APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
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 (12C14N). 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.
ARRAY(0x2fb2388)- Publication:
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Astronomy and Astrophysics
- Pub Date:
- March 2021
- DOI:
- arXiv:
- arXiv:2102.01706
- Bibcode:
- 2021A&A...647A..64F
- Keywords:
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- stars: abundances;
- stars: chemically peculiar;
- globular clusters: individual: NGC 6723;
- techniques: spectroscopic;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Astronomy &
