The symbiotic binary V1016 Cygni, early stage of a planetary nebula.

Summary. New spectroscopic observations of the radio- star with infrared excess V 1016 Cyg in the range 3800-10900 A have been obtained at Asiago in 1971-1974. During the present quasi-stationary phase in B and V, increasing excitation is shown by the strengthening of He ii, [Fe vi] and [Fe vn] lines, which coexist with low-excitation features like 0 I, [Fe ii] and absorption bands of TiO and VO. The physical characteristics indicate that a very hot star excites a nebula which is ejected by a long-period variable. This latter may be responsible for the strong infrared excess. An evolutionary trend is suggested, linking symbiotic stars and BQ[] stars to V 1016 Cyg, leading next to the formation of a compact planetary nebula. The comparison of V 1016 Cyg with very slow novae, like RR Tel and RT Ser, indicates these latter are also proto-planetary candidates. Key words: combination spectra radio-stars infrared sources - planetary nebulae stellar evolution