The disappearing act: a dusty wind eclipsing RW Aur

RW Aur is a young binary star that experienced a deep dimming in 2010-2011 in component A and a second even deeper dimming from summer 2014 to summer 2016. We present new unresolved multiband photometry during the 2014-2016 eclipse, new emission line spectroscopy before and during the dimming, archive infrared photometry between 2014 and 2015, 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 RWAur dropped in brightness to R = 12.5 in 2016 March. 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 10 in 2014, coinciding with the dimming event, confirming previous reports. The blueshifted part of the Ha 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 disc around RW Aur A we arrive at the conclusion that the obscuring screen is part of a wind emanating from the inner disc.