X-ray properties of cataclysmic variable stars
In this thesis, I study the entire sample of non-magnetic cataclysmic variables observed with the Japanese satellite ASCA, presenting a detailed analysis of the spectral and temporal behaviour of these twenty-nine targets. The spectral analysis indicates that all the targets in the ASCA sample appear to be X-ray under-luminous, with only three possible exceptions. This indicates that energy is being lost from the accretion disk in a non-radiative way. Since a third of the observations require additional absorption above that expected from interstellar alone, both the X-ray under-luminosity and the excess absorption observed spectrally may be attributed to the existence of accretion disk-winds. The spectral analysis also indicates that the under-lying spectra of all non-magnetic cataclysmic variables may be more complicated than at first thought, since those spectra containing the highest number of counts require more sophisticated multi-temperature modelling of the X-ray source. Further spectra results suggests that there may be some previously unidentified magnetic systems in the ASCA sample. Such systems give away their identity through having a much harder spectrum than the non-magnetic systems, and both LS Peg and V426 Oph should be considered as weakly magnetic candidates. The temporal analysis reveals other unusual members. SS Cyg appears to be unusually faint during an observation made during quiescence, and a four-fold difference is observed in VW Hyi during two optically quiescent states, suggesting that the inner disk behaves almost independently of the outer disk. ASCA observations caught Z Cam during both an optical outburst, and during the transition to another outburst. The unique transition observation shows the X-ray count rate falling by a factor of three as the source becomes optically thick. High levels of absorption are detected in the X-ray spectra throughout both the outburst and transitional observations, greater than that expected from interstellar absorption alone.