Measuring the alpha-abundance of subsolar-metallicity stars in the Milky
  Way's central half-parsec: testing globular cluster and dwarf galaxy infall
  scenarios
  While the Milky Way Nuclear star cluster has been studied extensively, how it
formed is uncertain. Studies have shown it contains a solar and supersolar
metallicity population that may have formed in-situ, along with a subsolar
metallicity population that may have formed via mergers of globular clusters
and dwarf galaxies. Stellar abundance measurements are critical to
differentiate between formation scenarios. We present new measurements of
[$M/H$] and $\alpha$-element abundances [$\alpha/Fe$] of two
subsolar-metallicity stars in the Galactic Center. These observations were
taken with the adaptive-optics assisted high-resolution (R=24,000) spectrograph
NIRSPEC in the K-band (1.8 - 2.6 micron). These are the first $\alpha$-element
abundance measurements of sub-solar metallicity stars in the Milky Way nuclear
star cluster. We measure [$M/H$]=$-0.59\pm 0.11$, [$\alpha/Fe$]=$0.05\pm 0.15$
and [$M/H$]= $-0.81\pm 0.12$, [$\alpha/Fe$]= $0.15\pm 0.16$ for the two stars
at the Galactic center; the uncertainties are dominated by systematic
uncertainties in the spectral templates. The stars have an [$\alpha/Fe$]
in-between the [$\alpha/Fe$] of globular clusters and dwarf galaxies at similar
[$M/H$] values. Their abundances are very different than the bulk of the stars
in the nuclear star cluster. These results indicate that the sub-solar
metallicity population in the Milky Way nuclear star cluster likely originated
from infalling dwarf galaxies or globular clusters and are unlikely to have
formed in-situ.
