Spectral evolution of Nova (V 723) Cassiopeiae 1995: pre-maximum stage

The monitoring of spectral evolution of the very slow nova V723 Cas started at the Asiago Astrophysical Observatory just on the announcement of discovery. In this paper the spectral evolution during the long pre-maximum stage, which lasted from August to December 1995, is reported. 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 components. The emission lines gradually weakened with time and the absorption components developed. The mean of the blue-shifts of the absorption components with respect to the emissions was about -126 km s(-1) , in September 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 lines, except for Hα , once nearly disappeared in November when the nova slightly brightened to V =~ 8.6. Some emission lines appeared again several days before the beginning of the final rise to maximum luminosity, then a pure absorption spectrum of F type supergiant was seen on the maximum of V =~ 7.1 at the middle of 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_⊙. Table 5 is only available in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http:// cdsweb.u-strasbg.fr/Abstract html