Probing the nature of GCs multiple populations through chemistry: Li and heavy elements

Globular clusters have been widely studied in terms of light element variations present in their different stellar populations. However, the nature of the polluter(s) responsible for this phenomenon is still debated. The study of heavy elements and their relation to light ones can provide further constraints. To do so, this thesis studied two samples looking to approach the problem from different aspects. In the first one 217 stars of the metal-poor globular cluster, NGC 6752 were analysed through spectrum synthesis on GIRAFFE and UVES spectra to get the Li, Na, Mg, Al, Ca, Sc, Cu, Y, and Ba abundances. By doing so, this thesis aims both to gain insight into the nature of the polluter(s) responsible for the abundance variations and the C-N, Na-O, Al-Mg anti-correlations associated with the multiple-population phenomenon and to explore the possible contribution of asymptotic giant branch stars of different stellar masses to the internal pollution in the cluster. In addition to a continuous Li depletion of the average content from unevolved to evolved stars, there was detected a large Li spread at every log g. There were identified second-generation stars with Li content suggesting the need for Li production, known to happen in intermediate-mass (4-8 Msun) asymptotic giant branch stars through the Cameron-Fowler mechanism. Moreover, there were not found clear relations between the light s-process elements (represented by Y II) or heavy ones (represented by Ba II) with light elements (Li, Na, or Al). This indicates that the polluter(s) responsible for the Na (Al) or Li production does not produce large amounts of Y II and Ba II. Furthermore, the comparison with models discards a possibly significant contribution to the cluster pollution from AGB stars with masses lower than 5 Msun. In the second one, a large sample of 210 stars of 18 globular clusters with a large range of metallicities was analysed. The abundances of Cu, Y, Ba, La, and Eu were derived through spectral synthesis applied to UVES spectra. Using the mentioned data, the present thesis aims to analyse both the individual chemical enrichment and the overall behaviour of these clusters with respect to the galactic field. With some exceptions these clusters follow closely the patterns found in the field for stars with similar metallicity, however, a significant spread was found in some clusters suggesting enrichment in s- and/or r-process elements. In addition, it was found evidence of a weak -but significant- correlation between Y/Ba and Na in the mid-metallicity regime, which will be further investigated. Finally, intriguing suggestions of different chemical enrichment in n-capture elements between in-situ and accreted clusters, in which the first display a steeper distribution along with the orbital energy compared to the second ones. This result should be compared with chemical evolution models.