Accretion disc radii in eclipsing cataclysmic variables

We present a graphical method for estimating accretion disc radii in eclipsing cataclysmic variables (CVs), based on methods developed by Sulkanen, Brasure & patterson, and Schwarzenberg-Czerny. Application of this method to 35 eclipsing systems enables us to find systematic differences between the disc radii of the various CV subclasses. The discs of nova-like variables exceed 60 per cent of the radius of the Roche lobe of the white dwarf primary, and tidal truncation of the disc appears possible in many of these systems. The discs in most nova remnants exceed 80 per cent of the primary's Roche lobe radius. The discs of quiescent dwarf novae fill ∼50 per cent of the primary's Roche lobe, whereas in outburst dwarf novae disc radii resemble those of the high mass-transfer rate, steady-state disc systems. Although, for a given CV, there is a strong correlation between the allowed values of the disc radius predicted by the graphical method (expressed as a fraction of the radius of the primary's Roche lobe) and allowed values of the mass ratio, we do not find such a correlation between members of the same CV subclass.