Self-enrichment by asymptotic giant branch stars in globular clusters: comparison between intermediate and high metallicities

We present theoretical evolutionary sequences of intermediate-mass stars  ( M = 3 ? 6.5 M_⊙)  with metallicity   Z = 0.004  . Our goal is to test whether the self-enrichment scenario by massive asymptotic giant branch stars may work for the high-metallicity globular clusters, after previous works by the same group showed that the theoretical yields by this class of objects can reproduce the observed trends among the abundances of some elements, namely the O–Al and O–Na anticorrelations, at intermediate metallicities, i.e.  Fe/H]=?1.3  . We find that the increase in the metallicity favours only a modest decrease of the luminosity and the temperature at the bottom of the envelope for the same core mass, and also the efficiency of the third dredge-up is scarcely altered. On the contrary, differences are found in the yields, due to the different impact that processes with the same efficiency have on the overall abundance of envelopes with different metallicities. We expect the same qualitative patterns as in the intermediate-metallicity case, but the slopes of some of the relationships among the abundances of some elements are different. We compare the sodium–oxygen anticorrelation for clusters of intermediate metallicity ( Z ≈ 10^?3) and clusters of metallicity large as in these new models. Although the observational data are still too scarce, the models are consistent with the observed trends, provided that only stars of   M ? 5 M_⊙  contribute to self-enrichment.