The Inner Rim Structures of Protoplanetary Discs

TL;DR

This paper investigates the structure of the inner rims of protoplanetary discs, revealing they are diffuse regions influenced by dust properties, with a new analytical model for rim location based on detailed sublimation physics.

Contribution

It introduces a detailed sublimation physics implementation in radiative transfer modeling and provides an analytical expression for the inner rim location based on dust and stellar properties.

Findings

Inner rims are diffuse, not sharp walls.

High surface densities and large grains reduce rim radius.

An analytical formula for rim location is derived.

Abstract

The inner boundary of protoplanetary discs is structured by the dramatic opacity changes at the transition from the dust-containing to a dust-free zone. This paper explores the variety and limits of inner rim structures in passively heated dusty discs. For this study, we implemented detailed sublimation physics in a fast Monte Carlo radiative transfer code. We show that the inner rim in dusty discs is not an infinitely sharp wall but a diffuse region which may be narrow or wide. Furthermore, high surface densities and large silicate grains as well as iron and corundum grains decrease the rim radius, from a 2.2AU radius for small silicates around a 47 Solar luminosity Herbig Ae star typically to 0.4AU and as close as 0.2AU. A passive disc with grain growth and a diverse dust composition must thus have a small inner rim radius. Finally, an analytical expression is presented for the rim location as a function of dust, disc and stellar properties.