Spectral evolution of nova CYG 1978.

Abstract

The evolution of the spectrum of Nova Cygni 1978 from the principal to the nebular stages is investigated. Spectrograms were obtained in the blue (between 3900 and 5100 A) and red (5600-6840 A) between September 13 and December 18, 1978. The principal spectrum of the nova, taken around maximum light on September 13, is found to be characterized by crowded, blue shifted absorption lines of neutral and singly ionized metals. During the diffuse enhanced and Orion phases, the intensities of the absorption components are observed to be very weak, with the spectrum dominated by emission features, indicating that most of the material of this fast nova was expelled at the primary outburst. The nebular stage was reached by November 5, at a brightness more than 4 magnitudes below maximum, with the appearance of the characteristic nebular lines. The radial velocities of the absorption systems are found to range from -661 (principal spectrum) to -2115 km/sec (Orion spectrum), with an additional highly blue shifted emission line apparent from September 16 to 19. Results are compared with those obtained by IUE in the satellite UV, and an absolute magnitude at maximum of -8.0 + or - 0.2 is estimated.