Computer Science – Sound
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21933713s&link_type=abstract
American Astronomical Society, AAS Meeting #219, #337.13
Computer Science
Sound
Scientific paper
For comparison with recent measurements of turbulent line broadening in protoplanetary disks, we present a series of local magnetohydrodynamic (MHD) simulations of the magnetorotational instability (MRI) in protoplanetary disks. We use these simulations to characterize the distribution of turbulent velocities in such disks, as a function of radius and height above the mid-plane. These simulations include ideal MHD calculations as well as calculations with an MRI-inactive dead zone created by a height-dependent Ohmic resistivity. In the ideal case, the disk mid-plane is characterized by a velocity distribution that peaks near 0.1 of the local sound speed, while supersonic velocities are reached at z > 3H (where H is the vertical pressure scale height). Velocities of 0.01 of the sound speed persist near the mid-plane in dead zones, but the MRI-active surface layers have velocities characteristic of the ideal MHD runs (including a supersonic component). The velocities in the surface layers are roughly consistent with recent sub-mm observations. We also compare our MHD results to hydrodynamic simulations in which large-scale forcing is used to initiate similar turbulent velocities. The qualitative trend of increasing velocity with height, seen in the MHD case, persists for forced turbulence and is likely a generic property of disk turbulence. These velocity distributions are highly isotropic, suggesting that the disk inclination angle plays a very minor role. Based on these results, very precise measurements of the turbulent velocity at different heights within the disk or spatially resolved observations that probe the inner disk and the dead zone region are needed to test whether the MRI is responsible for protoplanetary disk turbulence. We acknowledge support from both NASA and NSF in carrying out this work.
Armitage Philip J.
Beckwith Kris
Simon Jacob B.
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