ORIGIN OF MATTER AND EVOLUTION OF GALAXIES: International Symposium on Origin of Matter and Evolution of Galaxies 2005: New Horizon of Nuclear Astrophysics and Cosmology
847(2006); http://dx.doi.org/10.1063/1.2234375View Description Hide Description
Astronomers have begun to measure the fundamental parameters of cosmology through the observation of very distant Type Ia supernovae. Over the past decade more than 300 spectroscopically confirmed high‐redshift supernovae have been discovered. These supernovae are used as standardized candles to measure the history of the expansion of the universe. Under the current standard model for cosmology these measurements indicate the presence of a heretofore unknown dark energy causing a recent acceleration in the expansion of the universe.
At this time supernova measurements of the cosmological parameters are no longer limited by statistical uncertainties, rather systematic uncertainties are the dominant source of error. These include the effects of evolution (further back in time do the supernovae behave the same way?), the effect of intergalactic dust on the brightness of the supernovae and the relationship between supernovae and their environments. Here I present exciting new developments in the field of cosmology using Type II‐P supernovae as standardized candles and the prospect of using them to independently measure the cosmological parameters.
847(2006); http://dx.doi.org/10.1063/1.2234376View Description Hide Description
We investigate the cosmological evolution in a brane‐world scenario in which the bulk is not empty. Rather, exchange of mass‐energy between the bulk and the bane is allowed. The expansion history of the universe and the evolution of matter fields on the brane are then modified due to this exchange. We show that the flow of matter realizes an accelerating expansion of the brane, which mimics the dark energy. We investigate the constraints from various cosmological observations on the flow of matter from the bulk into the brane. Interestingly, it is possible to have a Λ = 0 cosmology to an observer in the brane which satisfies standard cosmological constraints including the CMB temperature fluctuations, Type Ia supernovae at high redshift, and the matter power spectrum.
847(2006); http://dx.doi.org/10.1063/1.2234377View Description Hide Description
We present lithium abundances for 28 halo subgiants based on high resolution, high signal‐to‐noise ratio spectra. Excluding the known lithium‐rich subgiant BD +23 3912, the maximum abundances are log ε(Li) = 2.35. While subgiants evolve from stars hotter than the main sequence turn‐off with shallower convection zones that may have depleted lithium to a lesser degree, lithium abundances in halo subgiants are not in agreement with the primordial value as predicted from standard big bang nucleosynthesis combined with recent results from WMAP.
847(2006); http://dx.doi.org/10.1063/1.2234378View Description Hide Description
The observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, by the WMAP satellite, has provided a determination of the baryonic density of the Universe (Ω bh 2) with an unprecedented precision. Using this value, the primordial abundances of the light elements can be calculated in the framework of the Standard Big‐Bang Nucleosynthesis model (SBBN). While the agreement is excellent for D and good for 4 He, there is a difference of a factor of ≈3 for 7 Li. In addition, in a few halo stars, 6 Li has also been observed at a level well above SBBN predictions. To enable a more reliable calculation of these 7 Li and 6 Li yields, two nuclear reactions important for the nucleosynthesis of 7 Li and 6 Li have been studied experimentally: D(α, γ)6Li and 7Be(d,p)2α. Even though, the lithium primordial production is not well understood, BBN can be used to constrain theories beyond the standard model, for instance, scalar‐tensor theories of gravity.
847(2006); http://dx.doi.org/10.1063/1.2234379View Description Hide Description
Photonuclear reactions play crucial roles in various processes of nucleosynthesis occurring in the universe. A laser‐Compton backscattered γ‐ray beam and an active target technique will be a promising tool for precise measurements of low‐energy photon‐induced nuclear reactions relevant to nucleosynthesis.
Determination of the astrophysical 8 Li(n, γ)9 Li reaction rate from the measurement of 2 H(8 Li,9 Li)1 H reaction847(2006); http://dx.doi.org/10.1063/1.2234380View Description Hide Description
The cross section of the 8 Li(n, γ)9 Li reaction has attracted much attention for many years because of its importance in nuclear astrophysics. The single particle spectroscopic factor, S 1,3/2 for the ground state of 9Li = 8Li ⊗ n derived from the transfer reaction of 8Li(d, p)9Li was used to calculate the direct radiative capture reaction rates of 8Li(n, γ)9Li at energies of astrophysical interest. The present result shows that the 8Li(n, γ)9Li direct capture reaction may play an important role in the astrophysical environments of inhomogeneous big bang and type II supernovae.
