Astronomy and Astrophysics, volume 376, 878-884 (2001/9-4)
HST NICMOS photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4.
ORTOLANI S., BARBUY B., BICA E., RENZINI A., ZOCCALI M., RICH R.M. and CASSISI S.
Abstract (from CDS):
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 (1.1µm) and F160W (1.6µm) (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 Δm110=m110HB-m110TO 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.
Galaxy: globular clusters: individual: NGC 6528, Terzan 5, Liller 1, Terzan 4, UKS 1 - stars: CM diagram
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