KU CYGNI - NEW SPECTROSCOPIC AND PHOTOMETRIC SOLUTIONS OF A LONG-PERIOD ACCRETION-DISK BINARY

We present new photometric and spectroscopic analyses of the totally e clipsing accretion-disk binary KU Cygni. Weak lines in the H alpha and lambda 7774 Angstrom spectral regions yield radial-velocity curves of both stars. We obtain new photometric solutions with the revised Wils on eclipsing binary computer model. In spite of complications from an accretion disk around the hotter star, we find a fairly reliable simul taneous lybv solution. The mass ratio, a compromise of spectroscopic a nd photometric results, is near 0.12. The hotter star rotates supersyn chronously and is somewhat over-massive for its luminosity, while the K giant contact component has a mass of about 0.5 M.. A separate ultra violet solution reveals about one magnitude of excess u Light in prima ry-eclipse totality. This excess, discovered by Popper, is probably un eclipsed disk light. KU Cyg shares these characteristics with several other long-period Algol-type binaries. (C) 1995 American Astronomical Society.