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Santi Cassisi |
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It had always been considered that the value of
studying GCs is that they host simple, single stellar populations,
i.e., that stars belonging to the same cluster share the same
distance, age and chemical composition. However, in recent times, on
the basis of accurate photometric and spectroscopic investigations,
several exciting results have been obtained, such as the existence
of anti-correlations between some chemical elements, the presence of
multiple stellar populations in the same cluster, and peculiar
features along the Horizontal Branch. Many of these outcomes
severely challenge our understanding of stellar evolution and of
evolution/formation mechanism of stellar clusters. |