Zeeman-Doppler imaging of solar-type and AP stars. IV. Maximum entropy reconstruction of 2D magnetic topologies.

Recently Semel (1989) introduced the technique of Zeeman-Doppler Imaging (ZDI) which essentially consists of Doppler Imaging using the Stokes V (circular polarization) profile. A code which uses maximum entropy principles to recover the distribution of brightness, abundance, and magnetic fields across the surface of stars is presented. For brightness and abundance mappings, the code is found to produce results comparable to those found in the literature. The first reconstructions of magnetic test structures from the Stokes V parameter alone show that this quantity contains enough spatial information to recover spotted images but not dipolar ones. According to the magnetic topologies that may be expected in solar-type or Ap stars, it is concluded that ZDI may be well adapted in deriving magnetic maps of active RS CVn systems, while it is anticipated that the use of the two other Stokes parameters (linear polarizations) are needed to derive reliable results for Ap stars.