Visible and Infrared Studies of Cataclysmic Variable Stars

Citation

Berriman, Graham (1983) Visible and Infrared Studies of Cataclysmic Variable Stars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/psse-c523. https://resolver.caltech.edu/CaltechETD:etd-09082008-130459

Abstract

The purpose of this Thesis is to investigate the infrared properties of Cataclysmic Variable Stars, in particular, to develop the techniques needed to study the contributions to the infrared light of the red dwarf and the accretion disc around its white dwarf companion. A particular requirement of these techniques is that they do not rely on a model of the poorly understood discs. They can be applied not only to Cataclysmic Variable Stars, but also to other interacting systems containing a red star, such as symbiotic stars.

Analysis of the visible to infrared colours of fourteen largely uneclipsing systems, based on flux ratio diagrams, shows that the red dwarfs and the opaque gas in the disc supply most of the infrared light, but the contributions of each vary widely from system to system, with more light coming from the red dwarfs in the longer period systems than in the shorter period ones. For nearly all the systems studied, upper limits can be found to the fluxes of the red dwarfs that are approximately independent of spectral type and of the conditions in the accretion discs.

In highly inclined systems, measurements of the amplitudes of the tidally induced ellipsoidal variations of the red dwarfs provide a more precise measure of the proportion of light coming from the red dwarf. A technique to simulate the light curves of tidally distorted red dwarfs successfully accounts for the infrared light curves of U Geminorum, a system in which the red dwarf supplies nearly all the infrared light.

Completing the Thesis is a visible and infrared study of the eclipsing dwarf nova OY Carina in quiescence. This system has been studied because in the visible, the red dwarf is seen to eclipse the white dwarf. Analysis of these eclipses, based on the assumption that the red dwarf fills its Roche Lobe, allows the determination of several fundamental properties of the system: the inclination of the system is 73.5° to 81°, the mass of the white dwarf lies in the broad range 0.4-1.4 M_⊙ and the red dwarf lies either on or slightly below the Main Sequence mass radius relation. The principal source of uncertainty in the analysis is that the semi-amplitude of the radial velocity variations of the white dwarf is poorly known. The infrared light curves show an eclipse of the disc and, half a cycle later, a secondary minimum produced by the ellipsoidal variations of the red dwarf and its eclipse by the disc. The depth of this minimum and the colours of the system imply that the red dwarf supplies approximately one-half of the uneclipsed light of the system and that it eclipses more than three-fifths of the light of the disc. The latter result requires that the K magnitude of the red dwarf lies in the range 14.2 to 14.7. The distance to the system, as deduced from these limits and an estimate of the surface brightness of the red dwarf lies in the range 100 to 300pc. The infrared light of the disc comes largely from optically thin emission; the opaque gas occupying most of the disc does not supply much of infrared light because the disc is atypically small and more highly inclined compared with other systems.

Thesis Files