The search for multiple populations in Magellanic Cloud Clusters - III. No evidence for multiple populations in the SMC cluster NGC 419

We present the third paper about our ongoing Hubble Space Telescope survey for the search for multiple stellar populations (MPs) within Magellanic Cloud clusters. We report here the analysis of NGC 419, an similar to 1.5 Gyr old, massive (greater than or similar to 2 x 10(5) M-circle dot) star cluster in the Small Magellanic Cloud (SMC). By comparing our photometric data with stellar isochrones, we set a limit on [N/Fe] enhancement of less than or similar to+0.5 dex and hence we find that no MPs are detected in this cluster. This is surprising because in the first two papers of this series, we found evidence for MPs in four other SMC clusters (NGC 121; Lindsay 1, NGC 339, NGC 416), aged from 6 Gyr up to similar to 10-11 Gyr. This finding raises the question whether age could play a major role in the MPs phenomenon. Additionally, our results appear to exclude mass or environment as the only key factors regulating the existence of a chemical enrichment, since all clusters studied so far in this survey are equally massive (similar to 1-2 x 10(5) M-circle dot) and no particular patterns are found when looking at their spatial distribution in the SMC.