Ultraviolet observations of the 1980 eclipse of the symbiotic star CICyg.

The paper presents secular and eclipse variations of ultraviolet lines and continua in the course of nearly a complete orbit of CI Cygni. High-excitation resonance lines show minimal effects of eclipse, while intercombination lines have faded and show pronounced but nontotal eclipse effects. The observations are examined in terms of mass transfer from the extended cool envelope of the red giant to a compact secondary. The formation of an accretion disk is a transitory phenomenon in which viscosity eventually dissipates the disk over orbital time scales. The intercombination line emission is explained by a large-scale low-density nebula, and it is found that the resonance line emission apparently arises in a large volume emitting region, possibly formed through shock collision from interacting stellar winds from the primary and secondary.