APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
Piatti, Andrés E.; Beers, Timothy C.; Placco, Vinicius M.; Minniti, Dante; Chiappini, Cristina; Lane, Richard R.; Geisler, Doug; Fernández-Trincado, José G.; Queiroz, Anna. B. A.; Barbuy, Beatriz; Moni Bidin, Christian; Chaves-Velasquez, Leonardo; Villanova, Sandro; Vieira, Katherine; Alonso-García, Javier; Pérez-Villegas, Angeles; Carigi, Leticia; Tang, Baitian; Muñoz, Ricardo R.; Roman-Lopes, Alexandre; Singh, Harinder P.; Romero-Colmenares, María; Soto, Mario; Souza, Stefano O.; Kundu, Richa; Palma, Tali; Alves-Brito, Alan; Chun, Sang-Hyun; Longa-Peña, Penelope
Chile, France, United States, Vatican City, Mexico, South Korea, Brazil, Germany, China, Argentina, India, Colombia
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.
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