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Journal Articles

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.*

AIP Conference Proceedings 1016, p.421 - 423, 2008/05

https://doi.org/10.1063/1.2943612

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 $$alpha$$-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 $$^{12}$$C($$n,gamma$$)$$^{13}$$C($$alpha,n$$)$$^{16}$$O and in some cases the subsequent $$^{16}$$O($$n,gamma$$)$$^{17}$$O($$alpha,n$$)$$^{20}$$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.

Journal Articles

Neutron-capture nucleosynthesis in the He-flash convective zone in extremely metal-poor stars

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

AIP Conference Proceedings 847, p.455 - 457, 2006/07

https://doi.org/10.1063/1.2234457

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 $$^{13}$$C created by proton captures on abundant $$^{12}$$C in He layer strongly depend on the resultant abundances of nuclei. We showed that under circumstances initially devoid of metals, the heavy $$s$$-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 ($$^{12}$$C(n,$$gamma$$)$$^{13}$$C($$alpha$$,n)$$^{16}$$O and $$^{16}$$O(n,$$gamma$$)$$^{17}$$O($$alpha$$,n)$$^{20}$$Ne).

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