Very massive star winds as sources of the short-lived radioactive isotope ²⁶Al

¹ Geneva Observatory, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: sebastien.martinet@unige.ch
² Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
³ Institute for Physics and Mathematics of the Universe (WPI), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8583, Japan
⁴ Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
⁵ IMPMC, CNRS – UMR 7590, Sorbonne Université, Muséum national d’Histoire Naturelle, 75005 Paris, France
⁶ Department of Astronomy and Astrophysics, University of Chicago, 5640 S Ellis Ave, Chicago, IL 60637, USA

Received: 3 March 2022
Accepted: 27 May 2022

Abstract

Context. The ²⁶Al short-lived radioactive nuclide is the source of the observed galactic diffuse γ-ray emission at 1.8 MeV. While different sources of ²⁶Al have been explored, such as asymptotic giant branch stars, massive stellar winds, and supernovae, the contribution of very massive stars has not been studied so far.

Aims. We study the contribution of the stellar wind of very massive stars, here, stars with initial masses between 150 and 300 M_⊙, to the enrichment in ²⁶Al of the galactic interstellar medium.

Methods. We studied the production of ²⁶Al by studying rotating and non-rotating very massive stellar models with initial masses between 150 and 300 M_⊙ for metallicities Z = 0.006, 0.014, and 0.020. We compared this result to a simple Milky Way model and took the metallicity and the star formation rate gradients into account.

Results. We obtain that very massive stars in the Z = 0.006 − 0.020 metallicity range might be very significant contributors to the ²⁶Al enrichment of the interstellar medium. Typically, the contribution of the winds of massive stars to the total quantity of ²⁶Al in the Galaxy increases by 150% when very massive stars are considered.

Conclusions. Despite their rarity, very massive stars might be important contributors to ²⁶Al and might overall be very important actors for nucleosynthesis in the Galaxy.