Origin of Matter and Evolution of Galaxies 2000

The following sections are included:

• Preface

• Opening address

• Contents

We study primordial nucleosynthesis in the presence of a net lepton asymmetry. We explore a previously unnoted region of the parameter space in which very large baryon densities 0.1 ≤ Ω_b ≤ 1 can be accommodated within the light-element constraints. This parameter space consists of large ν_μ and ν_τ degeneracies with a moderate ν_e degeneracy. Constraints on this parameter space from cosmic microwave background fluctuations are discussed [1]. We also study the r-process nucleosynthesis in neutrino-driven winds of gravitational core collapse SNell. Appropriate physical conditions are found for successful r-process nucleosynthesis, which meet with several features of heavy elements discovered recently in metal-deficient halo stars.

A model describing the chemical evolution in each cloud of the Galactic halo is presented. The inhomogeneous nature introduced by supernova explosions is incorporated into this model. It is found that if field stars are formed from shells of individual supernova remnants and globular clusters are formed from cloud-cloud collisions the observed metallicity distribution functions of both objects can be reproduced.

The aim of this contribution is that presenting the interesting and important astrophysical aspects of light elements (LiBeB) in the early stages of Galaxy, based on a model of SN-induced chemical evolution^1,2; (1)Abundances of light elements observed in metal-poor stars can be used as their age indicators. (2)Our model determines the primordial ⁷Li abundance precisely, and it gives an independent constraint on the baryon density of Universe. (3)We estimate the possibility of distinguishing the models of standard Big-Bang Nucleosynthesis and non-standard (inhomogeneous) Big-Bang Nucleosynthesis, by future observations of Be abundances in metal-poor stars.

The ground-based technique has opened a way of detecting γ-rays at ~1 TeV energy by collecting the energetic photons with detection area ~ 10⁴m² and angular resolution ~ 0.1°. The next step of improving sensitivity is now going to be taken to exploit, to a larger extent, violent energetic phenomena in which the process of particle acceleration plays a dominant role. The basic concept of the currently going-on projects for the next generation γ-ray telescope is described in this paper, paying an attention on how and why the current status of very high energy γ-ray astronomy needs to be developed for improvements.

We calculate stability, evolution and explosion of massive Pop III stars. We find the upper limit mass of the pulsationally stable Pop III ZAMS stars is about 130M_⊙, and the mass loss rate of unstable stars may be low. The nucleosynthesis results are compared with abundances of metal-poor halo stars to constrain the IMF of Pop III stars. The interesting trends of the observed ratios [Zn, Co, Mn, Cr/Fe] of the very metal-poor stars can be related to the mass ratio between the complete Si burning region and the incomplete Si burning region. We find that yields of Type II supernovae and Fe core collapse hypernovae can be consistent with the very low metal star abundances, if significant amount of complete Si-burning products are mixed out in the ejecta.

Presolar grains are stardust extracted from meteorites. They remain intact after they formed in circumstellar envelopes or in supernova ejecta, keeping pristine information of their parent stars. The most commonly observed stellar sources are asymptotic giant branch (AGB) stars and supernovae (SNe). Mainstream SiC grains are believed to have formed in thermally pulsing AGB stars. Carbon, N, and ²⁶Al observed in the grains reflect core and shell H and He burning. The Si isotopic ratios of the grains reflect both neutron capture in the He-shell and initial isotopic compositions of the parent stars. The isotopic ratios of heavy elements show s-process signatures. Silicon carbide of type X, low-density graphite, and silicon nitride (Si₃N₄) most likely formed in supernova ejecta. Their isotopic ratios can be explained if a jet of material from the innermost Si-rich zones is mixed with material of the outer He-rich zones. However, the SN models do not produce enough ¹⁵N and ²⁹Si to account for the grain data.

