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