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High quality seeing V, I and Gunn z imaging of Terzan 4: a blue horizontal branch bulge globular cluster *
S. Ortolani 1,
B. Barbuy 2 and
E. Bica 3
Received 4 January 1996 / Accepted 29 August 1996
We study the globular cluster Terzan 4 projected close to the Galactic center, by means of V, I and Gunn z Colour-Magnitude Diagrams. The images were obtained under exceptional seeing conditions (0.35" - 0.55") at the ESO New Technology Telescope equipped with SUSI. We derive a reddening of E(B-V) = 2.35 amd a distance from the Sun = 8.3 kpc for Terzan 4.
From the similarity of the VI Colour-Magnitude Diagrams of Terzan 4 and M30, in particular the presence of a blue horizontal branch, it could be as metal-poor as [Fe/H] -2.0. It is therefore another blue horizontal branch globular cluster located close to the Galactic center.
Key words: globular clusters: individual: Terzan 4; M 30; general HR diagram Galaxy: center
Online publication: July 3, 1998