标题： APOGEE发现一颗化学特性异常的恒星，该恒星来自NGC 6723并被银河系核球捕获 显示英文标题

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

摘要： 银河系中心（核心）区域充满了大量金属含量适中的恒星，这些恒星的大气中氰化物（$^{12}$C$^{14}$N）显著富集。其中一些天体，也被称为氮增强恒星，被假定为银河系古老形成历史的遗迹。尽管已经观察到氮增强恒星与球状星团中独特化学模式的化学相似性，但尚未证明场星与球状星团之间的直接联系。在本研究中，我们报告了对银河系核心球状星团NGC 6723的高分辨率近红外光谱观测，以及意外发现了一颗位于星团之外（靠近潮汐半径）但轨道相似的恒星，2M18594405$-$3651518，这提供了第一个明确的证据，表明这颗恒星很可能曾经是星团成员，最近被抛出。其氮丰度比([N/Fe]$\gtrsim + 0.94$)明显高于典型的银河系场星水平，并表现出明显的重元素（$s$-过程元素，如Ce、Nd和Yb）富集，同时伴有适度的碳富集；所有这些特征都是球状星团中的已知例子。这一结果表明，银河系核心区域的一些氮增强恒星可能起源于球状星团的潮汐破坏。 显示英文摘要

摘要： 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 ($^{12}$C$^{14}$N). 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$-$3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio ([N/Fe]$\gtrsim + 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.