Chemical evolution of $^{26}$Al and $^{60}$Fe in the Milky Way

Abstract

We present theoretical mass estimates of 26 Al and 60 Fe throughout the Galaxy, performed with a numerical chemical evolution model including detailed nucleosynthesis prescriptions for both stable and radioactive nuclides. We compared the results for several sets of stellar yields taken from the literature, either for massive, low and intermediate mass stars, nova systems (only for 26 Al) and supernovae Type Ia, and then computed the total masses of 26 Al and 60 Fe in the Galaxy. In particular, we have studied the bulge and the disc of the Galaxy in a galactocentric radius range between 0 and 22 kpc. We have assumed that the bulge region (between 0 and 2 kpc) evolved very quickly suffering a strong burst of star formation, while the disc formed more slowly and inside-out, in agreement with previous works, which reproduced the majority of observational constraints. We have compared our results with the 26 Al mass observed by the γ-ray surveys COMPTEL and INTEGRAL, in order to select the best model. Concerning 60 Fe, for which we do not have any observed mass value, we have just predicted its mass to provide a theoretical predictions to be confirmed or disproved by future observations. We have found that low and intermediate mass stars as well as Type Ia supernovae contribute negligibly to the two isotopes, while massive stars are the dominant source. The contribution from novae is, however, necessary to reproduce the observed mass of 26 Al, and this is a new result. Our best model predicts a mass of 2.12 M of 26 Al, in agreement with observations, while for 60 Fe our best mass estimate is around ∼ 1.05 M . We have also predicted the present rate of injection of 26 Al and 60 Fe in the Galaxy and compared it with previous results, and we have predicted a larger present time rate of injection along the disc, relative to previous works.

Origin of the elements

“…When including ejecta of such nova explosions, a few not highly abundant isotopes up to Mg and Si can be considered to have a nonnegligible contribution from novae (José et al 2004;José and Coc 2005). There exist also indications that novae can play an important role in the production of 7 Li (D'Antona and Matteucci 1991;Romano et al 2001;Izzo et al 2015) and 26 Al (Vasini et al 2022).…”

The Galactic Nova Rate: Estimates from the ASAS-SN and Gaia Surveys

“…Another radioactive isotope created during a nova eruption is formation rate (Diehl et al 2006). However, the recent study of Vasini et al (2022) shows that novae are likely to be significant contributors to the Galactic 26 Al budget, perhaps accounting for the majority of the 26 Al mass (see also Bennett et al 2013). The uncertainty in the nova rate makes determining such nucleosynthetic contributions difficult.…”