Search

We investigate the significance of isomers on a kilonova associated with neutron star mergers (NSMs) for the first time. We calculate the evolution of abundances and energy generation rates ($\dot{\epsilon}_{\rm nuc}$) of ejecta from NSMs, taking into account $\beta^-$ decay through isomers. We find that for ejecta with electron fraction ($Y_e$) of $0.2-0.3$, $\dot{\epsilon}_{\rm nuc}$ is appreciably changed from those without isomers, due to the large change in timing of $\beta^-$ decay through the isomeric states of ${}^{123, 125, 127} \rm Sn$ and ${}^{128} \rm Sb$. In particular, the effects of the isomers on $\dot{\epsilon}_{\rm nuc}$ are prominent for ejecta of $Y_e \sim 0.25$, which could emit a fraction of an early, blue component of a kilonova observed in GW170817. When the excitation from a ground state to its isomeric state is important, the isomers of ${}^{129} \rm Sb$ and ${}^{129, 131} \rm Te$ also cause additional and appreciable change in $\dot{\epsilon}_{\rm nuc}$. Furthermore, we demonstrate that larger amounts of lanthanide-free ejecta result in a better fit of an observed light curve of the kilonova in GW170817 if the isomers are taken into account., Comment: 6 pages, 4 figures. Accepted for publication in MNRAS

The isotope $^{98}\mathrm{Tc}$ decays to $^{98}\mathrm{Ru}$ with a half-life of $4.2\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\text{ }\mathrm{yr}$ and could have been present in the early Solar System. In this Letter, we report on the first calculations of the production of $^{98}\mathrm{Tc}$ by neutrino-induced reactions in core-collapse supernovae (the $\ensuremath{\nu}$ process). Our predicted $^{98}\mathrm{Tc}$ abundance at the time of solar system formation is not much lower than the current measured upper limit raising the possibility for its detection in the not too distant future. We show that, if the initial abundance were to be precisely measured, the $^{98}\mathrm{Tc}$ nuclear cosmochronometer could be used to evaluate a much more precise value of the duration time from the last core-collapse supernova to the formation of the solar system. Moreover, a unique and novel feature of the $^{98}\mathrm{Tc}$ $\ensuremath{\nu}$-process nucleosynthesis is the large contribution ($\ensuremath{\sim}20%$) from charged current reactions with electron antineutrinos. This means that $^{98}\mathrm{Tc}$ becomes a unique new $\ensuremath{\nu}$-process probe of the temperature of the electron antineutrinos.

Many alternative models are proposed, though remarkable agreement is obtained on the primordial abundance of standard BBN. As an approach to nonstandard models, first we investigate a possibility that neutrinos or antineutrinos are degenerate. An excess density of neutrinos speeds up the expansion of the universe, leaving more neutrons at the onset of nucleosynthesis. In addition, degenerate electron-neutrinos shift less neutrons through β-equilibrium. Performing χ2 analysis for the calculated and observed abundances of 4He and D, we determine the plausible ranges of the degeneracy parameter and the baryon-to-photon ratio. Next, we explore BBN under the brane-world cosmology. The Friedmann-like equation is derived in the five-dimensional universe. It is found that more 4He is produced than in standard BBN because of rapid expansion due to the interaction energy on the brane. Finally, we examine thermal evolution in the early universe including a decaying cosmological term which is treated as a source of the gravitational field.

We review the recent progress in the Big-Bang nucleosynthesis which includes the standard and nonstandard theory of cosmology, effects of neutrino degeneracy, and inhomogeneous nucleosynthesis within the framework of a Friedmann model. As for a nonstandard theory of gravitation, we adopt a Brans–Dicke theory which incorporates a cosmological constant. We constrain various parameters associated with each subject.

