Accretion Flow and Precession Phenomena in Cataclysmic Variables

Rolfe, Daniel James (2001). Accretion Flow and Precession Phenomena in Cataclysmic Variables. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fcef

Abstract

Cataclysmic variables are interacting binaries where the accretion flow is usually the dominant source of emission. They provide a valuable opportunity to study accretion, the most potent source of energy in the universe. This thesis presents optical studies of two such systems, V348 Pup and IY UMa, providing new insights into a variety of accretion phenomena.

V348 Pup has a'persistently hot accretion disc, while in IY UMa the disc undergoes a series of outbursts in which it changes from a cool state to a much hotter, brighter state. We view both systems from close to the plane of the disc, making it possible to employ indirect imaging techniques to map both the spatial and velocity distributions of accretion flow.

V348 Pup harbours a precessing asymmetric disc, as does IY UMa during superoutburst, leading to a super hump modulation in luminosity as the companion tidally interacts with the precessing disc. The disc shape in IY UMa as it shows ‘late’ superhumps at the end of a superoutburst is found, and a simple model reveals varying energy dissipation at the stream-disc impact to be the source of the late superhumps. This study finds that this might also be the mechanism producing the superhumps in V348 Pup.

Spectroscopy reveals that V348 Pup is an SW Sex type star, where anomalous line emission is dominated by a source other than the accretion disc. This study supports the model in which some of the accretion stream overflows the disc and is expelled from the system by a magnetic propeller anchored in the disc.

Spectroscopy of IY UMa during outburst reveals rapidly changing accretion flow, with reprocessing of radiation in the outer disc and on the companion star, and possibly spiral shock waves in the disc. Quiescent observations reveal absorption features from the donor star, along with emission from the stream-disc impact and accretion disc.

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