Issue |
A&A
Volume 468, Number 2, June III 2007
The XMM-Newton extended survey of the Taurus molecular cloud
|
|
---|---|---|
Page(s) | 529 - 540 | |
DOI | https://doi.org/10.1051/0004-6361:20066318 | |
Published online | 02 January 2007 |
X-rays from T Tauri: a test case for accreting T Tauri stars
1
Paul Scherrer Institut, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland e-mail: guedel@astro.phys.ethz.ch
2
CASA, 389, University of Colorado, Boulder, CO 80309-0389, USA
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, USA
Received:
29
August
2006
Accepted:
8
November
2006
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 (1010 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
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.
Key words: stars: coronae / stars: formation / stars: pre-main sequence / X-rays: stars / stars: individual: T Tauri
© ESO, 2007
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