Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

TL;DR

This study reveals that the weak s-process contributes significantly to the production of light n-capture elements in a metal-poor star, challenging previous assumptions about its insignificance in such stars.

Contribution

It provides the first evidence of weak s-process element production in a metal-poor star, using detailed abundance analysis of ET0097.

Findings

Weak s-process contributes ~82% to Sr, 84% to Y, and 58% to Zr in ET0097.

ET0097 shows overabundances of light n-capture elements but not heavier ones.

The star's elements originate from massive star processes, including primary and r-processes.

Abstract

Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(a;n)25Mg in massive stars, which means that metal-poor weak s-process stars could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr should mainly come from the primary weak s-process. The contributed fractions of the primary weak s-process to the Sr, Y and Zr abundances of ET0097 are about 82%, 84% and 58% respectively, suggesting that the CEMP star ET0097 should have the footprints of the weak s-process. The derived result should be a significant evidence that the weak s-process elements can be produced in metal-poor massive stars.