A HGMN COMPANION TO THE CEPHEID SU CYG

We report here the discovery of a chemically peculiar star of the HgMn type as a companion to the classical Cepheid variable SU Cyg. This is the first investigation of a HgMn star in a binary system in which a star of a more advanced evolutionary stage is the primary. The age of the Cepheid provides an estimate to the age of the chemical peculiarit ies which is independent of the photometric calibration of HgMn field stars. From a synthetic spectrum analysis it is determined that the Hg Mn star, SU Cyg B, displays the abundance deficiency for nitrogen and enhancements for manganese (+1.5 dex) and the very heavy elements merc ury (+5.8 dex) and platinum (+5.0 dex). Absorption from the strong tra nsitions Au II lambda 1740 and Tl II lambda 1908 each implies abundanc e enhancements of 3.0 dex. A search through the IUE and HST/GHRS spect ral archives reveals several binary-Cepheid companions which are candi dates for chemically peculiar stars.