Identification of a new relatively old star cluster in the Small Magellanic Cloud

Abstract

We present results on the age and metallicity estimates of the astonishingly unstudied Small Magellanic Cloud (SMC) cluster ESO 51-SC09, from CCD BVI photometry obtained at the ESO NTT with the EMMI attached. ESO 51-SC09 turns out to be a relatively small cluster (FWHM = 10 ± 1 pc) located ∼4◦ northward from the galaxy center. We report for the first time a mean cluster age of 7.0 ± 1.3 Gyr and a mean cluster metallicity of [Fe/H] = −1.00 ± 0.15 dex, concluding that ESO 51-SC09 belongs to the group of the oldest SMC clusters. We found that the cluster is projected onto a dominant field stellar population older (age ∼10–13 Gyr) and more metal-poor ([Fe/H] = −1.3 ± 0.2 dex), so that the cluster could reach its current location because of its orbital motion.