On the decentred dipole and dipolequadrupole magnetic field models for Ap stars.
Abstract
Summary. Series developments for the effective field, He, and the mean surface field, Hs, of a decentred magnetic dipole are derived. This model yields almost the same He curves as the dipolequadrupole field if the quadrupole contribution is relatively small and if the axes of the dipole and the quadrupole coincide. Oetken's analysis (1977), based on this dipolequadrupole field and which uses only photographic He measurements, results in models which are contradicted by the observed Hs values, particularly if the quadrupole component is large. Furthermore it will be demonstrated that, with an adequate orientation of the axes, a moderately decentred dipole field may generate crossover, even in the absence of abundance patches. Finally, some of the analyses that include abundance inhomogeneities on the stellar surface, are discussed. Key words: Ap stars  deceutred magnetic dipole  dipolequadrupole fields  crossover  analysis
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 1979
 Bibcode:
 1979A&A....77..286D
 Keywords:

 A Stars;
 Magnetic Dipoles;
 Quadrupoles;
 Stellar Magnetic Fields;
 Stellar Models;
 Abundance;
 Field Strength;
 Harmonic Analysis;
 Polynomials;
 Series (Mathematics);
 Astrophysics;
 Ap Stars:Magnetic Fields