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The brightest magnetic chemically peculiar stars theta Aur and eps UMa weretargeted by numerous studies of their photometric and spectroscopicvariability. Detailed maps of chemical abundance spots were repeatedly derivedfor both stars. However, very little information on the magnetic fieldgeometries of these stars is available. In this study we aim to determinedetailed magnetic field topologies of theta Aur and eps UMa based on modern,high-resolution spectropolarimetric observations. Both targets were observed inall four Stokes parameters using the Narval and ESPaDOnS spectropolarimeters. Amulti-line technique of least-squares deconvolution was employed to detectpolarisation signatures in spectral lines. These signatures were modelled witha Zeeman-Doppler imaging code. We succeeded in detecting variable circular andlinear polarisation signatures for theta Aur. Only circular polarisation wasdetected for eps UMa. We obtained new sets of high-precision longitudinalmagnetic field measurements using mean circular polarisation metal lineprofiles as well as hydrogen line cores, which are consistent with historicaldata. Magnetic inversions revealed distorted dipolar geometries in both stars.The Fe and Cr abundance distributions, reconstructed simultaneously withmagnetic mapping, do not show a clear correlation with the local magnetic fieldproperties, with the exception of a relative element underabundance in thehorizontal field regions along the magnetic equators. Our study provides thefirst ever detailed surface magnetic field maps for broad-line, weak-fieldchemically peculiar stars, showing that their field topologies arequalitatively similar to those found in stronger-field stars. The Fe and Crchemical abundance maps reconstructed for theta Aur and eps UMa are at oddswith the predictions of current theoretical atomic diffusion calculations.

Magnetic field topologies of the bright, weak-field Ap stars theta Aurigae and epsilon Ursae Majoris