paper

Secular evolution of viscous and self-gravitating circumstellar discs

arXiv:0812.1306 · doi:10.1111/j.1365-2966.2008.14376.x

Abstract

We add the effect of turbulent viscosity via the α-prescription to models of the self-consistent formation and evolution of protostellar discs. Our models are non-axisymmetric and carried out using the thin-disc approximation. Self-gravity plays an important role in the early evolution of a disc, and the later evolution is determined by the relative importance of gravitational and viscous torques. In the absence of viscous torques, a protostellar disc evolves into a self-regulated state with disk-averaged Toomre parameter Q \sim 1.5-2.0, non-axisymmetric structure diminishing with time, and maximum disc-to-star mass ratio ξ= 0.14. We estimate an effective viscosity parameter α_eff associated with gravitational torques at the inner boundary of our simulation to be in the range 10^{-4}-10^{-3} during the late evolution. Addition of viscous torques with a low value α= 10^{-4} has little effect on the evolution, structure, and accretion properties of the disc, and the self-regulated state is largely preserved. A sequence of increasing values of αresults in the discs becoming more axisymmetric in structure, being more gravitationally stable, having greater accretion rates, larger sizes, shorter lifetimes, and lower disc-to-star mass ratios. For α=10^{-2}, the model is viscous-dominated and the self-regulated state largely disappears by late times. (Abridged)

13 pages, 11 figures, accepted for publication in MNRAS

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