Abundances of heavy metals and lead isotopic ratios in subluminous B stars

Abundances of heavy metals and lead isotopic ratios in subluminous B stars Abstract. We present a detailed abundance analysis of high-resolution ultraviolet echelle spectra of five subdwarf B stars obtained with HST-STIS The goal of our observations was to test the hypothesis that pulsations in sdBs are correlated to the surface abundances of iron-group elements. We study two pulsators and three non-pulsators and determined abundances for 25 elements including the iron group and even heavier elements such as tin and lead using LTE spectrum synthesis techniques. We find strong enrichments of heavy elements up to 2.9 dex with respect to solar which are probably caused by atomic diffusion processes. No clear-cut correlation between pulsations and metal abundances becomes apparent Abundances for lead isotopes are derived from very high resolution spectra using an UV line of triply ionised lead. As Pb terminates the s-process sequence Pb isotopic abundance ratios yield important constraints. It is very difficult to measure them in hot stars. For the first time we were able to measure them in two subluminous B stars and conclude that the 207 Pb/ 208 Pb is solar.