The chemical inventory of peculiar globular clusters: a divergence from the norm

This PhD Thesis was aimed at obtaining a chemical characterization of the stellar populations of three peculiar stellar systems, namely ω Centauri, Liller 1, and M 54. Historically these systems were classified as globular clusters due to their morphology, but nowadays it is widely recognized that they are actually more complex systems than previously believed. ω Centauri is the most massive system among the globular clusters, but with a wide metallicity spread that is not usually observed in genuine globulars. Moreover, ω Centauri displays the typical features of globular clusters, i.e. the anticorrelations among light-elements. I investigated the role of the complete MgAl burning chain in shaping the stellar populations of ω Centauri. Liller 1 is a massive and metal-rich stellar system located in the Bulge of the Milky Way. Very recently it was found to host two different populations of stars: an old and metal-poor subpopulation (13 Gyr and [Fe/H]= −0.3 dex) and a young and metal-rich one (∼ 2 Gyr and [Fe/H] = +0.3 dex). Thanks to its peculiar properties Liller 1 was suggested to be a remnant of the early epoch of Bulge formation. I presented a complete chemical characterization of the Liller 1 populations, finding that its stars follow the same chemical pattern of the Bulge field, with the metal-poor stars being enhanced in [α/Fe] and the metal-rich stars having solar scaled [α/Fe]. M 54 is a massive globular cluster located at the center of the remnant of the Sagittarius dwarf galaxy, that akin to ω Centauri displays a wide metallicity spread. It is considered to be part of the nuclear star cluster of the Sagittarius galaxy. I analyzed the largest high-resolution spectroscopic dataset obtained so far of M 54 members, finding evidence that the complete MgAl burning chain was active in this cluster.