Expanding Envelope of Nova Cygni 1992

Abstract

Available spectroscopic, HST and radio imaging observations of Nova Cygni 1992 (= V 1974 Cyg) were used to derive the kinematic model of expanding nova envelope which consists of two major components: a fast-moving low-mass outer envelope and a slow high-mass inner envelope. Both envelopes can be well approximated by geometrically thin equatorial rings and axially symetric polar blobs. Outer envelope was detected as the outer edge of the radio shell as well as spectroscopically as double absorptions in P Cygni spectral line profiles. The blobs and rings of the inner envelope was resolved as very stable peaks in emission line profiles during the nebular stage. Inner envelope images were taken also by HST. We have calculated the inclination angle of the ring plane against the cellestial sphere using RV of absorption lines, RV of the peaks of emission line profiles and HST image of the shell taken 467 days after the outburst. The resulting value of i = 32º.4 ± 0.6 enabled us to determine the true expansion velocities of the gaseous structures of both envelopes. During the first 50 days after outburst the outer envelope was accelerated by the hot wind from 1500 kms^-1 to 5300 km s^-1 reaching its terminal velocity. On the day 91 the envelope encountered the preoutburst circumstellar shell (containing material expelled during previous outbursts) and decelerated. The slow high-mass envelope was accelerated by the wind from 830 kms^-1 to 895 km s^-1 (ring) and 1015 km s^-1 (blob).