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Title: Eclipsing white dwarf binaries
Author: Parsons, S. G.
ISNI:       0000 0004 2726 1163
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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Recent years have seen an explosion in the number of eclipsing binaries containing white dwarfs. In the last few years the number of systems has increased from 7 to over 40, thanks mainly to large surveys such as the Sloan Digital Sky Survey and the Catalina Sky Survey. Many of these systems are survivors of the common envelope phase during which the two stars orbit within a single envelope which is rapidly thrown off through loss of energy and angular momentum. Detailed analysis of these systems can yield extremely precise physical parameters for both the white dwarf primary and its companion star. Stellar masses and radii are some of the most fundamental parameters in astronomy and can be used to test models of stellar structure and evolution. They can also be used to constrain the evolutionary history of the binary system offering us the chance to better understand the common envelope phase itself. In this thesis I present high-precision studies of several eclipsing post common envelope binaries. I use a combination of high-speed photometry and high-resolution spectroscopy to measure the masses and radii of both stars in each system. I compare these results to evolutionary models and theoretical mass-radius relations and find that, on the whole, the measured masses and radii agree well with models. However, the main-sequence companion stars are generally oversized compared to evolutionary models, although this deviation is much less severe at very low masses (< ∼ 0.1M⊙). I also find that the measured masses and radii of carbon-oxygen core white dwarfs are in excellent agreement with theoretical models. Conversely, the first ever precision mass-radius measurement of a low-mass helium core white dwarf appears undersized compared to models. Large scale surveys have also begun to identify double white dwarf eclipsing binaries. In this thesis I present a study of one of these systems and show the potential, as a double-lined spectroscopic binary, of measuring precise parameters for both stars in the future. Finally, I show that the mid-eclipse times of eclipsing binaries containing white dwarfs can be measured to a high enough precision that we can monitor them for evidence of period changes. I find that many systems show complex variations in their eclipse times and in many cases the only mechanism able to produce these changes is one or more sub-stellar objects in orbit around the binary. However, I show that care must be taken when attempting to detect planets in binary systems using eclipse timings.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy