Publication Date:
2016-05-01
Description:
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 x 10 27 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 x 10 27 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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