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

We present results on the age and metallicity estimates of the astonishingly unstudied 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 deg 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.