Astron. Astrophys. 343, 861-864 (1999)

An improved orbital ephemeris for Cygnus X-1

C. Brocksopp ¹, A.E. Tarasov ², V.M. Lyuty ³ and P. Roche <sup>1

1</sup> Astronomy Centre, University of Sussex, Falmer, Brighton, UK
² Crimean Astrophysical Observatory, 334413, Nauchny, Crimea, Ukraine
³ Sternberg Astronomical Institute, Universitetskii pr.13, 119899 Moscow, Russia

Received 24 August 1998 / Accepted 19 November 1998

Abstract

By accumulating all available radial velocity data and combining it with our own spectroscopy we present a new and improved ephemeris for Cygnus X-1 (V1357 Cygni/HDE226868). We initially calculate an orbital period of days and then, by including the more recent radial velocities of LaSala et al. (1998) and Sowers et al. (1998) we refine this to days. Using 27 years' worth of photometry, we also calculate a photometric period of - remarkably similar to the spectroscopic one.

Key words: X-rays: stars stars: individual: Cygnus X-1 stars: binaries: spectroscopic ephemerides

Correspondence to: cb@star.cpes.susx.ac.uk

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and discussion
  • 2.1. Spectroscopy
  • 2.2. Photometry
• 3. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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