The proton–capture reaction on ²⁴Mg has been investigated in the bombarding energy range of E_p=0.2–1.7 MeV. Properties of low–energy resonances have been measured. From the experimental results, accurate proton partial widths, γ–ray partial widths and total widths have been deduced. The present experimental information establishes the ²⁴Mg+p reaction rates over the temperature range T=0.02–2.0 GK with statistical uncertainties of less than 21%. Based on our results, we can rule out the recent suggestion that the total width of the E_R=223 keV resonance has a significant influence on the reaction rates. The astrophysical implications for hydrogen burning of ²⁴Mg at low stellar temperatures in globular cluster red giant stars are discussed.

Utilizing the imaging spectroscopic capabilities of the Japanease X-ray satellite ASCA, we measured Si and Fe abundances of 40 nearby clusters of galaxies. The spatially averaged Fe abundances of the intracluster medium (ICM) are 0.2–0.3 solar, with only weak dependence on the temperature of the intracluster medium, hence on the cluster richness. In contrast, the spatially averaged Si abundance is observed to increase from 0.3 to 0.6–0.7 solar from the poorer to richer clusters. These results suggest that the supernovae of both type-Ia and type-II significantly contribute to the metal enrichment of the intracluster medium, with the relative contribution of type-II supernovae increasing towards richer clusters. Many clusters exhibit a central increment in the Fe abundance, which is more pronounced in lower temperature clusters; +(0.1–0.2) solar at kT > 5 keV, while +(0.2–0.3) solar at 1.5 < kT < 4 keV. These central excess metals are thought to be ejected from cD galaxies. Several low temperature cD type clusters also show significant Si abundance increase by +(0.1–0.2) solar at the central region. Compared with the Si-rich abundances observed in outer regions of rich clusters, the Si to Fe abundance ratio of central excess metals tends to be near the solar ratio, implying that type Ia products from cD galaxies are dominant in the central excess metals.

We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2 at the Galactic center region. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low energy cutoff below about 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted from the core of the molecular cloud toward the Galactic center by about 1–2 arcminute. Since 6.4-keV line is a K-alpha line from neutral iron, these features indicate that the molecular cloud is irradiated by an external X-ray source, and emits fluorescent and scattered X-rays. Thus Sgr B2 may be called an "X-ray reflection nebula". This new category of X-ray source is similar to the X-ray diagnosis of the material. We can obtain the information about the abundance of the molecular cloud from the X-ray spectrum. The "X-ray reflection nebula" is a probe for revealing the Galactic center environment.

Cosmic Ray Observation for Nuclei Astrophysics (CORONA) program is a large-scaled spacecraft or space station approach for nuclear composition of relativistic cosmic rays 10 ≦ Z ≦ 92 and of low-energy isotopes 1 ≦ Z ≦ 58 in space. A large area Spectrometer for Ultraheavy Nuclear Composition (SUNC) and a Large Isotope Telescope Array (LITA) are proposed in this program. CORONA program focuses on the composition of elements beyond the iron-peak nuclei (Z > 60) and the isotopic composition of ultraheavy particles (Z > 30) in galactic cosmic rays as well as solar and interplanetary particles. The observation of nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis of cosmic ray sources, chemical evolution of galactic material, the characteristic time of cosmic rays, heating and acceleration mechanism of cosmic ray particles. Observation of solar particle events also make clear the physical process of transient solar events emitting wide range of radio, X-ray/gamma-ray, plasma and energetic particle radiation, and particle acceleration mechanism driven by CME.

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANC). These coefficients, which provide the normalization of the tail of the overlap function, determine S-factors for direct capture reactions at astro-physical energies. A variety of proton transfer reactions have been used to measure ANC's. As a test of the technique, the ¹⁶O(³He,d)¹⁷F reaction has been used to determine ANC's for transitions to the ground and first excited states of ¹⁷F. The S-factors for ¹⁶O(p,γ)¹⁷F calculated from these ¹⁷F → ¹⁶O + p ANC's are found to be in very good agreement with recent measurements. Following the same technique, the ¹⁰B(⁷Be,⁸B)⁹Be and ¹⁴N(⁷Be,⁸B)¹³C reactions have been used, along with optical model parameters for the radioactive beams that were obtained from a study of elastic scattering of loosely bound p-shell nuclei, to measure the ANC appropriate for determining ⁷Be(p,γ)⁸B. The results from the two transfer reactions provide an indirect determination of S₁₇(0).

