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SUMMARY:The role of photoevaporation in disc dispersal - Clarke\, C (Cambr
 idge)
DTSTART:20090817T153000Z
DTEND:20090817T160000Z
UID:TALK19472@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:I first recapitulate former work explaining how the interplay 
 between viscous evolution and extreme ultraviolet (EUV) photoevaporation p
 roduces a characteristic pattern of disc clearing\, which invoves first ra
 pid viscous draining of the inner disc (within a few A.U.) followed by rap
 id photoevaporation of the outer disc. This behaviour sets in at late time
 s when the accretion rate through the disc is very low ($ im 10^{10} M_odo
 t$ yr$^{-1}$). \n\nI then describe recent work which demonstrates that\, c
 ontrary to previous estimates\, Xray photoevaporation is in fact likely to
  be a major disc dispersal agent. The sequence of disc clearing phases is 
 qualitatively similar to that described above but with two key differences
 : i) the photoevaporation rate is ten times higher and thus this clearing 
 sets in earlier\, when the disc accretion rate is $ im 10^{-9} M_odot$ yr$
 ^{-1}$ and ii) a combination of the greater penetrating power of Xrays and
  the somewhat lower temperatures attained by Xray heated gas compared with
  the EUV case means that the peak wind mass loss occurs at $ im 20 $ A.U..
  The size of the inner hole is thus $ im 4$ times larger than in EUV photo
 evaporative models. \n\nWe discuss the implications of this new result for
  models of disc clearing and the production of transition discs.
LOCATION:Seminar Room 1 Newton Institute
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