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We give new constraints on the cosmological evolution with a decaying cosmological term from the recent observations of temperature-redshift relations. In our study, the cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the photon temperature is different from that of the standard ΛCDM model. We can obtain the parameter region derived from the CMB temperature observation.

We examine explosive nucleosynthesis during neutrino-driven, aspherical supernovae of Population III stars, based on two-dimensional (2D) hydrodynamic simulations of the explosion of 11-40M⊙ stars with zero metallicity. The magnitude and asymmetry of the explosion energy are estimated with the simulations. By post-processing calculations with a large nuclear reaction network, we have evaluated abundances and masses of ejecta from the aspherical SNe. We find that the evaluated abundance patterns are similar to those observed in extremely metal poor stars, as shown in spherical and 2D models, in which the explosion is manually and spherically initiated. Matter mixing induced via standing accretion shock instability is important for the abundances and masses of the SN ejecta.

We investigate the nucleosynthesis during the stellar evolution and the jet-like supernova explosion of a massive star of 70 M⊙ having the solar metallicity in the main sequence stage. The nucleosynthesis calculations have been performed with large nuclear reaction networks, where the weak s-, p-, and r-processes are taken into account. As a result s-elements of 60 > A > 90 and r-elements of 90 > A > 160 are highly overproduced relative to the solar system abundances. We find that the Sr-Y-Zr isotopes are primarily synthesized in the explosive nucleosynthesis which could be one of the sites of the lighter element primary process (LEPP).

We examine explosive nucleosynthesis during neutrino-driven, aspherical supernovae (SNe) of Population (Pop) III stars, based on two-dimensional (2D) hydrodynamic simulations of the explosion of 11-40M⊙ Pop III stars. The magnitude and asymmetry of the explosion energy are estimated with the simulations. By post-processing calculations with a large nuclear reaction network, we have evaluated abundances and masses of ejecta from the aspherical SNe. We find that the evaluated abundance patterns are similar to those observed in extremely metal poor stars, as shown in spherical and 2D models, in which the explosion is manually and spherically initiated. Faint SNe of 11 and 15M⊙ progenitors show large [C/Fe] > 0.7, as observed in C-enhanced metalpoor stars. Moreover, observed increasing trend of [C/O] towards for lower [O/H] could rely on a fact that [C/O] increases and [O/H] decreases for a progenitor with a lower mass.

We investigate the effects of a new 3-α reaction rate (OKK rate) on a He flash of a He accreting neutron star in a binary system. Since ignition points determine the properties of a thermonuclear flash of type I X-ray bursts, we examine the cases of different accretion rates, dM/dt (Ṁ). We find that, at low accretion rates, nuclear burning occurs at the He layers of rather low densities. As a consequence, He ignition would occur at accretion rate lower than M&dot ≃3×10−8M⊙yr−1 Furthermore we find that the OKK rate is consistent with the available observations of X-ray bursts on a He accreting neutron star. We advocate that the OKK rate is better than the previous rate for the astrophysical phenomena of X-ray burst due to He accretion.

Effect of a new 3-alpha reaction rate on the s-process during the evolution of a massive star of 25 solar mass is investigated for the first time, because the s-process in massive stars have been believed to be established with only minor change. We find that the s-process with use of the new rate during the core helium burning is very inefficient compared to the case with the previous 3-alpha rate. However, the difference of the overproduction is found to be largely compensated by the subsequent carbon burning. Since the s-process in massive stars has been attributed so far to the neutron irradiation during core helium burning, our finding reveals for the first time the importance of the carbon burning for the s-process during the evolution of massive stars.

We investigate the nucleosynthesis that includes the production of heavy elements beyond 7Li in the inhomogeneous big‐bang nucleosynthesis. We can get the parameter regions from light elements of 4He and D for the baryon‐to‐photon ratio obtained by CMB. In these allowed parameter region, we have confirmed that the heavy elements beyond Fe can be produced appreciably, where p‐ and/or r‐elements are produced well compared to the solar system abundances.

