Variable white dwarfs in the SuperWASP archive. A search for sub-stellar and planetary companions

This PhD thesis is an investigation of the characteristics and detection limits for transit signals due to sub-stellar and terrestrial companions to white dwarfs in the SuperWASP survey. The work is described as follow: there is an introductory chapter on the field of white dwarfs and exoplanets. In chapter 2 I describe the SuperWASP project, the two SuperWASP telescopes the problematics of data analysis and the results obtained so far. In chapter 3 I discuss the simulations I performed to investigate the characteristics of the transit signals due to sub-stellar and planetary companions to white dwarfs and the detection limits derived for SuperWASP light-curves by means of my optimised version of Box-Least Square (BLS) algorithm. In chapter 4 I present a study of 194 spectroscopically identified white dwarfs which are a cross-correlation of the McCook & Sion catalogue and the SuperWASP archive. In addition, I derive upper limits to the frequency of sub-stellar and planetary companions to white dwarfs using my sample and the results obtained from my simulations. In chapter 5 I present a variability study for the sample of 194 white dwarfs. I have investigated the light-curves of the 194 white dwarfs in the sample to search for photometric variability due to non-radial pulsations, the presence of star spots in magnetic white dwarfs, and to irradiation and reflection effects on low-mass close companions. Finally, in chapter 6 I conclude and present my project for future work.