EDP Sciences
Free access
Issue A&A
Volume 474, Number 2, November I 2007
Page(s) L25 - L28
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20078143

A&A 474, L25-L28 (2007)
DOI: 10.1051/0004-6361:20078143


The X-ray soft excess in classical T Tauri stars

M. Güdel1, 2 and A. Telleschi1

1  Paul Scherrer Institut, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland
    e-mail: [guedel;atellesc]@astro.phys.ethz.ch
2  Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

(Received 22 June 2007 / Accepted 6 September 2007)

Aims.We study an anomaly in the X-ray flux (or luminosity) ratio between the O VII $\lambda\lambda$21.6-22.1 triplet and the O VIII Ly$\alpha$ line seen in classical T Tauri stars (CTTS). This ratio is unusually high when compared with ratios for main-sequence and non-accreting T Tauri stars (Telleschi et al. 2007c, A&A, 468, 443). We compare these samples to identify the source of the excess. A sample of recently discovered X-ray stars with a soft component attributed to jet emission is also considered.
Methods.We discuss data obtained from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) project, complemented by data from the published literature. We also present data from the CTTS RU Lup.
Results.All CTTS in the sample show an anomalous O VII/O VIII flux ratio when compared with WTTS or MS stars. The anomaly is due to an excess of cool, O VII emitting material rather than a deficiency of hotter plasma. The excess plasma must therefore have temperatures of $\la$2 MK. This soft excess does not correlate with UV excesses of CTTS, but seems to be related to the stellar X-ray luminosity. The spectra of the jet-driving TTS do not fit into this context.
Conclusions.The soft excess depends both on the presence of accretion streams in CTTS and on magnetic activity. The gas may be shock-heated near the surface, although it may also be heated in the magnetospheric accretion funnels. The soft component of the jet-driving sources is unlikely to be due to the same process.

Key words: stars: coronae -- stars: formation -- stars: pre-main sequence -- X-rays: stars

© ESO 2007

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)