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

Abstract

We present the 26 Al and 60 Fe yields produced by a generation of solar metallicity stars ranging in mass between 11 and 120 M . We discuss the production sites of these -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 26 Al yield together with the contributions of the He convective shell, the C convective shell, and the explosive Ne/C burning to the 60 Fe yield. We conclude that, at variance with current beliefs, 26 Al is mainly produced by the explosive C/Ne burning over most of the mass interval analyzed here, while 60 Fe 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 1.8 photons per Lyman continuum photon, R GxL , and the 60 Fe/ 26 Al -ray line flux ratio. R GxL is found to be roughly constant along the Galactic plane (and of the order of 1:25 ; 10 À11 ), while the 60 Fe/ 26 Al ratio has been recently measured by both RHESSI (0:17 AE 0:05) and SPI (INTEGRAL) (0:11 AE 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 2 Velorum, and we find that a quite large range of initial masses, at least from 40 to 60 M , do eject an amount of 26 Al (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.

Using population synthesis of massive stars to study the interstellar medium near OB associations

“…At the last point of the stellar tracks the radioactive yields from the supernova explosions are added. We have two prescriptions for calculating the yields: in the default mode (yieldsLC2006) we use the yields calculated by Limongi & Chieffi (2006). The yields are found based on the initial mass of the stars, interpolating linearly between their data points.…”

“…A similar tracer is the isotope 60 Fe, observed by its 1173 keV and 1333 keV decay lines (Smith 2004;Harris et al 2005). This isotope is also emitted in the supernova explosions (Limongi & Chieffi 2006). The lifetime of 60 Fe has recently been revised to ∼3.8 Myr, from the previous estimate of ∼2 Myr (Rugel, private communication).…”

“…Typically, massive stars eject a few 10 −5 M of 26 Al through their winds and supernova (SN) explosions (see e.g. Limongi & Chieffi 2006), and the total mass of 26 Al in the Milky Way is estimated to be 2.8 ± 0.8 M (Diehl et al 2006). A similar tracer is the isotope 60 Fe, observed by its 1173 keV and 1333 keV decay lines (Smith 2004;Harris et al 2005).…”

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…Interim approaches beyond piston or thermal bomb models [20,34,53,81] try to mimic multi-D neutrino heating in a spherical approach in order to obtain more appropriate predictions of the explosion energy, mass cut between neutron star and ejecta, as well as nucleosynthesis (including the effects of neutrinos on Y e , the proton/nucleon ratio): Fröhlich et al [15] multiplied neutrino-capture rates by a factor, causing additional ν-heating, to obtain observed explosion energies. Ugliano, Ertl, and Sukhbold et al [68] introduced a tuned, time-dependent central neutrino source that approximately captures the essential effects of (3D) neutrino transport (PHOTB).…”

“…CCSNe contribute to galactic evolution via their wind ejecta, and after explosion via (a) ejecta of essentially unburned matter from the outer stellar zones and (b) explosively processed matter from the inner ejecta. 60 Fe (half-life 2.6 × 10 6 y) is an example for (a) and goes back to hydrostatic burning stages [34,37,81]. Recent findings show that it can witness the last CCSNe near the solar system about 2 to 3 million years ago [30,76].…”