The dimming of RW Auriga. Is dust accretion preceding an outburst?

TL;DR

This paper models how reactivation of a dead zone in a protoplanetary disk can rapidly send large amounts of dust towards the star, potentially causing the observed dimming events in RW Aur A before an outburst.

Contribution

It introduces a new mechanism involving dead zone reactivation that explains rapid dust accretion and dimming events in young stellar objects.

Findings

Dust is rapidly accreted towards the star within ~15 years.

Dust-to-gas ratios can reach approximately 5 during these events.

Dust accretion precedes increased gas accretion by a few years.

Abstract

RW Aur A has experienced various dimming events in the last years, decreasing its brightness by $\sim 2\ \textrm{mag}$ for periods of months to years. Multiple observations indicate that a high concentration of dust grains, from the protoplanetary disk's inner regions, is blocking the starlight during these events. We propose a new mechanism that can send large amounts of dust close to the star on short timescales, through the reactivation of a dead zone in the protoplanetary disk. Using numerical simulations we model the accretion of gas and dust, along with the growth and fragmentation of particles in this scenario. We find that after the reactivation of the dead zone, the accumulated dust is rapidly accreted towards the star in around 15 years, at rates of $\dot{M}_\textrm{d} = 6 \times 10^{-6}\, \textrm{M}_\odot/\textrm{yr}$ and reaching dust-to-gas ratios of $\epsilon \approx 5$, preceding an increase in the gas accretion by a few years. This sudden rise of dust accretion can provide the material required for the dimmings, although the question of how to put the dust into the line of sight remains open to speculation.