The role of rotation on the yields of the two γ-ray emitters 26Al and 60Fe ejected by massive stars
Agnese Falla, Lorenzo Roberti, Marco Limongi, Alessandro Chieffi
TL;DR
This study demonstrates that rotation is essential to reproduce the Galactic $^{60}$Fe/$^{26}$Al gamma-ray flux ratio observed by INTEGRAL, a result unattainable with non-rotating models. By employing a homogeneous FRANEC-based grid of massive-star models (mass range $13$–$120\,M_\odot$, rotation $v_{\rm rot}=0$–$300$ km s$^{-1}$) and a 335-isotope network, the authors compute wind and explosive yields for $^{26}$Al and $^{60}$Fe and then integrate them over a Salpeter IMF ($x=1.35$) and two rotation-distribution schemes (Gaussian and IDROV). They show $^{60}$Fe/$^{26}$Al is about $0.24$–$0.26$ for rotating populations, while the non-rotating case yields $\sim0.06$, well below the observed range of $0.18$–$0.24$. This indicates that rotation significantly alters convective structure, mass loss, and nucleosynthesis pathways, enabling rotating massive-star models to match Galactic gamma-ray observations. The work provides a robust link between stellar physics and Galactic chemical evolution, highlighting rotation as a key ingredient in predicting isotope yields in the Milky Way.
Abstract
We show that the observed 60Fe/26Al flux ratio provided by the SPectrometer on INTEGRAL satellite (0.24 +- 0.04) can be reproduced only if rotation is taken into account in the computation of the stellar models. Predictions from non-rotating stellar models yield to a significantly lower ratio (0.062), which is incompatible with the observed value. The adopted models and the associated yields are based on a combination of models already published by Limongi & Chieffi (2018) complemented by additional ones fully consistent with the original grid, allowing a finer resolution in the initial rotational velocity distribution.