847(2006); http://dx.doi.org/10.1063/1.2234381View Description Hide Description
The discovery and analysis of metal‐poor stars lead to insight into conditions when the Universe and Galaxy were young. We present the rationale for studying such objects (which become progressively rarer at lowest abundance), with a description of their systematic discovery, culminating in the recent analysis of two objects having [Fe/H] < −5.0. We discuss the Metallicity Distribution Function of metal‐poor stars and the abundance patterns of several elements, from Li through to the heavy‐neutron‐capture elements. Relatively few (∼50) stars with [Fe/H] < −3.0 have been analyzed at high spectral resolution and high signal‐to‐noise. As one proceeds to lowest abundance one finds astounding overabundances of some or all of the CNO group and the lighter elements. This diversity among the most metal‐poor stars has yet to be fully understood.
847(2006); http://dx.doi.org/10.1063/1.2234382View Description Hide Description
We present an elemental abundance analysis of HE 1327‐2326, the most iron‐deficient star known, based on a comprehensive investigation of spectra obtained with the Subaru Telescope. HE 1327‐2326 is either in its main sequence or subgiant phase of evolution, hence it is essentially unevolved. The chemical abundances of this star have the following properties, which provide new constraints on models of nucleosynthesis processes that occurred in first‐generation objects:
(1)The iron abundance (NLTE) is [Fe/H]= −5.45. This value is 0.2 dex lower than that of HE 0107‐5240, the previously most iron‐poor object known. No object having [Fe/H]= −5 ∼ −4 is known to date.
(2)This star, as well as HE 0107‐5240, exhibits extremely large overabundances of carbon relative to solar ratios ([C/Fe]∼ +4).
(3)HE 1327‐2326 exhibits remarkable overabundances of the light elements (N, Na, Mg and Al), while HE 0107‐5240 shows only relatively small excesses of N and Na.
(4)A large overabundance of Sr is found in HE 1327‐2326 as compared to other extremely low metallicity stars.
(5)The Li I 6707 Å line, which is detected in the great majority of metal‐poor dwarfs and warm subgiants, is not found in HE 1327‐2326. The upper limit on the Li abundance we determine (log ε (Li) < 1.5) is clearly lower than the expected value from the Spite plateau.
847(2006); http://dx.doi.org/10.1063/1.2234383View Description Hide Description
The discoveries of two extremely iron‐poor stars with [Fe/H]<−5, HE0107‐5240 and HE1327‐2326 provided the great opportunities of verifying whether these stars are the survivors of the first generation stars; the very weak lines of detected metals in their atmospheres can be extrinsic source that is the accretion from interstellar gas or from binary companion, rather than intrinsic one. In this work, we explore the possibility that these stars were born in binary systems from the primordial clouds by considering the results of stellar evolution and nucleosynthesis in metal‐free models of low to intermediate mass AGB stars. Observed abundance patterns for these 2 stars are in agreement with the results and can be explained by the binary scenario that observed stars disguise their surface abundances by the mass transfer in the binary system. In particular, we first demonstrated the reproduction of Sr without large enhancement of Ba through the neutron capture reactions in the helium flash convective region of AGB models without any iron seeds for s‐process. The apparent lack of stars in −5 < [Fe/H] < −4 may suggest the effect of dilution by the surface convection at the red giant branch. If this is true, other Pop.III survivors can be discovered at the main sequence having [Fe/H] ∼ −3, whose surface abundances are changed by the mass transfer from evolved companions in binary systems.
847(2006); http://dx.doi.org/10.1063/1.2234384View Description Hide Description
The recent discovery of a hyper metal‐poor (HMP: −5 ≲ [Fe/H] ≲ −4) star have raised a challenging question if these HMP stars are first generation stars in the Universe. We argue that these HMP stars are the second generation stars being formed from gases which were chemically enriched by the first generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars with important similarities and differences. We can reproduce these abundance features with the core‐collapse “faint” supernova models which undergo extensive matter mixing and fallback during the explosion (mixing‐fallback model). We also show that the abundance patterns of extremely metal‐poor (EMP: −4 ≲ [Fe/H] ≲ −3) stars are well‐reproduced by a 25 M ⊙ hypernova mixing‐fallback model and those of very metal‐poor (VMP: −3 ≲ [Fe/H] ≲ −2) stars are well‐reproduced by a model integrated by Salpeter’s initial mass function over 13 – 50 M ⊙ models.
