Galactic chemical evolution and 26Al production by supernovae.

Nucleosynthesis in the intermediate mass range (carbon through nickel) has been calculated for a grid of stellar masses between 10 and 40 M_⊙ for solar metallicity, and 12 and 75 M_⊙ for zero metallicity, with a total of 26 stars evolved to the presupernova state. Explosions have been simulated in 13 of these and the final nucleosynthetic yields, including the ν-process, determined. Except for the products of the neutrino process (fluorine and boron), the presupernova abundances of isotopes lighter than about A=40 (including ²⁶Al), closely resemble the final yields. These results, when incorporated into a multi-zone model for Galactic chemical evolution that includes contributions from lower mass stars and Type Ia supernovae, give present day abundances that are in good agreement with those observed in the solar system when a particular choice is made for the ¹²C(α,γ)¹⁶O reaction rate (S(300 keV)=0.17 MeV barns). We find the production rate of ²⁶Al in the present epoch to be 1.78-2.14 M_⊙ Myr^-1, depending on the choice and range of the initial mass function. This result, which is consistent with the HEAO-3, SMM, and so far the COMPTEL observations, suggests that the dominant source of ²⁶Al in the Galaxy is from the supernova of Types II and Ib.