We reinvestigate effects of neutrino oscillations on the production of 7Li and 11B in core-collapse supernovae (SNe). During the propagation of neutrinos from the proto-neutron star, their flavors change and the neutrino reaction rates for spallation of 12C and 4He are affected. In this work corrected neutrino spallation cross sections for 4He and 12C are adopted. Initial abundances involving heavy s-nuclei and other physical conditions are derived in a new calculation of the SN 1987A progenitor in which effects of the progenitor metallicity are included. A dependence of the SN nucleosynthesis and final yields of 7Li and 11B on the neutrino mass hierarchy are shown in several stellar locations. In the normal hierarchy case, the charged current reaction rates of electron neutrinos are enhanced, and yields of proton-rich nuclei, along with 7Be and 11C, are increased. In the inverted hierarchy case, the charged current reaction rates of electron antineutrinos are enhanced, and yields of neutron-rich nuclei, along with 7Li and 11B, are increased. We find that variation of the metallicity modifies the yields of 7Li, 7Be, 11B, and 11C. This effect is caused by changes in the neutron abundance during SN nucleosynthesis. Therefore, accurate calculations of Li and B production in SNe should take into account the metallicity of progenitor stars., 25 pages, 22 figures, 3 tables, accepted for publication in ApJ, minor corrections added

We investigate the observational constraints on the inhomogeneous big-bang nucleosynthesis that Matsuura et al. (2005) suggested that states the possibility of the heavy element production beyond 7Li in the early universe. From the observational constraints on light elements of 4He and D, possible regions are found on the plane of the volume fraction of the high-density region against the ratio between high- and low-density regions. In these allowed regions, we have confirmed that the heavy elements beyond Ni can be produced appreciably, where p- and/or r-process elements are produced well simultaneously.

We investigate the nucleosynthesis in a massive star of 70 M_solar with solar metallicity in the main sequence stage. The helium core mass after hydrogen burning corresponds to 32 M_solar. Nucleosynthesis calculations have been performed during the stellar evolution and the jetlike supernova explosion of a collapsar model, where the weak s-, p-, and r-processes are taken into account. We confirm that s-elements of 60 < A < 90 are highly overproduced relative to the solar abundances in the hydrostatic nucleosynthesis. During oxygen burning, p-elements of A > 90 are produced via photodisintegrations of seed s-elements. However, the produced p-elements are disintegrated in later stages except for ^{180}Ta. In the explosive nucleosynthesis, elements of 90 < A < 160 are significantly overproduced relative to the solar values owing to the r-process. Only heavy p-elements (N > 50) are overproduced via the p-process. Compared with the previous study of r-process nucleosynthesis calculations in the collapsar model of 40 M_solar by Fujimoto et al. 2007, 2008, our jet model cannot contribute to the third peak of the solar r-elements and intermediate p-elements. Averaging the overproduction factors over the progenitor masses with the use of Salpeter's IMF, we suggest that the 70 M_solar star could contribute to the solar weak s-elements of 60 < A < 90 and neutron-rich elements of 90 < A < 160. We confirm the primary synthesis of light p-elements in the ejected matter of high peak temperature. The ejected matter has [Sr/Eu] \sim -0.4, which is different from that of a typical r-process-enriched star CS22892-052 ([Sr/Eu] \sim -1). We find that Sr-Y-Zr isotopes are primarily synthesized in the explosive nucleosynthesis in a similar process of the primary production of light p-elements, which has been considered as one of the sites of a lighter element primary process (LEPP)., 25 pages, 13 figures, 2 tables, accepted for publication in Progress of Theoretical Physics

We investigate the nucleosynthesis of a massive star whose mass in the main sequence stage is Mms = 70 M that corresponds to the helium core or helium star of Mα = 32 M . Numerical calculations of the nucleosynthesis are performed during the stage of hydrostatic stellar evolution until the core composed of iron-group nuclei (Fe core) begins to collapse. A collapsar model whose jets are driven by two-dimensional magnetohydrodynamical effects of a differentially rotating core is constructed. The explosive nucleosynthesis inside the jets of a specified collapsar model is followed along the trajectories of stream lines. We combine the results of both detailed hydrostatic and explosive nucleosyntheses to compare the solar system abundances. We show that the agreement is considerably improved compared with the case without the detailed hydrostatic nucleosynthesis included. We suggest that many radioactive nuclei such as Ti and Ni are produced if the jets continue for more than 10 s, which would become crucial for the observation of abundance distribution in young supernova remnants.

