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

¹ Università di Padova, Dept. di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: ortolani@pd.astro.it
² Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil e-mail: barbuy@iagusp.usp.br
³ Universidade Federal do Rio Grande do Sul, Dept. de Astronomia, CP 15051, Porto Alegre 91501-970, Brazil e-mail: bica@if.ufrgs.br
⁴ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany e-mail: arenzini@eso.org
⁵ Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562, USA e-mail: rmr@astro.ucla.edu
⁶ Osservatorio Astronomico Collurania, 64100 Teramo, Italy e-mail: cassisi@astrte.te.astro.it

Corresponding author: M. Zoccali, mzoccali@eso.org

Received: 5 June 2001
Accepted: 16 July 2001

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 μm) and F160W (1.6 μm) (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 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 (~) 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.