EVOLUTION OF MAGNETIZED PROTOPLANETARY DISKS

We investigate the global evolution of a turbulent protoplanetary disk in its viscous stage, incorporating the effects of Maxwell stress due to a large-scale magnetic held permeating the disk. We assume that th e viscous stress is given by an alpha model. A magnetic field is produ ced contemporaneously by an alpha Omega dynamo mechanism and the resul tant Maxwell stress assists the viscous stress in providing the means for disk evolution. The aim of this work is to compare the evolution o f magnetized and nonmagnetized disks driven by turbulent viscosity of the same magnitude and thus assess the effects of a self-generated mag netic field on the structure and dynamical evolution of protoplanetary disks. Two illustrative examples corresponding to two different initi al conditions are considered: a high-mass case that starts with a disk of 0.245 M. and angular momentum of 5.6 x 10(52) g cm(2) s(-1), and a low-mass case that starts with a disk of 0.11 M. and angular momentum of 1.8 x 10(52) g cm(2) s(-1). For each of these two cases the radial development of a disk is calculated numerically assuming a fiducial v alue of the dimensionless viscosity parameter alpha(ss) = 0.01, as wel l as alpha(ss) = 2 x 10(-3). In all cases the central star has a mass equal to 1 M. The most striking feature of magnetized disk evolution i s the presence of the surface density bulge located in the region of t he disk where the dynamo mechanism cannot support a magnetic field. Th e bulge persists for a time of the order of 10(5)-10(6) yr. The presen ce and persistence of the surface density bulge may have important imp lications for the process of planet formation and the overall characte ristics of resultant planetary systems.