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On the Distance to Cygnus X-1 (HDE 226868)

Published online by Cambridge University Press:  07 February 2017

Jesse Bregman ,
Dennis Butler ,
Edward Kemper ,
Alan Koski ,
R. P. Kraft  and
R. P. S. Stone
Jesse Bregman
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973
Dennis Butler
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973
Edward Kemper
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973
Alan Koski
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973
R. P. Kraft
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973
R. P. S. Stone
Affiliation:
Contributions from the Lick Observatory No. 385, Astrophys. J. Letters185, LI 17, November 15, 1973

Abstract

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From U, B, V photometry of 104 stars in a field of radius ~ 30′ centered on the X-ray binary star Cyg X-1 (HDE 226868), we have studied the color excess E(B–V) as a function of distance. Spectral types were observed de novo for 42 of these stars. We conclude that HDE 226868 cannot be nearer than 1 kpc, and is probably at a distance of 2.5 kpc or more. The primary component is therefore a luminous OB star of mass ~30 M⊙, and the X-ray component has a minimum mass ~6 M⊙.

Type
Part III: Accretion of Matter and X-Ray Sources
Information
Symposium - International Astronomical Union , Volume 64: Gravitational Radiation and Gravitational Collapse , 1974 , pp. 181
Copyright
Copyright © Reidel 1974