Long-Lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks

TL;DR

This study uses high-resolution hydrodynamic simulations to show that dust asymmetries at dead zone edges in protoplanetary disks can persist for millions of years, driven by continuous dust trapping and replenishment at vortex sites.

Contribution

It demonstrates that dust asymmetries caused by vortices at dead zone edges are long-lived and resilient, even with feedback effects, unlike planet-induced vortices.

Findings

Dust asymmetries can last for over 2.5 million years.

Vortices at dead zone edges are replenished, preventing full destruction.

Asymmetric features are accompanied by a distant dust ring.

Abstract

A number of transition disks exhibit significant azimuthal asymmetries in thermal dust emission. One possible origin for these asymmetries is dust trapping in vortices formed at the edges of dead zones. We carry out high-resolution, two-dimensional hydrodynamic simulations of this scenario, including the effects of dust feedback. We find that, although feedback weakens the vortices and slows down the process of dust accumulation, the dust distribution in the disk can nonetheless remain asymmetric for many thousands of orbits. We show that even after $10^4$ orbits, or $2.5$ Myr when scaled to the parameters of Oph IRS 48 (a significant fraction of its age), the dust is not dispersed into an axisymmetric ring, in contrast to the case of a vortex formed by a planet. This is because accumulation of mass at the dead zone edge constantly replenishes the vortex, preventing it from being fully destroyed. We produce synthetic dust emission images using our simulation results. We find that multiple small clumps of dust may be distributed azimuthally. These clumps, if not resolved from one another, appear as a single large feature. A defining characteristic of a disk with a dead zone edge is that an asymmetric feature is accompanied by a ring of dust located about twice as far from the central star.