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

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