Novae

Novae are interacting binary systems in which a white dwarf is accreting matter from a companion star, either a main-sequence dwarf or occasionally an evolved star like a red giant.

VLBA image of RS Oph (O'Brien et al 2006)
Radio image of RS Ophiuchi

Nova explosions are caused by runaway thermonuclear reactions in the material accreted onto the whte dwarf leading to a sudden brightening at optical wavelengths accompanied by the ejection of matter at speeds of several hundreds to thousands of km per second. The ejected matter is a mix of material from the companion, processed by nuclear reactions and, perhaps, some material from the white dwarf.

The expanding ejecta are often not spherical and it is commonly assumed that this is the result of interaction with the companion star in a common-envelope like phase (although other factors like the magnetic field and spin of the white dwarf cannot be excluded).

Nova systems are excellent laboratories for studying a wide range of astrophysical phenomena including accretion, nuclear reactions, shock waves, jet formation, photoionisation and dust formation. In some cases (when the white dwarf grows in mass as a result of accretion) even providing possible Type Ia supernova progenitors.

Working with colleagues from several UK and international universities, our group has for many years carried out theoretical and observational studies of novae, linking them to planetary nebulae and supernovae, and combining modelling with observation at wavelengths ranging from the radio to the X-ray. The work includes: multifrequency monitoring of novae in outburst; structural studies of nova ejecta using a combination of imaging and spectroscopy; and hydrodynamic simulations of mass-loss using parallelised numerical codes developed in-house and also applied to PNe and astrophysical jets.

Current work focuses on the use of e-MERLIN and VLBI to image the expanding ejecta and shock waves at very high angular resolution. This is combined with observations at other wavelengths to develop models for the 3-dimensional structure of the ejecta. We are particularly interested in understanding the mechanisms that shape the ejecta, in improving estimates of the mass ejected and answering the question of whether the white dwarfs in some novae will exceed the Chandrasekhar limit and explode as supernovae. 

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