Recently, the central source of Cassiopeia A (Cas A) has been observed, which indicates that the star has large mass and high effective temperature. We suspect that the compact object cools by the standard neutrino emission. We assume that the compact object contains quark matter with colour superconductivity and calculate cooling curves. Considering the Quark‐Hadron Mixed Phase, we obtain cooling curves which are found to be consistent with the observations.

We investigate r‐process nucleosynthesis during magneto‐hydrodynamic supernova explosions driven by rapid rotations strong magnetic fields. These types of supernovae are very important not only for magnetar formation sites, but also for astronomical r‐process sites in astrophysics. Our r‐process nucleosynthesis simulations are based on the astronomical supernova explosion models, which follow the long‐term evolution in special relativistic magneto‐hydrodynamic simulations. We perform an r‐process nucleosynthesis simulation for magneto‐hydrodynamic jet supernova models based on a large nuclear reaction network including fully nuclear reactions. In our results, we find that a jet‐like supernova explosion model with strong magnetic field can occur successful r‐process nucleosynthesis.

We investigate explosive nucleosynthesis in a delayed neutrino‐driven, supernova explosion aided by standing accretion shock instability (SASI), based on two‐dimensional hydrodynamic simulations of the explosion of a 15 M⊙ star. We take into accounts neutrino heating and cooling as well as change in electron fraction due to weak interactions appropriately, in the two‐dimensional simulations. We assume the isotropic emission of neutrinos from the neutrino spheres with given luminosities. and the Fermi‐Dirac distribution of given temperatures. We find that the stalled shock revives due to the neutrino heating aided by SASI for cases with Lνe≥3.9×1052ergss−1 and the as‐pherical shock passes through the outer layers of the star (≥10,000 km), with the explosion energies of ∼1051ergs.Next we examine abundances and masses of the supernova ejecta. We find that masses of the ejecta and 56Ni correlate with the neutrino luminosity, and 56Ni mass is comparable to that observed in SN 1987A. We also find that abundance pattern of the supernova ejecta is similar to that of the solar system, for cases with high explosion energies of >1051ergs. We emphasize that 64Zn, which is underproduced in the spherical case, is abundantly produced in slightly neutron‐rich ejecta.

We investigate the possibility of the r‐process during the magnetohydrohynamical explosion of supernova in a massive star of 13 solar mass with the effects of neutrinos induced. We adopt five kinds of initial models which include properties of rotation and the toroidal component of the magnetic field. The simulations which succeed the explosions are limitted to a concentrated magnetic field and strong differential rotation. Low Ye ejecta produce heavy elements and the third peak can be reprocuced. However, the second peak is low because Ye distribution as a function of radius is steep and ejecta corresponding to middle Ye is very few.

Effects of a new triple‐α reaction rate on the ignition of carbon‐oxygen white dwarfs accreting helium in a binary systems have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type la supernova. We examine the cases of different accretion rates of helium and different initial masses of the white dwarf, which was studied in detail by Nomoto[4]. We find that for all cases from slow to intermediate accretion rates, nuclear burnings are ignited at the helium layers. As a consequence, carbon deflagration would be triggered for the lower accretion rate compared to that of dM/dt≃4×1O−8 M⊙ yr−1 which has been believed to the lower limit of the accretion rate for the deflagration supernova. Furthermore, off‐center helium detonation should result for intermediate and slow accretion rates and the region of carbon deflagration for slow accretion rate is disappeared.

We investigate nucleosynthesis inside magnetically driven jets ejected from rotating, magnetized massive stars, or collapsars, based on long‐term, magnetohydrodynamic simulations of the core collapse of six collapsars with the various distributions of magnetic fields and angular momentum before the collapse. We follow the evolution of the abundances of about 4000 nuclides from the collapse phase to the ejection phase and through the jet generation phase using a large nuclear reaction network. We find that the r‐process successfully operates in the jets from three collapsars, so that U and Th are synthesized abundantly, even when the collapsar have a relatively small magnetic field (1010 G) and a moderately rotating core before the collapse. The abundance patterns inside the jets are similar to that of the r‐elements in the solar system.

