Evolution of protoplanetary discs with magnetically driven disc winds

¹ School of Arts & Sciences, University of Tokyo, 3-8-1, Komaba, Meguro, 153-8902 Tokyo, Japan
e-mail: stakeru@ea.c.u-tokyo.ac.jp
² Department of Physics, Nagoya University, Nagoya, 464-8602 Aichi, Japan
³ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁴ Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, 181-8588 Tokyo, Japan
⁵ Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France

Received: 18 May 2016
Accepted: 1 September 2016

Abstract

Aims. We investigate the evolution of protoplanetary discs (PPDs) with magnetically driven disc winds and viscous heating.

Methods. We considered an initially massive disc with ~0.1 M_⊙ to track the evolution from the early stage of PPDs. We solved the time evolution of surface density and temperature by taking into account viscous heating and the loss of mass and angular momentum by the disc winds within the framework of a standard α model for accretion discs. Our model parameters, turbulent viscosity, disc wind mass-loss, and disc wind torque, which were adopted from local magnetohydrodynamical simulations and constrained by the global energetics of the gravitational accretion, largely depends on the physical condition of PPDs, particularly on the evolution of the vertical magnetic flux in weakly ionized PPDs.

Results. Although there are still uncertainties concerning the evolution of the vertical magnetic flux that remains, the surface densities show a large variety, depending on the combination of these three parameters, some of which are very different from the surface density expected from the standard accretion. When a PPD is in a wind-driven accretion state with the preserved vertical magnetic field, the radial dependence of the surface density can be positive in the inner region <1−10 au. The mass accretion rates are consistent with observations, even in the very low level of magnetohydrodynamical turbulence. Such a positive radial slope of the surface density strongly affects planet formation because it inhibits the inward drift or even causes the outward drift of pebble- to boulder-sized solid bodies, and it also slows down or even reversed the inward type-I migration of protoplanets.

Conclusions. The variety of our calculated PPDs should yield a wide variety of exoplanet systems.