The potential magnetic field of AB Doradus: comparison with Zeeman-Doppler images

We have modelled the global-magnetic-field topology of the young, rapidly rotating KO dwarf AB Dor by assuming that the field is potential and using as a boundary condition Zeeman-Doppler images of the surface radial field obtained over three consecutive years. For each of the observed radial-field distributions, we calculate the azimuthal component of the corresponding potential field. We then compare at each epoch (by means of cross-correlation) the potential and observed azimuthal-field distributions, and find that there is a good correlation for magnetic features at latitudes below 60 degrees. Above this latitude, the potential field fails to reproduce the almost unidirectional band of azimuthal field that is observed and the correlation is correspondingly poor.