The disappearing act: A dusty wind eclipsing RW Aur

TL;DR

This study investigates the deep and variable dimming events of the young binary star RW Aur, revealing that the obscuring material is likely part of a wind from the inner disk, with implications for accretion and disk dynamics.

Contribution

The paper provides new multi-band photometry and spectroscopy data during the 2014-16 eclipse, offering insights into the nature of the obscuring wind and accretion processes in RW Aur.

Findings

RW Aur dimmed to R=12.5 in March 2016.

Short-term variability suggests unstable accretion flow.

Obscuring screen is part of a wind from the inner disk.

Abstract

RW Aur is a young binary star that experienced a deep dimming in 2010-11 in component A and a second even deeper dimming from summer 2014 to summer 2016. We present new unresolved multi-band photometry during the 2014-16 eclipse, new emission line spectroscopy before and during the dimming, archive infrared photometry between 2014-15, as well as an overview of literature data. Spectral observations were carried out with the Fibre-fed RObotic Dual-beam Optical Spectrograph on the Liverpool Telescope. Photometric monitoring was done with the Las Cumbres Observatory Global Telescope Network and James Gregory Telescope. Our photometry shows that RW Aur dropped in brightness to R = 12.5 in March 2016. In addition to the long-term dimming trend, RW Aur is variable on time scales as short as hours. The short-term variation is most likely due to an unstable accretion flow. This, combined with the presence of accretion-related emission lines in the spectra suggest that accretion flows in the binary system are at least partially visible during the eclipse. The equivalent width of [O I] increases by a factor of ten in 2014, coinciding with the dimming event, confirming previous reports. The blue-shifted part of the $H\alpha$ profile is suppressed during the eclipse. In combination with the increase in mid-infrared brightness during the eclipse reported in the literature and seen in WISE archival data, and constraints on the geometry of the disk around RW Aur A we arrive at the conclusion that the obscuring screen is part of a wind emanating from the inner disk.