THE ECLIPSE OF THE SYMBIOTIC STAR BF CYG

Like SY Mus and EG And, BF Cyg is another classical symbiotic system w here the effects of Rayleigh scattering can be observed close to eclip se. Here we re-analyzed the ultra-violet observations made by IUE betw een 1979 and 1989 in order to study the continuum variations due to ec lipse effects. We concluded that besides Rayleigh scattering as source of continuum opacity acting at the cool giant star's extended atmosph ere, another source of opacity wavelength independent could act at oth er phases in BF Cyg. We also give estimates of extinction factors, as was defined in Pereira ct al. [A&A, 293, 783 (1995)], and the variatio n of the column density of the neutral hydrogen against phase. The obs erved variation between the cycles 1979-1981 and 1986-1989 could be, i n principle, attributed to some modification the in the giant's wind. (C) 1996 American Astronomical Society.