Abstract
Classical nova (CN) outbursts are the result of a thermonuclear runaway (TNR) in the accreted envelope of a white dwarf (WD) in a close, mass-transferring binary system with a companion star. 3-dimensional (3D) CN studies demonstrate that temperature fluctuations along the WD-envelope interface during the TNR cause instabilities that dredge up WD material into the envelope thus enriching the metallicity of CN ejecta up to about 60 per cent. In 1D CN simulations, the mixing phase during the TNR is typically not modelled. Instead, mixed-composition material composed of a mixture of WD- and Solar-composition material is accreted atop the WD to simulate the instantaneous mixing of accreted material with the underlying WD. However, mixed-composition material accretion produces less realistic CN outbursts. In this dissertation, we present the imposed diffusive mixing (IDM) method of WD-envelope mixing during the TNR in 1D CN simulations. With our IDM method, we accrete Solar-composition material atop WDs and mix the accreted material with the underlying WD at the start of the TNR as reported by 3D TNR simulations. We simulate a parameter space of CN outburst models with WD masses between 0.6 and 1.3 Solar masses and of carbon-oxygen or oxygen-neon composition and use our IDM method to increase the accreted envelope metallicity from 10 to 40 per cent with WD material at the TNR. We investigate how these parameters affect the key features and nucleosynthetic yields of our outbursts. We quantify the contribution of individual CN outbursts to the interstellar medium and comment on the role of CNe in Galactic lithium-7 enrichment. We also model CN outbursts without IDM but with variable accretion rates and chemical diffusion at the WD-envelope interface to determine the range of features these models produce and to compare them to our IDM CN models. Our IDM models typically eject one to two orders of magnitude less lithium-7 mass than previously predicted in the literature. However, our models with variable accretion rates and chemical diffusion eject nearly two orders of magnitude more lithium-7 mass than our IDM models thus we hypothesise that CN outbursts may be an important source of Galactic lithium-7. All of our CN models eject more mass than they accrete hence all our nova-producing WDs decrease in mass with every outburst, contrary to studies that report CN outbursts grow WDs in mass. Finally, we investigate how consecutive CN outbursts atop the same WD affect the properties of the WD and hence make a comment on the viability of CNe as the progenitors of type Ia supernovae.