Optical studies of V404 Cyg, the X-ray transient GS 2023 + 338 - IV. The rotation speed of the companion star
- 1 November 1994
- journal article
- letter
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 271 (1) , L5-L9
- https://doi.org/10.1093/mnras/271.1.l5
Abstract
We have resolved the rotationally broadened absorption features of the secondary star in the black hole X-ray transient GS 2023 + 338 (= V404 Cyg). Using template stars that cover spectral types G8-K2 and luminosity classes III to V, we derive a rotation speed of V(rot) sin i = 39.1 +/- 1.2 km s-1. This implies a mass ratio of q = M(c)/M(x) = 0.060-0.005(+0.004) for the case of a tidally locked and Roche-lobe-filling secondary. Furthermore, the updated radial velocity curve of the companion star permits us to refine the mass function to 6.08 +/- 0.06 M., thus confirming and strengthening the case for a black hole primary in V404 Cyg. An updated version of the orbital parameters is also presented.Keywords
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