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Following the 1980 eclipse of the 855 day period symbiotic binary CI Cyg, we were confronted with a data set showing high excitation resonance lines which were largely uneclipsed but brightening on an orbital timescale, and intercombination lines exhibiting pronounced but nontotal eclipses and which were fading on an orbital timescale. Our model invoked a low density dissipating nebula surrounding the hot companion to explain the intercombination lines, and a shock between stellar winds to interpret the resonance lines. Subsequent synoptic observations have revealed continuing changes in the W emission line fluxes, consistent with those described above, except for the brightening of Mg I1 and the emergence of strong, not previously seen [Mg VI emission. Post-outburst and phase dependent changes must be included in any interpretation of this system as the archetypal symbiotic binary. We anticipate that critical observations will be made during the 1982 October eclipse.

Publication Date





Ci Cygni, eclipse, ultraviolet, UV


Instrumentation | Stars, Interstellar Medium and the Galaxy


In Y. Kondo, J.M. Mead, & R.D. Chapman (Eds.), Advances in Ultraviolet Astronomy: Four Years of IUE Research. Proceedings of a Symposium held at NASA Goddard Space Flight Center, Greenbelt, Maryland, March 30-April 1, 1982.

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Ci Cygni Since the 1980 Eclipse



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