Origin of CEMP stars: What helium and lithium can tell us about CEMP stars?

TL;DR

This paper investigates the origins of CEMP stars by analyzing how processed material from previous stars, especially helium and lithium abundances, explains their unique surface compositions and formation history.

Contribution

It proposes that CEMP stars inherit their peculiar abundances from source stars that experienced mixing and selective mass ejection, providing new insights into their formation and chemical signatures.

Findings

CEMP stars' abundance patterns originate from material processed in previous stars.

Some CEMP stars may be helium-rich and lithium-poor due to their formation from nearly pure ejecta.

Partial mixing and selective mass loss in source stars explain observed chemical signatures.

Abstract

We show that the peculiar surface abundance patterns of Carbon Enhanced Metal Poor (CEMP) stars has been inherited from material having been processed by H- and He-burning phases in a previous generation of stars (hereafter called the ``Source Stars''). In this previous generation, some mixing must have occurred between the He- and the H-burning regions in order to explain the high observed abundances of nitrogen. In addition, it is necessary to postulate that a very small fraction of the carbon-oxygen core has been expelled (either by winds or by the supernova explosion). Therefore only the most outer layers should have been released by the Source Stars. Some of the CEMP stars may be He-rich if the matter from the Source Star is not too much diluted with the InterStellar Medium (ISM). Those stars formed from nearly pure ejecta would also be Li-poor.