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Astron. Astrophys. 338, 1006-1014 (1998)

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1. Introduction

Nova Cas 1995 (V723 Cas) was discovered by M. Yamamoto (IAU Circ. 6213) on 1995 August 24 as a star of magnitude 9.2. The monitoring of spectral evolution of this object started in our observatory just on the announcement of discovery. Some preliminary reports have been made by Iijima and Rosino (IAU Circulars 6214, 6365, 6703), by Della Valle et al. (IAU Circular 6214) and by Munari et al. (IAU Circulars 6259, 6284).

The unusually slow evolution of this nova has been reported in some previous works. For example, about two years passed from the light maximum to the beginning of nebular stage (Iijima & Rosino 1997). This time is roughly twice of the known slowest classical novae such as RR Pic (Lunt 1926; Spencer 1931) and HR Del (e.g. Hutchings 1971; Sanyal 1974; Yamashita 1975; Rafanelli & Rosino 1978). Some theoretical works (e.g. Kovetz & Prialnik 1985; Livio 1992; Kato & Hachisu 1994) have suggested that such slowest explosions occur on white dwarfs of which masses are close to the lower limit to perform the explosions ([FORMULA]). Detailed studies of this nova, therefore, may be important to advance our knowledge about the critical condition of novae's explosions. In this paper we present the results of spectroscopic works carried out during the long pre-maximum stage which lasted from August to December 1995. The distance to the nova, the absolute magnitude at maximum luminosity, and the mass of the white dwarf are estimated.

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998