Mass Determinations of Cataclysmic Variables

Cataclysmic variables (CVs) are a class of closely interacting binary system that undergo mass transfer from a Roche lobe filling secondary star to a white dwarf primary star, usually via a gas stream and an accretion disc. A bright spot is formed where the gas stream meets the edge of the accretion disc. The light curves of CVs can be complex, with the accretion disc, white dwarf and bright spot all being eclipsed in rapid succession. When observed with time resolutions of the order of a few seconds, this eclipse structure allows the system parameters to be determined to a high degree of precision, with relatively few assumptions. In this thesis I present new, high-speed photometry of 20 eclipsing CVs. For 6 objects, I am able to determine the system parameters by fitting a parameterised model to the observed eclipse light curve (the photometric method). In addition, I perform an updated analysis of 11 CVs that were previously analysed by my group, bringing the total sample size of eclipsing CVs with precise mass determinations in this thesis to 17. I find the secondary stars in CVs are oversized in comparison to standard models. I show that this can be explained by either enhancing the mass-transfer rate, or by modifying the stellar physics of the secondary stars. Distinguishing between these two possibilities is not possible given the available data.

I perform an independent check of the photometric method by deriving system parameters for one object using well known spectroscopic methods. The parameters derived are found to be consistent with the photometric method, thus supporting its accuracy and validity.

Finally, I look at the infrared spectra of a short period CV. I am able to make a direct detection of the secondary star and place some constraints on the spectral type of the secondary star.