A question of personalities: evolution of viscous and wind-driven protoplanetary discs in the presence of dead zones

Abstract

ABSTRACT Whether the angular momentum of protoplanetary discs is redistributed by viscosity or extracted by magnetized winds is a long-standing question. Demographic indicators, such as gas disc sizes and stellar accretion rates, have been proposed as ways of distinguishing between these two mechanisms. In this paper, we implement one-dimensional gas simulations to study the evolution of ‘hybrid’ protoplanetary discs simultaneously driven by viscosity and magnetized winds, with dead zones present. We explore how the variations of disc properties, including initial disc sizes, dead zone sizes, and angular momentum transport efficiency, affect stellar accretion rates, disc surface density profiles, disc sizes, disc lifetimes, and cumulative mass-loss by different processes. Our models show that the expansion of the gas disc size can be sustained when the majority of angular momentum is removed by the magnetized wind for individual protoplanetary discs. However, when we can only observe discs via demographic screenshots, the variation of disc sizes with time is possibly diminished by the disc ‘personalities’, by which we mean the variations of initial disc properties among different discs. Our ‘hybrid’ models re-assess association of the two demographic indicators with mechanisms responsible for angular momentum transport and suggest that additional diagnostics are required to assist the differentiation.