GALACTIC CHEMICAL EVOLUTION OF PRIMARY ELEMENTS IN THE SOLAR NEIGHBORHOOD .2. ELEMENTS AFFECTED BY THE S-PROCESS

We apply the analytical model developed previously to the Galactic che mical evolution of elements that in the Solar system come primarily fr om the s-process, but at low metallicities are believed to come primar ily from the r-process. We find that a 'primary' production model is i ndicated for the s-process, but with two separate time delays that are treated in the 'delayed production' approximation and turn out to be of the order of 37 Myr and 2.7 Gyr, corresponding to progenitor masses of about a and 1.5 M., respectively. While the latter component fits in well with current models of s-process synthesis of material in the Solar system, the early component raises some difficulties because asy mptotic giant branch (AGE) stars of high mass and low metallicity are observed to generate a high ratio of heavy to light s-process elements , whereas the field stars presumed to represent the effects of Galacti c chemical evolution still have Solar system-like heavy to light ratio s.