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arXiv · astro-ph/0107459

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

S. Ortolani·B. Barbuy·E. Bica·A. Renzini·M. Zoccali·R. M. Rich·S. Cassisi
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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 and F160W (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 $Δm_{110}=m_{110}^{HB}- m_{110}^{TO}$ 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 ($\sim 20%$) 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.

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S. Ortolani, B. Barbuy, E. Bica, A. Renzini, M. Zoccali, R. M. Rich, S. Cassisi. 2001-07-24. HST NICMOS Photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4. https://doi.org/10.1051/0004-6361%3A20011045

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