MSc PHYSICS DISSERTATION
Detailed Population Synthesis Studies of Cataclysmic Variables
Jonas Goliasch
Wednesday, October 28, 2009
3:30 pm
Hamilton 300
I will present the results of an extensive population synthesis study on the ensemble properties of the present-day Cataclysmic Variable (PDCV) distribution. Differences between the results of similar theoretical studies and actual observations have raised questions regarding the validity of the current understanding of CV formation and evolution. In particular the discovery of CV systems within the so-called "period gap" is frequently raised by opponents of the interrupted magnetic braking scenario. One of the main goals of this study was to explore the effects of nuclear evolution of the donors on our galactic PDCV distribution, as it was believed that nuclear evolution could provide some insight into to both of these issues. Using Monte Carlo methods, several zero-age CV (ZACV) distributions were generated to explore the parameter space associated with the formation of CVs and to test the overall robustness of the conclusions with respect to these parameters (e.g., initial mass function and birth-rate function). The evolution of successful CV systems was modeled through a Henyey-type stellar evolution code containing the latest generation of input physics. One of the main conclusions is that HeWD primaries are likely to contribute significantly to the PDCV population, and their Pmin occurs at a different orbital period than for systems with COWD primaries. Additionally, the nuclear evolution of the donor smears out the Pmin spike for COWD systems. Nuclear evolution of the donor also allows for the existence of systems within the period gap. Another significant discovery is a sharp drop in the mass-transfer rate at Pmin. Assuming that detectability scales with mass-transfer rate, this can possibly explain the absence of observed period bouncers.
