  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.
