AGB evolution and nucleosynthesis at low-metallicity constrained by the star formation history of our galaxy

Abstract

We construct a binary population synthesis model to constrain the AGB evolution models from the star formation history of the Galaxy through the comparisons of model stars with observed extremely metal-poor stars. The binary population model includes the effects of AGB evolution and binary mass transfer for a given IMF and binary period distribution function. We discuss the origins of extremely metal-poor stars with enhancement of carbon or nitrogen, with the possible effect of mass loss at low-metallicity taken into account. Our results strongly support high-mass dominated star formation during the early epoch of the Galaxy in order to explain the observed frequency of carbon and nitrogen enhancements that are thought to result from mass transfer from a former AGB binary companion. Our model also favours the suppression of mass loss at low-metallicity to reduce the number of the possible progenitors of nitrogen-enhanced stars when we adopt a massive star dominated IMF. Show more