Simultaneous observations of the symbiotic star BF Cygni.

Simultaneous ultraviolet/optical spectrophotometry and infrared photometry for the low excitation symbiotic star BF Cygni are presented. The analysis of the data suggests that three different components are present in the UV to IR energy distribution. A hot subdwarf with R = 0.48 solar radius and T not less than 60,000 K if the distance is 2.3 kpc is accreting matter from the wind of an M5 giant. A nebular region emitting mainly hydrogen and helium recombination continuum is fed by part of the wind photoionized by radiation of the hot source, and only a small cone-shaped region surrounding the cool giant remains neutral. There is evidence that accretion does not play any important role in the energetics of the system, given the discussed orbital parameters, unless the mass loss rate of the giant would be extremely high.