Nucleosynthesis in Rotating massive stars and Abundances in the Early Galaxy

TL;DR

This paper explores how axial rotation in low-metallicity massive stars influences chemical mixing, surface element enrichment, and mass loss, significantly impacting early galactic chemical evolution and the formation of CEMP stars.

Contribution

It introduces the role of stellar rotation at low metallicity in enhancing mixing, surface enrichment, and mass loss, affecting early universe nucleosynthesis and galaxy evolution.

Findings

Rotation increases primary nitrogen, carbon, neon production.

Enhanced mixing leads to surface CNO enrichment.

Rotation influences early galactic chemical evolution and CEMP star formation.

Abstract

We discuss three effects of axial rotation at low metallicity. The first one is the mixing of the chemical species which is predicted to be more efficient in low metallicity environments. A consequence is the production of important quantities of primary $^{14}$N, $^{13}$C, $^{22}$Ne and a strong impact on the nucleosynthesis of the {\it s}-process elements. The second effect is a consequence of the first. Strong mixing makes possible the apparition at the surface of important quantities of CNO elements. This increases the opacity of the outer layers and may trigger important mass loss by line driven winds. The third effect is the fact that, during the main-sequence phase, stars, at very low metallicity, reach more easily than their more metal rich counterparts, the critical velocity\footnote{The critical velocity is the surface equatorial velocity such that the centrifugal acceleration compensates for the local gravity.}. We discuss the respective importance of these three effects as a function of the metallicity. We show the consequences for the early chemical evolution of the galactic halo and for explaining the CEMP stars. We conclude that rotation is probably a key feature which contributes in an important way to shape the evolution of the first stellar generations in the Universe.