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

Understand

Studies of nucleosynthesis in neutrino-driven winds from nascent neutron stars show that the elements from Sr through Ag with mass numbers A~88-110 are produced by charged-particle reactions (CPR) during the alpha-process in the winds.

• Accordingly, we have attributed all these elements in stars of low metallicities ([Fe/H]<-1.5) to low-mass and normal supernovae (SNe) from progenitors of ~8-11M_sun and ~12-25M_sun, respectively, which leave behind neutron stars.
• 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.
• The high-resolution data now available on Sr abundances in Galactic halo stars show that there is a great shortfall of Sr relative to Fe in many stars with [Fe/H]<-3.