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Title: Accretion discs in T Tauri stars and interacting binaries
Author: Armitage, P. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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This thesis explores aspects of the theory of accretion discs in two astrophysical environments; around young low-mass stars - T Tauri stars, and in mass transfer binaries. A particular aim is to consider the role that magnetic fields - including fields within the disc and those of the central star - may play in controlling the evolution of the star-disc system. T Tauri stars are known to be magnetically active, and the first part of the thesis considers the structure and evolution of discs around magnetic T Tauri stars. I extend prior models to examine the effect of time-varying magnetic fields on the disc, and show that some of the long-term photometric variability in T Tauri systems could be caused by the influence of magnetic cycles on the accretion disc. The evolution of the star-disc system on much longer timescales is then investigated by combining pre-main-sequence stellar evolution models with those for the disc. The resulting model is used to examine the rotation rates of magnetically braked T Tauri stars, and the possible influence of close binary companions on those rotation rates. The second part of the thesis considers accretion discs in interacting binary systems. A magnetic dynamo within the disc is a promising candidate mechanism for the origin of the viscosity in accretion discs, and I discuss the implications of an operating dynamo for observations of dwarf novae. A simple model is presented in which the prominent outbursts seen in these systems have a direct origin in the physics of the underlying disc dynamo. I also present the results of three dimensional simulations of the interaction between the gas stream from the mass-donating star and the accretion disc. The hydrodynamic calculations show that a significant fraction of the stream gas can ricochet off the outer rim of the disc and overflow towards smaller radii, and the implications of this for models and observations of Cataclysmic variables and low-mass X-ray binaries are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available