Roughly two-thirds of all stars are locked in binary or higher-multiple systems. Given that over 97% of all stars also end their lives as white dwarfs, it is not surprising that more and more white dwarfs are being found as part of binary systems. A general introduction to white dwarfs and binary stars is presented in Chapter 1 and the techniques used throughout this thesis are presented in Chapter 2. Then, Chapters 3 and 4 present detailed studies of two close double white dwarf binaries. The first, CSS 41177, is also an eclipsing binary, which allows for detailed measurements of the white dwarf masses and radii. With the help of statistical analyses of far-ultraviolet spectroscopy from the Hubble Space Telescope, I also determine the effective temperatures and surface gravities of both stars. For the second binary, SDSS J1257+5428, previous publications were inconclusive, and therefore prompted the far-ultraviolet HST observations featured in this thesis. Using these data, I present a detailed analysis of the system and the still paradoxical results which indicate that the more massive of the two white dwarfs is younger rather than older than its lower-mass white dwarf companion. In Chapter 5 I detail the observations and aims of my eclipse timing programme, set up to measure apparent and/or real variations in the orbital periods of close white dwarf binaries. With more than 600 high-speed eclipse light curves, spread over more than 70 targets, I try to find general trends and hints of the underlying cause of such variations. Chapter 6 then presents a detailed study of the eclipsing semi-detached white dwarf + M-dwarf binary HUAqr, which is part of the timing programme. In fact, it is one of the most controversial targets in this programme, since none of the theoretical explanations fit the large-scale eclipse timing variations observed in this binary. Finally, I end with a concluding summary in Chapter 7.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:668920 |
| Date | January 2015 |
| Creators | Bours, Madelon Catherina Petra |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/73257/ |
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