KU CYG and its Eccentric Accretion Disk
Abstract
The profile of the H alpha emission line from the accretion disk, observed in March 1989, at phase phi=-0.0447, when the approaching part of the disk was partly eclipsed by the secondary, shows effects of a large disk eccentricity and of its finite geometrical thickness. The latter produces obscuration of the inner surface of the disk by its outer edge, an effect which strongly depends on inclination. Analysis of the observed profile allows determination of the major semi-axis of the disk: a_d=0.48+/-0.01, its eccentricity e_d=0.31+/-0.07, and the orbital inclination: i=86.0+/-0.1. With this inclination, the solution based on phases of contacts of the primary eclipse gives q=M_2/M_1=0.13+/-0.01 which, together with K_2=90.7 km/s (Olson et al. 1995), gives M_1=3.83+/- 0.07Modot, M_2=0.50+/-0.04Modot, and A=(5.43+/-0.04) times 1012 cm. Photometric and spectroscopic data available for KU Cyg suggest behavior similar to that observed in dwarf novae of the SU UMa type (Osaki 1989): The disk becomes occasionally very large, eccentric, and precessing. Tidal effects, removing angular momentum from its outer parts, result then in an enhanced accretion; while insufficient to produce thermal instability, it is observable as a minor brightening. In the case of KU Cyg these processes have characteristic time scales of, roughly, few years.
- Publication:
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Acta Astronomica
- Pub Date:
- July 1997
- Bibcode:
- 1997AcA....47..345S
- Keywords:
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- BINARIES: ECLIPSING;
- STARS: INDIVIDUAL: KU CYG