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SUMMARY:New Ideas on Mechanisms of Angular Momentum Transport and Variabil
 ity in Boundary Layers of Accretion Disks  - Roman Rafikov (Princeton)
DTSTART:20130523T153000Z
DTEND:20130523T163000Z
UID:TALK42882@talks.cam.ac.uk
CONTACT:Jay Farihi
DESCRIPTION:Disk accretion onto a weakly magnetized central object\, e.g. 
 a white dwarf or a neutron star\, is inevitably accompanied by the formati
 on of a boundary layer near the surface\, in which matter slows down from 
 the highly supersonic orbital velocity of the disk to the rotational veloc
 ity of the star. Here I will describe a novel\, robust mechanism of the an
 gular momentum transport inside the astrophysical boundary layers. Using h
 igh resolution 2D and 3D hydrodynamical simulations in the equatorial plan
 e of a boundary layer we generically find that the supersonic shear in the
  boundary layer excites non-axisymmetric quasi-stationary acoustic modes t
 hat are trapped between the surface of the star and a Lindblad resonance i
 n the disk. These modes rotate in a prograde fashion\, are stable for hund
 reds of orbital periods\, and have a pattern speed that is less than and o
 f order the rotational velocity at the inner edge of the disk. Dissipation
  of acoustic modes in weak shocks provides a universal mechanism for angul
 ar momentum and mass transport even in purely hydrodynamic (i.e. non-magne
 tized) boundary layers. Periodicity of these trapped modes may be relevant
  for explaining the variability seen in accreting compact objects. 
LOCATION:Sackler Lecture Theatre\, IoA (tea at 4:00 pm)
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