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


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An improved orbital ephemeris for Cygnus X-1

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

1 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 [FORMULA] days and then, by including the more recent radial velocities of LaSala et al. (1998) and Sowers et al. (1998) we refine this to [FORMULA] days. Using 27 years' worth of photometry, we also calculate a photometric period of [FORMULA] - 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

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999

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