Radially Magnetized Protoplanetary Disk: Vertical Profile

Abstract

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, is wound up by the disk shear, and is pushed downward by a combination of turbulent mixing and ambipolar and Ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field $B_r\sim (10^{-4}$-$10^{-2})(r/\mathrm{AU}{)}^{-2}$ G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner $\sim 1$ AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around $10^{-8}{M}_{\odot }$ yr${}^{-1}$ are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk, and the implications for planet migration, are investigated in the accompanying paper.

25 pp, 20 figures, Astrophysical Journal, in press

References in corpus (8)

• Global simulations of protoplanetary disks with ohmic resistivity and ambipolar diffusion
• Heat and Dust in Active Layers of Protostellar Disks
• Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
• Accretion Discs with Strong Toroidal Magnetic Fields
• On the Linear Stability of Weakly-Ionized, Magnetized Planar Shear Flows
• Advances in exoplanet science from Kepler
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Cited by in corpus (5)

• Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced?
• Secular transport during disk dispersal: the case of Kepler-419
• Rossby Wave Instability and Long-Term Evolution of Dead Zones in Protoplanetary Discs
• Close-in giant-planet formation via in-situ gas accretion and their natal disk properties
• Constrained Evolution of a Radially Magnetized Protoplanetary Disk: Implications for Planetary Migration