Elemental abundance analyses with DAO spectrograms - XII. The mercury-manganese stars HR 4072A and 7775 and the metallic-lined star HR 4072B.

This paper presents fine analyses of three sharp-lined stars, the mercury-manganese stars HR 4072A and 7775 and the metallic-lined star HR 4072B, consistent with previous studies of this series. MR 4072A and 7775 exhibit Pt II, Au II and Hg II lines in their spectra, while HR 7775 also shows lines of several singly ionized rare earth species. MR 4072B is very deficient in both Ca and Sc, the signature of the Am stars. For the HgMn stars, [C/Si] marginally anticorrelates with log Si/H as in normal A and λ Boo stars. The large He depletions and other departures from the solar pattern, however, argue strongly against a simple Venn-Lambert hypothesis for these stars.