We have made detailed calculations of the composition of magnetically driven jets ejected from collapsars, or rapidly rotating massive stars, based on long-term magnetohydrodynamic simulations of their core collapse with various distributions of magnetic field and angular momentum before 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 only in energetic jets (> 1e51 ergs), such that U and Th are synthesized abundantly, even when the collapsar has a relatively weak magnetic field (1e10 G) and a moderately rotating core before the collapse. The abundance patterns inside the jets are similar to those of the r-elements in the solar system. About 0.01-0.06 Msun neutron-rich, heavy nuclei are ejected from a collapsar with energetic jets. The higher energy jets have larger amounts of Ni56, varying from 0.00037 to 0.06Msun. Less energetic jets, which eject small amounts of Ni56, could induce a gamma-ray burst (GRB) a supernova, such as GRB 060505 or GRB 060614. Considerable amounts of r-elements are likely to be ejected from GRBs with hypernovae, if both the GRB and hypernova are induced by jets that are driven near the black hole., 10 pages, 14 figures, 1 table, Accepted for publication in the Astroph ysical Journal

We investigate synthesis of heavy elements in a collapsar. We have calculated detailed composition of magnetically driven jets ejected from a collapsar, which is based on long-term, magneto-hydrodynamic simulations of a rapidly rotating massive star of 40Msun during core collapse. We follow evolution of abundances of about 4000 nuclides from the collapse phase to the ejection phase through the jet generation phase with use of two large nuclear reaction networks. We find that the r-process successfully operates in the jets, so that U and Th are synthesized abundantly when the progenitor has large magnetic field of 10^{12} G and rapidly rotating core. Abundance pattern inside the jets is similar compared to that of r-elements in the solar system. Heavy neutron-rich nuclei \sim 0.01Msun can be ejected from the collapsar. The detailed abundances depend on nuclear properties of mass model, beta-decay rate, and fission, for nuclei near the neutron drip line. Furthermore, we find that p-nuclei are produced without seed nuclei: not only light p-nuclei, such as Se74, Kr78, Sr84, and Mo92, but also heavy p-nuclei, In113, Sn115, and La138, 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, Mo92, In113, Sn115, and La138 deficient in the SNe, are significantly produced in the ejecta., Comment: 16 pages, 19 figures, submitted to the Astrophysical Journal

We investigate $r$-process nucleosynthesis during the magnetohydrodynamical (MHD) explosion of supernova in a massive star of 13 $M_{\odot}$. Contrary to the case of the spherical explosion, jet-like explosion due to the combined effects of the rotation and magnetic field lowers the electron fraction significantly inside the layers above the iron core. We find that the ejected material of low electron fraction responsible for the $r$-process comes out from the silicon rich layer of the presupernova model. This leads to the production up to the third peak in the solar $r$-process elements. We examine whether the fission affects the $r$-process paths by using the full nuclear reaction network with both the spontaneous and $\beta$-delayed fission included. Moreover, we pay particular attention how the mass formula affects the $r$-process peaks with use of two mass formulae. It is found that both formulae can reproduce the global abundance pattern up to the third peak though detailed distributions are rather different. We point out that there are variations in the $r$-process nucleosynthesis if the MHD effects play an important role in the supernova explosion.

We investigate nucleosynthesis inside an accretion disk formed during a collapse of a massive star. The mass accretion rate and the mass of a central object vary with time according to a fall-back scenario. The disk is confirmed to be dominated by advection. A considerable amount of Fe-group elements is produced inside the disk through a sequence of ( α , γ ) reactions, and the processed material is ejected via outflows. The collapsar accretion disk is an promising site for production of heavy elements.

We investigate the r-process that occurs due to the explosion from an inner region of the Fe-core. It is shown that the solar r-process abundances are rather well reproduced for a model of 13 M ⊙ . We also examine whether the fission affects final r-process abundances by using the full nuclear reaction network with both spontaneous and the β -delayed fission included. Moreover, we pay attention how the mass formula affects the r-process peaks by using two networks.

