APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
Date Issued
2021
Author(s)
Fernandez-Trincado, Jose G.
Beers, Timothy C.
Minniti, Dante
Carigi, Leticia
Placco, Vinicius M.
Chun, Sang-Hyun
Lane, Richard R.
Geisler, Doug
Villanova, Sandro
Souza, Stefano O.
Barbuy, Beatriz
Perez-Villegas, Angeles
Chiappini, Cristina
Queiroz, Anna. B. A.
Tang, Baitian
Alonso-Garcia, Javier
Piatti, Andres E.
Palma, Tali
Alves-Brito, Alan
Bidin, Christian Moni
Roman-Lopes, Alexandre
Munoz, Ricardo R.
Singh, Harinder P.
Kundu, Richa
Chaves-Velasquez, Leonardo
Romero-Colmenares, Maria
Longa-Pena, Penelope
Soto, Mario
Vieira, Katherine
DOI
http://dx.doi.org/10.1051/0004-6361/202040255
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 ((CN)-C-12-N-14). 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] greater than or similar to +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.


