Discovery of a Metal-Poor Field Giant with a Globular Cluster
  Second-Generation Abundance Pattern
  We report on detection, from observations obtained with the APOGEE
spectroscopic survey, of a metal-poor ([Fe/H] $= -1.3$ dex) field giant star
with an extreme Mg-Al abundance ratio ([Mg/Fe] $= -0.31$ dex; [Al/Fe] $= 1.49$
dex). Such low Mg/Al ratios are seen only among the second-generation
population of globular clusters, and are not present among Galactic disk field
stars. The light element abundances of this star, 2M16011638-1201525, suggest
that it could have been born in a globular cluster. We explore several origin
scenarios, in particular studying the orbit of the star to check the
probability of it being kinematically related to known globular clusters. We
performed simple orbital integrations assuming the estimated distance of
2M16011638-1201525 and the available six-dimensional phase-space coordinates of
63 globular clusters, looking for close encounters in the past with a minimum
distance approach within the tidal radius of each cluster. We found a very low
probability that 2M16011638-1201525 was ejected from most globular clusters;
however, we note that the best progenitor candidate to host this star is
globular cluster $\omega$ Centauri (NGC 5139). Our dynamical investigation
demonstrates that 2M16011638-1201525 reaches a distance $|Z_{max}| < 3 $ kpc
from the Galactic plane and a minimum and maximum approach to the Galactic
center of $R_{min}<0.62$ kpc and $R_{max}<7.26$ kpc in an eccentric
($e\sim0.53$) and retrograde orbit. Since the extreme chemical anomaly of
2M16011638-1201525 has also been observed in halo field stars, this object
could also be considered a halo contaminant, likely been ejected into the Milky
Way disk from the halo. We conclude that, 2M16011638-20152 is also
kinematically consistent with the disk but chemically consistent with halo
field stars.
