Near-Infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity Bulge Globular Clusters

Abstract

Using the SofI imager at ESO/NTT and NIRSPEC spectrograph at KeckII, we have obtained J,K images and echelle spectra covering the range 1.5 - 1.8 micron for the intermediate metallicity Bulge globular clusters NGC6539 and UKS1. We find [Fe/H]=-0.76 and -0.78, respectively, and an average alpha-enhancement of +0.44 dex and +0.31 dex, consistent with previous measurements of metal rich Bulge clusters, and favoring the scenario of rapid chemical enrichment. We also measure very low 12C/13C=4.5 +/-1 isotopic ratios in both clusters, suggesting that extra-mixing mechanisms due to cool bottom processing are at work during the evolution along the Red Giant Branch. Finally, we measure accurate radial velocities of <v_r>=+31 +/-4Km/s and <v_r>=+57 +/-6Km/s and velocity dispersion of about 8 Km/s and 11 Km/s for NGC6539 and UKS1, respectively.