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The Populations of Carina. II. Chemical Enrichment

Published version
Peer-reviewed

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Authors

Norris, JE 
Yong, D 
Venn, KA 
Casagrande, L 

Abstract

Chemical abundances are presented for 19 elements in a sample of 63 red giants in the Carina dwarf spheroidal galaxy (dSph), based on homogeneous 1D/LTE model atmosphere analyses of our own observations (32 stars) and data available in the literature (a further 31 independent stars). The (Fe) metallicity and [α/Fe] distribution functions have mean values and dispersions of -1.59 and 0.33 dex ([Fe/H] range: -2.68 to -0.64) and 0.07 and 0.13 dex ([α/Fe] range: -0.27 to 0.25), respectively. We confirm the finding of Venn et al. that a small percentage (some 10% in the present investigation) of the sample shows clear evidence for significant enrichment by Type Ia supernova (SN Ia) ejecta. Calcium, with the most accurately determined abundance of the α-elements, shows an asymmetric distribution toward smaller values of [Ca/Fe] at all [Fe/H], most significantly over -2.0 < [Fe/H] < -1.0, suggestive of incomplete mixing of the ejecta of SNe Ia with the ambient medium of each of Carina's generations. Approximate color-magnitude diagram age estimates are presented for the sample, and together with our chemical abundances, compared with the results of our previous synthetic color-magnitude diagram analysis, which reported the details of Carina's four well-defined populations. We searched for the Na-O anticorrelation universally reported in the Galaxy's globular clusters and confirm that this phenomenon does not exist in Carina. We also found that one of the 32 stars in our sample has an extremely enhanced lithium abundance - A(Li)NLTE = +3.36, consistent with membership of the ~1% group of Li-rich stars in dSph described by Kirby et al.

Description

Keywords

galaxies: abundances, galaxies: dwarf, galaxies: individual (Carina), stars: abundances

Journal Title

Astrophysical Journal, Supplement Series

Conference Name

Journal ISSN

0067-0049
1538-4365

Volume Title

230

Publisher

IOP Science
Sponsorship
European Research Council (320360)
Studies at RSAA, ANU, of the Galaxy’s most metal-poor stars and its dwarf galaxy satellite systems by J.E.N. and D.Y. are supported by Australian Research Council grants DP0663562, DP0984924, DP120100475, DP150100862, and FT140100554. K.A.V. acknowledges support from the Canadian NSERC Discovery Grants program. This work was partly supported by the European Union FP7 program through ERC grant no. 320360.