IUE Observations of CH Cygni Continuum During 1979–1986

The symbiotic system CH Cygni: An analysis of the shocked nebulae at different epochs

“…This is interpreted by model m1 exp which represents the nebula downstream of the shock propagating outwards the system. Model m1 exp is shock dominated (U=0) and explains most of the line ratios observed by Mikolajewska et al (1988) at JD 2446086 (20/1/1985 - Table 3). The slopes at JD 2446212 (26/5/1985) and 2446776 (11/12/1986) can also be fitted by the same m1 exp model in the radiation dominated case, adopting a relatively low U.…”

“…The [OIII] 4363 and 5007 lines appeared only in November 1984, when the outburst was almost over. At the same epoch the UV 4.e-7 a radiation dominated (U 0); b upper limit in radiation-bound models; c by mass spectrum indicated that several high ionization emission lines (NV, CIV, SiIV, HeII, OIII]) had appeared , Mikolajewska et al 1988. The decrease in density at the end of the outburst was indicated by the ratio of FeII/ [FeII] and CIII] 1906/1909.…”

“…Before 1985 (Mikolajewska et al 1988). Emission lines of HeI 5876 were present during the whole outburst except in the beginning.…”

“…In particular, the UV line ratios to Lyα =10 calculated by model m1 exp are compared with the observations by Mikolajewska et al (1988, Table 3) at JD 2446086 (20/1/1985. This model is shock dominated, as the spectrum is emitted from gas in the external side of the expanding nebula, facing the observer.…”

The symbiotic star CH Cygni

“…In January 1985, at the end of the active phase that started in 1977, the UV and optical line ratios (Mikolajewska et al 1988) revealed that we were facing the circumstellar medium of the WD opposite the red giant, on the basis of the FWHM of the forbidden lines and of the densities that must avoid collisional deexcitation of the forbidden lines. In this region, the dynamical consequences of the WD outburst can be compared with those of a supernova explosion, though on a different scale.…”