Aluminium-26 from Massive Binary Stars. I. Nonrotating Models

Aluminium-26 is a short-lived radionuclide with a half-life of 0.72 Myr, which is observed today in the Galaxy via γ-ray spectroscopy and is inferred to have been present in the early solar system via analysis of meteorites. Massive stars are considered the main contributors of ²⁶Al. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the ²⁶Al yields has not been investigated since Braun & Langer. Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10 M _⊙ ≤ M ≤ 80 M _⊙) nonrotating single and binary stars of solar metallicity (Z = 0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the ²⁶Al yield can either increase or decrease in a binary system. For binary systems with primary masses up to ∼35-40 M _⊙, the yield can increase significantly, especially at the lower mass end, while above ∼45 M _⊙ the yield becomes similar to the single-star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass loss in binary systems to the total ²⁶Al abundance produced by a stellar population is minor. On the other hand, if massive star mass loss is the origin of ²⁶Al in the early solar system, our results will have significant implications for the identification of the potential stellar, or stellar population, source.

This paper is dedicated to the celebration of the 100th birthday of Margaret Burbidge, in recognition of the outstanding contributions she has made to nuclear astrophysics (Burbidge et al. 1957).