Salgado, CCSalgadoDa Costa, G SG SDa CostaYong, DDYongSalinas, RRSalinasNorris, J EJ ENorrisMackey, A DA DMackeyMARINO, AnnaAnnaMARINOMilone, A PA PMilone2023-07-242023-07-2420220035-8711http://hdl.handle.net/20.500.12386/34327Using spectra obtained with the VLT/FORS2 and Gemini-S/GMOS instruments we have investigated carbon, nitrogen and sodium abundances in a sample of red giants in the Small Magellanic Cloud cluster Kron 3. The metallicity and luminosity of this cluster are comparable to those of Galactic globular clusters although with a notably younger age of $\sim$ 6.5 Gyr. Specifically we have investigated the strengths of the CH ($\lambda$ 4300 A) and CN ($\lambda$ 3800, $\lambda$ 4215) molecular bands finding a bimodality of CN band-strengths and a CH/CN anti-correlation. Application of spectrum synthesis techniques reveals a large spread ($\sim$1.2 dex) in nitrogen abundance and a spread in [C/Fe] of $\sim$0.3 dex after applying corrections for evolutionary mixing. We have also estimated sodium abundances from the strengths of the Na D lines finding a range of $\sim$0.8 dex in [Na/Fe] that correlates positively with the N abundances. This is the first star-by-star spectroscopic demonstration of correlated Na, N abundance variations in an intermediate-age star cluster, adding to existing photometric and spectroscopic indications of the presence of multiple populations in such clusters with masses in excess of $\sim 10^5$ solar masses. Our results confirm that the mechanism(s) responsible for the multiple populations observed in globular clusters cannot be an early cosmological effect applying only in old clusters, and provide a key additional factor in the quest to understand the origin of the abundance anomalies.STAMPAenArticle10.1093/mnras/stac17242-s2.0-85138603326https://academic.oup.com/mnras/article/515/2/2511/6612747FIS/05 - ASTRONOMIA E ASTROFISICA