[en] We discuss the possibility of the r-process nucleosynthesis in the core-collapse supernova of a low mass progenitor (9M_[odot]). This progenitor is composed of an O+Ne+Mg core and has a possibility to explode promptly prior to the neutrino heating. We simulate the prompt supernova explosion with one dimensional spherically symmetric hydrodynamics. In our results, this model cannot produce a successful supernova explosion by the prompt shock. We then obtain explosions by artificial enhancement of shock energy, and argue whether this type of supernovae can be the major r-process site in the Galaxy

[en] We investigate the black hole-neutron star binary merger in the contest of the r-process nucleosynthesis. Employing a hydrodynamical model simulated in the framework of full general relativity, we perform nuclear reaction network calculations. The extremely neutron-rich matter with the total mass 0.01 M_⊙ is ejected, in which a strong r-process with fission cycling proceeds due to the high neutron number density. We discuss relevant astrophysical issues such as the origin of r-process elements as well as the r-process powered electromagnetic transients. (paper)

[en] We determined the total reaction rate of the ¹¹C(α,p)¹⁴N reaction relevant to the nucleosynthesis in explosive hydrogen-burning stars. The measurement was performed by means of the thick target method in inverse kinematics with ¹¹C RI beams. We performed the identification of the ground-state transition and excited-state transitions using time-of-flight information for the first time.

[en] We study the few body reactions in explosive nucleosynthesis of light-to-heavy mass elements in various astrophysical conditions. In neutrino-driven winds of gravitational core collapse of SNeII, several light nuclei as well as heavy unstable nuclei play significant roles in producing r-process elements. We discuss how the three-body reaction ⁴He(αn, γ)⁹Be, whose cross section is poorly known, plays very critical role. We make note that several other reactions in the r-process are relevant to a big-bang nucleosynthesis. We discuss briefly a galactic chemical evolution. (author)

[en] Recent works show that the r-process can proceed by competition between neutron capture and β-decay in low temperature environments (< 5 × 10⁸ K; cold r-process) where photo-disintegration plays no role. This is in contrast to the traditional picture of the r-process in high temperature environments (∼ 1 × 10⁹ K; hot r-process) where the (n, γ)-(γ, n) equilibrium holds. In this study, we explore nucleosynthesis calculations based on a site-independent model to elucidate the physical conditions leading to cold and hot r-processes.

[en] Recent one-dimensional (1D) hydrodynamical simulations of core-collapse supernovae (CCSNe) with a sophisticated treatment of neutrino transport indicate the neutrino-driven winds being proton-rich all the way until the end of their activity. This seems to exclude all possibilities of neutron-capture nucleosynthesis, but provide ideal conditions for the νp-process, in neutrino winds. New 2D explosion simulations of electron-capture supernovae (ECSNe; a subset of CCSNe) exhibit, however, convective neutron-rich lumps, which are absent in the 1D case. Our nucleosynthesis calculations indicate that these neutron-rich lumps allow for interesting production of elements between iron group and N = 50 nuclei (Zn, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, with little Ga). Our models do not confirm ECSNe as sources of the strong r-process (but possibly of a weak r-process up to Pd, Ag, and Cd in the neutron-rich lumps) nor of the νp-process in the subsequent proton-rich outflows. We further study the νp-process with semi-analytic models of neutrino winds assuming the physical conditions for CCSNe. We also explore the sensitivities of some key nuclear reaction rates to the nucleosynthetic abundances. Our result indicates that the ν/p-process in CCSNe (other than ECSNe) can be the origin of p-nuclei up to A = 108, and even up to A = 152 in limiting conditions.

[en] We examine nucleosynthesis in the electron capture supernovae of progenitor asymptotic giant branch stars with an O-Ne-Mg core (with the initial stellar mass of 8.8 M _sun). Thermodynamic trajectories for the first 810 ms after core bounce are taken from a recent state-of-the-art hydrodynamic simulation. The presented nucleosynthesis results are characterized by a number of distinct features that are not shared with those of other supernovae from the collapse of stars with iron core (with initial stellar masses of more than 10 M _sun). First is the small amount of ⁵⁶Ni (0.002-0.004 M _sun) in the ejecta, which can be an explanation for the observed properties of faint supernovae such as SNe 2008S and 1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the spectroscopic result of the Crab nebula (the relic of SN 1054). Second is the large production of ⁶⁴Zn, ⁷⁰Ge, light p-nuclei (⁷⁴Se, ⁷⁸Kr, ⁸⁴Sr, and ⁹²Mo), and in particular, ⁹⁰Zr, which originates from the low Y_e (0.46-0.49, the number of electrons per nucleon) ejecta. We find, however, that only a 1%-2% increase of the minimum Y_e moderates the overproduction of ⁹⁰Zr. In contrast, the production of ⁶⁴Zn is fairly robust against a small variation of Y_e . This provides the upper limit of the occurrence of this type of events to be about 30% of all core-collapse supernovae.

[en] A quasi-analytic study on ONeMg novae is performed to examine explosive nucleosynthesis in wide range of white dwarf and envelope masses. Comparing our results with recent observations enables us to constrain those two parameters. About a half of observed ONeMg novae may have attained high envelope masses such as ∝10^-4M _odot, then obtained high burning temperatures ∝3-4 x 10⁸ K. Those may have produced significant amount of ²²Na. Leakage out of CNO material via alpha captures of ^14,15O is not of importance in our results but initially enhanced neon in the envelope must be seed nuclei for heavy element production by the rp-process. (orig.)

[en] We examine r-process nucleosynthesis in a 'prompt supernova explosion' from an 8 - 10 M_-bar progenitor star. We simulate energetic prompt explosions by enhancement of the shock-heating energy, in order to investigate conditions necessary for the production of r-process nuclei in such events. The r-process nucleosynthesis is calculated using a nuclear reaction network code including relevant neutron-rich isotopes with reactions among them. The highly neutronized ejecta (Y_e∼0.14-0.20) leads to robust production of r-process nuclei; their relative abundances are in excellent agreement with the solar r-process pattern

[en] Astrophysical stellar reactions at extremely high temperatures involve a variety of problems both in nuclear reactions and nuclear structures. Specifically, the problems in the νpprocess were discussed in this talk based on our recent experimental results with low-energy RI beams and a simulation study. The νp-process is one of the key processes for investigating the mechanism of type II supernovae, and the process could be possibly responsible for 'the excess production' of p-nuclei around mass 90-100. Alpha cluster resonances have been discovered experimentally to play a crucial role for the stellar (α, p) reactions just above the alpha threshold. Neutron induced reactions in the proton-rich nuclear regions in the νp-process are also suggested to play an important role, which involve nuclear structures of high level density at high excitation energies, probably giant resonances. The discussion also covered the p-nuclei production through the νp-process at around mass 100.