The dust storm in RW Aurigae

The T Tauri star RW Aur A entered a very deep drop in brightness in 2013, and has since then remained at a level of about 3 magnitudes fainter in V than normal. We have carried out spectroscopic and photometric observations of the star with the aim to reveal the nature of this dimming.  The photospheric spectrum of RW Aur A and signatures of accretion have not changed indicating that the dimming is external and caused by a foreground obscuration by dust grains giving rise to a grey extinction. The forbidden [OI] and [SII] lines, formed in distant parts of the wind (jets), became strong relatively to the dimmed stellar spectrum meaning that only the star and its immediate surrounding were obscured, but not the distant wind.  NIR photometry in the JHKLM bands shows that when the star faded in V and JHK it became brighter in L and M. The K-L and L-M colours indicate excess radiation of a black-body at about 1000 K.  The most probable explanation is that the excess radiation in L and M comes from hot dust near the star, and that this dust is responsible for the dimming in the visual range. We propose that dust has been stirred up from the inner disk into the line-of-sight as the cause of this unusual phenomenon.