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-4.5Suda, Takuma*; Komiya, Yutaka*; Nishimura, Takanori*; Iwamoto, Nobuyuki; Aikawa, Masayuki*; Fujimoto, Masayuki*
AIP Conference Proceedings 1016, p.43 - 48, 2008/05
The first stars in our Universe are the useful probes for the star formation history in the very early Universe. In order to identify these survivors, we should consider the effect of changing surface abundances during their long lives. The surface abundances are modified by the accretion of gas from the interstellar matter and/or the binary mass transfer. The latter can affect the abundance pattern through the evolution of primary star that experienced the internal mixing and dredge-up during thermally pulsating AGB. The top three of the iron deficient stars are reported as the candidates of the first stars. These stars have [Fe/H] -4.5 and share the common feature of large enhancement of C. We argue that these abundance patterns are testified to the evolutionary characteristics of the first stars with low- and intermediate-mass by trying to constrain the mass of primary under the assumption that they were the survivors of secondary stars in the binary system when they were born.
Nishimura, Takanori*; Aikawa, Masayuki*; Iwamoto, Nobuyuki; Suda, Takuma*; Fujimoto, Masayuki*; Iben, I. Jr.*
AIP Conference Proceedings 1016, p.421 - 423, 2008/05
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.
Nishimura, Takanori*; Iwamoto, Nobuyuki; Suda, Takuma*; Aikawa, Masayuki*; Fujimoto, Masayuki*; Iben, I. Jr.*
AIP Conference Proceedings 847, p.455 - 457, 2006/07
We investigated the progress of nucleosynthesis in the helium flash driven convective zone which triggers the mixing of hydrogen into this convective zone in the extremely metal-poor, asymptotic giant branch stars with low and intermediate masses. The amounts of C created by proton captures on abundant C in He layer strongly depend on the resultant abundances of nuclei. We showed that under circumstances initially devoid of metals, the heavy 
-process elements such as Sr, Ba and even Pb can be formed with light elements as seeds which are produced via two neutron-recycling reactions (C(n,
)C(,n)O and O(n,)O(,n)Ne).
