Multiple populations in globular clusters: Unified efforts from stellar
  evolution and chemical evolution models
  Recent stellar evolution models for globular clusters (GCs) in multiple
population paradigm suggest that horizontal-branch (HB) morphology and mean
period of type ab RR Lyrae variables are mostly determined by He & CNO
abundances and relative ages for subpopulations. These parameters are also
provided by chemical evolution models constructed to reproduce the Na-O
anti-correlation. Therefore, a consistency check is possible between the
synthetic HB and chemical evolution models. Furthermore, by combining them, a
better constraint might be attained for star formation history and chemical
abundances of subpopulations in GCs. We find, from such efforts made for four
GCs, M4, M5, M15, and M80, that consistent results can be obtained from these
two independent studies. In our unified model, He and Na abundances gradually
increase over the generation, and therefore, the various extensions observed in
both HB morphology and Na-O chemical pattern depend on the presence of later
generation stars after the second generation. It is schematically shown that
this observed diversity, however, would not be naturally explained by the
models requiring dilution. Further spectroscopic observations are required, for
metal-poor GCs in particular, to obtain a more detailed constraint from this
approach.
