Radius measurements of cataclysmic variable accretion disks

Abstract. Cataclysmic variables (CVs) are interacting binary systems with a white dwarf primary and a low-mass main sequence star secondary. The secondary star fills its Roche lobe and transfers mass onto the white dwarf. Often the gas flow forms an accretion disk around the primary. CVs are characterised by outbursts caused by changes in the mass transfer. In outbursts they can brighten from a couple of magnitudes to tens of magnitudes. Between the outbursts CVs are said to be in quiescence. Accretion disks in cataclysmic variables are the main source of emission in visual wavelengths. Thus, with their assistance, much has been revealed about the stars forming CVs and the ongoing mass transfer process between them. The outburst cycle has been thought to affect the size of the accretion disk: its radius has been thought to shrink in quiescence and expand in outburst. This idea has been recently questioned, and the seemingly varying radius might be caused by radii measurement methods tracking the location of the gas stream hitting the accretion disk instead the actual edge of the disk. In this thesis the standard model for CVs is reviewed and the formation of characteristically double-peaked emission lines from accretion disks is explained. The knowledge is then applied to measuring the radius of the accretion disk of OY Carinae in quiescence. It is found to be close to its theoretical maximum value, not significantly smaller as it should be if the disk size varied during the outburst cycle. This result backs up the idea of a consistently large accretion disk