Tracing back a second-generation star stripped from Terzan 5 by the Galactic bar

TL;DR

This paper uncovers a star with second-generation globular cluster characteristics, likely stripped from Terzan 5 by the Galactic bar, revealing insights into the Galaxy's early formation and chemical evolution.

Contribution

It demonstrates how chemodynamical analysis combining Gaia and APOGEE data can trace stars back to their parent clusters, shedding light on Galactic bulge formation.

Findings

SOS1 star shows second-generation globular cluster chemical signatures.

SOS1 was likely stripped from Terzan 5 about 350 million years ago.

Terzan 5 may be a primordial building block of the Galactic bulge.

Abstract

The Galactic bulge hosts the Milky Way's oldest stars, possibly coming from disrupted globular clusters (GCs) or the bulge's primordial building blocks, making these stars witnesses to the Galaxy's early chemical enrichment. The Galactic bar currently dominates the bulge's region, altering the orbits of objects formed before its formation and complicating the trace of the field stars' original clusters. Here, we present the discovery of a fossil record of this evolution, SOS1 -- a star trapped in the bar, exhibiting significant enhancements in nitrogen, sodium, and aluminum, typical of second-generation GC stars. SOS1 also shows an s-process Ce enhancement, suggesting an old age and early enrichment by fast-rotating massive stars in the Galaxy's earliest phases. With the purpose of finding the SOS1's parent GC, we derive its precise chemodynamical properties by combining high-precision proper motions from Gaia with APOGEE detailed chemical abundances. Our analysis suggests that SOS1 was possibly stripped from the GC Terzan 5 by the Galactic bar's gravitational influence approximately 350 Myr ago. We also found chemical similarities suggesting that SOS1 belonged to the most metal-poor, ancient, and peripheral stellar population of Terzan 5. These results not only support the hypothesis that Terzan 5 is a remnant of a primordial building block of the Galactic bulge, but also suggest this cluster continues losing stars to the bar. Our method highlights how powerful the use of chemodynamical properties in the Gaia era is for tracing the Galaxy's evolutionary history.