SPECTRAL EVOLUTION OF NOVA (V-723) CASSIOPEIAE 1995 - PRE-MAXIMUM STAGE

The monitoring of spectral evolution of the very slow nova V723 Cas st arted at the Asiago Astrophysical Observatory just on the announcement of discovery. In this paper the spectral evolution during the long pr e-maximum stage, which lasted from August to December 1995, is reporte d. Emission lines of H I and Fe II were prominent in the early stage. Most of the lines were accompanied by P Cygni type absorption componen ts. The emission lines gradually weakened with time and the absorption components developed. The mean of the blue-shifts of the absorption c omponents with respect to the emissions was about -126 km s(-1) in Sep tember and -96 km s(-1) in December 1995. Some lines of Fe I, Fe II, Y II, Sc II, Ba II, etc, appeared in the later stage. All emission line s, except for Her, once nearly disappeared in November when the nova s lightly brightened to V similar or equal to 8.6. Some emission lines a ppeared again several days before the beginning of the final rise to m aximum luminosity, then a purl absorption spectrum of F type supergian t was seen on the maximum of V similar or equal to 7.1 at the middle o f December. The absorption components of Si II lines at 634.7 and 637. 1 nm showed fairly different profiles from those of the other metallic lines, which suggests a complicated gas motion in the atmosphere. The distance and the absolute magnitude at maximum are estimated to be 2. 95 +/- 0.7 kpc and M-v(max) = -6.1 +/- 0.5, respectively. The mass of the white dwarf in this system may be about 0.58 +/- 0.07 M-circle dot .