The nearby Cygnus region harbours a strong concentration of massive stars: about 170 O stars distributed in half a dozen associations, thereafter called the Cygnus complex. It was observed by CGRO/COMPTEL to shine at 1809 keV. The flux measured by COMPTEL was found to be 2-3 times higher than predicted from the stellar models available in the late 1990s-early 2000s. Now, the Cygnus complex has been re-evaluated using INTEGRAL/SPI observations and improved stellar models.
About 5 years of INTEGRAL observations were used to derive the spectra of the 26Al (see POM June 2009) and 60Fe decay lines from Cygnus. The 1809 keV (26Al) flux from Cygnus is ~ 6.0 x 10-5 ph/cm2/s, while we derived an upper-limit on the 60Fe line flux at 1173/1332 keV of 1.6 x 10-5 ph/cm2/s. Yet, when taking into account the Galactic foreground and background contribution in the direction of Cygnus, it turns out that only ~ 60% of the 1809 keV flux, (3.9 ±1.1) x 10-5 ph/cm2/s, is attributable to the Cygnus complex itself.
The results have been compared with population synthesis predictions based on recent stellar models including some effects of stellar rotation and a coherent estimate of the contribution of SNIb/c. As shown in the Figure, the observations now agree with the theoretical predictions (the vertical shaded bar indicates our estimated current position along the time axis).
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