Classical and recurrent novae occur within close binary systems,
containing a white dwarf (WD) that accretes hydrogen rich material
from its companion. The material is typically transferred from the
companion to the WD via an accretion disk that forms around the WD
and lies in the binary plane. Once the accreted layer on the
surface of the WD attains a critical temperature and pressure
hydrogen burning ignites which leads to a thermonuclear runaway
that ejects the accreted envelope.
The systems can be sub-classified in a number of ways; for
example, via the number of recorded eruptions into Classical Novae
(one eruption) or Recurrent Novae (multiple eruptions); via the
evolutionary state of the donor, a main sequence, sub-giant or red
giant star; or by the form of the early outburst spectra, Fe II,
He/N, or neon novae.
While the study of individual novae within our own Galaxy, the
Milky Way, can be carried out with great precision across the
entire electromagnetic spectrum, our position inside the Galaxy
severely limits our ability to study the underlying population in
detail. Hence, we turn to extragalactic populations where we
can obtain a relatively unbiased view of many novae. The
prime target for extragalactic surveys is the Andromeda Galaxy
(M31), but many systems have been studied in detail.
Director of Studies: Dr Matt Darnley
Novae, particularly the Recurrent Novae (RNe) that harbour either sub-giant or red giant secondary donor stars have long been touted as potential progenitors of Type Ia Supernovae (SNe), via the single-degenerate (SD) channel. Studies of nearby SN Ia have in some cases pointed towards a SD progenitor, whereas others have shown evidence of a double degenerate (DD) route, but the vast majority have an uncertain origin. More recently, it has been proposed that various pathways (from both SD and DD channels) may actively contribute to the observed SN Ia population, and that the dominance of any pathway may depend on the galaxy morphology or parent stellar population.
While the Nova rate, and hence size of the Nova population, of any galaxy can be relatively easily determined, the proportion of those Novae that contain either sub-giant or red giant donors (the potential SN Ia progenitors) is unknown. In recent years, the Nova group at the ARI has been working to determine the extent of this population, in order to evaluate the contribution Novae may make to the overall SN Ia rate for a given galaxy. Our approach is two fold; studying individual Novae and RNe, and their progenitors, in the Galaxy in great detail, while also surveying the entire Nova population and their progenitors in nearby galaxies, such as M31.
The work of a PhD student in this area would be broadly
observational, with the Liverpool Telescope (LT) providing the
majority of the photometric and spectroscopic observations of
erupting novae, with progenitor work generally utilising archival
data, in particular from the Hubble Space Telescope. A number of
possible projects are available in this area, some focusing
Galactically, some extragalactically, with different emphases on
imaging and spectra. All of the projects would involve the PhD
student running all or part of a large Nova observing programme on
the LT and reacting to new eruptions. The PhD student will have
the opportunity to work with a number of our close collaborators,
here in the UK, and internationally.