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|Title:||Accretion disc viscosity: what do warped discs tell us?|
|Authors:||King, Andrew R.|
Lubow, S. H.
Pringle, J. E.
|Publisher:||Oxford University Press for Royal Astronomical Society|
|Citation:||Monthly Notices of the Royal Astronomical Society, 2013, 431 (3), pp. 2655-2660|
|Abstract:||Standard, planar accretion discs operate through a dissipative mechanism, usually thought to be turbulent, and often modelled as a viscosity. This acts to take energy from the radial shear, enabling the flow of mass and angular momentum in the radial direction. In a previous paper, we discussed observational evidence for the magnitude of this viscosity, and pointed out discrepancies between these values and those obtained in numerical simulations. In this paper, we discuss the observational evidence for the magnitude of the dissipative effects which act in non-planar discs, both to transfer and to eliminate the non-planarity. Estimates based on the model by Ogilvie, which assumes a small-scale, isotropic viscosity, give alignment time-scales for fully ionized discs which are apparently too short by a factor of a few compared with observations, although we emphasize that more detailed computations as well as tighter observational constraints are required to verify this conclusion. For discs with low temperature and conductivity, we find that the time-scales for disc alignment based on isotropic viscosity are too short by around two orders of magnitude. This large discrepancy suggests that our understanding of viscosity in quiescent discs is currently inadequate.|
|Rights:||Copyright © the authors, 2013. This article is distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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