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 \sim 0.53 ) 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 .