出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The metal-free and extremely metal-poor stars of low- and intermediate-masses experience a mixing
event of hydrogen into the convection driven by the helium shell flashes during early TP-AGB
phase, differently from metal-rich stars. We study the nucleosyntesis in the helium convective
zone with hydrogen mixing by computing the progress of nucleosynthesis with 13C formed from
the mixed proton as a neutron source by a nuclear network covering from hydrogen through sulfur.
In the dearth of the pristine metals, the neutron-recycling reactions, 12C(n;g )13C(a;n)16O,
and the subsequent 16O(n;g )17O(a;n)20Ne reactions promote the syntheses of oxygen through
magnesium and still heavier elements, including their neutron-rich isotopes and the odd atomic
number elements. Our results are compared with the observations of the most iron-deficient,
carbon-rich stars of HE 0107-5240 ([Fe=H] = 5:3), HE 1327-2326 ([Fe=H] = 5:4) and HE
0557-4840 ([Fe=H] = 4:75) to show that their peculiar abundance patterns of light elements can
be reproduced in terms of the nucleosynthesis of metal-free AGB stars of different masses. These
three stars were born as the low-mass members of Population III binaries and later subject to the
surface pollution both by the mass transfer in the binary systems and by the accretion of interstellar
gas. The other extremely metal-poor stars also have evolved from the binaries with low- and
intermediate-mass primary stars.
