thesis
Physical properties of eclipsing white dwarf binaries
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Abstract
Close binaries containing compact objects come in many different forms, but have one thing
in common: their evolution involves at least one common envelope phase and angular momentum
losses. However, many aspects of these two fundamental processes are still poorly understood. Ample
observational input holds the key to improving our understanding, as only then can theoretical
models be properly calibrated and tested. Close binaries containing a white dwarf are perhaps the
best-suited class of objects to provide such input, due to their ubiquity. White dwarf binaries that additionally
display eclipses are of added interest, as accurate and model-independent determinations
of fundamental stellar parameters, such as the masses and radii of the binary components, can only
be obtained in such systems.
In this thesis, I present a study of eclipsing white dwarf binaries. I identify SDSSJ 0110+1326,
SDSSJ 0303+0054, SDSSJ 1210+3347, SDSSJ 1435+3733 and SDSSJ 1548+4057 as new eclipsing,
detached, post-common-envelope, white dwarf +M-dwarf binaries. I use follow-up photometric and
spectroscopic observations, as well as a light curve fitting technique to measure their orbital periods,
and derive the masses, radii and radial velocities of the binary components. These five systems have
been identified as part of the first dedicated search for eclipsing post-common-envelope binaries
and almost double the existing population. The measurements of the stellar parameters, and others
obtained from similar systems, are of great value both for the calibration of the common envelope
equations and for testing the mass-radius relations of white dwarfs and low-mass main sequence
stars. I also identify HS 2325+8205 as a new eclipsing and very frequently outbursting dwarf nova.
Combined constraints from photometric and spectroscopic observations are used to infer the binary
and stellar parameters. The combination of eclipses, frequent outbursts, brightness range and
high declination make HS 2325+8205 an ideal laboratory for detailed studies of accretion discs and
accretion processes in close binaries. Finally I study the cataclysmic variable V455And, in an attempt
to verify the presence of non-radial pulsations in the white dwarf primary. This is achieved
by analysing ten-years worth of photometric observations using time-series analysis techniques and
Fourier transforms. The results are indeed consistent with white dwarf pulsations, although a very
complex behaviour of the power spectra is revealed, most likely a result of the rapid rotation of the
accreting white dwarf primary