The nature of the 2014-2015 dim state of RW Aur revealed by X-ray, optical, and NIR observations

Abstract

The binary system RW Aur consists of two classical T~Tauri stars (CTTSs). The primary recently underwent its second observed major dimming event ($\Delta V\sim 2$mag). We present new, resolved Chandra X-ray and UKIRT near-IR (NIR) data as well as unresolved optical photometry obtained in the dim state to study the gas and dust content of the absorber causing the dimming. The X-ray data show that the absorbing column density increased from $N_H<0.1\times 10^{22}$cm${}^{-2}$ during the bright state to $\approx 2\times 10^{22}$cm${}^{-2}$ in the dim state. The brightness ratio between dim and bright state at optical to NIR wavelengths shows only a moderate wavelength dependence and the NIR color-color diagram suggests no substantial reddening. Taken together, this indicates gray absorption by large grains ($\gtrsim 1\mu$m) with a dust mass column density of $\gtrsim 2\times 10^{-4}$gcm${}^{-2}$. Comparison with $N_H$ shows that an absorber responsible for the optical/NIR dimming and the X-ray absorption is compatible with the ISM's gas-to-dust ratio, i.e., that grains grow in the disk surface layers without largely altering the gas-to-dust ratio. Lastly, we discuss a scenario in which a common mechanism can explain the long-lasting dimming in RW Aur and recently in AA Tau.

5 pages, 4 figures, accepted by A&A letters

References in corpus (5)

• Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
• A tidal encounter caught in the act: modelling a star-disc fly-by in the young RW Aurigae system
• Another deep dimming of the classical T Tauri star RW Aur A
• Observation of enhanced X-ray emission from the CTTS AA Tau during a transit of an accretion funnel
• X-ray to NIR emission from AA Tauri during the dim state - Occultation of the inner disk and gas-to-dust ratio of the absorber

Cited by in corpus (17)

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• Analysis of colour and polarimetric variability of RW Aur A in 2010-2018
• The disappearing act: A dusty wind eclipsing RW Aur
• The 1600 Angstrom Emission Bump in Protoplanetary Disks: A Spectral Signature of H${}_2$O Dissociation
• Recurring Occultations of RW Aurigae by Coagulated Dust in the Tidally Disrupted Circumstellar Disk
• Star-disk interactions in multi-band photometric monitoring of the classical T Tauri star GI Tau
• Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy
• Multi-epoch monitoring of the AA Tau like star V354 Mon - Indications for a low gas-to-dust ratio in the inner disk warp
• Stable and Unstable Regimes of Mass Accretion onto RW Aur A
• Optical dimming of RW Aur associated with an iron rich corona and exceptionally high absorbing column density
• Time-Variable Jet Ejections from RW Aur A, RY Tau and DG Tau
• The dimming of RW Auriga. Is dust accretion preceding an outburst?
• The jet of the young star RW Aur A and related problems
• Inhomogeneous dust eclipses in young stars. The case of CQ Tauri
• RW Aur B: a modest UX Ori type companion of the famous primary
• RW Aur A : SpeX Spectral Evidence for Differentiated Planetesimal Formation, Migration and Destruction in an 3 Myr Old Excited CTTS System