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Chiba, Satoshi; Koura, Hiroyuki; Maruyama, Toshiki; Ota, Masahisa*; Tatsuda, Sayuki*; Wada, Takahiro*; Tachibana, Takahiro*; Sumiyoshi, Kosuke*; Otsuki, Kaori*; Kajino, Toshitaka*
AIP Conference Proceedings 1016, p.162 - 167, 2008/05
Effect of the 
-delayed fission in r-process abundance is investigated. The data base for the fission fragment mass distribution used in the r-process network calculation is constructed based on the 2-center shell model and Langevinequation. The -decay rates (no emissive, neutron emission and -delayed fission) are also newly calculated with the gross theory. The differences appeared in the final element abundance calculated with and without fission process are demonstrated and the mass region modified by the fission products is presented.
and 
cross sections of the 
C(
O reaction at 
1.4 MeV using pulsed 
beamsMakii, Hiroyuki; Nagai, Yasuki; Mishima, Kenji*; Segawa, Mariko; Shima, Tatsushi*; Ueda, Hitoshi; Igashira, Masayuki*
AIP Conference Proceedings 1016, p.215 - 220, 2008/05
The C(O reaction plays an important role in stellar evolution at the stage of helium-burning. However, the cross section at low energy still has a large uncertainty mainly due to the poor determination of the 
ratio. We have installed a new system to measure the 
-ray angular distribution of the C(O reaction to accurately determine the 
and 
. In this experiment, we used high efficiency anti-Compton NaI(Tl) spectrometers to detect a -ray from the reaction with a large S/N ratio, intense pulsed beams to discriminate true events from neutron induced background with a time-of-flight method, and the monitoring system of target thickness. We succeeded in removing a background due to neutrons and could clearly detect the -ray from the C(O reaction with high statics.
Os, 
Os, and 
Os and the Re-Os chronologySegawa, Mariko; Nagai, Yasuki*; Masaki, Tomohiro*; Temma, Yasuyuki*; Shima, Tatsushi*; Mishima, Kenji*; Igashira, Masayuki*; Goriely, S.*; Koning, A.*; Hilaire, S.*
AIP Conference Proceedings 1016, p.448 - 450, 2008/05
Re-Os pair is known as the most promising nuclear cosmochronometer with considerable potential. However, there remains non-trivial problems related to an excited neutron capture reaction of Os at a stellar temperature. Firstly, Os is produced and depleted by the slow process nucleosynthesis. Hence, it is necessary to obtain both the production and depletion rates of Os. Secondly, Os is depleted not only by its ground state neutron capture reaction but also by an excited state neutron capture reaction of Os in a stellar temperature. In the present study, we have measured the neutron capture reaction cross sections for Os, Os and Os accurately and neutron inelastic scattering reaction cross section for Os off the ground state of Os to its 9.75 keV first excited state in the neutron energy range from 10 to 100 keV.
-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.
Iwamoto, Nobuyuki
AIP Conference Proceedings 1016, p.127 - 133, 2008/05
We evolve thermally pulsing AGB star models in the mass of 
. The metallicity is assumed to be [Fe/H] 
. The 1 and 
AGB models produce Li in an H-flash event. The occurrence of this event is associated with the ingestion of protons from the overlying H-rich envelope into the He-flash driven convective shell during thermal pulse phase. The resulting Li abundances are higher than the primordial one. The present investigation also confirms the efficient production of Li by the HBB in the intermediate-mass AGB stars. If these AGB stars belong to a binary system with a low-mass companion, mass loss from the primary AGB star transfers the materials enriched in Li to the surface of the secondary star and makes the surface composition Li-rich. The nucleosynthesis of the other light elements is also followed until the end of the AGB phase. We find that the yields of the low metallicity AGB stars well reproduce the abundance patterns of extremely metal-poor stars.
Tominaga, Nozomu*; Umeda, Hideyuki*; Maeda, Keiichi*; Iwamoto, Nobuyuki; Nomoto, Kenichi*
AIP Conference Proceedings 1016, p.49 - 54, 2008/05
We investigate hydrodynamical and nucleosynthetic properties of the jet-induced explosion of a population III 40M
star with a two-dimensional special relativistic hydrodynamical code and compare the abundance patterns of the yields with those of the metal-poor stars. We conclude that (1) the ejection of Fe-peak products and the fallback of unprocessed materials can account for the abundance patterns of the extremely metal-poor stars and that (2) the jet-induced explosion with different energy deposition rates can explain the difference of the abundance patterns of the metal-poor stars.
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.