We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind and a nuclear reaction network. Far from a central black hole, the composition of accreting gas is taken to be that of an O-rich layer of a massive star before core collapse. We find that the disk consists of five layers characterized by dominant elements: O16, Si28, Fe54 (and Ni56), He4, and nucleons, and the individual layers shift inward with keeping the overall profiles of compositions as the accretion rate decreases. Ni56 are abundantly ejected through the wind from the inner region of the disk with the electron fraction \simeq 0.5. In addition to iron group, elements heavier than Cu, in particular Cu63 and Zn64, are massively produced through the wind. Various neutron-rich nuclei can be also produced in the wind from neutron-rich regions of the disk, though the estimated yields have large uncertainties.

Presolar grains have large isotopic anomalies revealing the traces of nucleosynthesis at their birth, and thus they are considered to originate from stellar outflows and supernova ejecta. These grains have been extracted from primitive meteorites, and the isotopic ratios of each individual grain have been analyzed in the laboratory. Several isotopic signatures of SiC X and low-density graphite grains indicate an origin in supernovae. We investigate the isotopic ratios of Type II supernova ejecta with large-scale mixing so as to reproduce the ratios of as many ratios from supernovae as possible. We pursued the evolution and the supernova explosion of a massive star using a 4 M☉ He star model and calculated detailed nucleosynthesis by postprocessing. We then show how many isotopic ratios of each individual grain agree with those of the mixtures of the supernova ejecta under appropriate mixing ratios. We assume two cases of mixtures with artificial mixing ratios: one consists of Si/S, O/Ne, He/C, and He/N layers, and the other consists of Ni, Si/S, He/C, and He/N layers. We select the isotopic ratios of 12C/13C, 14N/15N, 26Al/27Al, 29Si/28Si, 30Si/28Si, and 44Ti/48Ti from eleven SiC X grains and four low-density graphite grains that contain evidence for the original presence of the short-lived isotope 44Ti. For one SiC X grain and one low-density graphite grain, four isotopic ratios are reproduced by the corresponding mixtures. For seven SiC X grains and three graphite grains, three isotopic ratios agree with those of the mixtures. Most mixtures that reproduce the isotopic ratios of the grains have a large contribution from the He/N layer. The characteristics of the mixtures are found to be 0.01 0.1. For C/O < 0.1, the isotopic ratios of most grains are not reproduced.

Taking into account the increasing mass of a central object through fall-back, we investigated nucleosynthesis inside an accretion disk formed during a core collapse of a massive star. It has been confirmed that the disk is an advection-dominated accretion flow supported by gas or radiation pressure. A sequence of (α, γ) reactions take place and Fe-group elements are produced inside the disk. At the early phase of the fall-back, when O-rich materials inflow, the ejected gas contains abundant 54 Fe and 56,58 Ni. At the late phase the in-coming material is He-rich and the out-going gas is abundant of 44 Ti as well as Fe and Ni. Provided that the processed gas outflows from the inner region up to the ejection radius, rej, we find that the ejected mass of the heavy elements is not very sensitive to rej, as long as we take rej ≥ 50 rg, because these elements are produced mainly in the region 20–100 rg.

Using both shell-flash and realistic models on accreting neutron stars with the full nuclear reaction network up to Bi, we investigate the detailed relation between the final products of the rp-process and the ignition pressure. We find that nuclear fuels of H and 4 He are almost burned out after the flash and that the mass number of synthesized nuclei reaches to '100 in the pressure range from 10 23 to 10 23.5 dyn cm � 2 for an eutron star of 1.4Mand 10 km radius. Furthermore, p-nuclei up to 126 Xe are found to be produced after the flash, thanks to our large network. The postprocess nucleosynthesis for accretion rates of 3 � 10 � 10 ,3 � 10 � 9 , and 10 � 8 Myr � 1 , which corresponds to an ignition pressure from 10 22:7 to 10 22:9 dyn cm � 2 , reveals that H is exhausted completely during the burst. This is because H decreases significantly as a result of the steady burning before the burst and convective mixing at the initial stage; we find that 64 Zn is the most abundant element after the burst. Subject headings: accretion, accretion disks — nuclear reactions, nucleosynthesis, abundances — stars: neutron — X-rays: bursts

