A view of the Galactic halo using beryllium as a time scale

TL;DR

This study explores beryllium abundances in halo stars to understand the Galaxy's formation history, revealing two distinct stellar populations with different star formation timelines.

Contribution

It demonstrates that beryllium can serve as a cosmochronometer and uncovers two halo star populations with different chemical and formation histories.

Findings

Halo stars separate into two components in log(Be/H) vs. [alpha/Fe] diagram.

One component aligns with evolutionary model predictions.

The local halo is not a uniform population with a clear age-metallicity relation.

Abstract

Beryllium stellar abundances were suggested to be a good tracer of time in the early Galaxy. In an investigation of its use as a cosmochronometer, using a large sample of local halo and thick-disk dwarfs, evidence was found that in a log(Be/H) vs. [alpha/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined.