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SUMMARY:How to brake down a contracting protostar ? - Prof. Jonathan Ferre
 ira (University of Grenoble)
DTSTART:20141021T120000Z
DTEND:20141021T130000Z
UID:TALK52332@talks.cam.ac.uk
CONTACT:Dr. Jaroslav Dudik
DESCRIPTION:Classical T Tauri stars are the prototypes of contracting sola
 r-mass proto-stars that are accreting material from their surrounding circ
 umstellar disc. As a consequence of both accretion and contraction\, they 
 should undergo a spin-up during their accreting phase. But this is not wha
 t observations tell us. Instead\, they seem to retain a rather constant an
 gular speed as long as the disc remains present. This observational eviden
 ce has lead to the so called « disk-locking paradigm » and to one of the
  most challenging issues of star formation theory.   \n   \nIt will be arg
 ued that the star-disc interaction cannot\, per se\, lead to the required 
 braking torque. Instead\, the angular momentum excess of the star-inner di
 sc system must be expelled away\, the most natural way being probably in t
 he form of outflows. Such a situation has been considered extensively in t
 he past\, in particular within the X-wind model (Shu et al 1994). But\, af
 ter a critical exam of the necessary conditions prevailing in the X-wind l
 aunching zone\, we will be lead to the conclusion that such a configuratio
 n may never be reached. An alternative process should then be searched for
 . It seems that one possibility of efficiently braking down protostars cou
 ld lie in time dependent accretion-ejection events\, as evidenced in some 
 MHD numerical experiments.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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