1 Introduction

CH Cyg, as a highly interesting object, has a remarkable place among the symbiotic stars. It has been generally accepted to be a binary consisting of a cool M6-7III late type giant and a hot component surrounded by an accretion complex formed from the cool giant's wind (Mikolajewski et al. 1990). Its irregular outbursts show a bunch of exotica like flickering, jet activity, high ionization lines, X-ray and radio emission, dust cocoon etc. (Munari et al. 1996). The outbursts, which differ from each other, have been separated by quiescent phases of different duration (Wallerstein & Cassinelli 1968; Bruch 1986; Garcia 1986; Mikolajewski et al. 1990; Bode et al. 1991; Kotnik-Karuza et al. 1992; Orio 1993; Jurdana & Kotnik-Karuza 1994; Kotnik-Karuza & Jurdana-Sepic 1997). Although some recent works have recognized the importance of quiescent phases for understanding the physical mechanisms of symbiotic stars and the nature of the outbursts, spectroscopic works dealing with the quiescent states of CH Cyg have still been rather restricted.

The fact that CH Cyg was in the extended period of inactivity before 1963 (Muciek & Mikolajewski 1989), as well as the complex behaviour of its spectroscopic and photometric parameters which is extremely difficult to interpret consistently, make each observation of this star, as a unique and unrepeatable event, an extremely important contribution to its understanding.

After its longest quiescent phase in the last few decades, CH Cyg showed signs of renewed activity in 1990 (Panov & Ivanova 1992) which represented an introduction to a new large outburst lasting from 1990-1995 (Munari et al. 1995). The results of these observations shed doubt on the models constructed in the meantime and turned again our attention to the optical spectra of this star taken at the Haute Provence Observatory in the quiescent period from June 1987 to January 1989 (Kotnik-Karuza et al. 1992).