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SUMMARY:Cosmic Ray Propagation in Molecular Clouds - Kedron Silsbee (Max-P
 lanck-Institut für extraterrestrische Physik)
DTSTART:20181126T140000Z
DTEND:20181126T150000Z
UID:TALK115489@talks.cam.ac.uk
CONTACT:Cleo Loi
DESCRIPTION:I will give a brief overview of the acceleration and propagati
 on of cosmic rays in our Galaxy\, and their effects on molecular clouds. I
  will then focus on the interaction of low energy cosmic rays with molecul
 ar clouds.  Cosmic rays are the dominant source of ionisation in dense mol
 ecular clouds.  Understanding the cosmic ray ionisation rate is therefore 
 a necessary input to simulations of the gas dynamics (as the strength of n
 on-ideal MHD effects depends on the ionisation)\, and to interpreting obse
 rvations of molecules in these clouds.  Unfortunately there is uncertainty
  on the factor of 10 level in the cosmic ray ionisation rate in these regi
 ons.  This arises from both uncertainty in the abundance of the sub-relati
 vistic cosmic rays responsible for the majority of the ionisation\, as wel
 l as uncertainty in the propagation. I will then discuss two areas I have 
 been working on.  First\, is the role of magnetic mirroring and focussing 
 in the propagation of cosmic rays in molecular clouds.  I will show that t
 hese typically almost exactly cancel out\, but if there are regions of low
  magnetic field surrounded by higher field\, then the ionisation rate can 
 be significantly reduced.  Finally\, there is increasing observational evi
 dence to suggest that the decrease in the ionisation rate with increasing 
 column density is steeper than would be expected given our current underst
 anding.  I will discuss a couple of ideas to explain this apparent steeper
 -than-expected attenuation of cosmic rays. 
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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