Abstract
IntegratedUBV colours have been computed for synthetic clusters older than one billion years and for two chemical composition: (a)Y=0.30;Z=10−4 and (b)Y=0.30;Z=10−2, taking into account the contribution to the integrated light of Main Sequence, subgiant, red giant and horizontal branch stars. It has been found that integrated colours depend onZ and allow an estimate of the metal content, however not generally. Horizontal branch stars contribute to the integrated colours of clusters not significantly and the contribution of stars in more advanced phases (e.g., asymptotic branch stars) is almost negligible.
Old clusters in LMC and SMC have been studied in terms of colour calibrations and this analysis has been supplemented, when possible, by photometric and spectroscopic data of individual stars. It was found that in the LMC clusters withZ=10−2 andt>5×109 yr are lacking, clusters with relatively blue colours are similar, both in age and chemical composition, to the halo galactic globular clusters. Moreover, there is a group of clusters with 1×109≤t≤5×109. In the SMC clusters withZ=10−2 andt>5×109 yr are lacking and clusters with 1×109≤t≤5×109 are rare. Clusters with relatively blue colours are interpreted with the following parameters:t=5×109 yr, 10−4≤Z≤10−3 andY=0.20.
The implication of these results on the chemical history of the two galaxies is discussed.
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Barbaro, G. The system of old clusters in the magellanic clouds. Astrophys Space Sci 83, 143–162 (1982). https://doi.org/10.1007/BF00648546
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DOI: https://doi.org/10.1007/BF00648546