Cyclotron humps in AM Her systems: variations around the orbit in DP Leo

We present new phase-resolved spectra of DP Leo which show prominent cyclotron humps when the cyclotron-emission region is viewed perpendicularly to the magnetic field. One hump, at ∼15 890 cm-1, is particularly prominent. The hump positions have been analysed using a more accurate model, and this yields a revised estimate for the magnetic field of 32±1 MG. We have also identified Zeemand features in the spectra at certain phases which yield a similar field strength. By differentiating the light curve we have independently confirmed the extent of the emission arc as 50-600, and have found that the bulk of the emission area is probably located ahead in phase and at lower latitudes than the position at which the emission peaks. (author)