CaII Triplet Spectroscopy of Small Magellanic Cloud Red Giants. II. Abundances for a Sample of Field Stars

摘要

We have obtained metallicities of ~ 360 red giant stars distributed in 15Small Magellanic Cloud (SMC) fields from near-infrared spectra covering theCaII triplet lines using the VLT + FORS2. The errors of the derived [Fe/H]values range from 0.09 to 0.35 dex per star, with a mean of 0.17 dex. Themetallicity distribution of the whole sample shows a mean value of [Fe/H] =-1.00 +- 0.02, with a dispersion of 0.32 +- 0.01, in agreement with global mean[Fe/H] values found in previous studies. We find no evidence of a metallicitygradient in the SMC. In fact, on analysing the metallicity distribution of eachfield, we derived mean values of [Fe/H] = -0.99 +- 0.08 and [Fe/H] = -1.02 +-0.07 for fields located closer and farther than 4 deg. from the center of thegalaxy, respectively. In addition, there is a clear tendency for the fieldstars to be more metal-poor than the corresponding cluster they surround,independent of their positions in the galaxy and of the clusters' age. We arguethat this most likely stems from the field stars being somewhat older andtherefore somewhat more metal-poor than most of our clusters.