847(2006); http://dx.doi.org/10.1063/1.2234385View Description Hide Description
Two series of models and their yields are presented in this paper. The first series consists of 20 M ⊙ models with varying initial metallicity (solar down to Z = 10−8) and rotation (υ ini = 0 – 600 km s−1). The second one consists of models with an initial metallicity of Z = 10−8, masses between 20 and 85 M ⊙ and average rotation velocities at these metallicities (υini = 600 – 800 km s−1). The most interesting models are the models with Z = 10−8 ([Fe/H]∼ −6.6). In the course of helium burning, carbon and oxygen are mixed into the hydrogen burning shell. This boosts the importance of the shell and causes a reduction of the size of the CO core. Later in the evolution, the hydrogen shell deepens and produces large amount of primary nitrogen. For the most massive models (M ≳ 60 M ⊙), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing.
The yields of the fast rotating 20 M ⊙ models can best reproduce (within our study) the observed abundances at the surface of extremely metal poor (EMP) stars. The wind of the massive models can reproduce the CNO abundances of the carbon‐rich UMPs, in particular for the most metal poor star known to date, HE1327‐2326.
847(2006); http://dx.doi.org/10.1063/1.2234386View Description Hide Description
We present results for the chemical evolution of the Milky Way including predictions for elements from Deuterium to Europium. A comparison with the most accurate and recent data allows us to draw important conclusions on stellar nucleosynthesis processes as well as on mechanisms of galaxy formation.
847(2006); http://dx.doi.org/10.1063/1.2234387View Description Hide Description
Classical models of galactic evolution predict a smooth rise in heavy‐element abundance (metallicity) with time. We test this prediction with a new, large and unbiased sample of long‐lived stars in the solar neighbourhood and find that several of the key tests fail to support the classical predictions. In agreement with earlier studies, our observed metallicity distribution function is deficient in low‐mass metal‐poor stars from the generation that produced the heavy elements seen in the Sun and younger stars. In contrast to some earlier studies, we find no clear rise in overall metallicity with time in the Solar neighbourhood; we also find that the galactic disk has experienced kinematic heating throughout its life, and identify groups of stars that may be traces of dwarf galaxies that have merged with the Milky Way.
847(2006); http://dx.doi.org/10.1063/1.2234388View Description Hide Description
Observed large scatters in abundance ratios of neutron‐capture elements relative to iron in metal‐poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. On the other hand, recent studies of metal‐poor stars show considerable small dispersions for abundance ratios of C‐Zn. We discuss whether such variations of scatters in abundance ratios can be explained by a consistent chemical evolution model. We also attempt to constrain the origins of r‐process elements, comparing predictions by an inhomogeneous chemical evolution model with new observational results with Subaru HDS.
847(2006); http://dx.doi.org/10.1063/1.2234390View Description Hide Description
We discuss production of light elements (Li, Be) in energetic type Ic supernovae (SNe Ic) and how newly synthesized light elements are transferred to stars of the next generation. We have pointed out that spallation reactions involving N and He become important in an explosion of a rotating metal‐poor star if the progenitor still keeps a fraction of the He layer at SN explosion. In this kind of explosions, 6Li is produced by a fusion reaction He+He. Simultaneously, most of Be is produced through the spallation reaction He+N. This scenario suggests that there must be intrinsic scattering in abundance of Li isotopic ratios among metal‐poor stars because the mass range of stars concerned here is limited to ≳ 40 M ⊙ and light element yields should be sensitive to the degree of rotation.
847(2006); http://dx.doi.org/10.1063/1.2234391View Description Hide Description
Features in nucleosynthesis and emission processes in jet‐like aspherical hypernova explosions are presented. The aspherical model yields large (Co, Zn)/Fe and small (Mn, Cr)/Fe as are consistent with abundance patterns in metal‐poor halo stars, indicating important contribution of hypernovae in the early Galactic chemical evolution. The same model also yields large amount of 44Ti. As for emission features, this model is found to reproduce successfully the optical light curve and spectra of hypernova SN 1998bw. The viewing angle is close to the polar direction. The same model explains a peculiar [OI] 6300Å profile observed in SN 2003jd, only if the viewing angle is different from that for SN 1998bw. These analyses support the validity of the aspherical models, therefore the use of the models as a reference model for hypernova nucleosynthesis. In addition, theoretical prediction is presented for high energy emissions from the decays of56 Ni and56Co.