JultikaUniversity of Oulu repository

Abstract

This Masters thesis focuses on studying the kinematics of the outer accretion disk in cataclysmic variables. Cataclysmic variables are a type of interacting binary stars featuring a white dwarf and a main sequence star. Accretion disks in cataclysmic variables are born, when a secondary star still in main sequence overfills its Roche lobe and starts leaking gas towards the primary star (the white dwarf). The extent of the accretion disk has been a cause for discussion; methods measuring it from the hot spot, the place where accretion stream hits the disk, characteristically lead to smaller radii than measuring the radius from outer disk velocities. However, disk size estimates from the outer disk velocities heavily depend on the velocity field. The aim here is to check how close the outer accretion disk is to Keplerian velocities and simple three-body orbits. To do this, they are compared to simulated accretion disks using Smoothed Particle Hydrodynamics. Same comparisons are then done against observational data using Doppler tomography. Our study finds that the Keplerian velocity at the tidal truncation limit can safely be used as a lower limit for orbit-averaged disk. Furthermore, last non-intersecting three-body orbit seems to trace the disk edge quite well, and it can be used as an estimate for accretion disk size.