The Nucleosynthesis of ²⁶Al and ⁶⁰Fe in Solar Metallicity Stars Extending in Mass from 11 to 120 M_☉: The Hydrostatic and Explosive Contributions

We present the ²⁶Al and ⁶⁰Fe yields produced by a generation of solar metallicity stars ranging in mass between 11 and 120 M_☉. We discuss the production sites of these γ-ray emitters and quantify the relative contributions of the various components. We provide the contributions of the wind, the C convective shell, and the explosive Ne/C burning to the total ²⁶Al yield together with the contributions of the He convective shell, the C convective shell, and the explosive Ne/C burning to the ⁶⁰Fe yield. We conclude that, at variance with current beliefs, ²⁶Al is mainly produced by the explosive C/Ne burning over most of the mass interval analyzed here, while ⁶⁰Fe is mainly produced by the C convective shell and the He convective shell. By means of these yields we try to reproduce two quite strong observational constraints related to the abundances of these nuclei in the interstellar medium, i.e., the number of γ_1.8 photons per Lyman continuum photon, R_GxL, and the ⁶⁰Fe/²⁶Al γ-ray line flux ratio. R_GxL is found to be roughly constant along the Galactic plane (and of the order of 1.25 × 10^-11), while the ⁶⁰Fe/²⁶Al ratio has been recently measured by both RHESSI (0.17 ± 0.05) and SPI (INTEGRAL) (0.11 ± 0.03). We can quite successfully fit simultaneously both ratios for a quite large range of exponents of the power-law initial mass function. We also address the fit to γ² Velorum, and we find that a quite large range of initial masses, at least from 40 to 60 M_☉, do eject an amount of ²⁶Al (through the wind) compatible with the current upper limit quoted for this W-R star: such a result removes a long-standing discrepancy between the models and the observational data.