Activity cycles and polar caps on solar-like stars
Moira Jardine (School of Physics and Astronomy, St Andrews)
Duncan MacKay (School of Mathematics and Statistics, St Andrews)
Gaitee Hussain (ESTEC)
While the Sun produces spots at low to intermediate latitudes, it has been known
for some time now that more rapidly-rotating stars have spots at much higher
latitudes, even extending up to the rotation pole. For the most rapid rotators,
we can determine the surface magnetic polarities from Zeeman-Doppler imaging.
While a solar model of flux emergence and transport would predict that the
high-latitude flux should be unipolar, Zeeman-Doppler images show it to be of
mixed polarity. In order to determine how such a flux distribution might arise,
we have modelled the surface field evolution of a rapid rotator as new bipoles
emerge and are transported by differential rotation, meridional flow and
supergranular diffusion. To produce the observed high-latitude intermingling of
flux, the latitude at which flux emerges through the surface must be increased
to values of 50 to 70 degrees and the meridional flow must be increased by a
factor of 10 over the solar value to around 100 m/s.
http://star-www.st-and.ac.uk/~mmj/