WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. II. RADIAL DEPENDENCE AND GLOBAL PICTURE
- Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)
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. It was shown in our previous work that at 1 AU, the magnetorotational instability (MRI) is completely suppressed when both ohmic resistivity and ambipolar diffusion (AD) are taken into account, resulting in a laminar flow with accretion driven by magnetocentrifugal wind. In this work, we study the radial dependence of the laminar wind solution using local shearing-box simulations. The scaling relation on the angular momentum transport for the laminar wind is obtained, and we find that the wind-driven accretion rate can be approximated as M-dot approx. 0.91 x 10{sup -8}R{sub AU}{sup 1.21}(B{sub p}/10 mG){sup 0.93} M{sub Sun} yr{sup -1}, where B{sub p} is the strength of the large-scale poloidal magnetic field threading the disk. The result is independent of disk surface density. Four criteria are outlined for the existence of the laminar wind solution: (1) ohmic resistivity dominated the midplane region, (2) the AD-dominated disk upper layer, (3) the presence of a (not too weak) net vertical magnetic flux, and (4) sufficiently well-ionized gas beyond the disk surface. All these criteria are likely to be met in the inner region of the disk from {approx}0.3 AU to about 5-10 AU for typical PPD accretion rates. Beyond this radius, the angular momentum transport is likely to proceed due to a combination of the MRI and disk wind, and eventually completely dominated by the MRI (in the presence of strong AD) in the outer disk. Our simulation results provide key ingredients for a new paradigm on the accretion processes in PPDs.
- OSTI ID:
- 22121822
- Journal Information:
- Astrophysical Journal, Vol. 772, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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