New Insights: the Accretion Process and Variable Wind from TW Hya. (arXiv:1303.1536v1 [astro-ph.SR]):
For the first time in a classical T Tauri star, we are able to trace an
accretion event signaled by an hour-long enhancement of X-rays from the
accretion shock and revealed through substantial sequential changes in optical
emission line profiles. Downflowing turbulent material appears in H-alpha and
H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in
flux. Two hours after the X-ray accretion event, the optical veiling increases
due to continuum emission from the hot splashdown region. The response of the
stellar coronal emission to the heated photosphere follows about 2.4 hours
later, giving direct evidence that the stellar corona is heated in part by
accretion. Then, the stellar wind becomes re-established. A model that
incorporates the dynamics of this sequential series of events includes: an
accretion shock, a cooling downflow in a supersonically turbulent region,
followed by photospheric and later, coronal heating. This model naturally
explains the presence of broad optical and ultraviolet lines, and affects the
mass accretion rates currently determined from emission line profiles. These
results, coupled with the large heated coronal region revealed from X-ray
diagnostics, suggest that current models are not adequate to explain the
accretion process in young stars.
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