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Mono-stable hydromagnetic stellar differential rotatio
  Nordita Astrophysics seminars

Wednesday 03 September 2014
from 13:30 to 14:15
at 122:026
Speaker : Bidya Binay Karak (Nordita)
Abstract : Late-type stars rotate differentially owing to anisotropic turbulence in their outer convection zones. The rotation is called solar-like (SL) when the equator rotates fastest and anti-solar (AS) otherwise. Hydrodynamic simulations explain a transition from SL to AS rotation as the influence of rotation on convection is reduced, but the opposite transition occurs at a different point in the parameter space. The system is bistable, i.e., SL and AS rotation profiles can both be stable. Aims: We study the effect of a dynamo-generated magnetic field on the large-scale flows, particularly on the possibility of bistable behavior of differential rotation. Methods: We solve the hydromagnetic equations numerically in a rotating spherical shell up to +/- 75 degr latitude (wedge geometry) for a set of different radiative conductivities controlling the relative importance of convection. Results: A transition from SL to AS rotation is confirmed, but there is no bistability due to a strong influence of self-consistently generated magnetic fields on the differential rotation. In all cases, both differential rotation and meridional circulation have significant magnetic cycle related variations that are comparable to the solar observations. AS rotation profiles are obtained when the rotational influence on convection is weak, although magnetic cycles are more regular than for SL rotation. Conclusions: Purely hydrodynamic simulations of differential rotation are shown to be of limited relevance as magnetic fields, self-consistently generated by dynamo action, significantly affect the rotation profiles.


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