A multi-wavelength study of cataclysmic variable stars

This thesis investigates the properties of two cataclysmic variables which have previously been considered to be non-magnetic systems. The goal of this work is to constrain the component star masses and other physical parameters of these systems using multi-wavelength observations.

I carry out spectroscopic studies on the eclipsing nova-like system RW Tri in the ultraviolet, far red, and near infrared. I produce a simple absorption model to show that one possible scenario for the origin of ultraviolet narrow absorption features, seen in Hubble Space Telescope observations, is a ring-like structure with height above the orbital plane, centred on the primary star. I re-analyse far red data from the Isaac Newton Telescope, using the tomographic technique of `skew-mapping' to obtain the radial velocity amplitude of the secondary star. I have made new observations of RW Tri in the near infrared using the United Kingdom Infra-Red Telescope to determine the accuracy of the secondary star radial velocity amplitude. The measured secondary star radial velocity has been combined with ultraviolet absorption line analysis and existing optical emission line data, to calculate the mass ratio, and hence the mass of the component stars. The rotational velocity of the secondary star has also been obtained from the infrared observations, and combined with the radial velocity of the secondary star to calculate more reliable component star masses.

OY Car, an eclipsing dwarf nova, was observed at X-ray wavelengths using XMM-Newton. I study the light curves, and measure the extent of the boundary layer in the system. I also observe significant quasi-sinusoidal variations with an underlying periodicity of 2233 seconds, which may be the spin period of the white dwarf primary star. These results imply that OY Car may be weakly magnetic, and could therefore belong to a new class of intermediate polars below the period gap. Investigations of the eclipse profile lead to an estimate of the component star masses.