http://arxiv.org/abs/1612.00883

The planet-forming region of protoplanetary disks is cold, dense, and therefore weakly ionized. For this reason, MHD turbulence is thought to be mostly absent, and another mechanism has to be found to explain gas accretion in these regions. It has been proposed that magnetized winds, launched from the ionized disk surface, could drive accretion in the presence of a large scale magnetic field. The efficiency and the impact of these surface winds on the disk structure is still highly uncertain. We present the first global simulations of a weakly ionized disk which exhibits large-scale magnetized winds. We also study the impact of self-organization, which was previously demonstrated only in non-stratified models. We perform numerical simulations of stratified disks with the PLUTO code. We compute the ionization fraction dynamically, and account for all three non-ideal magnetohydrodynamic (MHD) effects: Ohmic and ambipolar diffusions, and the Hall drift. Simplified heating and cooling due to non-thermal radiation is also taken into account in the disk atmosphere. We find that disks can be accreting or not, depending on the configuration of the large-scale magnetic field. Magneto-thermal winds, driven both by magnetic acceleration and heating of the atmosphere, are obtained in the accreting case. In some cases, these winds are asymmetric, ejecting predominantly on one side of the disk. The wind mass loss rate depends primarily on the average ratio of magnetic to thermal pressure in the disk midplane. The non-accreting case is characterized by a meridional circulation, with accretion layers at the disk surface and excretion in the midplane. Finally, we observe self-organization, resulting in axisymmetric rings of density and associated pressure “bumps”. The underlying mechanism and its impact on observable structures are discussed.

Read this paper on arXiv…

W. Bethune, G. Lesur and J. Ferreira
Tue, 6 Dec 16
49/71

Comments: 22 pages, 33 figures, submitted to A&A on 14/11/2016