The two measurements, performed in connection with the solar neutrino problem, are described. The ⁷Be(d,n)⁸B reaction was measured at E_c.m. = 5.8 and 8.3 MeV for deducing the S₁₇(0) factor for the ⁷Be(p,γ)⁸B reaction. The angular distribution data were analyzed by using a distorted-wave Born approximation. The S₁₇(0) factor for the ⁷Be(p,γ)⁸B reaction was derived to be 27.4 ± 4.4 eV b through the asymptotic normalization constant extracted from the experimental data. The β-decay of ⁴⁰Ti was studied by measuring the β-delayed proton- and γ-emission. The half-lives for ⁴⁰Ti are determined to be 54±2 ms. Based on the experimental ⁴⁰Ti β-decay strength, the neutrino absorption cross-section was determined to be (14.3±0.3)×10^-43 cm².

The Coulomb dissociation of ⁸B into ⁷Be and a proton was measured at E(⁸B) = 254 MeV/u. The astrophysical S₁₇-factors for the ⁷Be(p,γ)⁸B reaction were extracted at E_cm = 0.25 – 2.78 MeV yielding the zero-energy S₁₇-factor relevant to the solar neutrino problem to be S₁₇(0) = 20.6 ± 1.2 ± 1.0 eV-b. Our results agree with the direct measurement results of Vaughn et al., Filippone et al., and Hammache et al. as well as the Coulomb dissociation results of Motobayashi et al. and Kikuchi et al. at E(⁸B) ≈ 50 MeV/u.

The design and construction of a low-energy, high current accelerator for the study of fusion reactions are reported. The accelerator can produce an intense beam of ³He¹⁺ and ³He²⁺ ions of more than 1mA. It enables us to provide extremely fine cross-section measurements of the ³He(³He,2p)α at 40 to 50 keV. A detection efficiency for proposed detector assembly of ΔE-E counter telescope is simulated with GEANT program and it expects a detection efficiency about 10% for the two proton coincidence for ³He+³He→2p+α. Deuter contaminations in target chamber is estimated to be less than ppm by quadrupole mass spectrometer. To further develop the study of nuclear astrophysics, a plasma target as an experimental apparatus for electron screening effects is proposed. Some parts of such apparatus are assembled. A combination ECR plasma target with a high current ion generator is under construction. The facility will be installed in the underground laboratory, Oto Cosmo Observatory. The facility has just started to operate and, as explained here, it already has been used for the double beta decay measurement and dark matter search programs. The present status of the experimental apparatus and its development are described.

Measurements of nuclear reactions on radioactive isotopes are necessary to understand stellar explosions such as novae and X-ray bursts. We have recently measured the ¹⁷F(p,p)¹⁷F, ¹⁷F(p,α)¹⁴O, ¹⁸F(p,p)¹⁸F, and ¹⁸F(p,α)¹⁵O excitation functions with beams of radioactive ions produced at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. Our experimental setup includes a Silicon Detector Array and the Daresbury Recoil Separator coupled to a windowless, differentially-pumped hydrogen gas target system. We have also measured the ¹²C(p,γ)¹³N cross section to commission our recoil separator for proton capture reactions on radioactive isotopes. To support these measurements, we are making unique calculations of isotope synthesis in stellar explosions to determine the effect of nuclear physics uncertainties on explosion model predictions. We are also making detailed evaluations of some nuclear reactions rates that are important input for explosion models.

