Abstract
THE X-ray source Cyg X-2 has been optically identified with a fifteenth magnitude blue object1. Initial spectroscopic observations2–4 revealed the presence of broad Balmer absorption lines, a narrow, strong Ca II K line and a narrow emission line of He II λ4,686. Radial velocity variations were evident, with the indication that the emission and absorption line velocities varied 180° out of phase. Photometric monitoring4 showed the object to vary erratically on a time scale of minutes. Later spectroscopic observations5,6 confirmed the changes in radial velocity, but no certain evidence of binary motion could be demonstrated. A more recent spectroscopic observation7 showed the He II emission to have developed a P-Cygni profile, and emission at λλ4,640–50 due to C III–N III was present. I report here the results of additional spectroscopic observations of this object.
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BOPP, B. Spectroscopic Variations in Cyg X-2. Nature 247, 139 (1974). https://doi.org/10.1038/247139a0
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DOI: https://doi.org/10.1038/247139a0
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