Abundance anomalies in red giants with possible extragalactic origins unveiled by APOGEE-2

TL;DR

This study investigates chemical abundance anomalies in red giants, suggesting some may originate from extragalactic sources or migrated within the galaxy, based on orbital and chemical analysis.

Contribution

It provides a new orbital and chemical analysis linking abundance anomalies in red giants to possible extragalactic origins or internal galaxy migration mechanisms.

Findings

Stars with enhanced Al and N and Mg underabundances may originate from the outer halo or accreted satellites.

A subset of N- and Al-rich stars with Mg deficiency are consistent with inner halo kinematics.

Bar-induced resonant trapping could explain the migration of some stars to the inner halo.

Abstract

By performing an orbital analysis within a Galactic model including a bar, we found that it is plausible that the newly discovered stars that show enhanced Al and N accompanied by Mg underabundances may have formed in the outer halo, or were brought in by satellites field possibly accreted a long time ago. However, another subsample of three N- and Al-rich stars with Mg-deficiency are kinematically consistent with the inner stellar halo. A speculative scenario to explain the origin of the atypical chemical composition of these stars in the inner halo is that they migrated to the inner stellar halo as unbound stars due to the mechanism of bar-induced resonant trapping.