Spectroscopic study of four metal-poor carbon stars from the Hamburg/ESO Survey: On confirming the low-mass nature of their companions

TL;DR

This study provides a detailed high-resolution spectroscopic analysis of four metal-poor carbon stars, confirming their binary nature and low-mass AGB companions, and explores their elemental abundance patterns to understand early Galactic chemical evolution.

Contribution

First detailed high-resolution spectroscopic analysis of four metal-poor carbon stars from the Hamburg/ESO Survey, confirming their binary status and low-mass AGB companions.

Findings

HE 0457-1805 and HE 1241-0337 are CEMP-s stars

HE 0920-0506 is a CH star

HE 1327-2116 is a CEMP-r/s star

Abstract

Elemental abundances of extrinsic carbon stars provide insight into the poorly understood origin and evolution of elements in the early Galaxy. In this work, we present the results of a detailed spectroscopic analysis of four potential carbon star candidates from the Hamburg/ESO Survey (HES) HE~0457$-$1805, HE~0920$-$0506, HE~1241$-$0337, and HE~1327$-$2116. This analysis is based on the high-resolution spectra obtained with Mercator/HERMES (R$\sim$86,000) and SUBARU/HDS (R$\sim$50,000). Although the abundances of a few elements, such as, Fe, C, and O are available from medium-resolution spectra, we present the first ever detailed high-resolution spectroscopic analysis for these objects. The object HE~0457$-$1805 and HE~1241$-$0337 are found to be CEMP-s stars, HE~0920$-$0506 a CH star, and HE~1327$-$2116 a CEMP-r/s star. The object HE~0457$-$1805 is a confirmed binary, whereas the binary status of the other objects is unknown. The locations of program stars on the absolute carbon abundance A(C) vs [Fe/H] diagram point at their binary nature. We have examined various elemental abundance ratios of the program stars and confirmed the low-mass nature of their former AGB companions. We have shown that the i-process models could successfully reproduce the observed abundance pattern in HE~1327$-$2116. The parametric model based analysis performed for HE~0457$-$1805, HE~0920$-$0506, and HE~1241$-$0337 based on the FRUITY models confirmed that the surface chemical composition of these three objects are influenced by pollution from low-mass AGB companions.