High-Resolution Infrared Spectra of Bulge Globular Clusters: The Extreme Chemical Abundances of Terzan 4 and Terzan 5*

摘要

Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the range 1.5–1.8 μm 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 [α/Fe] ≈ +0.5 dex in Terzan 4 and [α/Fe] ≈ +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 supernovae. Finally, we measure very low 12C/13C ≤ 10 ratios in all the giant stars, confirming that extra-mixing mechanisms due to cool bottom processing occur during evolution along the RGB.