Cool Stars 14 - Submitted Abstract # 283
This version created on 05 October 2006

Stellar activity in terms of dynamo modes


Dominique M. Fluri, Institute of Astronomy, ETH Zurich, Switzerland
Svetlana V. Berdyugina, Institute of Astronomy, ETH Zurich, Switzerland

Cool, rapidly rotating stars exhibit enhanced magnetic activity with
cyclic behavior on various time scales.  In particular, the longitude
of the dominant activity region switches quasi-periodically by 180
degrees, which is known as the 'flip-flop' phenomenon.  We introduce a
new approach for the interpretation of stellar activity cycles based
on light curve modeling with dipole and quadrupole dynamo modes.  The
goals are to identify the underlying reasons for the occurrence of
active longitudes and flip-flops and to determine the large-scale
magnetic field configuration on cool active stars.  We discuss the
observational signatures of different combinations of the dynamo modes
and identify four fundamental mechanisms that can create active
longitudes and flip-flops.  Furthermore, the proposed method is able
to reproduce the basic properties of two prototypical long-term
photometric behaviors of cool active stars.  The new method allows us
to study different mechanisms resulting in active longitudes and
flip-flops and to determine empirically the magnetic field
configuration on cool active stars.  It serves also as a tool for
comparing results of theoretical dynamo models with observations.

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