SPECTROSCOPIC AND PHOTOMETRIC BEHAVIOR OF NOVA-CYGNI-1992 IN THE 1ST 9 MONTHS FOLLOWING OUTBURST

We present the results of UBV photometry and high dispersion 360-500 n m spectroscopy of Nova Cygni 1992 (= V 1974 Cyg), obtained between Feb ruary 25 and November 9, 1992. Our data cover the early decline, trans ition and nebular stages of the evolution of the nova. We discuss the photometric and spectroscopic behaviour of the star during the first n ine months after outburst and briefly compare our findings with the da ta already published by other authors. We have classified the nova as a fast one with t2,V = 16 d, t2,B=23 d, and t3,V = 42 d, t3,B=51 d. We have derived the absolute magnitudes of the nova at maximum to be M0, V = -7.67 and M0,B = -7.49. The latter value yields a mass of 0.83 M. for the white dwarf component. The values of the distance modulus 12.2 3 and the colour excess E(B-V) = +0.32 correspond to a distance r = 1. 77 kpc. We have found a period of 0.814 days by period analysis of pho toelectric V data obtained before the nova declined 3m. During the neb ular stage, forbidden lines of highly ionized neon were prominent, con firming the O-Ne-Mg classification of the nova. The outburst of Nova C ygni 1992 was apparently caused by a super-Eddington thermonuclear run away on the surface of an evolutionarily eroded O-Ne-Mg white dwarf.