KU Cygni.
Abstract
In the 38-day eclipsing binary system, KU Cyg, the smaller star has a spectrum resembling that of an F-type supergiant, but possibly arising in a shell surrounding a hotter star. The larger star, a distorted late K-type giant, probably fills its critical equipotential surface. This star, while observationally the fainter, is bolometrically somewhat the more luminous component. There is an emitting ring around the smaller star, similar to those discussed by Struve in other systems. Photometric and spectrographic observations, while not definitive, reveal some features of particular interest. (a) Either the smaller star is greatly overmassive (more than 20 M0) for its luminosity (Mb,1 -0.6), or the apparent velocity variation of the larger star, observed only during eclipse, does not result from orbital motion. In the latter case a much smaller mass results if displacements of the emission lines are interpreted as due to gravitational motion in a ring about the smaller star. (b) There are large intrinsic variations in light from one cycle to another, not due to the larger, distorted star. There are also appreciable changes of light between first and fourth contacts of each eclipse not explainable in terms of changes in the radius and temperature of a star. (c) There is a strong ultraviolet continuum at total eclipse, responsible for the ultraviolet excess reported in an earlier note. The continuum does not appear to be Balmer emission. An appreciable ultraviolet excess at totality has also been observed for RZ Oph, a system with spectra similar to those of KU Cyg.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1964
- DOI:
- 10.1086/147743
- Bibcode:
- 1964ApJ...139..143P