Chemical tagging in the SDSS-III/APOGEE survey: new identifications of
  halo stars with globular cluster origins
  We present new identifications of five red giant stars in the Galactic halo
with chemical abundance patterns that indicate they originally formed in
globular clusters. Using data from the Apache Point Observatory Galactic
Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey
Data Release 12 (DR12), we first identify likely halo giants, and then search
those for the well-known chemical tags associated with globular clusters,
specifically enrichment in nitrogen and aluminum. We find that 2% of the halo
giants in our sample have this chemical signature, in agreement with previous
results. Following the interpretation in our previous work on this topic, this
would imply that at least 13% of halo stars originally formed in globular
clusters. Recent developments in the theoretical understanding of globular
cluster formation raise questions about that interpretation, and we concede the
possibility that these migrants represent a small fraction of the halo field.
There are roughly as many stars with the chemical tags of globular clusters in
the halo field as there are in globular clusters, whether or not they are
accompanied by a much larger chemically untaggable population of former
globular cluster stars.
