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