Rapid Photometric and Spectroscopic Variations of the X-Ray Source CYG X-2

Fluctuations of 0.04 mag on a time scale of minutes have been found in the optical flux of the candidate star for Cyg X-2. Comparison of radial velocities on a well-widened spectrogram with those of Lynds shows large changes, confirming an earlier suspicion of binary motion by E. M. Burbidge. The systemic velocity is y = -250 km/sec. A lower limit of 300 km/sec for the orbital velocity of one component relative to the other is indicated. The system parameters are m = m_1 + m_2 = 1, P < 0.4 M_☉ (days), and ɑ < 0.01 M_☉ a.u., indicative of a very close binary system (m = m_1 + m_2). Eclipses are probable and may have been observed. Spectroscopic evidence may be present for gas streams moving with speeds of greater than 700 km/sec. Three independent arguments are given why the optical flux cannot primarily be non-thermal radiation connected with the production of the X-rays.