The ²¹Na(p,γ)²²Mg reaction is believed to play an important role determining the amount of the long-lived, radioisotope ²²Na in the universe. This nuclide is important as a target of current and future generations of gamma ray telescopes, since its production is part of the pathway of a nova, and because its daughter, ²²Ne, has been found in pre-solar grains in meteorites. Unfortunately the rate of this reaction has never been measured primarily due to the fact that ²¹Na is radioactive (T_½ = 23 s). This report describes an experimental program aimed at measuring this rate using inverse kinematics at the new radioactive beams facility, ISAC. A new recoil mass separator, DRAGON, is being constructed to perform this and similar reaction rate studies; the status of this new facility is presented. New information on the levels of ²²Mg, studied using a p, t reaction is also presented.

One of the critical stellar reactions for the onset of explosive hydrogen burning, ¹⁵O(α,γ)¹⁹Ne, is discussed with our recent experimental effort and a new possibility in our new RIB project. This reaction was investigated experimentally by indirect methods. Single particle nature of the threshold states was studied by the analog reactions, (d,t) and (d,³He) on ²⁰Ne. The α-branching ratios for some states were also measured by a coincidence measurement of a triton and α from ¹⁹F(³He,t)¹⁹Ne*(α)¹⁵O(g.s.). Experimental plan for the problem was also discussed that uses a new low-energy RIB facility at CNS, called CRIB, which will come into operation soon.

In this paper I will review the physics involved in the collapse-driven Supernova, paying particular attention to some selected issues concerning both one- and multi-dimensional aspects of the dynamics of supernova.

Equation of state with kaon condensate is derived in isentropic and neutrino-free or trapping matter. Both are important ingredients to study the possibility of the delayed collapse of a protoneutron star. Solving the TOV equation, we discuss the static properties of the protoneutron star and implications for its delayed collapse.

OMNIS, the Observatory for Multiflavor NeutrInos from Supernovae, is being planned for siting in the Center for Applied Repository and Underground Research, CARUS, in New Mexico. OMNIS will consist of 14 kT of lead and iron which, when irradiated by neutrinos from a supernova, will produce secondary neutrons. Detection of the neutrons then will signal the arrival of the supernova neutrinos. A supernova at the center of the Galaxy, will produce about 2000 events in OMNIS, mostly from neutral current interactions. OMNIS' combination of lead and iron modules gives it particular sensitivity to neutrino oscillations of the type ν_μ → ν_e or ν_τ → ν_e. Its intrinsic timing capability, better than 0.1 ms, gives it the (probably statistics limited) capability to measure neutrino mass from the time-of-flight shifts in the luminosity curves of the neutrinos of different flavors to a few eV/c². OMNIS will also be able to detect differences in the luminosity cutoffs of the different flavors in the event of the fairly prompt collapse to a black hole, which might allow diagnostics on that collapse process.

Super-Kamiokande has started since 1st of April, 1996. We are searching for the supernova neutrinos from not only our galaxy but also extra-galactic source within 100kpc distance with a full detection efficiency. We present recent results from the observation of Super-Kamiokande. There is no evidence of supernovae explosion in obtained data. The 90%-confidence level upper limit to the rate of supernovae explosion is obtained by 0.58 yr^-1 within 100kpc distance, and also obtained by 0.28 yr^-1 within our galaxy, if we accumulate the Kamiokande 4.26 yr's result.

The unphysical result of the negative mass square of the electron neutrinos recently reported in several tritium β-decay experiments, is one of the most attractive subjects. As a possible scenario to explain the anomaly, we have assumed a reaction with relic neutrinos which are predicted by the standard big bang cosmology. If such neutrinos could exist, the interaction of the relic neutrinos with the target tritium, ν_e + ³H → ³He + e^- could be laid under the large amount of the β-decay process, , which would cause a peak-like structure beyond the end-point in the Kurie plot. Based on the assumption, we evaluated the cross section from the event rate found in the peak by re-fitting to the 1991 data published by Mainz Group. In this talk we will provide a scenario that could account for the evaluated cross section by assuming a coherent state of the neutrino sea, which would result much lower temperature than the prediction from the standard big bang cosmology.

