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NGC 6229 is a relatively massive outer halo globular cluster that isprimarily known for exhibiting a peculiar bimodal horizontal branch morphology.Given the paucity of spectroscopic data on this cluster, we present a detailedchemical composition analysis of 11 red giant branch members based on highresolution (R ~ 38,000), high S/N (> 100) spectra obtained with theMMT-Hectochelle instrument. We find the cluster to have a mean heliocentricradial velocity of -138.1$_{-1.0}^{+1.0}$ km s$^{\rm -1}$, a small dispersionof 3.8$_{-0.7}^{+1.0}$ km s$^{\rm -1}$, and a relatively low (M/L$_{\rmV}$)$_{\rm \odot}$ = 0.82$_{-0.28}^{+0.49}$. The cluster is moderatelymetal-poor with <[Fe/H]> = -1.13 dex and a modest dispersion of 0.06 dex.However, 18% (2/11) of the stars in our sample have strongly enhanced[La,Nd/Fe] ratios that are correlated with a small (~0.05 dex) increase in[Fe/H]. NGC 6229 shares several chemical signatures with M 75, NGC 1851, andthe intermediate metallicity populations of omega Cen, which lead us toconclude that NGC 6229 is a lower mass iron-complex cluster. The light elementsexhibit the classical (anti-)correlations that extend up to Si, but the clusterpossesses a large gap in the O-Na plane that separates first and secondgeneration stars. NGC 6229 also has unusually low [Na,Al/Fe] abundances thatare consistent with an accretion origin. A comparison with M 54 and otherSagittarius clusters suggests that NGC 6229 could also be the remnant core of aformer dwarf spheroidal galaxy.

Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229