X-rays from T Tauri: A test case for accreting T Tauri stars

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作者：
Güdel, M. [1 ]
Skinner, S.L. [2 ]
Mel'nikov, S.Yu. [3 ]
Audard, M. [4 ,5 ,6 ]
Teileschi, A. [1 ]
Briggs, K.R. [1 ]
机构：
[1] Paul Scherrer Institut, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland
[2] CASA, 389, University of Colorado, Boulder, CO 80309-0389, United States
[3] Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, Astronomicheskaya ul. 33, Tashkent 700052, Uzbekistan
[4] Columbia Astrophysics Laboratory, Mail Code 5247, 550 West 120th Street, New York, NY 10027, United States
[5] Integral Science Data Centre, Ch. d'Ecogia 16, 1290 Versoix, Switzerland
[6] Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
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Astronomy and Astrophysics | 1600年 / 468卷 / 02期
关键词：
Context. The generation of X-rays in accreting T Tauri stars (TTS) is thought to be predominantly due to energy dissipation in magnetic fields; but alternative X-ray generation mechanisms have been proposed; such as heating in accretion shocks near the stellar surface; or in shocks forming in jets. Aims. We test models and trends discussed in the literature using X-ray data from the classical TTS T Tau. Methods. High-resolution spectroscopy from the Reflection Grating Spectrometers on XMM-Newton is used to infer electron densities; element abundances and the thermal structure of the X-ray source. We also discuss the ultraviolet light curve obtained by the Optical Monitor; and complementary ground-based photometry. A high-resolution image from Chandra constrains contributions from the two companions of T Tau N. Results. The X-ray grating spectrum is rich in emission lines; but shows an unusual mixture of features from very hot (30 MK) and very cool (1-3 MK) plasma; both emitted by similar amounts of emission measure. The cool plasma confirms the picture of a soft excess in the form of an enhanced O VII/O VIII Lyα flux ratio; similar to that previously reported for other accreting TTS. Diagnostics from lines formed by this plasma indicate low electron densities (&le1010 cm -3). The Ne/Fe abundance ratio is consistent with a trend in pre-main sequence stars in which this ratio depends on spectral type; but not on accretion. Conclusions. On the basis of line density diagnostics; we conclude that the density of the cool soft-excess plasma is orders of magnitude below that predicted for an accretion shock; assuming previously determined accretion rates of (3-6) × 10-8 Mo yr-1. We argue that loading of magnetic field lines with infalling material suppresses the heating process in a part of the corona. We thus suggest that the X-ray production of T Tau is influenced by the accretion process although the X-rays may not form in the bulk of the accretion footpoints. © ESO 2007;
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页码：529 / 540
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