Other
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109..650b&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 109, no. 2, p. 650-662
Other
42
Chronology, Color-Magnitude Diagram, Globular Clusters, Milky Way Galaxy, Astronomical Spectroscopy, Blue Stars, Charge Coupled Devices, Galactic Clusters, Galactic Halos, Interacting Galaxies, Metallicity, Morphology, Red Giant Stars
Scientific paper
We have obtained the first B,V CCD color-magnitude diagram (CMD) of the galactic globular cluster Arp 2. About 1600 stars have been measured between the tip of the red giant branch at V approximately 15.5 and V approximately 23.5, about two magnitudes below the main sequence turnoff. A centrally concentrated population of blue stragglers has been detected. The slope of the red giant branch and the overall CMD morphology are consistent with that of a metal-poor cluster, with (Fe/H) = -1.84 +/- 0.25. A preliminary spectroscopic measurement based on the Ca II triplet yields (Fe/H) = -1.73 +/- 0.05. The comparison of the CMD of Arp 2 with that of other clusters favors a value more metal-poor than that indicated by the Ca II triplet. In this respect, Arp 2 is similar to Ruprecht 106. Differential ages between Arp 2 and a number of reference clusters are obtained from the vertical age parameter, deltaHBTO and the horizontal age parameter, delta(B-V)RGBTO By requiring both age estimators to give consistent results, we find that Arp 2 is approximately 3 Gyr younger than the group of the metal-poor clusters and slightly older than Ruprecht 106. The detection of young metal-poor clusters (Fe/H) less than or = -1.8) implies a complex scenario for the origin of the galactic halo, possibly involving interactions with satellite galaxies and their cluster systems.
Buonanno Roberto
Corsi Carlo E.
Fahlman Gregory G.
Fusi Pecci Flavio
Richer Harvey B.
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