Are some CEMP-s stars the daughters of spinstars?

TL;DR

This study investigates whether some CEMP-s stars, typically explained by binary AGB pollution, could instead originate from the ejecta of rapidly rotating massive stars, called spinstars, by modeling their nucleosynthesis.

Contribution

It introduces detailed nucleosynthesis models of low-metallicity spinstars to evaluate their potential role in forming apparently single CEMP-s stars, challenging the AGB companion hypothesis.

Findings

Non-rotating source stars cannot explain observed abundances.

Most CEMP-s stars can be explained by a 25 M_sun spinstar with high initial rotation.

One star's high Pb abundance remains unexplained by current models.

Abstract

CEMP-s stars are long-lived low-mass stars with a very low iron content as well as overabundances of carbon and s-elements. Their peculiar chemical pattern is often explained by pollution from a AGB star companion. Recent observations have shown that most of the CEMP-s stars are in a binary system, providing support to the AGB companion scenario. A few CEMP-s stars, however, appear to be single. We inspect four apparently single CEMP-s stars and discuss the possibility that they formed from the ejecta of a previous-generation massive star, referred to as the "source" star. In order to investigate this scenario, we computed low-metallicity massive star models with and without rotation and including complete s-process nucleosynthesis. We find that non-rotating source stars cannot explain the observed abundance of any of the four CEMP-s stars. Three out of the four CEMP-s stars can be explained by a $25$ $M_{\odot}$ source star with $v_{\rm ini} \sim 500$ km s$^{-1}$ (spinstar). The fourth CEMP-s star has a high Pb abundance that cannot be explained by any of the models we computed. Since spinstars and AGB predict different ranges of [O/Fe] and [ls/hs], these ratios could be an interesting way to further test these two scenarios.