High-resolution spectroscopic analysis of four new chemically peculiar stars

TL;DR

This study provides detailed high-resolution chemical compositions of four chemically peculiar red giant stars, revealing their neutron-capture element enhancements and binary nature, and compares observations with s-process nucleosynthesis models.

Contribution

First detailed high-resolution chemical analysis of four peculiar red giants, including novel heavy element abundances and binary star identification.

Findings

All four stars show large neutron-capture element enhancements.

Three stars are likely CH or barium giants due to binary mass transfer.

HE 1255-2324 identified as a higher metallicity CEMP-r/s star.

Abstract

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{\deg}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 $^{12}$C/$^{13}$C 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{\deg}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{\deg}2688 and HE 2207-1746, which are probably CH stars.