Protostars and Planets VI, Heidelberg, July 15-20, 2013
Transport and Accretion Processes in Protoplanetary Disks: A New Paradigm
Bai, Xue-Ning (Harvard-Smithsonian Center for Astrophysics)
Non-ideal magnetohydrodynamical effects play a crucial role in determining the mechanism and efficiency of angular momentum transport as well as the level of turbulence in protoplanetary disks (PPDs), which are the key to understanding PPD evolution and planet formation. Most previous studies have considered only the effect of Ohmic resistivity under the framework of magnetorotational instability (MRI) driven accretion with dead zones. We show via self-consistent local numerical simulations that the inclusion of ambipolar diffusion (AD) changes the conventional picture qualitatively. In the inner disk around 1 AU, the MRI is suppressed due to the inclusion of AD, and the disk becomes completely laminar. Instead, a strong magnetocentrifugal wind can be launched in the presence of a weak vertical field threading the disk that efficiently drives disk accretion. With a parameter survey, we find that wind-dominated accretion with laminar disk is likely to extend to about 5-10 AU, with wind-driven accretion rate given by M_dot~ 0.91e-8 R_AU^(1.21)(B_z/10mG)^(0.93) M_sun/yr. Beyond this radius, angular momentum transport is likely to proceed through a combination of wind and the MRI, and eventually completely dominated by the MRI in the outer disk. Our simulation results provide key ingredients for a new paradigm for the accretion processes in PPDs.
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