The COMBS Survey -- III. The Chemodynamical Origins of Metal-Poor Bulge Stars

TL;DR

This study provides a detailed chemodynamical analysis of 319 metal-poor stars in the Galactic Bulge, revealing complex chemical signatures and potential links to ancient stellar populations and supernova events.

Contribution

It offers the first comprehensive chemodynamical characterization of metal-poor bulge stars, including elemental abundances and their association with Galactic structures.

Findings

Inner and outer bulge stars show higher chemical complexity than halo stars.

Identified stars with signatures of pair-instability supernovae.

Detected globular cluster-like chemical patterns in some bulge stars.

Abstract

The characteristics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way's formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require dynamical analyses to disentangle. In this work, we undertake a detailed chemodynamical study of the metal-poor stars in the inner Galaxy. Using R$\sim$ 20,000 VLT/GIRAFFE spectra of 319 metal-poor (-2.55 dex$\leq$[Fe/H]$\leq$0.83 dex, with $\overline{\rm{[Fe/H]}}$=-0.84 dex) stars, we perform stellar parameter analysis and report 12 elemental abundances (C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Zn, Ba, and Ce) with precisions of $\approx$0.10 dex. Based on kinematic and spatial properties, we categorise the stars into four groups, associated with the following Galactic structures: the inner bulge, the outer bulge, the halo, and the disk. We find evidence that the inner and outer bulge population is more chemically complex (i.e., higher chemical dimensionality and less correlated abundances) than the halo population. This result suggests that the older bulge population was enriched by a larger diversity of nucleosynthetic events. We also find one inner bulge star with a [Ca/Mg] ratio consistent with theoretical pair-instability supernova yields and two stars that have chemistry consistent with globular cluster stars.