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Published November 1967 | Published
Journal Article Open

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.

Additional Information

© 1967 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received October 3, 1967. We are greatly indebted to E. M. Burbidge for informing us of her results at an early date, to J. L. Greenstein for a very illuminating discussion, to Tom McCord for graciously lending his photometer to us, and to E. W. Dennison and his group, without whose data-system electronics the 100-inch photometry could not have been done. Kristian's work was supported in part by grants from the National Science Foundation and the Office of Naval Research.

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