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

Abstract

We have modelled the global-magnetic-field topology of the young, rapidly rotating K0 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°. 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.