RADIO OBSERVATIONS OF NOVA REMNANTS

Abstract

This thesis presents the analysis of radio observations of the nova KT Eri that was discovered on November 25th, 2009. Five epochs of radio observations are studied, covering 126 days after the nova outburst. The data were obtained by the Australia Telescope Compact Array (ATCA) at the frequencies of 5.5, 9, 17 and 19 GHz and are reduced here using the radio interferometry data reduction package MIRIAD.Radio emission has the advantage of not being subject to extinction by dust, compared to optical emission. Thus, it is a very useful tool for probing the physical parameters of nova eruptions. In this work, the radio observations of KT Eri are used to produce radio light curves at the aforementioned frequencies and derive conclusions about the physical properties of the nova shell.Following a review of novae and a description of radio interferometry and data reduction, the ATCA data on KT Eri are reduced and the flux densities are derived. The standard Hubble flow model for thermal radio emission from novae is then described and used to generate model light curves in an attempt to fit the observations to the model. For an electron temperature of 10^4 K and a distance of 5 kpc, plausible fits can be obtained to a single frequency, 5.5 GHz, leading to estimates for the values of the model parameters of a shell mass of ~ 10^-4 Mʘ, an ejection velocity of ~ 4000 km sec^-1 and a ratio of inner to outer velocity of 0.01. However, the results show that at higher frequencies this model is not consistent with the observations. A comparison with the nova V1723 Aql is noted, since this is another example of a classical nova that does not follow the Hubble flow model.Examination of the spectral indices reveals that the evolution of the KT Eri remnant over time does not agree with what is expected for a typical classical nova. Some characteristics of the light curves suggest that the emission from KT Eri could include a synchrotron component besides the thermal one. It is therefore discussed whether KT Eri is a recurrent nova after all.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Timothy O'Brien (Supervisor)