The Evolution of Cataclysmic Variable Stars

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).