%0 Journal Article
%T The Orbital Period of HDE226868/Cyg X-1
%A J. LaSala
%A P. A. Charles
%A R. A. D. Smith
%A M. Balucinska-Church
%A M. J. Church
%J Physics
%D 1998
%I arXiv
%R 10.1046/j.1365-8711.1998.02064.x
%X We present epoch 1996, high-quality radial velocity data for HDE 226868, the optical counterpart of Cygnus X-1. Combining our results with all published historical data, we have derived a new ephemeris for the system of HJD2450235.29 + n x 5.5998, which allows accurate orbital phase calculations to be made for any X-ray observations over the last 30 years. We find no evidence for any period change as has been suggested by Ninkov, Walker & Yang (1987). We discuss the shortcomings of previous work in establishing the period and orbital elements.
%U http://arxiv.org/abs/astro-ph/9812101v1