IRAS studies of galactic supershells

Using IRAS Skyflux images and a new catalog of OB stars in the Cygnus region, a complete infrared supershell surrounding the Cyg OB1 Association was identified. This supershell is seen as a conspicuous, well-defined 2 deg x 5 deg region deficient of IR emission, with a limb-brightened edge and dimensions of about 50 x 130 pc at 1.5 kpc. The shell's elongated morphology is consistent with OB-star subclustering over the approximately 10(exp 6) yr age of the bubble. With a parent star cluster still visible (10 O stars between 25 and 45 solar mass, 3 - 4 Wolf-Rayet stars, and the possibility of 3 - 5 more massive stars that died as supernovae) the Cyg OB1 supershell is an excellent object for studying the formation and evolution of Galactic supershells. A discrepancy between the less than or equal to 1 Myr bubble age estimated from its size and the 5 Myr cluster turnoff age (45 solar mass) may require non-coeval massive star formation to explain the number of post-main-sequence stars and limit the number of past supernovae.