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Colloquium Details
Date and time: Thursday, November 05, 2009 at 4:10 PM
Location: 807 Dennison
Speaker: Shantanu Basu from University of Western Ontario
Title/topic: The Formation and Long-Term Evolution of Circumstellar Disks
Abstract:
Circumstellar disks are an integral part of the star and planet formation process. Much depends on the rate at which mass can be transported toward a central (proto)star and angular momentum transported outward. For years, theorists have studied this process using axisymmetric models that evolve due to a generic form of time-independent viscosity of specified spatial dependence - the alpha viscosity approach. In a series of papers, we have studied disk evolution using a different approach, with global models that follow numerically the self-consistent formation (from cloud core collapse) and nonaxisymmetric evolution of circumstellar disks. We can follow the evolution of the disk for several million years after its formation. The disk evolution has an initial burst phase of accretion, during which the disk accretion rate is usually low (10^{-8}-10^{-7} Msun/yr) but is punctuated by brief bursts of high accretion rate (~ 10^{-4} Msun/yr) that are caused by gravitational instabilities. Later on, during the T Tauri phase, the disks settle into a self-regulated state, with low-amplitude nonaxisymmetric density fluctuations persisting for at least several million years. The global effect of gravitational torques due to these fluctuations is to produce disk accretion rates that are of the correct magnitude to explain observed T Tauri star accretion rates. I will also discuss the effect of adding an alpha viscosity to these models, which can unfortunately lead to a loss of the best features of the gravitationally self-regulated state.
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