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Title: TURBULENCE IN THE OUTER REGIONS OF PROTOPLANETARY DISKS. II. STRONG ACCRETION DRIVEN BY A VERTICAL MAGNETIC FIELD

We carry out a series of local, vertically stratified shearing box simulations of protoplanetary disks that include ambipolar diffusion and a net vertical magnetic field. The ambipolar diffusion profiles we employ correspond to 30 AU and 100 AU in a minimum mass solar nebula (MMSN) disk model, which consists of a far-ultraviolet-ionized surface layer and low-ionization disk interior. These simulations serve as a follow-up to Simon et al., in which we found that without a net vertical field, the turbulent stresses that result from the magnetorotational instability (MRI) are too weak to account for observed accretion rates. The simulations in this work show a very strong dependence of the accretion stresses on the strength of the background vertical field; as the field strength increases, the stress amplitude increases. For a net vertical field strength (quantified by β{sub 0}, the ratio of gas to magnetic pressure at the disk mid-plane) of β{sub 0} = 10{sup 4} and β{sub 0} = 10{sup 5}, we find accretion rates M-dot ∼10{sup -8}-10{sup –7} M{sub ☉} yr{sup –1}. These accretion rates agree with observational constraints, suggesting a vertical magnetic field strength of ∼60-200 μG and 10-30 μG at 30 AU and 100 AU, respectively, inmore » a MMSN disk. Furthermore, the stress has a non-negligible component due to a magnetic wind. For sufficiently strong vertical field strengths, MRI turbulence is quenched, and the flow becomes largely laminar, with accretion proceeding through large-scale correlations in the radial and toroidal field components as well as through the magnetic wind. In all simulations, the presence of a low-ionization region near the disk mid-plane, which we call the ambipolar damping zone, results in reduced stresses there.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309-0440 (United States)
  2. Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)
  3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
Publication Date:
OSTI Identifier:
22270960
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; AMBIPOLAR DIFFUSION; ASTROPHYSICS; COMPUTERIZED SIMULATION; CORRELATIONS; FAR ULTRAVIOLET RADIATION; LIMITING VALUES; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; NMR IMAGING; PROTOPLANETS; SOLAR NEBULA; STRESSES; TURBULENCE