Cool Stars 14 - Submitted Abstract # 19
This version created on 05 October 2006

Accretion shock emission modelled in TW Hydrae


Hans Moritz Guenther, Hamburger Sternwarte

Classical T Tauri stars (CTTS) are young, accreting pre-main sequence
objects.  Today it is believed that the accretion funnel follows
dipolar magnetic field lines and impacts at high stellar lattitude.  A
1-dim non-equilibrium stationary model of the post-shock accretion
zone is presented.  Fitting this to grating X-ray observations of CTTS
TW Hya with XMM-Newton and Chandra putting special emphasis on the
density and temperature sensitive He-like triplets of O VII and Ne IX
allows to accurately measure the infall velocity, which turns out to
match the free-fall velocity of 525 km/s, and the infall density.  The
total intensity directly translates into a mass accretion rate of
about 2e-10  solar masses/year, less then determined in the UV oder
optical range.  This may possibly be due to inhomogeneities in the
spot, because in X-rays we probe only the hottest part of the
post-shock zone.  Applying the model the total emission can be
decomposed into an accretion part, which explains the soft X-rays, and
a hot corona, fitted by 2 standard APEC components.  The already known
metal depletion is confirmed.  Applying the same model to the UV
emission as observed with FUSE correctly predicts the flux in the hot
O VI doublet at 1035 A, but totally fails to reproduce the observed
line shape.  This hints at a more complicated geometry than usually
assumed in the simple accretion funnel scenarios.

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