Rapidly rotating Population III stellar models as a source of primary nitrogen

TL;DR

This study models rapidly rotating Population III stars to understand their evolution and nucleosynthesis, revealing significant effects on primary nitrogen production and stellar structure, with implications for early universe chemical enrichment.

Contribution

It introduces detailed models of fast-rotating Population III stars, highlighting their unique evolution, nucleosynthesis, and feedback effects compared to previous non-rotating models.

Findings

Rapid rotation boosts primary 14N production.

Fast rotation causes extended convective zones during core He-burning.

Rotation influences stellar core sizes and final star fate.

Abstract

The first stars might have been fast rotators. This would have important consequences for their radiative, mechanical and chemical feedback. We discuss the impact of fast initial rotation on the evolution of massive Population III models and on their nitrogen and oxygen stellar yields. We explore the evolution of Population III stars with initial masses in the range of 9Msol < Mini < 120Msol starting with an initial rotation on the Zero Age Main Sequence equal to 70% of the critical one. We find that with the physics of rotation considered here, our rapidly-rotating Population III stellar models do not follow a homogeneous evolution. They lose very little mass in case mechanical winds are switched on when the surface rotation becomes equal or larger than the critical velocity. Impact on the ionising flux appears modest when compared to moderately-rotating models. Fast rotation favours, in models with initial masses above ~20Msol, the appearance of a very extended intermediate convective zone around the H-burning shell during the core He-burning phase. This shell has important consequences on the sizes of the He- and CO-cores and thus impacts the final fate of stars. Moreover, it has a strong impact on nucleosynthesis boosting the production of primary 14N. Fast initial rotation impacts significantly the chemical feedback of Population III stars. Observations of extremely metal-poor stars and/or starbursting regions are essential to provide constraints on the properties of the first stars.