Blue horizontal branch globular clusters towards the bulge: Terzan 9, NGC 6139 and NGC 6453

Free access article

Issue		Astron. Astrophys. Suppl. Ser. Volume 138, Number 2, August 1999


Page(s)		267 - 273
DOI		http://dx.doi.org/10.1051/aas:1999275

DOI: 10.1051/aas:1999275

Astron. Astrophys. Suppl. Ser. 138, 267-273

Blue horizontal branch globular clusters towards the bulge:
Terzan 9, NGC 6139 and NGC 6453

S. Ortolani¹ - E. Bica² - B. Barbuy³

Send offprint request: B. Barbuy

1 - Università di Padova, Dept. di Astronomia, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy and European Southern Observatory, Karl Schwarzschild Strasse 2, D-85749 Garching bei München, Germany
2 - Universidade Federal do Rio Grande do Sul, Dept. de Astronomia, CP 15051, Porto Alegre 91500-970, Brazil
3 - Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil

Received May 10; accepted June 7, 1999

Abstract:

We present V and I photometry of the globular clusters Terzan 9 and NGC 6453 for the first time, and also of NGC 6139.

The three clusters are projected towards the bulge. The Colour-Magnitude Diagram morphologies reveal that the sample clusters have blue horizontal branches. This characterizes an important fraction of the clusters projected on the bulge, with implications on the early Galaxy history.

From the colour-magnitude diagrams we derive reddenings of E(B-V) = 1.95, 0.77, 0.70 and distances $d_{\odot}\approx 4.9$ , 9.4, 8.5 kpc respectively for Terzan 9, NGC 6139 and NGC 6453. We conclude that these metal-poor clusters are within the bulge volume.

Key words: globular clusters: Terzan 9, NGC 6139, NGC 6453 -- HR diagram -- stars: horizontal branch

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