Spectroscopic Variations in Cyg X-2

Abstract

THE X-ray source Cyg X-2 has been optically identified with a fifteenth magnitude blue object¹. Initial spectroscopic observations^2–4 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 observations^5,6 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.