2023MNRAS.518.5414R

We present detailed chemical compositions of four stars on the first-ascent red giant branch that are classified as chemically peculiar, but lack comprehensive analyses at high spectral resolution. For BD+03°2688, HE 0457-1805, HE 1255-2324, and HE 2207-1746, we derived metallicities [Fe/H] = -1.21, -0.19, -0.31, and -0.55, respectively, indicating a range in Galactic population membership. In addition to atmospheric parameters, we extracted elemental abundances for 28 elements, including the evolutionary-sensitive CNO group and ¹²C/¹³C ratios. Novel results are also presented for the heavy elements tungsten and thallium. All four stars have very large enhancements of neutron-capture elements, with high [La/Eu] ratios indicating enrichments from the slow neutron capture (s-process). To interpret these abundances, all indicative of [s/Fe] >1.0, we compared our results with data from literature, as well as with predictions from the Monash and FRUITY s-process nucleosynthesis models. BD+03°2688, HE 1255-2324, and HE 2207-1746 show C/O >1, while HE 0457-1805 has C/O <1. Since HE 0457-1805 and HE 1255-2324 are binary stars, their peculiarities are attributable to mass transfer. We identified HE 0457-1805 as a new barium giant star, and HE 1255-2324 as a new CH star, in fact a higher metallicity analogue CEMP-r/s star; the single object reported in literature so far with similar characteristics is the barium star HD 100503 ([Fe/H] = -0.72). A systematic monitoring is needed to confirm the binary nature of BD+03°2688 and HE 2207-1746, which are probably CH stars.