Galactic chemical evolution: The role of the first stars

TL;DR

This paper discusses how the chemical signatures in ancient stars can reveal the properties of the first massive stars, emphasizing the role of fast rotation in early stellar generations and their impact on heavy element enrichment.

Contribution

It introduces an inhomogeneous chemical evolution model highlighting the influence of fast rotating metal-poor massive stars on early heavy-element production.

Findings

Fast rotating massive stars enhance s-process element production.

Chemical anomalies in old stars suggest early stellar populations were fast rotators.

The model explains observed abundance scatter in metal-poor halo stars.

Abstract

The massive First Stars (the first ones to contribute to the chemical enrichment of the Universe due to their short lifetimes) are long dead, and even though efforts to directly observe them in high redshift galaxies are underway, a step forward in this field will have to wait for JWST and ELT. The only way to currently validate the picture arising from the most modern hydro-dynamical simulations of the formation of First Stars is to search for their imprints left on the oldest stars in our Galaxy. Which imprints are we looking for? In the last years our group has found that many chemical anomalies observed in very metal-poor halo stars, as well in the oldest bulge globular cluster, suggest the first stellar generations to have been fast rotators. After giving a brief overview of the aforementioned results, we highlight the impact of fast rotating metal-poor massive stars on the chemical enrichment of heavy-elements such as Sr and Ba. Indeed, in fast rotating massive stars the s-process production is boosted. We will show, by means of an inhomogeneous chemical evolution model, based on stochastic approach to the star formation, that this fact offers a new twist in the interpretation of the abundance patterns and scatter observed in very metal-poor halo stars.