Chemical Evolution of the Juvenile Universe

Abstract

Only massive stars contribute to the chemical evolution of the juvenile universe corresponding to [Fe/H]<-1.5. If Type II supernovae (SNe II) are the only relevant sources, then the abundances in the interstellar medium of the juvenile epoch are simply the sum of different SN II contributions. Both low-mass (~8-11M_sun) and normal (~12-25M_sun) SNe II produce neutron stars, which have intense neutrino-driven winds in their nascent stages. These winds produce elements such as Sr, Y, and Zr through charged-particle reactions (CPR). Such elements are often called the light r-process elements, but are considered here as products of CPR and not the r-process. The observed absence of production of the low-A elements (Na through Zn including Fe) when the true r-process elements (Ba and above) are produced requires that only low-mass SNe II be the site if the r-process occurs in SNe II. Normal SNe II produce the CPR elements in addition to the low-A elements. This results in a two-component model that is quantitatively successful in explaining the abundances of all elements relative to hydrogen for -3<[Fe/H]<-1.5. This model explicitly predicts that [Sr/Fe]>-0.32. Recent observations show that there are stars with [Sr/Fe]<-2 and [Fe/H]<-3. This proves that the two-component model is not correct and that a third component is necessary to explain the observations. This leads to a simple three-component model including low-mass and normal SNe II and hypernovae (HNe), which gives a good description of essentially all the data for stars with [Fe/H]<-1.5. We conclude that HNe are more important than normal SNe II in the chemical evolution of the low-A elements, in sharp distinction to earlier models. (Abridged)

10 pages, 9 figures, to appear in Pub. Astron. Soc. Australia

References in corpus (8)

• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• Where, oh where has the r-process gone?
• Supernova Nucleosynthesis in Population III 13 -- 50 $M_{\odot }$ Stars and Abundance Patterns of Extremely Metal-Poor Stars
• Nucleosynthesis in the Early Galaxy
• New Extremely Metal-Poor Stars in the Galactic Halo
• Nucleosynthesis Modes in the High-Entropy-Wind of Type II Supernovae: Comparison of Calculations with Halo-Star Observations
• Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy
• r-Process Nucleosynthesis in Shocked Surface Layers of O-Ne-Mg Cores

Cited by in corpus (1)

• News on the s process from young open clusters