Vertical distribution of chromium in the atmospheres of HgMn stars

We use multiplet 30 $\ion{Cr}{ii}$ lines in the wings of H$_{\beta}$ to test the hypothesis of an anomalous concentration of Cr in the upper layers of the atmospheres of a sample of 10 HgMn stars. These lines are at different distances from the Hβ line center and are therefore formed at different depths in the stellar atmosphere. Except for HD 49606, all HgMn stars show an increase in Cr abundance with height in the stellar atmosphere. A similar vertical distribution of Cr, but less pronounced, has been previously found in Am stars. In contrast, no variation of Cr abundance with the depth has been found for the normal late B-type star HD 196426 and the weak magnetic late B-type star HD 168733. It is possible that in HgMn stars the vertical stratification parameter, a, depends on Teff, with the strongest vertical gradient being found in the hotter stars. No correlation was found between a and the average stellar abundance $\log \varepsilon$(Cr/H).