The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars

The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in characterising the formation and evolution of the first stars and the Galaxy since the extremely-poor (EMP) stars with [Fe/H] \leq -2.5 share the common features of carbon enhancement in their surface chemical compositions. The origin of these stars is not yet established due to the controversy of the origin of CEMP stars without the enhancement of s-process element abundances, i.e., so called CEMP-no stars. In this paper, we elaborate the s-process nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We find that the efficiency of the s-process is controlled by O rather than Fe at [Fe/H] \lesssim -2. We demonstrate that the relative abundances of Sr, Ba, Pb to C are explained in terms of the wind accretion from AGB stars in binary systems.Comment: The Proceedings of the Nuclei in the Cosmos XIV, in pres

The IMF of Extremely Metal-Poor Stars and the Probe into the Star-Formation Process of the Milky Way

We discuss the star formation history of the Galaxy, based on the observations of extremely metal-poor stars (EMP) in the Galactic halo, to gain an insight into the evolution and structure formation in the early universe. The initialmass function (IMF) of EMP stars is derived from the observed fraction of carbon-enhanced EXP (CEMP) stars among the EMP survivors, which are thought to originate from the evolution in the close binary systems with mass transfer. Relying upon the theory of the evolution of EMP stars and of their binary evolution, we find that stars of metallicity [Fe/H]<-2.5 were formed at typical mass of ~10M_sun. The top heavy IMF thus obtained is applied to study the early chemical evolution of the Galaxy. We construct the merging history of our Galaxy semi-analytically and derive the metallicity distribution function (MDF) of low-mass EMP stars that survive to date with taking into account the contribution of binary systems. It is shown that the resultant MDF can well reproduce the observed distribution of EMP survivors, and, in particular, that they almost all stem from a less-mass companion in binary systems. We also investigate how first stars affect the MDF of EMP stars.Comment: 5 pages, 4 figures, conference proceedings of First Star II

Multistable attractors in a network of phase oscillators with three-body interaction

Three-body interactions have been found in physics, biology, and sociology. To investigate their effect on dynamical systems, as a first step, we study numerically and theoretically a system of phase oscillators with three-body interaction. As a result, an infinite number of multistable synchronized states appear above a critical coupling strength, while a stable incoherent state always exists for any coupling strength. Owing to the infinite multistability, the degree of synchrony in asymptotic state can vary continuously within some range depending on the initial phase pattern.Comment: 5 pages, 3 figure

Atomistic Simulation of Crystal Change and Carbon Diffusion during Drawing of Pearlitic Steel Nano-sizedWire

Wire drawing is an efficient material processing technique for metals. Pearlitic steel is recognized as one of the most reliable and strong wire materials for industrial use. The microstructure of the pearlite phase, however, is quite complicated, with a lamellar structure containing alternating nanometer-thick layers of ferrite and cementite. In the present study, three-dimensional wire drawing models for pearlitic steel, in which a cementite layer occupies one half or one third of the wire cross section, are used in molecular dynamics simulations of the Fe-C system based on a pairwise potential. The results indicate that a body-centered cubic to face-centered cubic phase transition occurs in the ferrite layer during drawing. It is found that compressive hydrostatic stress is required to drive this phase transformation. The phase transition is followed by the formation of dislocations and grain boundaries. Cementite has an orthorhombic crystal structure and is more difficult to plastically deform than pure ferrite. During drawing of a pearlite wire, the large deformation of the ferrite layer compensates for the poor deformability of the cementite layer. The carbon content is important in pearlitic steel because carbon atoms can diffuse through all phases. As a indicator of the amount of carbon diffusion, the mean square displacement of carbon atoms is used. It is found that diffusion perpendicular to the ferrite/cementite interface tends to take place suddenly, but the total amount of diffusion is still less than that in the parallel direction

Nucleosynthesis in novae: experimental progress in the determination of nuclear reaction rates

The sources of nuclear uncertainties in nova nucleosynthesis have been identified using hydrodynamical nova models. Experimental efforts have followed and significantly reduced those uncertainties. This is important for the evaluation of nova contribution to galactic chemical evolution, gamma--ray astronomy and possibly presolar grain studies. In particular, estimations of expected gamma-ray fluxes are essential for the planning of observations with existing or future satellites.Comment: Invited contribution to the "Origin of Matter and Evolution of Galaxies" conference (OMEG07) with additional and color figure

Explosions inside Ejecta and Most Luminous Supernovae

The extremely luminous supernova SN2006gy is explained in the same way as other SNIIn events: light is produced by a radiative shock propagating in a dense circumstellar envelope formed by a previous weak explosion. The problems in the theory and observations of multiple-explosion SNe IIn are briefly reviewed.Comment: 9 pages, 6 figures, LateX aipproc.cls. A bit more details and color added to Fig.3. The 10th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG07), Sapporo, Japan, December 200