JultikaUniversity of Oulu repository

Abstract

In this thesis I will introduce the evolutionary stages of Cataclysmic Variables (CVs) and focus on their late evolution. Evolutionary stages of CVs are not very well understood and the standard model for it seems to not be able to explain all the observed phenomena. Long-term stable mass transfer is a key part of these binary stars and their evolution, but understanding the mechanics that enable the mass transfer is still a big challenge. Active research and new observations have answered some big questions in the last years, for example successfully observing the predicted period spike, but the late stages of CV evolution still need better understanding. Old CVs are believed to inhabit substellar stars, brown dwarfs, as their secondary stars but observing these very old systems has been one of the biggest challenges in the study of CV evolution today.

To understand the evolutionary path these systems follow, we must understand the structure and mass transfer of these systems as described in section 1. In this thesis I will use the observed period distribution of CVs to introduce many of the observed phenomena relating to late evolution of CVs. Possible mechanics behind angular momentum loss (AML) CVs experience will be discussed. Late evolutionary path as it is understood at this time will be provided. Different ways to possibly identify these late type CVs with substellar secondaries and few possible candidates for them are introduced.