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

Using the SOFI imager at ESO/NTT and the NIRSPEC spectrograph at Keck II, we have obtained J,K images and echelle spectra covering the range 1.5− 1.8 μm for the intermediate metallicity bulge globular clusters NGC 6539 and UKS 1. We find [Fe/H]=–0.76 and –0.78, respectively, and an average α-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 C/C ≈ 4.5 ± 1 isotopic ratios in both clusters, suggesting that extra-mixing mechanisms due to cool bottom processing are at work during evolution along the Red Giant Branch. Finally, we measure accurate radial velocities of < vr >= +31±4 km/s and < vr >= +57 ± 6 km/s and velocity dispersion of ≈8 km/s and ≈11 km/s for NGC 6539 and UKS 1, respectively,