CaTastrophe in the SMC - star clusters vs. field stars

D. GEISLER; M.C. PARISI; L. GRAMAJO

Garching

Simposio; A synoptic view of the Magellanic Clouds: VMC, GAIA and beyond; 2019

European Southern Observatory

We present results based on VLT and Gemini-S Ca Triplet (CaT) mediumresolution spectroscopy of some 200 red giant members of 29 SMC interme-diate - old age clusters. We derive mean cluster velocities to a few km/s andmean metallicities to 0.05 dex, as well as accurate velocities and metallic-ities for about 750 surrounding field giants. We investigate the metallicitydistribution, age-metallicity relation and metallicity gradient in great detailfor the SMC using this large and homogeneous database. We find somesurprising differences between the clusters and fields. The clusters displaya likely bimodal metallicity distribution while the field stars are unimodal.The clusters show no strong evidence of a metallicity gradient while the fieldstars show a strong negative gradient in the inner region of the galaxy thatappears to reverse sign in the outer region. The age-metallicity relation ofthe clusters shows a significant intrinsic metallicity dispersion at all ages, andno satisfactory fit to any current chemical evolution model. We discuss theseresults and their implications for the formation and evolution of the SMC.