Abundances and search for vertical stratification in the atmospheres of four HgMn stars

TL;DR

This study performs a detailed spectroscopic analysis of four HgMn stars, deriving chemical abundances and investigating vertical stratification, finding evidence of Mn stratification in one star, HD 178065.

Contribution

It provides the first detailed abundance analysis and stratification search for four HgMn stars using high-resolution UVES spectra, revealing Mn stratification in one star.

Findings

No significant stratification for most elements in most stars.

Detected Mn stratification in HD 178065 with a ~0.7 dex variation.

Derived chemical abundances consistent with previous studies.

Abstract

Using high resolution, high-S/N archival UVES spectra, we have performed a detailed spectroscopic analysis of 4 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 5 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 3\sigma upper limits of \Delta\log N_elem/N_tot~0.1-0.2 dex per unit optical depth. However, for Mn in the atmosphere of HD 178065 we find convincing evidence of stratification. Modeling 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 log \tau_5000=-3.6 to -2.8.