We have attributed the elements from Sr through Ag in stars of low metallicities ( { [ Fe / H ] } \lesssim - 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 \sim 8 – 11 M _ { \odot } and \sim 12 – 25 M _ { \odot } , 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 ] } \geq - 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 ] } \lesssim - 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 \sim 25 – 50 M _ { \odot } 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 \sim 24 \% of the bulk solar Fe inventory while normal SNe contributed only \sim 9 \% ( not the usually assumed \sim 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 .