We discuss the properties of the hyper-energetic Type Ic supernovae (SNe Ic) 1998bw and 1997ef. SNe Ic 1998bw and 1997ef are characterized by their large luminosity and the very broad spectral features. Their observed properties can be explained if they are very energetic SN explosions with the kinetic energy of E_K ≳ 1 × 10⁵² erg, originating probably from the core collapse of the bare C+O cores of massive stars (~ 30 – 40M_⊙). At late times, both the light curves and the spectra suggest that the explosions may have been asymmetric; this may help us understand the claimed connection with GRB's. Because these kinetic energies of explosion are much larger than in normal core-collapse SNe, we call objects like these SNe> "hypernovae". The mass of ⁵⁶Ni in SN 1998bw is estimated to be as large as 0.5 – 0.7 M_⊙ from both the maximum brightness and late time emission spectra, which suggests that the asymmetry may not be extreme.

Recently, COMPTEL has detected γ-rays of 1157keV from ⁴⁴Ti in the direction of the SNR RX J0852–0462¹. Since ⁴⁴Ti is a product of explosive nucleosynthesis and its half-life, τ, is about 60yrs, RX J0852–0462 must be a young supernova remnant and radiation is dominated by the ejecta rather than by interstellar matter. We have detected an X-ray emission line at 4.1 ± 0.2 keV which is thought to come from highly ionized Ca. The emission line is so far only seen in the northwest shell region of RX J0852–0462. The X-ray spectrum can be well fitted with that of thin hot plasma of cosmic abundances except that of Ca, which is overabundant by a factor of about 7. Assuming that most of the Ca is ⁴⁴Ca, which originates from ⁴⁴Ti by radioactive decay, we estimate that there is about 8 × 10^-4M_⊙ of Ca. Combining the amount of ⁴⁴Ca and the observed flux of the ⁴⁴Ti γ-ray line, the age of RX J0852–0462 is around 100yrs.

This paper reviews the chemical evolution of massive stars and their remnants using the ASCA results of X-ray spectroscopy. We demonstrate that the ASCA spectrum of Eta-Carinae provides direct evidence for the CNO cycle reaction at the surface layer of the massive star. Then we present distinct difference of line emission features in the X-ray spectra of young supernova remnants (SNR) of two types of supernovae, type Ia and type II. We show that the chemical composition of a galaxy can be estimated by aged SNR samples. Finally we discuss related topics of SNRs, in particular of particle acceleration in the SNRs.

Neutron stars provide a unique laboratory in which to explore the nuclear equation of state at high densities. Nevertheless, their interior structure and equation of state have remained a mystery. Recently, a number of advances have been made toward unraveling this mystery. The first direct optical images of a nearby neutron star have been obtained from HST. High quality data for X-ray emission from low-mass X-ray binaries, including observations of nearly coherent oscillations (NCO's) and quasi-periodic oscillations (QPOs) now exist. The existence of a possible absorption feature as well as pulsar light curves and glitches, and studies of soft-gamma repeaters, have all led to significant new constraints on the mass-radius relation and maximum mass of neutron stars. We also discuss how models of supernova explosion dynamics and the associated r-process nucleosynthesis also constrain the nuclear equation of state, along with heavy-ion and monopole resonance data. Recent work on the search for the Friedman-Chandrasekhar-Schutz instability and the effects of internal magnetic fields are also discussed. The overall constraints on the neutron star equation of state are summarized.

Photoneutron cross sections were measured for ⁹Be in the energy range from 1.78 to 6.11 MeV with laser-induced Compton backscattered γ rays. The data are compared with those from the Bremsstrahlung and the radioactive isotope measurements. γ-decay widths for the 1/2⁺ and 5/2^- states were deduced from the least-squares fit to the data as well as the energy-integrated cross section. Astro-physical implications are discussed.

