The Cygnus region: A laboratory for nucleosynthesis

We have observed the Cygnus region in the gamma-ray decay lines of 26Al and 60Fe with the INTEGRAL/SPI spectrometer. A study of the morphology of the 1809 keV emission from 26Al suggests an emission region centered about the massive star cluster Cyg OB2, with a characteristic size between 6° and 9° or possibly higher. Adopting this model for the emission of the Cygnus complex, a 2-σ upper limit of 1.6 × 10−5 ph cm−2 s−1 is obtained for the 60Fe emission, and a flux of (4.9 ± 1.1) × 10−5 ph −2 s−1 is obtained for the 26Al (with potential additional uncertainty due to the galactic background behind Cygnus). These measurements have been compared to population synthesis predictions based on the latest stellar evolution and nucleosynthesis calculations. The predicted flux in the 1809 keV line for the Cygnus region falls short of the SPI observation by a factor of two, but this discrepancy will very likely be removed by a revision of the clusters ages from new isochrones based on rotating models. Our upper limit on the 60Fe emission remains above the maximum value reached by the Cygnus complex over its entire lifetime. Interestingly, it seems, from the data at our disposal, that the contribution of the stellar winds and supernova explosions to the total 26Al budget are roughly equal for a solar metallicity population.