High quality seeing V , I and Gunn z imaging of Terzan 4 : a blue horizontal branch bulge globular cluster ?
نویسندگان
چکیده
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 d = 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.
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