Zeeman Doppler Mapping: On the Spuriousness and Nonuniqueness of Magnetic Maps*

Magnetic and abundance maps of chemically peculiar (CP) stars, derived with the help of Zeeman Doppler mapping (ZDM), have always been and still are used as arguments against atomic diffusion theory, even though it has been shown that the quasi-totality of published magnetic topologies of stars with strong fields violate the force-free condition and therefore are physically impossible. These magnetic geometries, despite being forbidden by (physical) law, are yet found capable of providing reasonable, sometimes even good fits to observed Stokes IQUV profiles. It appears that the main reason why the manifest spuriousness of the magnetic maps is not acknowledged lies in their purported uniqueness, a claim rarely if ever questioned. We intend to expose the fallacy of this presupposition. For this purpose we have identified in the literature those five CP stars with strong magnetic fields for which multiple magnetic and chemical maps have been published, all derived with the same family of codes. For each of these stars we have carried out intercomparisons between the respective recovered distributions of magnetic field and of abundances. Agreement between maps often turns out to be quite poor in regard to abundances, field topology, and absolute field strengths. Even maps based on exactly the same set of observations can differ considerably. It transpires that for any of the stars, ZDM inversions have resulted in a number of different, almost always spurious (in as much as physically impossible) magnetic topologies, which together with the accompanying, necessarily spurious, abundances cannot provide constraints on diffusion theory.