Carbon and Strontium Abundances of Metal-Poor Stars

TL;DR

This study measures carbon and strontium abundances in 100 metal-poor stars to identify neutron-capture-rich stars and analyze their chemical compositions, revealing a significant scatter in carbon enrichment and a consistent fraction of carbon-rich stars at low metallicities.

Contribution

First detailed measurement of both carbon and strontium in a large sample of metal-poor stars using spectral synthesis at moderate resolution.

Findings

9±4% of stars with [Fe/H]<-2 are carbon-rich

Large scatter in [C/Fe] below [Fe/H]=-2

Identification of neutron-capture-rich stars among the sample

Abstract

We present carbon and strontium abundances for 100 metal-poor stars measured from R$\sim $7000 spectra obtained with the Echellette Spectrograph and Imager at the Keck Observatory. Using spectral synthesis of the G-band region, we have derived carbon abundances for stars ranging from [Fe/H]$=-1.3$ to [Fe/H]$=-3.8$. The formal errors are $\sim 0.2$ dex in [C/Fe]. The strontium abundance in these stars was measured using spectral synthesis of the resonance line at 4215 {\AA}. Using these two abundance measurments along with the barium abundances from our previous study of these stars, we show it is possible to identify neutron-capture-rich stars with our spectra. We find, as in other studies, a large scatter in [C/Fe] below [Fe/H]$ = -2$. Of the stars with [Fe/H]$<-2$, 9$\pm$4% can be classified as carbon-rich metal-poor stars. The Sr and Ba abundances show that three of the carbon-rich stars are neutron-capture-rich, while two have normal Ba and Sr. This fraction of carbon enhanced stars is consistent with other studies that include this metallicity range.