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SUMMARY:Formation of structures around HII regions: Ionization feedback fr
 om massive stars - Pascal Tremblin (CEA Saclay)
DTSTART:20120430T150000Z
DTEND:20120430T160000Z
UID:TALK37626@talks.cam.ac.uk
CONTACT:Jérôme Guilet
DESCRIPTION:We present a new model for the formation of dense clumps and p
 illars around HII regions based on shocks curvature at the interface betwe
 en a HII region and a molecular cloud.  UV radiation leads to the formatio
 n of an ionization front and of a shock ahead. The gas is compressed betwe
 en them forming a dense shell at the interface. This shell may be curved d
 ue to initial interface or density modulation caused by the turbulence of 
 the molecular cloud. Low curvature leads to instabilities in the shell tha
 t form dense clumps while sufficiently curved shells collapse on itself to
  form pillars. When turbulence is high compared to the ionized-gas pressur
 e\, bubbles of cold gas have sufficient kinetic energy to penetrate into t
 he HII region and detach themselves from the parent cloud\, forming cometa
 ry globules. \n\nUsing computational simulations\, we show that these new 
 models are extremely efficient to form dense clumps and stable and growing
  elongated structures\, pillars\, in which star formation might occur. The
  inclusion of turbulence in the model shows its importance in the formatio
 n of cometary globules. Globally\, the density enhancement in the simulati
 ons is of one or two orders of magnitude higher than the density enhanceme
 nt of the classical "collect and collapse" scenario. The code used for the
  simulation is the HERACLES code\,  that comprises hydrodynamics with vari
 ous equation of state\, radiative transfer\, gravity\, cooling and heating
 .\n\nOur recent observations with Herschel and SOFIA and additional Spitze
 r data archives revealed many more of these structures in regions where OB
  stars have already formed such as the Rosette Nebula\, Horsehead Nebula\,
  Cygnus X\, M16 and Vela\, suggesting that the UV radiation from massive s
 tars plays an important role in their formation. We present a first compar
 ison  between the simulations described above and recent observations of t
 hese regions based on the line-of-sight velocity profiles and probability 
 density functions. 
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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