Physics – Atomic Physics
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ap%26ss.336...75b&link_type=abstract
Astrophysics and Space Science, Volume 336, Issue 1, pp.75-79
Physics
Atomic Physics
Accretion, Atomic Physics, Magnetic Fields, Stars: Individual (Tw Hydrae), Techniques: Spectroscopic, X-Rays: Stars
Scientific paper
Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares. In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S observation of the classical T Tauri star TW Hydrae has provided a wealth of spectroscopic diagnostics not available in lower signal-to-noise ratio observations. Using line ratios for electron temperature, electron density, and column density we have found that the shock produced by the accelerating material in the accretion stream behaves as predicted by standard theory. However, the properties of the post-shock plasma differ substantially from the predictions of standard 1D shock models (Brickhouse et al. in Astrophys. J. 710:1835, 2010). The accretion process apparently heats the stellar atmosphere up to soft X-ray emitting temperatures, providing hot ions to populate the magnetic corona, in loops, stellar wind, and/or jets. This gas is highly turbulent, as evidenced by non-thermal line broadening. The observed properties of the accretion-fed corona should constrain theoretical models of an accretion-driven dynamo.
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