The Nucleosynthesis of26Al and60Fe in Solar Metallicity Stars Extending in Mass from 11 to 120M⊙: The Hydrostatic and Explosive Contributions

Abstract

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 γ1.8 photons per Lyman continuum photon, RGxL, and the 60Fe/26Al γ-ray line flux ratio. RGxL 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.