[PPS04-P07] Testing magnetic accretion models against ALMA observations of the HL Tau disk
Keywords:ALMA, protoplanetary disks, HL Tau
Here we show that additional gas accretion powered by magnetic disk winds could resolve this paradox. Recent magnetohydrodynamic (MHD) simulations show that the magnetic diffusivity arising from weak ionization suppresses MHD turbulence. Yet accretion takes place as winds launched from the disk surface accelerate via magnetic forces, extracting orbital angular momentum (e.g., Bai & Stone 2013; Simon et al. 2013; Zhu et al. 2015). Based on the results of the recent MHD simulations, we construct a simple, one-dimensional magnetic accretion model where we incorporate the angular momentum transport due to both MHD turbulence and winds as well as the turbulent diffusion of dust particles along the disk's vertical direction. We find that our model simultaneously reproduces three important observational features of the HL Tau disk---the high accretion rate onto the central star, the absence of evidence for gravitational instability, and the geometrically thin subdisk of millimeter-sized dust particles---when the strength of the magnetic field driving the disk wind falls within a certain range. Direct observations of gas outflow from the disk surface and/or surface gas inflow toward the central star will provide further constraints on the mechanism of protoplanetary disk accretion.