Spectroscopic observations of PU Vulpeculae.

Optical and infrared spectrophotometric observations demonstrate that the nova-like variable PU Vulpeculae is a symbiotic binary composed of an M4-5 giant and a hot companion whose expanding atmosphere mimics an A supergiant. Fits to the optical/infrared data suggest the system is reddened by E(B-V) = 0.4-0.5. The 1979 outburst appears to be the result of a thermonuclear runaway on the surface of a white dwarf, as in the symbiotic novae AG Peg and RR Tel. Dust condensation in the expanding envelope ejected in the eruption, or an eclipse of the hot component by the M giant companion, can explain many features of the 1980 minimum, but neither mechanism provides a satisfactory explanation for all the available data.