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Astron. Astrophys. 327, 231-239 (1997)

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1. Introduction

A cataclysmic variable (CV) is a binary system which consists of a white dwarf (WD) primary and a late-type secondary. In the general picture, the secondary fills its Roche lobe and thus transfers mass via the Lagrange point [FORMULA] into the region where the gravitational field of the primary dominates. Due to its angular momentum, and in absence of strong magnetic fields, the transferred matter cannot fall directly onto the surface of the WD. By interaction between the particles, an accretion disk is formed around the WD which transports angular momentum to the outer part of the disk and matter to the inner part, i.e. finally via an inner boundary region onto the surface of the primary. In many cases, the accretion disk never reaches steady state. Its luminosity, released by viscous dissipation within the disk, is strongly variable, with phases of quiescence interrupted by outbursts. Such variability is a common feature of all CVs (for a comprehensive overview on CVs see Warner 1995).

WW Cet was first mentioned as a variable star by Luyten (1962), who already suspected its CV nature, which was later confirmed by Herbig (1962). Pacsyski (1963) first published a lightcurve, but could not identify any periodic features. He was also the first to suggest the possibility that the system belongs to the subclass of the Z Cam stars, which are distinguished from other dwarf novae by showing occasionally after an outburst a so-called standstill phase, which can last for weeks or even years. The system has been later indeed included as a Z Cam star in the General Catalogue of Variable Stars (GCVS, Kukarkin et al. 1969).

However, Warner (1987) argued that the long-term behaviour of WW Cet is very untypical of the Z Cam subclass. He instead proposed WW Cet to form a link between dwarf novae and VY Scl nova-like variables. Ringwald et al. (1996), who studied the long-term lightcurve of WW Cet in detail, came to a similar conclusion. This is especially interesting in the context of the hibernation model (Vogt 1982, Shara et al. 1986) which proposes an evolutional bond between several CV subgroups.

Further long-term photometric data can be found in Bateson & Dodson (1985) and in Bateson & McIntosh (1991). Optical low-resolution spectra have been published e.g. by Williams (1983) (during quiescence) and by Szkody et al. (1990) (near outburst). Klare et al. (1982) and La Dous (1990) present UV spectra, while the X-ray behaviour was studied e.g. by Vrtilek et al. (1994). A finding chart is provided by Downes & Shara (1993).

In this paper, we present new spectroscopic and photometric data on WW Cet. The spectroscopic and photometric measurements are described in Sect. 2, while system parameters are derived from these data in Sect. 3. In Sect. 4 we discuss the orbital behaviour of both data sets, and in Sect. 5 we summarize the results.

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998