Abstract

Poster - Splinter MeVSky   (MW-0337)

Contributions of massive stars and classical novae to Galactic 26Al

Manja Zimmerer, Thomas Siegert
Julius-Maximilians-Universität

The radioactive isotope Al-26 is believed to be mainly produced by massive stars and ejected into the interstellar medium through their winds and supernovae (SNe). Due to its lifetime of 1 Myr, it traces recent nucleosynthesis and star formation. Fe-60 is similarly long-lived (3.8 Myr), and only originates in SNe. Stellar evolution models in combination with Galactic Chemical Evolution (GCE) models over-predict the Fe-60/Al-26 ratio. Population synthesis models only match the observational constraints with an enhanced star formation rate (SFR) of > 5 Msun/yr. Classical novae may contribute significantly to the Al-26 production, potentially lowering the SFR inferred from massive stars, even though previous studies suggest only < 10% contribution. We determine the mass distribution of Al-26 as a function of Galactocentric radius and estimate the contribution of (very) massive stars and classical novae to the 1.8 MeV signal. We use 20 yr of INTEGRAL/SPI observations at 1.8 MeV to test different assumptions on the radial structure of Al-26 and compare the resulting mass distribution to different GCE models. We find significant contributions from classical novae which exceed prior studies for all tested models. Within uncertainties, we find a nova contribution to the persistent Al-26 mass in the Milky Way of > 50%. This alleviates tension in the Fe-60/Al-26 ratio and lowers the SFR from Al-26 gamma-ray measurements to 1 - 2 Msun/yr. Classical novae should not be neglected as sources of Al-26 because the Galactic 1.8 MeV line could hardly be explained by existing massive star evolution models alone. While it is difficult to gauge both contributions directly, next generation MeV telescopes, such as COSI, can potentially identify individual massive stars, such as gamma-2-Velorum.