2010MNRAS.405.1384T

Using high-resolution, high-signal-to-noise ratio archival UVES (Ultraviolet-Visual Echelle Spectrograph) spectra, we have performed a detailed spectroscopic analysis of four chemically peculiar HgMn stars (HD 71066, HD 175640, HD 178065 and HD 221507). Using spectrum synthesis, mean photospheric chemical abundances are derived for 22 ions of 16 elements. We find good agreement between our derived abundances and those published previously by other authors. For the five elements that present a sufficient number of suitable lines, we have attempted to detect vertical chemical stratification by analyzing the dependence of derived abundance as a function of optical depth. For most elements and most stars, we find no evidence of chemical stratification with typical 3σ upper limits of ΔlogN_elem/N_tot∼ 0.1-0.2dex per unit optical depth. However, for Mn in the atmosphere of HD 178065 we find convincing evidence of stratification. Modelling of the line profiles using a two-step model for the abundance of Mn yields a local abundance varying approximately linearly by ∼0.7 dex through the optical depth range logτ₅₀₀₀= -3.6 to -2.8.