Cool Stars 14 - Submitted Abstract # 228
This version created on 05 October 2006

Magnetic Properties of TW Hya Association


Hao Yang, Rice University
Christopher M. Johns-Krull, Rice University
Jeff A. Valenti, Space Telescope Science Institute

We report our magnetic field measurements of six TW Hya Association
(TWA) stars:  TWA 4, TWA 5A, TWA 7, TWA 8A, TWA 9A and TWA 9B.  These
measurements are an ongoing effort to measure magnetic fields of T
Tauri stars in clusters and associations of different ages, in order
to study the temporal evolution of magnetic properties on T Tauri
stars.  Here we analyze infrared (IR) echelle spectra of the six stars
and look for Zeeman broadening in four magnetically sensitive Ti I
lines near 2.2 microns.  The magnetic field strenths are obtained by
fitting the Zeeman broadening using NextGen model atmospheres.  We
also calculate the profiles of several nearby magnetically insensitive
CO lines from the models and compare with observation to ensure that
all other broadening mechanisms besides Zeeman broadening are properly
taken into account.

----------------------------------