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

Abstract

Context. The 26Al short-lived radioactive nuclide is the source of the observed galactic diffuse ?-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.