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SUMMARY:Magnetic fields and the red giant dipole dichotomy problem - Cleo 
 Loi (DAMTP)
DTSTART:20180123T130000Z
DTEND:20180123T140000Z
UID:TALK98641@talks.cam.ac.uk
CONTACT:Dr William Béthune
DESCRIPTION:Stars are self-gravitating fluids in which many types of waves
  can propagate. Constructive interference of these waves produces global m
 odes of oscillation\, the associated brightness fluctuations of which can 
 be detected and Fourier analysed to yield information about the stellar pr
 operties. Observations have revealed that a significant fraction of red gi
 ant stars have lower than expected amplitudes in their dipole modes\, impl
 ying larger damping rates of these modes than for the rest of the populati
 on (the "dipole dichotomy" problem). Indirect evidence points towards the 
 role of a deeply-buried magnetic field\, but a detailed understanding of h
 ow gravity waves interact with strong fields is thus far lacking.\n\nIn th
 is talk\, I will present the results of recent work attacking the problem 
 through a variety of linear\, nonlinear\, analytical and numerical approac
 hes. We uncover a rich variety of physical processes that emerge when the 
 field strength exceeds a certain critical threshold. In particular\, we fi
 nd that resonant interactions between gravity waves and Alfvén waves can 
 lead to a singularity that produces efficient damping through viscous diss
 ipation. Predicted damping rates are on par with those associated with con
 vection\, and lie in the range required to explain observations.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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