Nitrogen and sulfur abundance stratification in HD 135485

The observed overabundances of many chemical species relative to the expected cluster metallicity in Blue Horizontal Branch (BHB) stars appear as a result of atomic diffusion in their atmospheres. The slow rotation (v sin{i}<10 km s^{-1}) of hot (T_{eff}>11,500 K) BHB stars is consistent with this idea. Atomic diffusion can cause accumulation or depletion of some chemical species in particular layers of the stellar atmosphere, leading to vertical stratification of their abundances. In this report, we present preliminary results of abundance stratification analysis of the atmosphere of the metal-rich B-type star HD 135485, which is located close to the horizontal branch in the Hertzsprung-Russell diagram. In particular, our numerical simulations show that nitrogen and sulfur reveal signatures of vertical abundance stratification: these elements are overabundant in layers with optical depth log{τ_{5000}}<-1.0 and log{τ_{5000}}<-1.5, respectively, in comparison with the deeper (depleted) layers. We present here the first results showing stratification of these elements in a BHB star.