1, HD 226868 was carried out during 1996-2002 and the resultant spectra analysed in conjunction with 1.5-12 keV X-ray monitoring. We demonstrate that the Hα
Re-Evaluation of the Orbital Elements of HDE 226868 = Cyg X-1
We have scanned 75 high dispersion spectrograms of HDE 226868 = Cyg X-1 with the PDS microdensitometer of the David Dunlap Observatory in preparation for a detailed spectrophotometric study of the
Is X Persei an X-ray Source?
IT has recently been suggested1,2 that the star X Per (HD 24534) may be associated with the X-ray source 2U 0352 + 30. Other stars identified with X-ray sources are characterized by peculiar spectra
CygX-1/A candidate of the black hole
Among discrete galactic X-ray sources, Cyg X-1 has been noted for its peculiar features in several respects. It is one of the few sources with a hard power law spectrum extending beyond several
Identification of 2U0525 – 06 with 2Orionis
BLACK holes may be observed in the X-ray band1 and the discovery of X-ray sources in binary systems with non-luminous massive companions is the most convincing evidence of existence of black
OPTICAL SPECTROSCOPIC OBSERVATIONS OF Cyg X-1 = HDE 226868
We present the results of the spectroscopic observations of HDE 226868, the optical counterpart to the black hole X-ray binary Cyg X-1, from 2001 to 2006. We analyze the variabilities of the two
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