Matt Darnley's Web Site: Research

Classical and Recurrent Novae

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.

M31N 2008-12a

Extragalactic Populations

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.

PhD Projects

Novae, and their Potential as Progenitors of Type Ia Supernovae

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.

PhD Students

Director of Studies

Supervisory Team

PhD Examining

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