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

José G. Fernández-Trincado, Timothy C. Beers, Dante Minniti, Leticia Carigi, Vinicius M. Placco, Sang Hyun Chun, Richard R. Lane, Doug Geisler, Sandro Villanova, Stefano O. Souza, Beatriz Barbuy, Angeles Pérez-Villegas, Cristina Chiappini, Anna B.A. Queiroz, Baitian Tang, Javier Alonso-García, Andrés E. Piatti, Tali Palma, Alan Alves-Brito, Christian Moni BidinAlexandre Roman-Lopes, Ricardo R. Muñoz, Harinder P. Singh, Richa Kundu, Leonardo Chaves-Velasquez, María Romero-Colmenares, Penelope Longa-Peña, Mario Soto, Katherine Vieira

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

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.

Original languageEnglish
Article numberA64
JournalAstronomy and Astrophysics
Volume647
DOIs
Publication statusPublished - 1 Mar 2021

Keywords

  • Globular clusters: individual: NGC 6723
  • Stars: abundances
  • Stars: chemically peculiar
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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