The Massive M31 Cluster G1: Detailed Chemical Abundances from Integrated
  Light Spectroscopy
  G1, also known as Mayall II, is one of the most massive star clusters in M31.
Its mass, ellipticity, and location in the outer halo make it a compelling
candidate for a former nuclear star cluster. This paper presents an integrated
light abundance analysis of G1, based on a moderately high-resolution
(R=15,000) spectrum obtained with the High Resolution Spectrograph on the
Hobby-Eberly Telescope in 2007 and 2008. To independently determine the
metallicity, a moderate resolution (R~4,000) spectrum of the calcium-II triplet
lines in the near-infrared was also obtained with the Astrophysical Research
Consortium's 3.5-m telescope at Apache Point Observatory. From the
high-resolution spectrum, G1 is found to be a moderately metal-poor cluster,
with [Fe/H]=-0.98+/-0.05. G1 also shows signs of alpha-enhancement (based on
Mg, Ca, and Ti) and lacks the s-process enhancements seen in dwarf galaxies
(based on comparisons of Y, Ba, and Eu), indicating that it originated in a
fairly massive galaxy. Intriguingly, G1 also exhibits signs of Na and Al
enhancement, a unique signature of GCs -- this suggests that G1's formation is
intimately connected with GC formation. G1's high [Na/Fe] also extends previous
trends with cluster velocity dispersion to an even higher mass regime, implying
that higher mass clusters are more able to retain Na-enhanced ejecta. The
effects of intracluster abundance spreads are discussed in a subsequent paper.
Ultimately, G1's chemical properties are found to resemble other M31 GCs,
though it also shares some similarities with extragalactic nuclear star
clusters.
