Evidence for variable, correlated X-ray and optical/IR extinction towards the nearby, pre-main-sequence binary TWA 30

We present contemporaneous XMM-Newton X-ray and ground-based optical/near-IR spectroscopic observations of the nearby (D ≈ 42 pc), low-mass (mid-M) binary system TWA 30A and 30B. The components of this wide (separation ∼3400 au) binary are notable for their nearly edge-on disc viewing geometries, high levels of variability, and evidence for collimated stellar outflows. We obtained XMM-Newton X-ray observations of TWA 30A and 30B in 2011 June and July, accompanied (respectively) by Infrared Telescope Facility SpeX (near-IR) and VLT XSHOOTER (visible/near-IR) spectroscopy obtained within ∼20 h of the X-ray observations. TWA 30A was detected in both XMM-Newton observations at relatively faint intrinsic X-ray luminosities (L_X ∼ 8 × 10²⁷ erg s^-1) compared to stars of similar mass and age. The intrinsic (0.15-2.0 keV) X-ray luminosities measured in 2011 had decreased by a factor 20-100 relative to a 1990 (ROSAT) X-ray detection. TWA 30B was not detected, and we infer an upper limit on its X-ray Luminosity of L_X ≲ 3.0 × 10²⁷ erg s^-1. We measured a decrease in visual extinction towards TWA 30A (from A_V ≈ 14.9 to A_V ≈ 4.7) between the two 2011 observing epochs, and we find evidence for a corresponding significant decrease in X-ray absorbing column (N_H). The apparent correlated change in A_V and N_H is suggestive of variable obscuration of the stellar photosphere by disc material composed of both gas and dust. However, in both observations, the inferred N_H to A_V ratio is lower than that typical of the interstellar medium, suggesting that the disc is either depleted of gas or is deficient in metals in the gas phase.