The dust envelope of the symbiotic nova V1016 Cyg

Brightness and color variations of V1016 Cyg are studied using many years o f UBVRJHKLM photometric observations and information about its spectral ene rgy distribution in the intermediate IR (7.7 to 22.7 mum) obtained with the IRAS and ISO low-resolution spectrometers. Models for its stationary, sphe rically symmetrical, extended dust envelope are computed for two cases of h eating: by the radiation of the cool component only and by the combined rad iation from both components. Model fitting of the IRAS and ISO observations shows that the model with a single central source - the Mira star - provid es a better fit to the data, indicating that the hot component's radiation is appreciably reprocessed by the ambient gas medium and has almost no dire ct influence on the IR spectrum of the symbiotic nova. The mean spectral en ergy distributions measured by IRAS in 1983 and ISO on October 1, 1996, dif fer considerably. The observed evolution of the envelope's spectrum probabl y reflects an increasing grain concentration and decreasing grain temperatu re at the in ner edge of the envelope, associated with decreased luminosity and increased temperature of the hot component. The total mass-loss rate, gas-expansion velocity at the outer edge of the envelope, and upper limit t o the mass of the central radiation source are estimated. (C) 2001 MAIK "Na uka/Interperiodica".