The origin and internal structure of the magnetic fields of the CP stars

The dynamo and fossil theories for the origin of the magnetic fields of the CP stars are critically examined. It is deduced that the observed fields are unlikely to be the product of a contemporary dynamo situated in the convective core. The consequences for the fossil theory of an inhomogeneous, rope-like, internal field structure are investigated with the aid of self-consistent, time-dependent numerical models. It is found that models with inhomogeneous internal fields have relatively homogeneous surface fields. The observable effective and surface fields calculated for the ‘one-rope’ models are quite similar to those of the conventional displaced-dipole/oblique-rotator model. However, models in which the internal field is concentrated into two or more ropes of comparable strength seem unlikely to be consistent with the body of observational evidence, although the existence of such structures cannot be excluded in all circumstances.