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Astron. Astrophys. 319, 850-854 (1997)

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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

1 Università di Padova, Dept. di Astronomia, Vicolo dell'Osservatorio 5, I-35123 Padova, Italy
2 Universidade de São Paulo, CP 9638, São Paulo 01065-970, Brazil
3 Universidade Federal do Rio Grande do Sul, Dept. de Astronomia CP 15051, Porto Alegre, 91500-970, Brazil

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 [FORMULA] = 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] [FORMULA] -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

* Observations collected at the European Southern Observatory - ESO, Chile

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998