OPTICAL STUDIES OF V404-CYG, THE X-RAY TRANSIENT GS2023+338 .2. HIGH-RESOLUTION H-ALPHA SPECTROSCOPY IN QUIESCENCE

We present the results of high-resolution optical spectroscopy of V404 Cyg (the optical counterpart of the X-ray transient GS2023 + 338), conducted 13 months after the 1989 May outburst. The double-peaked H-alpha line exhibits a strong S-wave modulation from which we deduce a periodicity of 5.7 hr. The level of the continuum is also modulated on the same time-scale. We identify this behaviour with the orbital period of the system and find no evidence for variations on the recently reported 3.05-hr period of Leibowitz et al. There are also changes in the FWHM and peak separation, which evolves from widening to subsequent shrinking. Such variations suggest a very complex line profile consisting perhaps of several different components.