Fossil Imprints of the First Generation Supernova Ejecta in Extremely Metal-Deficient Stars

Using results of nucleosynthesis calculations for theoretical core-collapse supernova models with various progenitor's masses, it is shown that abundance patterns of C, Mg, Si, Ca, and H seen in extremely metal-deficient stars with [Fe/H] < -2.5 follow those seen in the individual first generation supernova remnants (SNRs). This suggests that most of the stars with [Fe/H] < -2.5 were made from individual supernova (SN) events. To obtain the ratio of heavy elements to hydrogen, a formula is derived to estimate the mass of hydrogen swept up by a SNR when it occurs in the interstellar matter with the primordial abundances. We use [Mg/H] to indicate the metallicities instead of [Fe/H]. The metallicities [Mg/H] predicted from these SNRs range from ~-4 to ~-1.5 and the mass of Mg in a SN is well correlated with its progenitor's mass. Thus the observed [Mg/H] in an extremely metal deficient star has a correspondence to the progenitor's mass. A larger [Mg/H] corresponds to a larger progenitor's mass. Therefore, so called `age-metallicity relation' does not hold for stars with [Fe/H] < -2.5. In contrast, the [Mg/Fe] ratios in the theoretical SNRs have a different trend from those in extremely metal-deficient stars. It is also shown that the observed trend of [Mg/Fe] can predict the Fe yield of each SN given the correspondence of [Mg/H] to the progenitor's mass. The Fe yields thus obtained are consistent with those derived from SN light curve analyses. This indicates that there is still a problem in modelling a core-collapse supernova at its beginning of explosion or mass cut.Comment: 6 pages, 4 figures, 1 table; Accepted for publication in the Astrophysical Journal Letter

Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds

Large-scale homogeneous surveys of Galactic stars may indicate that the elemental abundance gradient evolves with cosmic time, a phenomenon that was not foreseen in existing models of Galactic chemical evolution (GCE). If the phenomenon is confirmed in future studies, we show that this effect, at least in part, is due to large-scale winds that once enriched the disk. These set up the steep abundance gradient in the inner disk (R <14 kpc). At the close of the wind phase, chemical enrichment through accretion of metal-poor material from the halo onto the disk gradually reduced the metallicity of the inner region, whereas a slow increase in the metallicity proceeded beyond the solar circle. Our "wind+infall" model accounts for flattening of the abundance gradient in the inner disk, in good agreement with observations. Accordingly, we propose that enrichment by large-scale winds is a crucial factor for chemical evolution in the disk. We anticipate that rapid flattening of the abundance gradient is the hallmarks of disk galaxies with significant central bulges.Comment: 9 pages including 5 figures, accepted for publication in PAS

Age Dating of a High-Redshift QSO B1422+231 at Z=3.62 and its Cosmological Implications

The observed Fe II(UV+optical)/Mg II lambda lambda 2796,2804 flux ratio from a gravitationally lensed quasar B1422+231 at z=3.62 is interpreted in terms of detailed modeling of photoionization and chemical enrichment in the broad-line region (BLR) of the host galaxy. The delayed iron enrichment by Type Ia supernovae is used as a cosmic clock. Our standard model, which matches the Fe II/Mg II ratio, requires the age of 1.5 Gyr for B1422+231 with a lower bound of 1.3 Gyr, which exceeds the expansion age of the Einstein-de Sitter Omega_0=1 universe at a redshift of 3.62 for any value of the Hubble constant in the currently accepted range, H_0=60-80 km,s^{-1},Mpc^{-1}. This problem of an age discrepancy at z=3.62 can be unraveled in a low-density Omega_0<0.2 universe, either with or without a cosmological constant, depending on the allowable redshift range of galaxy formation. However, whether the cosmological constant is a required option in modern cosmology awaits a thorough understanding of line transfer processes in the BLRs.Comment: 7 pages including 3 figures, to appear in ApJ Letter

Effects of Geological Heterogenetiy in Watershed Area on Sediment Distribution and Benthic Macroinvertebrate Community in River System

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Contribution of Type Ia and Type II Supernovae for Intra-Cluster Medium Enrichment

The origin of the chemical composition of the intracluster medium (ICM) is discussed in this paper. In particular, the contribution from Type Ia supernovae (SNe Ia) to the ICM enrichment is shown to exist by adopting the fitting formulas which have been used in the analysis of the solar system abundances. Our analysis means that we can use the frequency of SNe Ia relative to SNe II as the better measure than $M_{Fe, SN Ia}/M_{Fe, total}$ for estimating the contribution of SNe Ia. Moreover, the chemical compositions of ICMs are shown to be similar to that of the solar system abundances. We can also reproduce the sulfur/iron abundance ratio within a factor of 2, which means that the abundance problem of sulfur needs not to be emphasized too strongly. We need more precise observations to conclude whether ICMs really suffer the shortage problem of sulfur or not.Comment: 20 pages, LaTeX text and 15 postscript figures. Accepted for publication in Astrophysical Journa

Nucleosynthesis in Type II Supernovae

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 $M_\odot$ to 70 $M_\odot$ are calculated. We examine the dependence of the supernova yields on the stellar mass, ^{12}C(\alpha, \gamma) ^{16}O} rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear Physics A, Vol. A616 (1997