The Dimming of RW Auriga: Is Dust Accretion Preceding an Outburst?

Abstract

RW Aur A has experienced various dimming events in recent years, decreasing its brightness by ∼2 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 toward the star in around 15 yr, at rates of and reaching dust-to-gas ratios of ϵ  ≈ 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.