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BVRI photometry of the galactic globular cluster NGC 6779

Citation:

Hatzidimitriou D, Antoniou V, Papadakis I, Kaltsa M, Papadaki C, Papamastorakis I, Croke BFW. BVRI photometry of the galactic globular cluster NGC 6779. [Internet]. 2004;348:1157 - 1163.

Abstract:

We present B, V, R and I photometry for NGC 6779 (M56), a metal-poor globular cluster in the galactic halo. The observations were performed using the 1.3-m telescope at Skinakas Observatory, in Crete. The reddening of the cluster was found to be E(B-V) = 0.32 ± 0.02 [E(V-I) = 0.43 ± 0.02], significantly higher than previous estimates. The metal abundance of the cluster was derived from various parametrizations of red giant branch characteristics and it was found to be [Fe/H]ZW=-2.20 ± 0.12 dex on the Zinn-West metallicity scale, or [Fe/H]CG=-2.00 ± 0.21 dex on the Carretta-Gratton scale. The distance modulus of the cluster is estimated to be (m-M)V= 15.62 ± 0.26 (or 14.62, if we correct for the reddening to the cluster). The horizontal branch of NGC 6779 shows a clear gap at (B-V)o= 0.0. Finally, the revised value for the metallicity of NGC 6779 led to a revision of its age to 13 Gyr, using the age-index calibrations of Salaris & Weiss.

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