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http://hdl.handle.net/20.500.12386/23303
Titolo: | Five Groups of Red Giants with Distinct Chemical Composition in the Globular Cluster NGC 2808 | Autori: | CARRETTA, Eugenio | Data pubblicazione: | 2015 | Rivista: | THE ASTROPHYSICAL JOURNAL | Numero: | 810 | Fascicolo: | 2 | Da pagina:: | 148 | Abstract: | The chemical composition of multiple populations in the massive globular cluster (GC) NGC 2808 is addressed with the homogeneous abundance reanalysis of 140 red giant branch stars. UVES spectra for 31 stars and GIRAFFE spectra for the other giants were analyzed with the same procedures used for about 2500 giants in 23 GCs in our FLAMES survey, deriving abundances of Fe, O, Na, Mg, Si, Ca, Ti, Sc, Cr, Mn, and Ni. Iron, elements from α capture, and those in the Fe group do not show intrinsic scatter. On our UVES scale, the metallicity of NGC 2808 is [Fe/H] =\-1.129+/- 0.005+/- 0.034 (± statistical ± systematic error) with σ = 0.030 (31 stars). The main features related to proton-capture elements are retrieved, but the improved statistics and the smaller associated internal errors allow us to uncover five distinct groups of stars along the Na-O anticorrelation. We observe large depletions in Mg, anticorrelated with enhancements of Na and also Si, suggestive of unusually high temperatures for proton captures. About 14% of our sample is formed by giants with solar or subsolar [Mg/Fe] ratios. Using the [Na/Mg] ratios, we confirm the presence of five populations with different chemical compositions that we call P1, P2, I1, I2, and E in order of decreasing Mg and increasing Na abundances. Statistical tests show that the mean ratios in any pair of groups cannot be extracted from the same parent distribution. The overlap with the five populations recently detected from UV photometry is good but not perfect, confirming that more distinct components probably exist in this complex GC. <P />Based on data collected at the ESO telescopes under program 072.D-0507 and during the FLAMES Science Verification program. | Acknowledgments: | We thank Angela Bragaglia for valuable help and discussions and Alessio Mucciarelli for providing his results for potassium. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has been funded by PRIN MIUR 2010-2011, project “The Chemical and Dynamical Evolution of the Milky Way and Local Group Galaxies” (PI F. Matteucci) . This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France and of NASA’s Astrophysical Data System. | URI: | http://hdl.handle.net/20.500.12386/23303 | URL: | https://iopscience.iop.org/article/10.1088/0004-637X/810/2/148 | ISSN: | 0004-637X | DOI: | 10.1088/0004-637X/810/2/148 | Bibcode ADS: | 2015ApJ...810..148C | Fulltext: | open |
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