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High spectral resolution studies of cool Ap stars reveal conspicuousanomalies of the shape and strength of many absorption lines. This is asignature of large atmospheric chemical gradients produced by the selectiveradiative levitation and gravitational settling of chemical species. Here wepresent a new approach to mapping the vertical chemical structures in stellaratmospheres. We have developed a regularized chemical inversion procedure thatuses all information available in high-resolution stellar spectra. The newtechnique for the first time allowed us to recover chemical profiles withoutmaking a priori assumptions about the shape of chemical distributions. We havederived average abundances and applied the vertical inversion procedure to thehigh-resolution VLT UVES spectra of the weakly magnetic, cool Ap star HD133792. Our analysis yielded improved estimates of the atmospheric parametersof HD 133792. We show that this star has negligible vsini and the mean magneticfield modulus <B>=1.1+/-0.1 kG. We have derived average abundances for 43 ionsand obtained vertical distributions of Ca, Si, Mg, Fe, Cr, and Sr. All theseelements except Mg show high overabundance in the deep layers and solar orsub-solar composition in the upper atmosphere of HD 133792. In contrast, the Mgabundance increases with height. We find that transition from themetal-enhanced to metal-depleted zones typically occurs in a rather narrowrange of depths in the atmosphere of HD 133792. Based on the derivedphotospheric abundances, we conclude that HD 133792 belongs to the rare groupof evolved cool Ap stars, which possesses very large Fe-peak enhancement, butlacks a prominent overabundance of the rare-earth elements.Comment: Accepted by A&A; 12 pages, 9 figure

Chemical stratification in the atmosphere of Ap star HD 133792