Sequential explosions of supernovae in an OB association and formation of a superbubble

From the standpoint of view that the early type stars are formed sequentially at an OB association, it is expected that the supernova explosions will also occur sequentially. The expansion law of a supernova remnant, which is formed by sequential explosions of supernovae, is studied. The superbubbles and supershells with radii of approximately 200-1000 pc are naturally explained by this model. Assuming that the sequential explosion of supernovae occurs at every OB association, the star formation rate in our Galaxy is deduced.