A Search For Eclipsing Companions To White Dwarf Stars

In this Thesis, I present a search for eclipsing companions to white dwarf stars, with the aim of studying and more accurately constraining the properties of evolved planetary systems. I first undertake an independent, ground-based survey of metal-rich white dwarfs with similar physical properties to WD1145+017, the first discovered white dwarf hosting a disrupting planetesimal. While no transit-like features are detected in the survey, photometric variability is discovered in two objects. I investigate the nature of such variability in both objects. At the time of writing this work, I am awaiting spectroscopic data for one of the targets in order to search for evidence of an unseen companion. The second object reveals no radial velocity variations, thus the most likely source of variability is determined to be accretion events from the surrounding environment. Moreover, I take part in analysing the white dwarf sample in Campaign 14 of the Kepler K2 mission, sampling 368 white dwarfs brighter than 20 mag. In the sample, I ?nd a brown dwarf totally eclipsing a white dwarf with a period of ~133 minutes. Only two other eclipsing white dwarf + brown dwarf systems were known previous to this discovery. Finally, I present the discovery of two post common-envelope binary systems in the Next Generation Transit Survey. The ?rst system consists of an M4 star orbiting a cool (~7500 K) white dwarf with a period of ~13.85 hours. Only one other system similar to this had been previously discovered. The second binary is a younger, hotter system, in which an ~18,000 K white dwarf is eclipsed by a late-K or early-M main sequence companion.