Abundances for a Large Sample of Red Giants in NGC 1851: Hints for a Merger of Two Clusters?

We present the abundance analysis of a sample of more than 120 red giants in the globular cluster (GC) NGC 1851, based on FLAMES spectra. We find a small but detectable metallicity spread. This spread is compatible with the presence of two different groups of stars with a metallicity difference of 0...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2010-10, Vol.722 (1), p.L1-L6
Main Authors: Carretta, E, Gratton, R. G, Lucatello, S, Bragaglia, A, Catanzaro, G, Leone, F, Momany, Y, D'Orazi, V, Cassisi, S, D'Antona, F, Ortolani, S
Format: Article
Language:English
Subjects:
ABUNDANCE
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
ELEMENTS
EVOLUTION
GALAXIES
METALS
STAR EVOLUTION
STARS
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Summary:We present the abundance analysis of a sample of more than 120 red giants in the globular cluster (GC) NGC 1851, based on FLAMES spectra. We find a small but detectable metallicity spread. This spread is compatible with the presence of two different groups of stars with a metallicity difference of 0.06-0.08 dex, in agreement with earlier photometric studies. If stars are divided into these two groups according to their metallicity, both components show Na-O anticorrelation (signature of a genuine GC nature) of moderate extension. The metal-poor stars are more concentrated than the metal-rich ones. We tentatively propose the hypothesis that NGC 1851 formed from a merger of two individual GCs with a slightly different Fe and {alpha}-element content and possibly an age difference up to 1 Gyr. This is also supported by number ratios of stars on the split subgiant and on the bimodal horizontal branches. The distribution of n-capture process elements in the two components also supports the idea that the enrichment must have occurred in each of the structures separately and not as a continuum of events in a single GC. The most probable explanation is that the proto-clusters formed into a (now dissolved) dwarf galaxy and later merged to produce the present GC.
ISSN:2041-8205
2041-8213
DOI:10.1088/2041-8205/722/1/L1