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A number of scenarios have been put forward to explain the origin of the chemical anomalies (and resulting complex colour-magnitude diagrams) observed in globular clusters (GCs), namely the AGB, Fast Rotating Massive Star, Very Massive Star, and Early Disc Accretion scenarios. We compare the predictions of these scenarios with a range of observations (including young massive clusters (YMCs), chemical patterns, and GC population properties) and find that all models are inconsistent with observations. In particular, YMCs do not show evidence for multiple epochs of star-formation and appear to be gas free by an age of ~3 Myr. Also, the chemical patterns displayed in GCs vary from one to the next in such a way that cannot be reproduced by standard nucleosynthetic yields. Finally, we show that the mass budget problem for the scenarios cannot be solved by invoking heavy cluster mass loss (i.e. that clusters were 10-100 times more massive at birth) as this solution makes basic predictions about the GC population that are inconsistent with observations. We conclude that none of the proposed scenarios can explain the multiple population phenomenon, hence alternative theories are needed.
Globular clusters (GCs) display anomalous light element abundances (HeCNONaMgAl), resembling the yields of hot-hydrogen burning, but there is no consensus yet on the origin of these ubiquitous multiple populations. We present a model in which a super
Evidence that the multiple populations (MPs) are common properties of globular clusters (GCs) is accumulated over the past decades from clusters in the Milky Way and in its satellites. This finding has revived GC research, and suggested that their fo
Globular cluster stars show chemical abundance patterns typical of hot-CNO processing. Lithium is easily destroyed by proton capture in stellar environments, so its abundance may be crucial to discriminate among different models proposed to account f
Since the discovery of chemically peculiar stars in globular clusters in the last century, the study of multiple populations has become increasingly important, given that chemical inhomogeneity is found in almost all globular clusters. Despite variou
We explain the multiple populations recently found in the prototype Globular Cluster (GC) NGC 2808 in the framework of the asymptotic giant branch (AGB) scenario. The chemistry of the five -or more- populations is approximately consistent with a sequ