Physical properties of eclipsing white dwarf binaries

Doctoral thesis English OPEN
Pyrzas, S.
  • Subject: QB
    arxiv: Astrophysics::Galaxy Astrophysics | Astrophysics::Cosmology and Extragalactic Astrophysics | Astrophysics::Earth and Planetary Astrophysics | Astrophysics::Solar and Stellar Astrophysics

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