On the magnetic flux distribution in magnetic CP stars

The robustness of the fossil field theory for the magnetic fields of the CP stars is examined, by following the evolution of initially inhomogeneous field structures of a topology consistent with a 'fossil' origin in the pre-stellar medium. It is suggested that when the initial field is such that its flux is not confined mostly to a single hemisphere of the star, then the resulting surface fields will usually be represented satisfactorily by the 'displaced dipole' model. However, if the initial field, whilst retaining the same topology, is largely confined to a single hemisphere of the star, the subsequent field structure may appear to have strong quadrupolar components. This may provide an explanation, consistent with the fossil theory of field origin, for the anomalous field origin, for the anomalous field variations observed for HD 37776. (author)