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The Evolution of Cataclysmic Variable Stars

Sahman, David (2018) The Evolution of Cataclysmic Variable Stars. PhD thesis, University of Sheffield.

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Abstract

Cataclysmic variables (CVs) are binary star systems comprising a white dwarf which is accreting material from a Roche-lobe filling companion, usually a late-main sequence or evolved star. The accreted material accumulates on the surface of the white dwarf and ultimately leads to a thermonuclear runaway explosion, called a nova eruption. There are ∼ 400 recorded novae and some have shown more than one eruption. These systems are the recurrent novae, and they are one of the leading progenitor candidates of Type Ia Supernovae. In this thesis, I describe how I used high speed spectroscopy to determine the component masses of the stars in the eclipsing recurrent nova CI Aquilae. The masses I determined suggest it is indeed a progenitor of a Type Ia supernova, and will explode in 10 Myr. The long term impact of nova events on the evolution of CVs is poorly understood, and may be the reason for the diversity of CV types observed at the same orbital period. One theory, known as hibernation theory, proposes that the nova event causes systems to cycle through the various classes of CVs, due to heating and bloating of the secondary. In the second part of this thesis, I undertook searches for nova shells around known CVs, in an effort to determine the frequency and life-cycle of novae. I examined over 150 systems and found one definite shell around V1315 Aquilae. I then used high–resolution spectroscopy to determine the mass and age of this shell. This is the first discovery of a nova shell around a novalike variable. By combining my search results with simulations and the results of other recent searches for nova shells, I find that the lifetime of the novalike state is broadly in line with the nova-induced cycle theory (hibernation theory).

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Physics and Astronomy (Sheffield)
Identification Number/EthosID: uk.bl.ethos.758354
Depositing User: David Sahman
Date Deposited: 05 Nov 2018 15:46
Last Modified: 25 Sep 2019 20:05
URI: http://etheses.whiterose.ac.uk/id/eprint/21700

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