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Instability in the winds of hot stars : Theory and simulation

Gomez, Edward L. 2004. Instability in the winds of hot stars : Theory and simulation. PhD Thesis, Cardiff University.

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Radiatively driven winds are a key component in a number of astrophysical settings, most notably the wind of hot massive stars. In this thesis we present the mechanism by which line radiation can drive hot star winds. In order to become familiar with the dynamics of numerical wind solutions in one and two dimensions, we also make calculations for winds driven by perfect gas pressure and continuum radiation pressure. The main emphasis of this work is to approximate the form of the line-driving as given by Owocki, Castor & Rybicki (1986), with an efficient algorithm, in a pure absorption (no scattering) case. We construct an efficient model for the solution to the line-driving problem and use this to investigate the dynamics of perturbations in the wind. Once we have shown that our method can reproduce the results of previous authors we add more physics to the model. We firstly change the shape of the line-profile function and observe that although this has a stabilizing effect on the flow the response of the wind to perturbations is largely unchanged. As separate refinement we move away from the pure absorption model and include the line drag phenomenon in the radiative driving calculation. This phenomenon also stabilizes the flow but its effect is decreases further from the central star and the downstream flow feels little of its influence. We use the results from all of our models of hot star winds to create synthetic spectral diagrams. The spectra created from the perturbed models resemble structures which are observed in the spectra of hot star winds called Discrete Absorption Components, the origin of which is unclear. We show that our models can be used to explain astrophysically observed structure and better understand the nature of hot star winds.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
ISBN: 9781303200113
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 06:02

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