Protoplanetary disc `isochrones' and the evolution of discs in the $\dot{M}-M_{\rm d}$ plane

TL;DR

This study compares viscous diffusion models of protoplanetary disc evolution with observational data, introducing disc isochrones to better understand accretion and disc mass relationships in young star-forming regions.

Contribution

It introduces the concept of disc isochrones in the accretion rate-disc mass plane and demonstrates their effectiveness in modeling observed disc properties.

Findings

Viscous models match Lupus data when evolutionary timescales are comparable to cluster age.

The models predict a sub-linear correlation between accretion rate and disc mass.

Angular momentum transport efficiency likely increases with radius.

Abstract

In this paper, we compare simple viscous diffusion models for the disc evolution with the results of recent surveys of the properties of young protoplanetary discs. We introduce the useful concept of `disc isochrones' in the accretion rate - disc mass plane and explore a set of Montecarlo realization of disc initial conditions. We find that such simple viscous models can provide a remarkable agreement with the available data in the Lupus star forming region, with the key requirement that the average viscous evolutionary timescale of the discs is comparable to the cluster age. Our models produce naturally a correlation between mass accretion rate and disc mass that is shallower than linear, contrary to previous results and in agreement with observations. We also predict that a linear correlation, with a tighter scatter, should be found for more evolved disc populations. Finally, we find that such viscous models can reproduce the observations in the Lupus region only in the assumption that the efficiency of angular momentum transport is a growing function of radius, thus putting interesting constraints on the nature of the microscopic processes that lead to disc accretion.