Structure of Protoplanetary Discs with Magnetically-driven Winds

TL;DR

This paper develops analytical models for protoplanetary discs with magnetically-driven winds, showing how winds influence disc structure, dust settling, and can explain observations of HL Tau.

Contribution

It introduces a new analytical framework incorporating wind effects based on recent MHD simulation insights, improving understanding of disc structure and dust dynamics.

Findings

Wind mass-loss reduces surface density in inner discs.

Winds lead to thinner dust layers in the disc.

Model explains HL Tau's high accretion and dust settling observations.

Abstract

We present a new set of analytical solutions to model the steady state structure of a protoplanetary disc with a magnetically-driven wind. Our model implements a parametrization of the stresses involved and the wind launching mechanism in terms of the plasma parameter at the disc midplane, as suggested by the results of recent, local MHD simulations. When wind mass-loss is accounted for, we find that its rate significantly reduces the disc surface density, particularly in the inner disc region. We also find that models that include wind mass-loss lead to thinner dust layers. As an astrophysical application of our models, we address the case of HL Tau, whose disc exhibits a high accretion rate and efficient dust settling at its midplane. These two observational features are not easy to reconcile with conventional accretion disc theory, where the level of turbulence needed to explain the high accretion rate would prevent a thin dust layer. Our disc model that incorporates both mass-loss and angular momentum removal by a wind is able to account for HL Tau observational constraints concerning its high accretion rate and dust layer thinness.