Preface

Summary

The history of cataclysmic variable star research mirrors the objects themselves: periods of relative inactivity punctuated by heightened or even explosive advances. Until about 1970 each resurgence of interest was a result of a distinct technological advance. In the past two decades the technological improvements have been almost continuous and the interest in cataclysmic variables has burgeoned from the realization that they have so much to offer. Not only are they of interest per se, exhibiting a challenging range of exotic phenomena covering the electromagnetic spectrum from radio waves to TeV gamma rays, and time scales from fractions of a second to millions of years, they are important for their relevance to other exciting areas of astrophysics.

For example, it has become evident that accretion discs are one of the most commonly occurring structures – probably all stars form from disc-like configurations, with material left over to provide planetary systems. A large fraction of binary stars form accretion discs at some stage of their evolution. Accretion discs are important in X-ray binaries – matter accreting onto neutron stars or black holes. Entire galaxies are initially gaseous discs, and most may develop central discs intermittently that fuel their active nuclei.

But it is in cataclysmic variables (CVs) that accretion discs are observed to best advantage – quasi-stable discs, unstable discs and transformations between them. In dwarf novae during outburst, or in nova-like variables in their high state, the light is dominated by emission from discs – and being almost two-dimensional their observed properties are strongly affected by the viewing angle. All are close double stars, and those with eclipses present unrivalled opportunities for determining spatially resolved physical structures.