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M_solar, using the self-similar solution of an optically thick advection dominated flow. Supercritical accretion is expected to occur in a supernova with fallback material accreting onto a new-born compact object. It is found that appreciable amounts of p-nuclei are synthesized via the p-process in supernova-driven supercritical accretion disks (SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs have similar feature to those of the oxygen/neon layers in Type II supernovae when the abundance of the fallback gas far from the compact object is that of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in the SSADs as in Type II supernovae. If the fallback gas is mixed with a small fraction of proton through Rayleigh-Taylor instability during the explosion, significant amounts of Mo92 are produced inside the SSADs. Ru96 and La138 are also produced when the fallback gas contains abundant proton though the overall abundance profile of p-nuclei is rather different from that of the solar system. The p-process nucleosynthesis in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if several percents of fallback matter are ejected via jets and/or winds., 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty, accepted for publication by the Astronomical Journal (March, 2003)

Comparing the latest observed abundances of 4He and D, we make a ?2 analysis to see whether it is possible to reconcile primordial nucleosynthesis using up-to-date nuclear data of NACRE II and the mean-life of neutrons. If we adopt the observational data of ${}^4_{}$He by Izotov et al., we find that it is impossible to get reasonable concordance against the standard Big-Bang nucleosynthesis. However, including degenerate neutrinos, we have succeeded in obtaining consistent constraints between the neutrino degeneracy and the baryon-to-photon ratio from detailed comparison of calculated abundances with the observational data of ${}^4_{}$He and D: the baryon-to-photon ratio in units of $10^{-10}$ is found to be in the range 6.02 < $��^{}_{10}$ < 6:54 for the specified parameters of neutrino degeneracy., 4 figures

The large abundance ratio of 44Ti/56Ni in Cassiopeia A is puzzling. In fact, the ratio seems to be larger than the theoretical constraint derived by Woosley & Hoffman. However, this constraint is obtained on the assumption that the explosion is spherically symmetric, whereas Cas A is famous for the asymmetric form of the remnant. Recently, Nagataki et al. calculated the explosive nucleosynthesis of axisymmetrically deformed collapse-driven supernova. They reported that the ratio of 44Ti/56Ni was enhanced by the stronger alpha-rich freezeout in the polar region. In this Letter, we apply these results to Cas A and examine whether this effect can explain the large amount of 41Ti and the large ratio of 44Ti/56Ni. We demonstrate that the conventional, spherically symmetric explosion model cannot explain the 44Ti mass produced in Cas A if its lifetime is shorter than ~80 yr and the intervening space is transparent to the gamma-ray line from the decay of 44Ti. On the other hand, we show that the axisymmetric explosion models can solve the problem. We expect the same effect from a three-dimensionally asymmetric explosion, since the stronger alpha-rich freezeout will also occur in that case in the region where the larger energy is deposited.

A quasi-analytic study on ONeMg novae is performed to examine 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 considerably high envelope masses such as ∼ 10 −4 M ⊗ , then obtained high burning temperatures ∼ 3–4 × 10 8 K. Those may have produced significant amount of 22 Na.

Oxygen to iron abundance ratios of metal-poor stars provide information on nucleosynthesis yields from massive stars which end in Type II supernova explosions. Using a standard model of chemical evolution of the Galaxy we have reproduced the solar neighborhood abundance data and estimated the oxygen and iron yields of genuine SN II origin. The estimated yields are compared with the theoretical yields to derive the relation between the lower and upper mass limits in each generation of stars and the IMF slope. Independently of this relation, we furthermore derive the relation between the lower mass limit and the IMF slope from the stellar mass to light ratio in the solar neighborhood. These independent relations unambiguously determine the upper mass limit of $m_u=50 \pm 10 M_sun$ and the IMF slope index of 1.3 - 1.6 above 1 M_sun. This upper mass limit corresponds to the mass beyond which stars end as black holes without ejecting processed matter into the interstellar medium. We also find that the IMF slope index below 0.5 M_sun cannot be much shallower than 0.8., 13 pages LaTex, 4 PostScript figures, to appear in ApJ (July 1, Vol.483)

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 ∼10−4 M⊙, then obtained high burning temperatures ∼ 3–4 × 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.

