Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 29 for “"Accretion disc"”.
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Studying Accretion Disc Winds with X-ray Spectroscopy
… results of my PhD research into the physics of accretion (infall) and ejection (outflow) of matter in compact objects. Accretion disc winds are formed of hot and ionised material launched by magnetic forces, radiation pressure or thermally from the discs of accretors. They have been discovered …
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Exploring the super-orbital periodic behaviour of X-Ray binaries
… and tidally-induced precession of the accretion disc, jet precession and the modulation of the mass-transfer rate due to an accretion disc instability or the effects of a third body.
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Understanding X-ray reflection as a probe of accreting black holes
… surrounding an accreting black hole from the accretion disc is investigated in the context of probing the structure of the central regions as well as the physical processes that power some of the brightest objects seen in the Universe. A method is devised to measure the emissivity profile of …
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Hydromagnetic Oscillations and Instabilities in Astrophysical Discs
… magnetized and differentially rotating, accretion flows provide an environment for the propagation of waves and the growth of instabilities unlike those normally encountered on Earth. In this dissertation, I investigate the properties of oscillations and instabilities in accretion discs, …
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Reverberation mapping of Active Galactic Nuclei
… to the incident ionizing continuum from the accretion disc. This delay is a consequence of light-travel time effects and directly enables the size of the BLR to be determined as RBLR = cτ (c is speed of light). Assuming virialized motions of the gas clouds in the BLR, and combining the …
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Accretion and outflow in black-hole x-ray binaries
… are known to produce X-ray emission through the accretion of mass from the companion star onto the black hole via an accretion disc, as well as radio emission originating from their jets. My thesis splits into two projects. On one hand, I focus on the connection between the X-ray emitting …
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Multiwavelength variability of black hole x-ray binaries in the low/hard state
… optical and infrared emission comes from a cold accretion disc with a large inner disc radius and a weak continuious jet is emitted from the central regions of the disc. In this thesis I study three black hole candidates which show low/hard state behaviour either most of the time (Cygnus X-1), …
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Spectra and variability of accreting black holes
… hole itself) most relevant to this work are the accretion disc and X-ray emitting corona. We use various methods to help determine their location, properties and relation to each other. In chapters 2 and 3, we consider how thermal emission from the accretion disc is affected by the coronal …
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Modelling the balmer line profiles in the spectra of symbiotic stars
… their origin is ascribed to emission from an accretion disc. The role which accretion discs play within the class of symbiotic stars however, is much more uncertain and modelling the lines on this basis could, if successful, help to strengthen the evidence for their presence in symbiotic …
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Superhumps in AM Canum Venaticorum stars
… secondary which is transferring mass via an accretion disc to a DB white dwarf. Under this model, the orbital periods of the AM CVn systems are in the range 1000 - 3000 s. The AM CVn systems show many of the accretion disc-related phenomena that are observed in non-magnetic (hydrogen-rich) …
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Using novel spectral-timing techniques to probe the rapid variability of X-Ray Binaries
… a powerful probe of the relationship between the accretion disc and corona in accreting compact objects. In this thesis, I present the use of variability techniques to disentangle the different variable components of X-ray spectra. By examining correlated variability over a range of timescales, I …
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Optical and near infrared observations of accretion processes in galactic compact objects
… X-ray Binaries, and to better understand the accretion processes in these systems. Accretion is essential in the formation of stars, planets and solar systems yet remains poorly understood. In this thesis, we present results that focus on the accretion processes in two important Low Mass X-ray …
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The broad spectral energy distributions of accreting white dwarfs
… I then use the SEDs to constrain the mass accretion rates by modelling the accretion disc as a series of concentric annuli, each of which radiates as a black body with effective temperature appropriate to the radius of that annulus. The resulting bestfit accretion rates are compared to …
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Shearing waves and the MRI dynamo in stratified accretion discs
Accretion discs efficiently transport angular momentum by a wide variety of as yet imperfectly understood mechanisms, with profound implications for the disc lifetime and planet formation. We discuss two different methods of angular momentum transport: first, generation of acoustic waves by mixing …
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On the Dynamics of Noncircular Accretion Discs
The classical picture of an accretion disc is of a geometrically thin, nearly axisymmetric, fluid flow undergoing supersonic circular motion and slowly accreting due to angular momentum transport by the disc turbulence. There are, however, strong theoretical and observational grounds for …
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Accretion topics in astrophysics
Accretion theory is essential for understanding a multitude of varied astronomical observations such as X-ray binaries, active galactic nuclei and gamma-ray bursts. In this document three works on accretion will be presented.The first one is on the structure of an inviscid accretion disc with small …
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Optical & X-ray Studies of Ultraluminous X-ray Sources
… mass black holes residing in a new extreme accretion state. This thesis works towards the conclusion of this debate, by developing our understanding of these systems and their environments. This work begins with a photometric survey of the optical counterparts of ULXs. The main aim of this …
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Multiband Observations of Recurrent Novae
… the nature of the companion star and the accretion disc. Observations of RS Oph are used to produce lightcurves of the decline from maximum to the post-outburst minimum. Analysis of optical and near-IR spectra following the 2010 outburst of U Sco leads to the determination of the reddening …
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The Dynamics of Magnetised Warped Discs
The study of warped discs and the study of magnetised discs have generally been performed in relative isolation, and comparatively little attention has been given to the complex interplay between these two aspects of accretion disc physics. This thesis aims to provide a synthesis of these disparate …
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Applications of Gaussian Processes at Extreme Lengthscales: From Molecules to Black Holes
… the latent emission signature from a black hole accretion disc. Furthermore, GPs are currently the workhorse model for Bayesian optimisation, a methodology foreseen to be a vehicle for guiding laboratory experiments in scientific discovery campaigns. The first contribution of this thesis is to …
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