Cool Stars 14 - Submitted Abstract # 219
This version created on 05 October 2006

The Structured Chromosphere and Wind of TW Hya


Andrea K. Dupree, CfA
Nancy S. Brickhouse, CfA
Eugene H. Avrett, CfA
Steven R. Cranmer, CfA
Tamas Szalai, University of Szeged

The nearby accreting T Tauri star, TW Hya is viewed almost pole-on so
it provides an opportunity to examine its accretion and wind
characteristics.  A continuous set of echelle spectra of TW Hya, taken
with MIKE on Magellan2 in April 2006 reveals systematic variations in
the flux, velocity, and the profile of the H-alpha emission line.
These variations appear to be consistent with the photometric period
of 2.8 days.  Absorption features reoccur at high velocity (100  and
200  km/s) in the wind.  Additional spectra from 2004 show a similar
repetitive pattern.  This behavior suggests that:  (a) accretion is
not uniformly distributed over the stellar hemisphere in view;  (b)
stable structures are present in the chromosphere, most likely due to
the stellar magnetic field configuration.  Semi-empirical models of
the atmosphere have been constructed to compute line profiles using
the PANDORA code and define the wind structure.  These calculations
suggest the mass loss rate is variable and comparable to the mass
accretion rates in the literature, requiring a very efficient
mechanism if the wind is powered only by accretion.

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