$s$-Process in Massive Carbon-Enhanced Metal-Poor Stars

TL;DR

This study investigates how massive, early-generation carbon-enhanced metal-poor stars produce heavy elements via the weak s-process, revealing significant nucleosynthesis up to barium influenced by initial composition and stellar mass.

Contribution

It demonstrates that massive CEMP stars can synthesize heavy elements up to Ba through the weak s-process, highlighting their role in early galactic chemical enrichment.

Findings

Substantial production of elements up to Sr in stars with [CNO] > -1.5.

Production of elements up to Ba for [CNO] > -0.5.

Yield increases linearly with initial Fe abundance.

Abstract

Observations suggest that the interstellar medium (ISM) might have been highly enriched in carbon at very early times. We explore nucleosynthesis in massive carbon-enhanced metal-poor (CEMP) stars of $12$--$40\,\mathrm{M}_\odot$ formed from such an ISM with ${\rm [Fe]}\leq-2$. We find substantial production of elements heavier than Fe, mostly up to Sr, by the weak \textsl{s}-process in stars with initial abundances of ${\rm [CNO]}\gtrsim-1.5$. Even heavier elements, up to Ba, can be produced for ${\rm [CNO]}\gtrsim-0.5$. The efficiency of this \textsl{s}-process is sensitive to the initial enhancement of C (or more generally, CNO) and mass of the star, with the yield increasing approximately linearly with the initial Fe abundance. The \textsl{s}-process in CEMP stars of $\gtrsim 20 \,\mathrm{M}_\odot$ with ${\rm [CNO]}\gtrsim -1.5$ can be an important source for heavy elements in the Early Galaxy.