HST NICMOS photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4

Abstract

We present results from NICMOS Hubble Space Telescope observations of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4, obtained through the filters F110W (1.1 mu m) and F160W (1.6 mu m) (nearly equivalent to J and H). For the first time the turnoff region of Liller 1 and the main sequence of Terzan 5 and Terzan 4 are reached, as well as the horizontal branch of UKS 1. The magnitude difference between the turnoff and the red horizontal branch Delta m₁₁₀=m₁₁₀^HB- m₁₁₀^TO is used as an age indicator. From comparisons with new isochrones in the NICMOS photometric system, we conclude that the two metal-rich clusters NGC 6528 and Terzan 5 are coeval within uncertainties ( ~ 20%) with 47 Tucanae. Liller 1 and UKS 1 are confirmed as metal-rich globular clusters. Terzan 4 is confirmed as an interesting case of a metal-poor cluster in the bulge with a blue horizontal branch. Based on observations collected with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-16555.