The Early Bolometric Evolution of Nova Cygni 1992

Abstract

We report on combined ultraviolet and optical observations of early stages of the outburst of Nova Cygni 1992. We show that the initial optical rise and decline were produced by the dramatic increase in UV line opacity and its gradual subsequent lifting as the ejecta expand. The source of the M_v - t₃ relation is easily understood in light of these low-resolution UV spectra. The multiwavelength data confirm the theoretical prediction that a nova evolves at a constant bolometric luminosity in the early stages of outburst. We verify the prediction for this nova for at least the first month of the outburst. The detection of far-UV radiation with the Voyager Ultraviolet Spectrometer and the detection of an increasing X-ray flux with Roentgen Satellite (ROSAT) imply that this phase lasted for more than 6 months.