APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge

2021/01/13 by José G. Fernández-Trincado, Timothy C. Beers, Dante Minniti +43 · 29 citations
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Blue straggler #Bulge #Galactic Center #Globular cluster #Horizontal branch #Milky Way #Physics #Star cluster #Stars #Stellar, planetary, and galactic studies #astro-ph.GA

paper · pdf · doi:10.1051/0004-6361/202040255

published in Astronomy and Astrophysics 647, A64 (EDP Sciences) · Astronomy & Astrophysics, in press. 16 pages, 8 figures, 2 tables

openalex publication_date 2021/01/13 · arxiv created 2021/02/02 · arxiv updated 2021/02/04 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06

Abstract

The central (‘bulge’) region of the Milky Way is teeming with a significant fraction of mildly metal-deficient stars with atmospheres that are strongly enriched in cyanogen ( 12 C 14 N). Some of these objects, which are also known as nitrogen-enhanced stars, are hypothesised to be relics of the ancient assembly history of the Milky Way. Although the chemical similarity of nitrogen-enhanced stars to the unique chemical patterns observed in globular clusters has been observed, a direct connection between field stars and globular clusters has not yet been proven. In this work, we report on high-resolution, near-infrared spectroscopic observations of the bulge globular cluster NGC 6723, and the serendipitous discovery of a star, 2M18594405−3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio ([N/Fe] ≳ + 0.94) is well above the typical Galactic field-star levels, and it exhibits noticeable enrichment in the heavy s -process elements (Ce, Nd, and Yb), along with moderate carbon enrichment; all characteristics are known examples in globular clusters. This result suggests that some of the nitrogen-enhanced stars in the bulge likely originated from the tidal disruption of globular clusters.

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