Browsing by Author "Allen, Sue"

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    Rapid oscillations in cataclysmic variables
    (1986) Allen, Sue; Warner, Brian
    Coherent and quasi-periodic rapid oscillations have been seen in the optical and X-ray light curves of more than 30 cataclysmic variables to date. The observational characteristics of these oscillations are reviewed, and current models discussed. To put the observations in context, a detailed review is given of the canonical model of cataclysmic variables and the variations that give rise to its various sub-classes. Observations of two systems of particular interest are presented, and their contributions to the modelling of rapid oscillations are discussed. High-speed photometry of the very bright nova-like variable CPD-48°1577 (IX Velorum) is shown to reveal low-amplitude oscillations with periods between 24 and 31 seconds. The oscillations are present in more than half of the runs, making this variable an attractive target for simultaneous observations in different wavelength bands. The dwarf nova Z Cha is one of four cataclysmic variables which show rapid oscillations as well as primary eclipses. Photometry of z Cha, archived at the University of Cape Town over a period of ten years, is searched for rapid oscillations. Two runs show oscillations, with periods of 24 and 28 seconds. They exhibit eclipse-related phase changes which show qualitative repetition within a run, but significant long-term variation. This behaviour has not been seen in any other cataclysmic variable, and makes z Cha a potentially powerful discriminating tool for models of oscillation and superoutburst.