Modelling of magnetic fields of CP stars II. Analysis of longitudinal field, crossover, and quadratic field observations

In recent years, the introduction and systematic application of new diagnostic techniques has enormously increased the opportunities to investigate magnetic fields of chemically peculiar (CP) stars. To approach the problem of modelling these fields, in previous papers we set up a theory aimed at describing the magnetic configuration due to the superposition of a dipole with an arbitrary quadrupole. The present work is a first application of this theory to spectropolarimetric observations of Stokes I and V . We have attempted to model nine magnetic CP stars by analysing their curves of longitudinal field, crossover and quadratic field. We found that the classical dipolar model is adequate in only one case, while in six cases it should definitely be ruled out. For two stars a specific dipole plus quadrupole model has been recovered.