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| Paper: |
Accretion Makes a Splash on TW Hydrae |
| Volume: |
448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun |
| Page: |
23 |
| Authors: |
Brickhouse, N. S. |
| Abstract: |
The Chandra Large Program on the Classical T Tauri star TW Hydrae (489 ksec, obtained over the course of
one month) brings a wealth of
spectral diagnostics to the study of X-ray emission from a young
star. The emission measure distribution shows two components separated
by a gap (i.e. no emission measure in between). Light curves for the
two components can then be constructed from the summed light curves of
the appropriate individual lines. The two light curves show
uncorrelated variability, with one large flare occurring only in the
hot component. We associate the hotter component with the corona,
since its peak temperature is ∼10 MK. Ne IX line ratio
diagnostics for temperature and density indicate that the source of
the cooler component is indeed the accretion shock, as originally
reported by Kastner et al. (2002). The temperature and density of the
accretion shock are in excellent agreement with models using mass
accretion rates derived from the optical. We require a third
component, which we call the “post-shock region,” from line ratio
diagnostics of O VII. The density derived from O VII is
lower than the density derived from Ne IX, contrary to standard
one-dimensional model expectations and from hydrodynamics simulations
to date. The column densities derived from the two ions are also
significantly different, with the column density from O VII
lower than that from Ne IX. This post-shock region cannot be
the settling flow expected from the cooling of the shock column, since
its mass is 30 times the mass of material that passes through the
shock. Instead this region is the splash of stellar atmosphere that
has been hit by the accretion stream and heated by the accretion
process (Brickhouse et al. 2010). |
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