Interpretation of extremely metal-poor stars as candidates of first generation stars

Nishimura, Takanori*; Aikawa, Masayuki*; Iwamoto, Nobuyuki  ; Suda, Takuma*; Fujimoto, Masayuki*; Iben, I. Jr.*

The evolution of extremely metal-poor stars of low- and intermediate-masses is distinct from those of metal-rich stars in that the convection driven by the helium shell flash can extend outward into the hydrogen-rich layer during TP-AGB phase. In the circumstance of [Fe/H]2.5, protons are mixed and converted into neutrons in the convective zone to promote nucleosynthesis through neutron and -captures. We study the nucleosynthesis in the helium-flash convective zone, induced by this hydrogen mixing. In the dearth of the pristine metals, the neutron-recycling reactions C()C()O and in some cases the subsequent O()O()Ne play and important role and catalyze the syntheses of O through Mg and still heavier elements. Based on these results, we assign the origin of two most iron-deficient stars to the Pop III stars, born out of the primordial gas.