We investigate nucleosynthesis in collapsars, based on long-term, magnetohydrodynamic simulations of a rapidly rotating massive star of 40M{center_dot} during the core collapse. We have calculated detailed composition of magnetically driven jets ejected from the collapsars, in which the magnetic fields before the collapse, are uniform and parallel to the rotational axis of the star and the magnitudes of the fields, B0, are 1010 G or 1012 G. We follow the evolution of chemical composition up to about 4000 nuclides inside the jets from the collapse phase to the ejection phase through the jet generation phase with use of a large nuclear reaction network. We find that the r-process successfully operates in the jets from the collapsar of B0 = 1012 G, so that U and Th are synthesized abundantly. Abundance pattern inside the jets is similar to that of r-elements in the solar system. Furthermore, we find that p-nuclei are produced without seed nuclei: not only light p-nuclei, such as 74Se, 78Kr, 84Sr, and 92Mo, but also heavy p-nuclei, 113In, 115Sn, and 138La, can be abundantly synthesized in the jets. The amounts of p-nuclei in the ejecta are much greater than those in core-collapse supernovae (SNe). In particular, 92Mo, 113In,more » 115Sn, and 138La deficient in the SNe, are significantly produced in the ejecta. On the other hand, in the jets from the collapsar of B0 = 1010 G, the r-process cannot operate and 56Ni, 28Si, 32S, and 4He are abundantly synthesized in the jets, as in ejecta from inner layers of Type II supernovae. An amount of 56Ni is much smaller than that from SN 1987A.« less

We investigate the big‐bang nucleosynthesis (BBN) in a Brans‐Dicke model with a varying Λ term. We find that the cosmic expansion rate differs appreciably from that of the Friedmann model during the BBN epoch . The produced abundances of 4He, D, and 7Li are consistent with both the observed ones and the baryon density obtained from WMAP.

We investigate nucleosynthesis inside jets in a gamma ray bursts (GRB). We have calculated detailed composition of magnetically driven jets related to GRBs with post‐processing calculation, which is based on long‐term, magneto‐hydrodynamic simulations of a rapidly rotating massive star of 40M⊙ during core collapse. We follow abundance evolution of about 4000 nuclides inside the jets from the collapse phase to the ejection phase through the jet generation phase with a large nuclear reaction network. We find that the r‐process successfully operates inside the jets, so that U and Th are synthesized abundantly. Abundance pattern inside the jets is similar compared to that of r‐elements in the solar system. Heavy neutron‐rich nuclei ∼ 0.001M⊙ can be ejected through the jets. Furthermore, we find that p‐nuclei are produced without seed nuclei: not only light p‐nuclei, such as 74Se, 78Kr, 84Sr, and 92Mo, but also heavy p‐nuclei, 113In, 115Sn, and 138La, can be abundantly synthesized in the jets. The amounts of p...

We investigate the presupernova evolution and the explosive nucleosynthesis in massive stars from 13 to 70 M⊙. The explosion energy is assumed to be 1–1.5×1051 erg. We found that the amount of 56Ni produced ranges from 0.07 to 0.15 M⊙. The ratio between the produced and solar abundance agrees with each other within factor 2–3 for A≤32. For the 12C(α,γ)16O rate, our results indicate that the higher rate in 1985 will be better than the lower one.

We have calculated nucleosynthesis during neon nova explosions over wide ranges of the white dwarfs and envelope masses. As the results, we found considerably high mass ratio of 26Al can be produced in some nova events with higher masses of the white dwarfs and the envelopes. In addition, such novae produce substantial amount of 22Na, which has been expected to be detected by CGRO, as well as the clue of the Ne‐E problem.

The maximum angular velocity of uniformly rotating nuetron stars is investigated. If we consider a hot neutron star stage after the birth from supernova explosions, an upper limit of the angular velocity for uniformly rotating neutron stars becomes a little smaller than that obtained by the equation of state for cold neutron matters.