2022ApJ...925...77B

While the Milky Way nuclear star cluster (MW NSC) 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 α-element abundances [α/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 α-element abundance measurements of subsolar-metallicity stars in the MW NSC. We measure [M/H] = - 0.59 ± 0.11, [α/Fe] = 0.05 ± 0.15 and [M/H] = - 0.81 ± 0.12, [α/Fe] = 0.15 ± 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 [α/Fe] in between the [α/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 subsolar-metallicity population in the MW NSC likely originated from infalling dwarf galaxies or globular clusters and are unlikely to have formed in situ.