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Non-axisymmetric instabilities in discs with imposed zonal flows
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-09-06)
We conduct a linear stability calculation of an ideal Keplerian flow on which a sinusoidal zonal flow is imposed. The analysis uses the shearing sheet model and is carried out both in isothermal and adiabatic conditions, ...
Secular evolution of eccentricity in protoplanetary discs with gap-opening planets
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2017-06)
We explore the evolution of the eccentricity of an accretion disc perturbed by an embedded planet whose mass is sufficient to open a large gap in the disc. Various methods for representing the orbit-averaged motion of an ...
Quasi-periodic oscillations and the global modes of relativistic, MHD accretion discs
The high-frequency quasi-periodic oscillations (HFQPOs) that punctuate the light curves of X-ray binary systems present a window onto the intrinsic properties of stellar-mass black holes and hence a testbed for general ...
The stress–pressure relationship in simulations of MRI-induced turbulence
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-01-01)
We determine how MRI (magnetorotational instability)-turbulent stresses depend on gas pressure via a suite of unstratified shearing box simulations. Earlier numerical work reported only a very weak dependence at best, ...
Growth of eccentric modes in disc–planet interactions
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-03-07)
We formulate a set of linear equations that describe the behaviour of small eccentricities in a protoplanetary system consisting of a gaseous disc and a planet. Eccentricity propagates through the disc by means of pressure ...
Nonlinear hydrodynamical evolution of eccentric Keplerian discs in two dimensions: validation of secular theory
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-03-11)
We perform global two-dimensional hydrodynamical simulations of Keplerian discs with free eccentricity over thousands of orbital periods. Our aim is to determine the validity of secular theory in describing the evolution ...
On the orbital evolution of a pair of giant planets in mean motion resonance
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-07-04)
Pairs of extrasolar giant planets in a mean motion commensurability are common with 2:1 resonance occurring most frequently. Disc–planet interaction provides a mechanism for their origin. However, the time-scale on which ...
On the formation of a quasi-stationary twisted disc after a tidal disruption event
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-08-24)
We investigate misaligned accretion discs formed after tidal disruption events that occur when a star encounters a supermassive black hole. We employ the linear theory of warped accretion discs to find the shape of a disc ...
On the energy dissipation rate at the inner edge of circumbinary discs
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2016-10-03)
We study, by means of numerical simulations and analysis, the details of the accretion process from a disc on to a binary system. We show that energy is dissipated at the edge of a circumbinary disc and this is associated ...
Zonal flow evolution and overstability in accretion discs
(Oxford University PressMonthly Notices of the Royal Astronomical Society, 2017-04-01)
This work presents a linear analytical calculation on the stability and evolution of a compressible, viscous self-gravitating (SG) Keplerian disc with both horizontal thermal diffusion and a constant cooling time-scale ...