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

Abstract

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.

Violent environment of the inner disk of RW Aurigae A probed by the 2010 and 2015 dimming events

“…Using hydrodynamical modelling, Dai et al (2015) have shown that a tidal bridge between the two stars can obscure RW Aur A and that the column density might be sufficient to explain the dimming (as initially proposed by Rodriguez et al 2013). Petrov et al (2015) have suggested that the extinction could be due to an outburst of a stellar wind entrapping dust grains of the inner region of the disk. Finally, Schneider et al (2015b) have proposed that the observations could be explained by geometric variations in the inner disk, similarly to the AA Tau system (e.g.…”

“…RW Aur A has recently undergone two major dimming events (Rodriguez et al 2013;Petrov et al 2015). The first one lasted for ∼180 days, with a dimming of 1.5−2 mag in the V band (Rodriguez et al 2013).…”

Star–Disk Interactions in Multiband Photometric Monitoring of the Classical T Tauri Star GI Tau

“…However, the occultation timescales of the dips (e.g., 5 days) are relatively long compared with the crossing timescale of an inner disk warp at the co-rotation radius. Alternative explanations, such as the dust being located in disk winds at larger radii, rather than in the disk itself, could explain the long survival time of the dust (Bans & Königl 2012;Petrov et al 2015Petrov et al , 2017.…”

“…The disk interpretation is challenged in one case (J1604-2130) by the measurement of a face-on inclination of an outer disk (Ansdell et al 2016a). In a second case (RW Aur), the occultation source is uncertain and may be a dusty wind (Petrov et al 2015;Schneider et al 2015b), a tidal encounter of the secondary star (Dai et al 2015), the combination of occultation and time-variable accretion (Takami et al 2016), or partial occultation of the inner disk (Facchini et al 2016).…”

The Mysterious Dimmings of the T Tauri Star V1334 Tau

“…It is possible that the occulting body may be a warp or perturbation in the surrounding disk, but this would require a close to edge-on geometry. It is possible that we are seeing a fluctuation in the inner disk structure or that winds have pushed material from the disk plane across our lineof-sight (Natta & Whitney 2000;Nelson et al 2000;Petrov et al 2015). However, we find no evidence for high disk winds in our TRES spectra.…”