We have examined explosive nucleosynthesis of p-nuclei during a neutrino-driven, aspherical supernova aided by both convection and standing accretion shock instability, based on a twodimensional hydrodynamic simulation of the explosion of a 15M star, with an explosion energy of ∼ 1051ergs. We find that p-nuclei are mainly produced by γ-processes, and that the nuclei lighter than 92Mo are abundantly synthesized in slightly neutron-rich bubbles with electron fractions of Ye ≤ 0.48, although masses of the bubbles are highly uncertain in the current hydrodynamic simulation. Abundances of the p-nuclei are comparable to those in a spherical model, and nuclei, 94Mo, 96Ru, and 98Ru, are underproduced compared with the solar system for our aspherical models, as in a spherical model. 138La and 180Ta, which are underproduced in the model are abundantly produced by charged current neutrino-interactions with 138Ba and 180Hf, respectively.

We investigate the r-process nucleosynthesis during the magnetohydrodynamical (MHD) explosion of a supernova in a helium star of 3.3 M⊙, where effects of neutrinos are taken into account using the leakage scheme in the two-dimensional (2D) hydrodynamic code. Jet-like explosion due to the combined effects of differential rotation and magnetic field is able to erode the lower electron fraction matter from the inner layers. We find that the ejected material of low electron fraction responsible for the r-process comes out from just outside the neutrino sphere deep inside the Fe-core. It is found that heavy element nucleosynthesis depends on the initial conditions of rotational and magnetic fields. In particular, the third peak of the distribution is significantly overproduced relative to the solar system abundances, which would indicate a possible r-process site owing to MHD jets in supernovae.

We investigate the possible range of the isotopic ratios of carbon and nitrogen in the mixture of different layers of supernovae with Z = Z ⊙ and Z = 0.1 Z ⊙ . We carry out the postprocessing nucleosynthesis calculations using the evolution profile of 4 M ⊙ He stars and that of the following supernova explosions to obtain abundance distributions. Main difference due to the metallicity is found in the range of the isotopic ratios of the mixture between the He/C-layer and the He/N-layer. Most of the isotopic ratios of SiC type X grains are inside the range of the isotopic ratios of the mixture between the He/C-layer and the He/N- or Si/S-layer of the supernova models.

Nucleosynthesis is investigated inside an accredition disk around a black hole of 50 – 10 3 M ⊙ located in a circumnuclear region of starburst galaxies. Nuclear reactions proceed through the hot CNO cycle to produce large amounts of 14 O and 15 O, which decay to 14 N and 15 N. The calculated N/O − O/H relation is found to be consistent with that observed in the most metal-poor galaxies. The accretion disk may be one of the promising sites of nitrogen production.

Using a shell flash model, we have investigated the relation between the endpoint of the rp-process and the ignition pressure. We have found a striking feature of the rp-process during the burst: nuclear fuel is almost burned out after the flash; the mass number of synthesized nuclei reaches to ∼ 100 for the typical pressure from 10 23 to 10 23.5 [dyn cm −2 ]. These results will severely constrain the model of type I X-ray bursts in reproducing the observational properties such as the shape of the light curve, the total radiated energy and the recurrence time.

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.

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 explosive nucleosynthesis in a non-rotating 15$M_\odot$ star with solar metallicity that explodes by a neutrino-heating supernova (SN) mechanism aided by both standing accretion shock instability (SASI) and convection. To trigger explosions in our two-dimensional hydrodynamic simulations, we approximate the neutrino transport with a simple light-bulb scheme and systematically change the neutrino fluxes emitted from the protoneutron star. By a post-processing calculation, we evaluate abundances and masses of the SN ejecta for nuclei with the mass number $\le 70$ employing a large nuclear reaction network. Aspherical abundance distributions, which are observed in nearby core-collapse SN remnants, are obtained for the non-rotating spherically-symmetric progenitor, due to the growth of low-mode SASI. Abundance pattern of the supernova ejecta is similar to that of the solar system for models whose masses ranges $(0.4-0.5) \Ms$ of the ejecta from the inner region ($\le 10,000\km$) of the precollapse core. For the models, the explosion energies and the \nuc{Ni}{56} masses are $ \simeq 10^{51} \rm erg$ and $(0.05-0.06) \Ms$, respectively; their estimated baryonic masses of the neutron star are comparable to the ones observed in neutron-star binaries. These findings may have little uncertainty because most of the ejecta is composed by matter that is heated via the shock wave and has relatively definite abundances. The abundance ratios for Ne, Mg, Si and Fe observed in Cygnus loop are well reproduced with the SN ejecta from an inner region of the $15\Ms$ progenitor., Comment: 15 pages, 1 table, 17 figures, accepted for publication in Astrophyscal Journal

