Moritz Guenther (Harvard-Smithsonian Center for Astrophysics)

Accretion, winds and jets
When Jan 11, 2013 from 10:30 AM to 12:00 PM
What
  • Colloquium
Where SH, Lecture hall
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Young stars and planetary systems form in molecular clouds. After the initial radial infall an accretion disk develops. The circumstellar envelope depletes and thus the absorption of the central star decreases. The high energy emission of these objects, the so-called classical T Tauri stars (CTTS) differs markedly from their main-sequence counterparts.

I will describe three different emission mechanisms that contribute to the observed X-ray and UV emission:

  1. A corona not unlike that observed on main-sequence stars.
  2. The accretion spot: The accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius by the stellar magnetic field. The inner edge of the disk is ionized by the stellar radiation, so that the accretion has to be funneled along the magnetic field lines. On the stellar surface an accretion shock develops, which is observable in a wide wavelength range including X-rays and UV excess.
  3. Furthermore, many (if not all) accreting systems also drive strong outflows which are ultimately powered by accretion. However, the exact driving mechanism is still unclear. Several components could contribute to the outflows: Slow, wide-angle disk winds, X-winds launched close to the inner disk rim, and thermally driven stellar winds. In any case, the outflows contain material of very different temperatures and speeds.


Accretion and outflows in the CTTS phase do not only determine stellar parameters like the rotation rate on the main-sequence, they also could have a profound impact on the environment of young stars.