RIKEN RI-Beam Factory (RIBF) is a next-generation heavy-ion accelerator facility, that aims at providing the most intense primary beam as high as 1pμA over a wide atomic range up to U. The maximum energy reaches 400 MeV/nucleon for light ions and 150 MeV/nucleon for Uranium. The intense primary beams and a large-acceptance fragment separator, Big-RIPS, allow efficient production of many unstable nuclei, and enable us to select them freely as a secondary RI beam over a wide range of proton and neutron numbers. RIBF will open a way to study the basic properties of very neutron rich nuclei, which are very important to describe the r-process.

Effects of uncertainties of key nuclear reaction rates in the crucial nuclear processes on type I X-ray burst modeling have been reviewed/investigated. Special attention is devoted to the ignition condition of the thermonuclear flash. It is found that in the rapid proton capture process (rp-process), the ignition depends on the rates of ¹³N(p,γ)¹⁴O, ¹⁴O(α,p)¹⁷F, and ¹⁵O(α,γ)¹⁹Ne. On the other hand, for the pure helium flash suggested from a recent observation of X-ray bursts, we infer that the NCO-reaction plays a key role in triggering the flash.

We study supernova explosions and the associated r-process using a nuclear-matter equation of state (EOS) derived by a relativistic many-body approach. Recently, we have completed a relativistic EOS table which spans the wide range of density, composition and temperature relevant to supernova explosions. We apply this EOS table to numerical simulations of the gravitational core collapse, subsequent evolution of the proto-neutron star, and the r-process. To derive the requisite nuclear-physics ingredients for supernova, we have constructed a relativistic mean field (RMF) framework based upon relativistic Brückner-Hartree-Fock theory. We have successfully applied the constructed RMF framework to the ground state properties of many nuclei in the nuclear chart. We apply this same RMF framework to derive the supernova EOS table. As examples of astrophysical applications of the EOS table, hydrodynamical simulations of core collapse have been performed. We have also performed numerical simulations of the hydrodynamics of the ν-driven wind from the nascent proto-neutron star. We find that a successful r-process is indeed possible with a short expansion time scale in the ν-driven wind above the massive and compact proto-neutron star.

Whether hyperons admixed in neutron star cores could be superfluid or not is investigated by a realistic approach to take account of the information on YY and YN interactions from hypernuclear data. It is found that the Λ-superfluid is surely realized, though in a restricted density region, and also the Σ^-- and Ξ^--superfluids have a strong possibility to be realized. A comment is given to the influences of hyperon components on neutron superfluidity.

Spontaneous magnetization of quark liquid is examined on the analogy with that in electron gas. It is pointed out that quark liquid has potential to be ferromagnetic at rather low densities, around nuclear saturation density. Some comments are given as for implications on magnetars.

It is theoretically postulated that the kaon condensation is happening in dense nuclear matter, especially neutron stars. However, little evidence is obtained from experiments. Study of the kaonic nuclei can answer the question as to the existence of kaon condensation in neutron stars. We show that the kaonic nuclei can be produced by the (K^-,p) and (K^-,n) reactions with cross sections experimentally measurable.

We present the result of the ASCA observation of a shell-like radio supernova remnant (SNR), G359.1–0.5. Unlike the radio morphology, X-rays from the SNR shows a center-filled structure. The spectrum of G359.1–0.5 has prominent Kα lines of He-like silicon and H-like sulfur. The plasma requires at least two temperature components: a lower temperature plasma (kT ~ 0.6 keV = 7 × 10⁶ K) and a sulfur-rich plasma with higher temperature (kT ~ 4.4 keV = 5 × 10⁷ K). The chemical composition of sulfur is found to be unusually high, larger than that of the solar vicinity by, at least, more than 10 times. We can estimate the total mass of silicon and sulfur to be 0.1M_⊙ and 0.3M_⊙, respectively, where M_⊙ is the mass of the sun of about 2 × 10³³g. No current theory of nucleosynthesis in supernova explosions allows larger mass production of sulfur than that of silicon. This problem is solved with the assumption that the sulfur distribution is localized somewhere in SNR.

No abstract received.

