Getting MADS: The age of the SMC cluster NGC 419 measured with Delta Scuti stars

Delta Scuti (dSct) are short period pulsating variable stars, tracers of an intermediate-age population (1-5 Gyr), located in the intersection between the main sequence and the instability strip. Based on the discovery of 54 dSct in the field of NGC 419, an intermediate-age globular cluster of the SMC, we find that only a handful of the dSct appear at the main sequence turnoff of the cluster while the majority is fainter. This is in stark contrast with its “twin” in the LMC, NGC 1846. Using theoretical isochrones with different ages and taking account of the locus of the instability strip and the dSct stars in the color-magnitude diagram, we predict that NGC 419 is younger (~1.2 Gyr) than previously thought. Additionally, this is the first sizeable detection of dSct stars ever made in the SMC, which allow us to estimate the density of dSct in the field of the SMC for the first time (~1.6 dSct/arcmin^-2). With this result, several tens of thousands of dSct stars are expected to be found in the whole body of the SMC. This will be accomplished with our new survey, the MAgellanic Delta Scuti survey (MADS). Finally, the comparison among several dSct catalogs reveal an interesting behaviour in the lower end of the period-luminosity plane for the dSct stars.