Dust dynamics in radially convective regions of protoplanetary disks

TL;DR

This study investigates how convective overstability-driven turbulence in protoplanetary disks influences dust concentration, revealing limitations on dust trapping efficiency due to feedback effects and background pressure gradients.

Contribution

We perform high-resolution spectral simulations to analyze dust dynamics in COS-active regions, highlighting the limited dust concentration achievable and the impact of dust feedback.

Findings

Dust densities increase by up to a factor of 10 due to zonal flows.

Dust feedback can suppress zonal flow formation even at low dust-to-gas ratios.

Dust concentration is limited to a dust-to-gas ratio of about 1 in COS-affected regions.

Abstract

Hydrodynamic instabilities likely operate in protoplanetary disks. One candidate, Convective Overstability (COS), can be triggered in regions with a negative radial entropy gradient. The ensuing turbulence and flow structures are expected to affect dust dynamics directly. We revisit the interaction between dust and the COS with high-resolution spectral simulations in the unstratified, axisymmetric Boussinesq shearing box framework. We find zonal flows, or pressure bumps, formed by the COS trap dust, as expected, but dust densities increase at most by a factor of $O(10)$ over its background value due to the zonal flows' unsteady nature. Furthermore, dust feedback can impede the formation of zonal flows, even at small dust-to-gas ratios $\epsilon \sim O(0.1)$. We interpret this phenomenon as a competition between the negative gas angular momentum flux associated with zonal flow formation and the positive dust angular momentum flux associated with its drift towards pressure maxima. Dust concentration significantly weakens when a large-scale radial pressure gradient induces a background dust drift. Ultimately, we find that dust concentration by COS-induced zonal flows is limited to $\epsilon \lesssim 1$. Whether this can be improved under more realistic geometries must be addressed with stratified and full 3D simulations at equivalent resolutions.