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

TL;DR

This study uses one-dimensional simulations to analyze how viscosity and magnetised winds influence protoplanetary disc evolution, highlighting the impact of initial conditions and dead zones on observable properties and the need for multiple diagnostics.

Contribution

It introduces hybrid models that combine viscosity and wind-driven mechanisms, providing new insights into disc evolution and the interpretation of demographic indicators.

Findings

Disc size expansion is sustained mainly by magnetised winds.

Variation in disc properties affects observable features and their evolution.

Additional diagnostics are needed to distinguish angular momentum transport mechanisms.

Abstract

Whether the angular momentum of protoplanetary discs is redistributed by viscosity or extracted by magnetised 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 magnetised 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 magnetised 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 additional diagnostics are required to assist the differentiation.