HIGH-QUALITY SEEING V, I AND GUNN-Z IMAGING OF TERZAN-4 - A BLUE HORIZONTAL-BRANCH BULGE GLOBULAR-CLUSTER

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 im ages 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 d(circle dot) = 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 ho rizontal branch, it could be as metal-poor as [Fe/H] approximate to -2 .0. It is therefore another blue horizontal branch globular cluster lo cated close to the Galactic center.