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Intermediate-mass, magnetic chemically peculiar (Ap) stars provide a uniqueopportunity to study the topology of stellar magnetic fields in detail and toinvestigate magnetically driven processes of spot formation. Here we aim toderive the surface magnetic field geometry and chemical abundance distributionsfor the extraordinary Ap star HD 75049. This object hosts a surface field of~30 kG, one of the strongest known for any non-degenerate star. We usedtime-series of high-resolution HARPS intensity and circular polarisationobservations. These data were interpreted with the help of magnetic Dopplerimaging and model atmospheres incorporating effects of a non-solar chemicalcomposition and a strong magnetic field. We refined the rotational period of HD75049 to Prot=4.048267+/-0.000036 d. We also derived basic stellar parameters,Teff=10250+/-250 K and logg=4.3+/-0.1. Magnetic Doppler imaging revealed thatthe field topology of HD 75049 is poloidal and dominated by a dipolarcontribution with a peak surface field strength of 39 kG. At the same time,deviations from the classical axisymmetric oblique dipolar configuration aresignificant. Chemical surface maps of Si, Cr, Fe, and Nd show abundancecontrasts of 0.5-1.4 dex, which is low compared with many other Ap stars. Nd isfound to be enhanced close to the magnetic pole, whereas Si and Cr areconcentrated predominantly at the magnetic equator. The iron distribution showslow-contrast features both at the magnetic equator and the pole. The morphologyof the magnetic field and the properties of chemical spots in HD 75049 arequalitatively similar to those of Ap stars with weaker fields. Consequently,whatever mechanism forms and sustains global magnetic fields inintermediate-mass main-sequence stars, it operates in the same way over theentire observed range of magnetic field strengths.

Magnetic field topology and chemical spot distributions in the extreme Ap star HD 75049