Mon. Not. R. Astron. Soc., 459, 2097-2105 (2016/June-3)
Evidence for variable, correlated X-ray and optical/IR extinction towards the nearby, pre-main-sequence binary TWA 30.
PRINCIPE D.A., SACCO G., KASTNER J.H., STELZER B. and ALCALA J.M.
Abstract (from CDS):
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 (LX ∼ 8 x 1027 erg/s) 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 LX <= 3.0 x 1027 erg/s. We measured a decrease in visual extinction towards TWA 30A (from AV ≃ 14.9 to AV ≃ 4.7) between the two 2011 observing epochs, and we find evidence for a corresponding significant decrease in X-ray absorbing column (NH). The apparent correlated change in AV and NH is suggestive of variable obscuration of the stellar photosphere by disc material composed of both gas and dust. However, in both observations, the inferred NH to AV 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.
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
magnetic fields - protoplanetary discs - circumstellar matter - stars: low-mass - stars: pre-main-sequence - stars: variables: T Tauri, Herbig Ae/Be - stars: variables: T Tauri, Herbig Ae/Be
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