Cool Stars 14 - Submitted Abstract # 155
This version created on 05 October 2006

Polar Caps on Active Stars:  Magnetic Flux Emergence and Transport


Moira Jardine, University of St Andrews
Duncan H. Mackay, University of St Andrews

In recent years, Zeeman Doppler Imaging (ZDI) of rapidly rotating
solar-like stars has shown high latitude magnetic flux patterns of
intermingled magnetic polarities.  Such high latitude intermingling of
positive and negative flux is inconsistent with our present
understanding of how magnetic flux emerges on the Sun and is
transported poleward.  To determine how these patterns may arise,
magnetic flux transport simulations are carried out.  These
simulations follow the evolution of the radial magnetic field at the
surface of the star as new magnetic bipoles emerge and are advected
poleward by the surface effects of differential rotation, meridional
flow and supergranular diffusion.  To produce intermingling of flux at
high latitudes, key parameters such as the emergence profiles and
transport coefficients are varied from presently used solar values.
In doing so it is found that in order to explain the high latitude
intermingling at least two of these parameters must be changed.
Firstly, the emergence profile must be extended to higher latitudes
(50-70  degres) and secondly the value of the meridional flow must be
increased by around a factor of 10  (100  m/s).  The results show that
the observed intermingling of high latitude flux can only occur
through a flux emergence and transport process that is significantly
different from that which occurs on the Sun.

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