Contributions of massive stars and classical novae to Galactic 26Al

@misc{zimmerer2026contributions,
  title = {{Contributions of massive stars and classical novae to Galactic 26Al}},
  author = {Manja L. Zimmerer and Thomas Siegert and Niklas C. Bauer and Tristan Bouchet and Patrik Ehrmann and Mika A. Gelowicz and Laura Eisenberger and Saurabh Mittal and Tomohiko Oka and Rudi Reinhardt and Manuel R. H. W. Skalka and Dimitris Tsatsis and Hiroki Yoneda and Arianna Vasini},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.34259},
  eprint = {2610.34259},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.34259},
}

TY  - UNPB
TI  - Contributions of massive stars and classical novae to Galactic 26Al
AU  - Manja L. Zimmerer
AU  - Thomas Siegert
AU  - Niklas C. Bauer
AU  - Tristan Bouchet
AU  - Patrik Ehrmann
AU  - Mika A. Gelowicz
AU  - Laura Eisenberger
AU  - Saurabh Mittal
AU  - Tomohiko Oka
AU  - Rudi Reinhardt
AU  - Manuel R. H. W. Skalka
AU  - Dimitris Tsatsis
AU  - Hiroki Yoneda
AU  - Arianna Vasini
PY  - 2026
DA  - 2026/10/25
PB  - arXiv
DO  - 10.48550/arxiv.2610.34259
UR  - https://arxiv.org/abs/2610.34259
AB  - The radioactive isotope 26Al is believed to be mainly produced by massive stars and ejected into the interstellar medium through their winds and supernovae. Due to its lifetime of 1.04 Myr, it traces recent nucleosynthesis and star formation. 60Fe is a similarly long-lived (lifetime 3.8 Myr) isotope, and only originating in ccSNe. Stellar evolution models in combination with Galactic Chemical Evolution (GCE) models tend to over-predict the 60Fe/26Al ratio. Population synthesis models that attempt to explain both, the 26Al mass in the Galaxy and its spatial distribution, only match the observational constraints with an enhanced star formation rate (SFR) of >5 Msun/yr. Classical novae may contribute to the 26Al production, potentially lowering the SFR inferred from massive stars and alleviating tension in the 60Fe/26Al ratio. However, previous studies suggest their contribution is negligible or < 10%. In this work we aim to determine the mass distribution of 26Al as a function of Galactocentric radius and estimate the contribution of (very) massive stars and classical novae to the 1.8 MeV signal. We are using 20 yr of INTEGRAL/SPI observations of the gamma-ray line at 1.8 MeV to test different assumptions on the radial structure of 26Al and compare the resulting mass distribution to different GCE models. For our baseline analysis, all tested source models prefer substantial nova contributions, with best-fit fractions of 77-84%. This alleviates tension in the 60Fe/26Al ratio and lowers the SFR from 26Al measurements accordingly to 1-2 Msun/yr. While it is difficult to gauge both contributions directly, next generation MeV telescopes can potentially identify individual massive stars, such as Gamma-2-Velorum.
ER  -