High resolution infrared spectra of bulge globular clusters: The extreme chemical abundances of Terzan 4 and Terzan 5

Abstract

Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the range $1.5-1.8 μ\rm m$ for the highly reddened bulge globular clusters Terzan 4 and Terzan 5. The clusters are of interest because a blue horizontal branch in Terzan 4 is consistent with very low metallicity, while Terzan 5 has been proposed as possibly the most metal rich known Galactic globular cluster. We report the first detailed abundance analysis for stars in these clusters, and we find [Fe/H]=--1.60 and --0.21 dex for Terzan 4 and Terzan 5, respectively, confirming the presence of a large metallicity spread in the bulge as well as in the halo of the Galaxy. We find $\rm [α/Fe]\approx+0.5$ dex in Terzan 4 and $\rm [α/Fe]\approx +0.3$ dex in Terzan 5, consistent with what has been found for field stars in the bulge. The enhanced $α-$element abundances are also consistent with rapid chemical enrichment, most likely by type II SNe. Finally, we measure very low $^{12}$C/$^{13}$C$\le10$ ratios in all the giant stars, confirming that extra-mixing mechanisms due to {\it cool bottom processing} occur during evolution along the RGB.