On the Production of 26Al by Wolf-Rayet Stars: Galactic Yield and Gamma-Ray Line Emissivity

The contribution of Wolf-Rayet stars to the 1.8 MeV gamma-ray line emissivity of the Galactic plane is estimated on the basis of a recent stellar evolution model developed in the framework of the Brussels-Saclay collaboration. The Al-26 production and destruction mechanisms in W-R stars are reviewed, and the ejection of Al-26 into the ISM is discussed. The amount of Al-26 ejected by the stellar winds are computed along with the associated gamma ray line luminosities, and the influence of the reaction rate uncertainties and of the input stellar physics on the above quantities is addressed. Various possibilities for the Galactic W-R distribution are discussed, and the total quantity of Al-26 ejected in the ISM in the past million years is estimated. The corresponding longitudinal gamma ray flux distribution in the Galactic plane is presented and discussed. It is concluded that the W-R stars are important Al-26 sources.