Understanding 26Al Emission from Cygnus

The COMPTEL observations of the galactic 1.809 MeV emission attributed to the radioactive decay of ²⁶Al have confirmed the diffuse nature of this interstellar emission line. One of the most significant features of the reconstructed intensity pattern is a flux enhancement towards Cygnus. This region is fairly young and contains a wealth of massive stars, most of them grouped in the Cygnus OB associations. Multi-frequency model fitting strongly supports the hypothesis of massive stars and their descendent supernovae being the dominant sources of interstellar ²⁶Al as observed by COMPTEL. Massive stars and supernovae are known to impart a large amount of kinetic energy into their surroundings causing shock regions and large cavities in the ISM. In addition, a significant fraction of the electro-magnetic radiation of these stars is emitted in the EUV regime leading to photoionisation of the surrounding medium. We applied a population synthesis model in combination with an 1D model of expanding superbubbles to the Cygnus OB associations. Besides the expected 1.809 MeV flux and the γ-ray line intensity due to interstellar ⁶⁰Fe we compute the sizes and expansion parameters of the expected HI-structures and the free–free emission intensities due to the photoionizing radiation from massive stars within this region of the sky. We discuss our present understanding of the Cygnus region with respect to the massive star census. Our model assigns about 70% of the 1.809 MeV intensity to six known OB associations, about 20% to known isolated sources and roughly 10% to an unknown diffuse component.