Peculiar abundances of the cool carbon star HE 1104-0957

Abstract

We present, for the first time, a detailed abundance analysis of the carbon star HE 1104$-$0957 based on high resolution (R$\sim$ 50\,000) spectra. Our analysis shows that the object is an extremely metal-poor star with [Fe/H] $\sim$ $-$2.96. We find that the object shows enhancement of carbon with [C/Fe] $\sim$ 1.82. However, it does not fall into any of the sub-groups of carbon-enhanced metal-poor (CEMP) stars based on the characteristic elemental abundance ratios used for the classification of various CEMP sub-groups. HE 1104$-$0957 is also found to exhibit an enhancement of oxygen and nitrogen with [O/Fe], and [N/Fe] $\sim$ 1.54, and 2.54 respectively. In HE 1104$-$0957, $\alpha$-elements are found to be slightly enhanced with [$\alpha$/Fe] $\sim$ 0.46. Fe-peak elements are also moderately enhanced in HE 1104$-$0957 with a value 0.63 with respect to Fe. Our analysis shows that HE 1104$-$0957 exhibits enhancement of neutron-capture elements, particularly r-process elements. The low-resolution spectra of this object shows the spectral features characteristics of a typical C-R star. However, We find that the surface chemical compositions of this object is contradictory to that expected for a C-R star. It requires a detailed analysis to better understand the abundance anomalies exhibited by this object.

Accepted for publication in Bulletin de la Société Royale des Sciences de Liège (BSRSL)