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

¹ Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copayapu 485, Copiapó, Chile
e-mail: jose.fernandez@uda.cl; jfernandezt87@gmail.com
² Institut Utinam, CNRS UMR 6213, Université Bourgogne-Franche-Comté, OSU THETA Franche-Comté, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
³ Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556, USA
⁴ Depto. de Cs. Físicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. Fernández Concha 700, Las Condes, Santiago, Chile
⁵ Vatican Observatory, 00120 Vatican City State, Italy
⁶ Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 70-264, 04510 Ciudad de México, Mexico
⁷ NSF’s National Optical-Infrared Astronomy Research Laboratory, Tucson, AZ 85719, USA
⁸ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
⁹ Departamento de Astronomí a, Casilla 160-C, Universidad de Concepción, Concepción, Chile
¹⁰ Departamento de Astronomía, Universidad de La Serena, 1700000 La Serena, Chile
¹¹ Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena. Benavente 980, La Serena, Chile
¹² Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
¹³ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 106, 22800 Ensenada, B.C., México
¹⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁵ Laboratório Interinstitucional de e-Astronomia – LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
¹⁶ School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, PR China
¹⁷ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile
¹⁸ Millennium Institute of Astrophysics, Santiago, Chile
¹⁹ Instituto Interdisciplinario de Ciencias Básicas (ICB), CONICET-UNCUYO, Padre J. Contreras 1300, M5502JMA Mendoza, Argentina
²⁰ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB Buenos Aires, Argentina
²¹ Universidad Nacional de Córdoba, Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina
²² Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, Ciudad Autónoma de Buenos Aires, Argentina
²³ Universidade Federal do Rio Grande do Sul, Instituto de Física, Av. Bento Gonçalves 9500, Porto Alegre, RS, Brazil
²⁴ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
²⁵ Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile
²⁶ Visiting astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, Coquimbo, Chile
²⁷ Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India
²⁸ European Southern Observatory, Alonso de Córdova 3107, 7630000 Vitacura, Santiago, Chile
²⁹ University of Nariño Observatory, Universidad de Nariño, Sede VIIS, Avenida Panamericana, Pasto, Nariño, Colombia
³⁰ Departamento de Física de la Universidad de Nariño, Torobajo Calle 18 Carrera 50, Pasto, Nariño, Colombia
³¹ Centro de Investigación en Astronomía, Universidad Bernardo O’Higgins, Avenida Viel 1497, Santiago, Chile

Received: 28 December 2020
Accepted: 6 January 2021

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.