Star clusters Magellanic Cloud

Discovery of Galactic Li-rich red giants (McKellar 1940) came years before either the proposal of the 7Be-transport mechanism or the identification of a luminous AGB star with a HBCE as a plausible site. Quantitative checks on production in such AGB stars (Sackmann Boothroyd 1992) were made possible with the discovery of Li-rich AGB stars in the LMC and SMC (Smith Lambert 1989, 1990 Plez et al. 1993) - see Fig. 3. These are being extended through observations of AGB stars in Magellanic Cloud clusters. Reliable distances to the Clouds enable the stellar luminosity and mass to be estimated, a task impossible with any precision for Galactic field stars. Confrontation of theory and observation confirmed that Li-production occurs in AGB stars of about 4-6 M0 at about the predicted level. Several factors stand between this result and an assessment of AGB stars as 7Li factories effective on the galactic scale. Uncertainties surround both the production of 7Li via the 7Be-transport mechanism and the return of the 7Li via the stellar winds. 

The three broad classifications (elliptical, spiral and irregular) of star clusters that also cluster together to form the Local Group that contains the Milky Way and the Andromeda Galaxy, along with the Small and Large Magellanic Clouds... 

At luminosities above the MS and S stars in the Magellanic Cloud clusters, we find cool (N type) carbon stars in which the third dredge-up has increased the C/O ratio to >1. There have been many studies of the carbon stars in the Magellanic Clouds a good review and comparison of this work with theory is given by Iben and Renzini (1983), with some more recent work being found in Lattanzio (1986). 

By observing the luminosities of the brightest AGB stars in clusters of different age in the Magellanic Clouds, the final AGB luminosity can be found as a function of age or initial mass a recent summary of this work is given by Mould and Aaronson (1987). For clusters of age 2-3x10 years, the final AGB luminosity is MboI = -5, in agreement with the... 

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