  Polar spots are often observed on rapidly-rotating cool stars, but the nature
of the magnetic field in these spots is as yet unknown. While Zeeman-Doppler
imaging can provide surface magnetic field maps over much of the observed
stellar surface, the Zeeman signature is suppressed in the dark polar regions.
We have determined the effect on the global coronal structure of three current
models for this polar field: that it is composed (a) of unipolar field, (b) of
bipolar regions or (c) of nested rings of opposite polarity. We take as an
example the young, rapid rotator AB Dor (rotation period = 0.514 days). By
adding these model polar fields into the surface field maps determined from
Zeeman-Doppler imaging, we have compared the resulting coronal structure with
the observable properties of the corona - the magnitude and rotational
modulation of the X-ray emission measure and the presence of slingshot
prominences trapped in the corona around the Keplerian co-rotation radius. We
find that only the presence of a unipolar spot has any significant effect on
the overall coronal structure, forcing much of the polar field to be open.
