High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6584 and NGC 7099

Abstract

We obtain high-resolution spectra of red giant branch stars in NGC 6584 and NGC 7099 to perform a detailed abundance analysis. We confirm cluster membership for these stars based on consistent radial velocities measured in this study and small pixel offsets between the observations of Sarajedini et al. and Piotto et al. We find mean metallicities of [Fe/H] = -1.53 ± 0.08 dex and [Fe/H] = -2.29 ± 0.07 dex for NGC 6584 and NGC 7099, respectively. We also find these clusters to be enhanced in their [α/Fe] ratios, consistent with what is expected for metal-poor globular clusters. Additionally, we find evidence of a statistically significant Na-O anti-correlation in both clusters. Finally, with the use of HST photometry, we compare the location of the enhanced and pristine populations in chromosome maps of the clusters to confirm previous photometric evidence of multiple stellar populations. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences, our results can be used to constrain pollution models.