We examine explosive nucleosynthesis during a delayed neutrino‐driven, supernova explosion aided by standing accretion shock instability, based on two‐dimensional hydrodynamic simulations of the explosion of a 15M⊙ progenitor. We find that abundance pattern of the supernova ejecta is similar to that of the solar system, for cases with high explosion energies of ≃1051 ergs. Aspherical distribution of Fe, Si, and O, which is observed in a nearby core‐collapse SN remnant such as Cas A, is obtained in spite of the explosion of the non‐rotating, spherical progenitor.

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.

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.

The Brans-Dicke model with a variable cosmological term ($BD\Lambda$) has been investigated with use of the coupling constant of $\omega=10^4$. Parameters inherent in this model are constrained from comparison between Big Bang nucleosynthesis and the observed abundances. Furthermore, the magnitude redshift ($m-z$) relations are studied for $BD\Lambda$ with and without another constant cosmological term in a flat universe. Observational data of Type Ia Supernovae are used in the redshift range of $0.01, Comment: Submitted to A&A, 4 pages, 3 figures

We investigate nucleosynthesis inside magnetically driven jets ejected from collapsars, or rotating magnetized stars collapsing to a black hole, based on two‐dimensional magnetohydrodynamic simulation of the collapsars during the core collapse. We follow the evolution of the abundances of about 4000 nuclides from the collapse phase to the ejection phase using a large nuclear reaction network. We find that the r‐process successfully operates only in the energetic jets (>1051 erg), so that U and Th are synthesized abundantly, even when the collapsars 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. The higher energy jets have larger amounts of 56Ni. Less energetic jets, which have small amounts of 56Ni, could induce GRB without supernova, such as GRB060505 and GRB060614.

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.

This is a reply report to astro-ph/0604264. We studied heavy element production in high baryon density region in early universe astro-ph/0507439. However it is claimed in astro-ph/0604264 that small scale but high baryon density region contradicts observations for the light element abundance or in order not to contradict to observations high density region must be so small that it cannot affect the present heavy element abundance. In this paper we study big bang nucleosynthesis in high baryon density region and show that in certain parameter spaces it is possible to produce enough amount of heavy element without contradiction to CMB and light element observations., Comment: 7 pages, 4 figures, References added, one more reference added

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...

For the rst time heavy element nucleosynthesis in the magneto‐hydrodynamical (MHD) explosions of core‐collapse supernovae are investigated using a massive star of 13M⊙ in a main sequence stage. Contrary to the case of the spherical explosion, jet‐like explosion due to the combined effects of the rotation and magnetic eld lowers the electron fraction signicantly inside the layers above the Fe‐core. Then, the anisotropic shock waves pass through the oxygen rich layers. As a consequence, we nd that the nucleosynthesis of the r‐ and p‐process proceeds appreciably compared to the models previously considered.

We present a new astrophysical site of the big bang nucleosynthesis (BBN) that are very peculiar compared with the standard BBN. Some models of the baryogenesis suggest that very high baryon density regions were formed in the early universe. On the other hand, recent observations suggest that heavy elements already exist in high red-shifts and the origin of these elements become a big puzzle. Motivated by these, we investigate BBN in very high baryon density regions. BBN proceeds in proton-rich environment, which is known to be like the p-process. However, by taking very heavy nuclei into account, we find that BBN proceeds through both the p-process and the r-process simultaneously. P-nuclei such as 92Mo, 94Mo, 96Ru, 98Ru whose origin is not well known are also synthesized., 6 pages, 7 figures