Volume 528, April 2011
|Number of page(s)||7|
|Section||Galactic structure, stellar clusters and populations|
|Published online||03 March 2011|
The globular cluster BH 176 revisited
1 Laboratoire d’Astrophysique de
Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue E. Belin, 31400
2 Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR, 369167, Russia
3 Isaac Newton Institute of Chile, SAO Branch, Russia
4 Instituto de Investigaciones en Astronomía Teórica y Experimental (IATE), Observatorio Astronómico OAC, Laprida 854, X5000BGR, Córdoba; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Avenida Rivadavia 1917, C1033AAJ, Buenos Aires, Argentina
Received: 2 August 2010
Accepted: 13 January 2011
Context. First classified as an open cluster, BH 176 lies in a crowded field at low galactic latitude. Later studies have labeled it a transition-type object, a metal-rich globular, or an open cluster, with distance estimates in the range of 15 to 85 kpc, indicating that the true nature of this cluster is rather uncertain.
Aims. Our aim is to determine more precisely the distance to BH 176, and, as a matter of consequence, its metallicity and age.
Methods. We have obtained two color–magnitude diagrams of BH 176, one in the infrared using the 2MASS point-source catalog, the other in the optical using FORS2 VLT archival images. We identified the red giant branch in the infrared and the red giant branch, red giant bump, red horizontal branch, subgiant branch, and main sequence turn-off in the optical, by selecting stars within ~2−3′ from the center of the cluster.
Results. We estimate a distance D ~ 15.1 ± 0.5 kpc from the visual magnitude of the red clump and a metallicity [Fe/H] ~ −0.10 ± 0.1 dex from the magnitudes and colors of the main features in the two color–magnitude diagrams. Fitting isochrones from the Padova database to the color–magnitude diagrams confirms our results.
Conclusions. BH 176 is an old metal-rich open or transition-type cluster, moderately close to the Galactic plane. It is a spectacular object for studying the early formation history of our Galaxy.
Key words: globular clusters: individual: BH 176 / Hertzsprung-Russell and C-M diagrams
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.