We propose a model in which the ultra high energy cosmic rays and gamma ray bursts are produced by collisions between neutron stars and axion stars. An acceleration of the cosmic ray is done by an electric field, ~ 10¹⁵ eV cm^-1, which is induced in the axion star by the strong magnetic field > 10¹² G of the neutron stars. On the other hand, gamma ray bursts are generated in the collisions between axion stars and neutron stars with relatively small magnetic field, e.g. ~ 10¹⁰ G. In the former case the axion star evapolates emitting ultra high energy cosmic rays before colliding directly with the neutron stars, while in the latter case the axion star collides directly with the neutron star and dissipates rapidly its whole energy in an outercrust of the neutron star, which leads to a gamma ray burst. To explain both phenomena we need to assume the mass of the axion such as 10^-9 eV. With this choice we can explain huge energies 10⁵⁴ erg of the gamma ray bursts as well as the ultra high energies ~ 10²⁰ eV of the cosmic rays. Additionally, it turns out that these axion stars are plausible candidates for MACHOs.

Exclusive measurements of neutrino-less double beta decays(0νββ) of ¹⁰⁰Mo were made by means of ELEGANT V. The present status of the double beta decay experiment with ELEGANT V is presented. The data at Oto lab., being combined with the data at Kamioka, gives stringent limits on half-lives for 0νββ and 〈m_ν〉 < 1.8eV for the Majorana neutrino mass.

Nucleosynthesis in aspherical hypernova explosions is calculated with a two-dimensional hydrodynamical code and a detailed neclear reaction network. The results are compared with observations of SN1998bw, whose late time spectrum unusual features are shown to be explained by the aspherical explosion model.

We studied the effects of jet-like explosion in SN 1987A. Calculations of the explosive nucleosynthesis and the matter mixing in a jet-like explosion are performed and their results were compared with the observations of SN 1987A. It was shown that the jet-like explosion model is favored because the radioactive nuclei ⁴⁴Ti is produced in a sufficient amount to explain the observed luminosity at 3600 days after the explosion. This is because the active alpha-rich freezeout takes place behind the strong shock wave in the polar region. It was also shown that the observed line profiles of Fe[II] are well reproduced by the jet-like explosion model. In particular, the fast moving component travelling at (3000-4000) km/s is well reproduced, which has not been reproduced by the spherical explosion models. Moreover, we concluded that the favored degree of a jet-like explosion to explain the tail of the light curve is consistent with the one favored in the calculation of the matter mixing. The concluded ratio of the velocity along to the polar axis relative to that in the equatorial plane at the Si/Fe interface is ~ 2 : 1. This conclusion will give good constraints on the calculations of the dynamics of the collapse-driven supernova. We also found that the required amplitude for the initial velocity fluctuations as a seed of the matter mixing is ~ 30%. This result supports that the origin of the fluctuations is the dynamics of the core collapse rather than the convection in the progenitor. The asymmetry of the observed line profiles of Fe[II] can be explained when the assumption of the equatorial symmetry of the system is removed, which can be caused by the asymmetry of the jet-like explosion with respect to the equatorial plane. In the case of SN 1987A, the jet on the north pole has to be stronger than that on the south pole in order to reproduce the observed asymmetric line profiles. Such an asymmetry may also be the origin of the pulsar kick. When we believe some theories that cause such an asymmetric explosion, the proto-neutron star born in SN 1987A will be moving in the southern part of the remnant.

The three-dimensional hydrodynamical N-body model of the formation of the Galaxy is presented. Since all previous numerical models of the Galaxy formation do not have a proper treatment of the chemical evolution and/or sufficient spatial resolutions, we have constructed the detailed model of the chemical and dynamical evolution of the Galaxy using our GRAPE-SPH code. Starting with the cosmologically motivated initial condition, we have obtained the qualitatively similar stellar system with the Galaxy.

