Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. IV. Abundances for a Large Sample of Field Stars and Comparison with the Cluster Sample

M.C. PARISI; D. GEISLER; G. CARRARO; J.J. CLARIÁ; S. VILLANOVA; L. GRAMAJO; A. SARAJEDINI; A. GROCHOLSKI

ASTRONOMICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2016 vol. 152 p. 58 - 71

0004-6256

This paper represents a major step forward in the systematic andhomogeneous study of Small Magellanic Cloud (SMC) star clusters andfield stars carried out by applying the calcium triplet technique. Wepresent in this work the radial velocity and metallicity ofapproximately 400 red giant stars in 15 SMC fields, with typical errorsof about 7 km s-1 and 0.16 dex, respectively. We addedto this information our previously determined metallicity values for 29clusters and approximately 350 field stars using the identicaltechniques. Using this enlarged sample, we analyze the metallicitydistribution and gradient in this galaxy. We also compare the chemicalproperties of the clusters and of their surrounding fields. We find anumber of surprising results. While the clusters, taken as a whole, showno strong evidence for a metallicity gradient (MG), the field starsexhibit a clear negative gradient in the inner region of the SMC,consistent with the recent results of Dobbie et al. For distances to thecenter of the galaxy less than 4°, field stars show a considerablysmaller metallicity dispersion than that of the clusters. However, inthe external SMC regions, clusters and field stars exhibit similarmetallicity dispersions. Moreover, in the inner region of the SMC,clusters appear to be concentrated in two groups: one more metal-poorand another more metal-rich than field stars. Individually considered,neither cluster group presents an MG. Most surprisingly, the MG for bothstellar populations (clusters and field stars) appears to reverse signin the outer regions of the SMC. The difference between the clustermetallicity and the mean metallicity of the surrounding field starsturns out to be a strong function of the cluster metallicity. Theseresults could be indicating different chemical evolution histories forthese two SMC stellar populations. They could also indicate variationsin the chemical behavior of the SMC in its internal and externalregions.