Computer Science – Sound
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........4t&link_type=abstract
Proquest Dissertations And Theses 2009. Section 0058, Part 0606 196 pages; [Ph.D. dissertation].United States -- New York: Corn
Computer Science
Sound
Accretion Disks, Diskoseismic, Corotation Resonance, Black Holes
Scientific paper
Diskoseismological modes of accretion disks around compact objects are explored, in particular p-modes and their interaction with the corotation resonance. A WKB treatment of wave super-reflection due to corotation resonance and corotation absorption is developed, with super-reflection depending on the gradient of the so-called "vortensity" of the background flow. This result is applied to the context of black hole accretion disks where the background spacetime can modify the vortensity gradient so that p-modes trapped in the inner region of the disk may be amplified. The inner boundary condition for such disks is also explored in detail, in particular the effect of a transonic flow near the innermost stable circular orbit of a black hole is examined.
The effect of the corotation absorption is also briefly examined for other diskoseismic modes with vertical structure, in particular c-modes are shown to be damped by the absorption, and their damping rate is calculated. The inner boundary condition for a magnetosphere-disk model is calculated, as well as that of a star-disk interface. It is shown that interface modes, modes generated at the inner boundary of the disk, can be strongly unstable in the magnetosphere-disk model, due to the Rayleigh-Taylor and Kelvin-Helmholtz instabilities. However, due to the suppressing effect of the disk vorticity in differential rotation, the Rayleigh Taylor instability is suppressed (in models with no shear between the disk and magnetosphere) when sound speed is sufficiently small, while the Kelvin-Helmhotz instability may still be active for small sound speed when there is shear between the magnetosphere and disk. Star-disk interface modes are found to be weakly unstable primarily due to wave absorption at the corotation. Lastly, a procedure for ray-tracing in the Kerr metric is described, and used to generate images and time-dependant observables from various disk models.
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