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Title: Accretion Disc Phenomena in Extreme Mass Ratio Cataclysmic Variables
Author: Smith, Amanda Jane
ISNI:       0000 0001 3420 6291
Awarding Body: Open University
Current Institution: Open University
Date of Award: 2007
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We study a variety of accretion phenomena under the umbrella of extreme mass ratio cataclysmic variables (CVs), employing both observation and numerical simulation. A primary focus is the superhump phenomenon and the underlying eccentric instability and accretion disc precession. We make a detailed examination of the relationship between superhump period excess, f, and system mass ratio, q. We conduct extensive high resolution three-dimensional smoothed particle hydrodynamic (SPH) simulations, improving upon the realism of previous work from both a numerical and physical perspective. We find a much improved match with observation. A complete compilation from the literature suggeSts an observed multi-valued f - q relation. Our simulations reveal the mechanism generating the superhump modulation, and we examine the distribution of eccentricity in the disc. The latter has bearing on disc precession rates. Other results include a quantifiable enhancement of tidal torques as the disc becomes eccentric, very low eccentricity growth rates particularly at high q, and damped eccentricity at very low q. We look for observational signatures of the underlying precessing accretion disc in AM CVn and HP Lib. Previous simulations predicted trailed spectra to evolve with precession phase, and we find this indeed to be the case. A long disc precession period S-wave is found in the line profiles, also foreseen by simulation. For VWHyi, we use the indirect imaging technique of Doppler interpret the phase dependent optical emission line profiles during quiescence. We find an ionisation structure in the region of impact between the accretion stream and disc. Strongly phasedependent HeII emission further suggests a hot cavity at the initial impact site. Our observations feature prominent white dwarf (WD) spectral features in the optical, and we make a determination of the WD mass using the gravitational redshift of an MgII photospheric absorption line.
Supervisor: Not available Sponsor: Not available
Qualification Name: Open University, 2007 Qualification Level: Doctoral
EThOS ID:  DOI: Not available