Abundances in metal-poor stars and chemical evolution of the early Galaxy

G. J. Wasserburg, Yongzhong Qian

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Abstract

We have attributed the elements from Sr through Ag in stars of low metallicities ([Fe/H] ≤ -1.5) to charged-particle reactions (CPR) in neutrino-driven winds, which are associated with neutron star formation in low-mass and normal supernovae (SNe) from progenitors of ∼ 8-11M and ∼ 12-25M, respectively. Using this rule and attributing all Fe production to normal SNe, we previously developed a phenomenological two-component model, which predicts that [Sr/Fe] ≥ -0.32 for all metal-poor stars. This is in direct conflict with the high-resolution data now available, which show that there is a great shortfall of Sr relative to Fe in many stars with [Fe/H] ≤ -3. The same conflict also exists for the CPR elements Y and Zr. We show that the data require a stellar source leaving behind black holes and that hypernovae (HNe) from progenitors of ∼ 25-50M are the most plausible candidates. If we expand our previous model to include three components (low-mass and normal SNe and HNe), we find that essentially all of the data are very well described by the new model. The HN yield pattern for the low - A elements from Na through Zn (including Fe) is inferred from the stars deficient in Sr, Y, and Zr. We estimate that HNe contributed ∼ 24% of the bulk solar Fe inventory while normal SNe contributed only ∼ 9% (not the usually assumed ∼ 33%). This implies a greatly reduced role of normal SNe in the chemical evolution of the low - A elements. This work was supported in part by US DOE grants DE-FG03-88ER13851 (G.J.W) and DE-FG02-87ER40328 (Y.Z.Q.). G.J.W acknowledges NASA's Cosmochemistry Program for research support provided through J. Nuth at the Goddard Space Flight Center. He also appreciates the generosity of the Epsilon Foundation.

Original languageEnglish (US)
JournalProceedings of Science
StatePublished - Dec 1 2008

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