Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy

• Published in: The Astrophysical journal 2008-11, Vol.687 (1), p.272-286
• Main Authors: Qian, Y.-Z, Wasserburg, G. J
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/591545

We have attributed the elements from Sr through Ag in stars of low metallicities to charged-particle reactions (CPRs) in neutrino-driven winds, which are associated with neutron star formation in low-mass and normal supernovae (SNe) from progenitors of similar to 8-11 [image] and similar to 12-25 [image], respectively. Using this rule and attributing all Fe production to normal SNe, we previously developed a phenomenological two-component model, which predicts that [image] 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 [image]. 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 similar to 25-50 [image] 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 similar to 24% of the bulk solar Fe inventory while normal SNe contributed only similar to 9% (not the usually assumed similar to 33%). This implies a greatly reduced role of normal SNe in the chemical evolution of the low- A elements.