Identification of Cygnus X-1 with HDE 226868

  title={Identification of Cygnus X-1 with HDE 226868},
  author={Charles T. Bolton},
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
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
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


The variable X-ray spectrum of Cyg XR-1
The variability of the X-ray spectrum of the discrete source Cyg XR-1 (α = 19h 56m δ = +35°.1) is reviewed. The variations observed in the energy region accessible to balloon borne detectors
Physical Sciences: Detection of Radio Emission from Cygnus X-1
The detection of Cyg X-1 with radio counterpart at a frequency of 1,415 MHz is reported, known to be highly variable and recently has been found to pulsate with a period of 73 ms.
Eclipsing Binary Model of Cygnus XR-1
The observations of the variable X-ray source Cygnus XR–1 may be consistently interpreted in terms of the eclipsing binary model for the source that was originally outlined in an article by myself2 (article 1).
Rapid Variations in the High Energy X-ray Flux from Cyg X-1
THE intensity of X-rays in the energy range 22.5–154 keV from the X-ray source Cyg X–1 was monitored for about 3 h on the night of April 5, 1971, using a balloon-borne telescope. There were
The semidetached eclipsing binaries (similar to Algol) seem to contradict the theory of stellar evolution, since the less massive components appear to be more evolved. Besides, they are overluminous,