Another deep dimming of the classical T Tauri star RW Aurigae A

Petrov, P. P.; Gahm, G. F.; Djupvik, A. A.; Babina, E. V.; Artemenko, S. A.; Grankin, K. N.
Astronomy & Astrophysics, Volume 577, id.A73, 4 pp. (2015).


Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ~3 mag in the V band and went into a long-lasting minimum. In 2010 the star underwent a similar fading, although less pronounced. These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds. 
Aims: We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention of gathering more information on the occulting body and the cause of the phenomenon. 
Methods: We collected spectra of the two components of RW Aur. The photometry was performed before and during the minimum. 
Results: The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading. However, blue-shifted absorption components related to the stellar wind increased in strength in certain resonance lines, and the profiles and strengths but not the fluxes of forbidden lines became drastically different. 
Conclusions: The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind or jet further out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk into the line of sight through the interaction with an enhanced wind.

Based on observations collected at the Nordic Optical Telescope, La Palma, Spain; Fast-Track Service program 50-409.