Aluminum Enhanced Metal-Poor Stars buried in the Inner Galaxy

TL;DR

This study identifies aluminum-rich, metal-poor stars in the Galactic bulge with eccentric orbits, suggesting they originated from globular clusters and provide insights into the Milky Way's formation history.

Contribution

It reports the discovery of 29 aluminum-enhanced, metal-poor stars in the bulge region, linking their chemical patterns to globular cluster origins and Galactic assembly processes.

Findings

29 Al-rich, metal-poor stars identified in the bulge

Stars exhibit chemical patterns similar to globular clusters

Stars have highly eccentric orbits indicating dynamic ejection

Abstract

Stars with higher aluminum and nitrogen enrichment are often the key pieces for the chemical makeup of multiple populations in almost all globular clusters (GCs). There is also compelling observational evidence that some Galactic components could be partially built from dissipated GCs. Thus, the identification of such kinds of stars among metal-poor field stars may provide insights on the composite nature of the Milky Way (MW) bulge and inner stellar halo, as well as reveal other chemical peculiarities. Here, based on APOGEE spectra, we report the discovery of 29 mildly metal-poor ([Fe/H]$\lesssim-0.7$) stars with stellar atmospheres strongly enriched in aluminum (Al-rich stars: [Al/Fe]$\gtrsim+0.5$), well above the typical Galactic levels, located within the Solar radius toward the bulge region, which lies in highly eccentric orbits ($e\gtrsim0.6$). We find many similarities for almost all of the chemical species measured in this work with the chemical patterns of GCs, so we conjecture that they have likely been dynamically ejected into the bulge and inner halo from GCs formed in situ and/or GC formed in different progenitors of known merger events experienced by the MW, such as the \textit{Gaia}-Sausage-Enceladus and/or Sequoia.