IUE high-resolution observations of the symbiotic star CHCygni: confirmation of the triple-star model

We present and analyse ultraviolet high-resolution spectra of CHCyg taken during the whole period of the International Ultraviolet Exploler (IUE) mission. Our analysis of the observed variation in the line spectrum confirms a triple-star model recently suggested for CHCyg. Radial velocities of emission lines, which are subject to eclipse in the symbiotic pair are placed at antiphase to those of the neutral metal absorptions from the infrared/optical spectrum. This is direct evidence for the orbital motion of the hot component in the inner binary of the triple system. Variation in the line profiles of highly ionized elements and Lyalpha also supports the triple-star nature of CHCyg. Fluxes in the Siriptsize IV, Si II and Al II I lines decreased considerably during the eclipse. Circumstellar emission in Lyalpha is produced by the radiation of the hot star. The central part of its profile (~1216-1220 Angstroms) remains unchanged during the eclipse, it arises at larger distances from the star. This implies that the hot component radiation was, in fact, practically constant during this time, and thus its observed considerable decline had to be caused only by the eclipse. The outer parts of the Lyalpha profile extend up to +/-2200kms(-1) , they are subject to eclipse, and thus reflect a high velocity outflow originating from the central star. Based on observations by the International Ultraviolet Explorer