Cool Stars 14 - Submitted Abstract # 136
This version created on 05 October 2006

Nonradial surface flow on giant stars


Michael Weber, Astrophysikalisches Institut Potsdam

After the detection of anti-solar differential rotation on giant stars
(i.e.  the pole spinning faster than the equator, see e.g.
Strassmeier et al.  2003), theoretical considerations have shown that
such a behaviour can be caused by strong pole-ward meridional flows
(Kitchatinov and Ruediger 2004).  Using time-series Doppler imaging to
reconstruct the change of spot patterns on active stars, one can not
only reconstruct differential rotation, but also latitudinal movements
of the reconstructed surface features.  But due to the lower accuracy
of the latitudes of the reconstructed spot features, the data
requirements are higher than for the detection of differential
rotation.  Using a sample of giant stars with know estimates of the
differential rotation, we searched for latitudinal changes of the spot
patterns in the reconstructed images.  Using averaged latitudinal
cross-correlation maps, we derived estimates for the magnitudes of the
meridional flow the available stars.  Plotting the differential
rotation values against the meridional flow, one can see a trend
towards poleward larger meridional flow for larger anit-solar
differential rotation rates, although the number of measurements and
the corresponding error bars are too large to draw conclusive results.

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