We calculate the final evolution of very massive population III stars in the mass range of 150 to 300 M_⊙ and obtain detailed nucleosynthesis yields of their explosions. We perform hydrodynamic simulations of the collapse-explosion process caused by e⁺e^--pair creation instability during their oxygen burning phase and calculate explosive nucleosynthesis with an extended nuclear reaction network. We then obtain the following results: 1) Population III Stars of 150 – 200M_⊙ explode as pair-instability supernovae. The upper mass limit for the explosion is between 200 – 300M_⊙. 2) In pair-instability supernovae, iron is produced more abundantly from more massive progenitors. 3) Pair-instability supernovae produce large amounts of Si, S, Ar and Ca relative to O. This is a similar characteristic as that of hypernovae (E ≥ 10⁵² erg), the progenitors of which have 30-40 M_⊙ on their main-sequence. 4) We compare our yields with those of the observed metal-deficient stars. The abundance patterns are not in good accord and it implies that pair-instability supernovae were not dominant in the early Galaxy. 5) We also calculate theoretical light curves of a pair-instability supernova and find that they are very luminous (L ~ 10⁴³ erg s^-1) because of the large production of ⁵⁶Ni.

The great portion of the elements are thought to be produced in the supernova (SN) explosions and gradually mixed into the interstellar matter (ISM) of the galaxies. We can trace the course of the chemical-pollution of the galaxies by observing the supernova remnants (SNRs) and ISM. We present the X-ray measurements of metal abundances of the Large Magellanic Cloud (LMC). All the archive data in the vicinity of the LMC taken with the Advanced Satellite for Cosmology and Astrophysics (ASCA) were used. The X-ray spectroscopy of the diffuse X-ray emission spreading over a large portion of the LMC was carried out in order to measure the metal abundance of the ISM directly. With the good spectral resolution of ASCA the nature of this diffuse X-ray emission was first confirmed to be thermal in origin, likely to be emitted from hot ionized ISM in the galaxy, because ASCA detected line emissions from various elements, which was beyond the capability of previous X-ray satellites. The X-ray spectrum of diffuse X-ray emission was reproduced by the Non-Equilibrium Ionization (NEI) model with temperature of ~ 1.2 keV. The overall elemental abundances determined from X-ray spectroscopy of ISM is found to be also consistent with previous results determined through X-ray SNR spectroscopy derived by Hughes, Hayashi and Koyama (1998) and previous optical and UV analysis, except overabundance of sulfer.

Neutrino-driven wind from young hot neutron star, which is formed by supernova explosion, is the most promising candidate site for r-process nucleosynthesis. We use spherical steady state flow model in general relativistic framework. Exploring wide parameter region which determines the expansion dynamics of the wind, we can find interesting physical conditions which lead to successful r-process nucleosynthesis.

We have extended the nuclear reaction network for 1 ≤ Z ≤ 10 in order to investigate the role of light neutron-rich nuclei in the r-process. We find that a new nuclear reaction flow path opens in the region of very light neutron-rich nuclei as the temperature decreases. This new reaction flow can affect the final abundances by up to a few orders of magnitude, while still producing the characteristic three r-process peaks as well as the hill of the rare-earth elements.

Equilibrium phase diagrams for neutron star matter at subnuclear densities are obtained at zero temperature. Spherical, rod-like and slab-like nuclei as well as spherical and rod-like nuclear bubbles are taken into account by using a compressible liquid-drop model. This model is designed to incorporate uncertainties in the nuclear surface tension and in the proton chemical potential in a gas of dripped neutrons. The resultant phase diagrams show that for typical values of these quantities, the phases with rod-like nuclei and with slab-like nuclei occur in the form of Coulomb lattice at densities below a point where the system becomes uniform. Thermal fluctuations leading to displacements of such nuclei from their equilibrium positions are considered through explicit evaluations of their elastic constants; these fluctuations can be effective at destroying the layered lattice of slab-like nuclei in the temperature region typical of matter in the neutron star crust.

The following sections are included:

• Symposium Program

• List of Participants

• Author Index