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Title: Radiative acceleration in the jets of SS433
Author: Anderson, Iain Moray
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1993
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First catalogued as entry number 433 in an objective prism survey of strong Hα emission line objects by Stephenson and Sanduleak in 1977, SS433 rose rapidly to fame in 1978 following the observation of moving hydrogen and helium lines in its optical spectrum. It has since proved to be an enduring astronomical puzzle. SS433 is a galactic object at a distance of some 5kpc and is located very near the centre of the supernova remnant W50 with which it is believed to be interacting. The consensus on the SS433 system itself is that it consists of a binary system comprising an OB star undergoing Roche-lobe overflow onto a supercritically accreting compact object, most probably a neutron star though possibly a black hole, leading to the formation of a geometrically thick accretion disc. Emergent from the narrow funnels of this thick disc are two oppositely aligned and highly collimated jets which move at a remarkably constant speed of 0.26c. The purpose of this thesis is to investigate the suitability of radiative acceleration as a mechanism for accelerating the jets to a speed of 0.26c and to determine whether such a mechanism can satisfy the stringent constraints on the constancy of the jets' speed imposed by observations. In the overview of the SS433 detailed in chapter 1, an historical account of the object is given as well as a summary of the observations and the many theotetical models that it has inspired. Though this review is by no means comprehensive, its length reflects the complexity of the object and the vast amount of work that has been published on it. Chapter 2 acts as a theoretical prelude to the remaining research chapters. In the first part of this chapter some common terms and definitions encountered in special relativity and radiative transfer are elucidated and some useful Lorentz invariants and Lorentz transformations are introduced. In the latter part of this chapter the general vector equation of motion of a spherical jet fragment moving within the time independent radiation field of a blackbody emitter is derived. Solutions to the general vector equation of motion for a spherical jet fragment, or 'bullet', moving within the radiation field of both infinite planar and infinite conical, isothermal blackbody radiators are sought in chapter 3. Terminal speeds which are dependent on the geometry of the radiator are found to exist. The degree to which radiation pressure can aid in the process of jet collimation is also assessed. Continuing the analysis of chapter 3, the first topic considered in chapter 4 is the motion of a bullet above an infinite, planar radiator for which the emergent, frequency integrated specific intensity is given by a generalisation to the Eddington limb darkening approximation. This is followed by an investigation of the motion of a bullet moving along the symmmetry axis of an infinite, conical radiator for which the surface temperature decays exponentially with increasing distance from the funnel apex. Applicability of this ad hoc temperature profile to SS433 is achieved by ensuring that the e-folding distance of the temperature profile is consistent with the observations. Brief sections on axial motion above a finite, isothermal, planar radiator and radial motion above an isotropic, spherical radiator then ensue. The concluding research of chapter 4 comprises an analysis of the axial equation of motion of a bullet moving within a finite accretion funnel. The funnel is modeled first as an isothermal, conical radiator and then as a conical radiator for which the run of temperature with distance from the funnel apex is given by that of a polytropic gas with an index appropriate for a radiation dominated regime. The results of the former model are found to be in surprisingly good agreement with the observations of SS433. Finally, in chapter 5 topics related to the work contained in this thesis and which could be considered in any further investigation are presented. These include suggestions for improving the 'bullet' model of chapters 2, 3 and 4 and the possible inclusion of a phenomenon which has been termed the 'Compton rocket' effect. Alhough a small proportion of the research contained in this thesis, principally part of chapter 3, consists of material which has previously been published by Icke (1989), the work presented here was undertaken independently and completed prior to the publication of Icke's results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available