Bibcode
                                    
                            Casares, J.; Charles, P. A.; Jones, D. H. P.; Rutten, R. G. M.; Callanan, P. J.
    Bibliographical reference
                                    Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 250, June 15, 1991, p. 712-725. Research supported by NWO and ASTRON.
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                        6
            
                        1991
            
  Citations
                                    61
                            Refereed citations
                                    55
                            Description
                                    The results of optical spectroscopy and photometry of V404Cyg, the
optical counterpart of the recently discovered X-ray transient GS2023 +
338, are presented. Optical spectra were obtained at the Roque de los
Muchachos Observatory with the 2.5-mm Isaac Newton Telescope. The
overall optical light curve was found to be similar to that of an
earlier outburst of this star, which was recorded as Nova Cyg 1938 and
classified as a classical nova. However, it is not a classical or
recurrent nova, as the large range in optical brightness and intense and
variable X-ray emission at maximum indicate that the system must be a
low-mass X-ray binary. The reddened spectrum and interstellar absorption
features indicate a probable distance in the range of 1-3 kpc. CCD
photometry reveals that the source is variable, but gives no indication
of the orbital period. Multicomponent fitting to the complex He II
4686-A line and subsequent analysis of various asymmetry parameters do
not show any clear trend or periodicity.