  We have investigated the possibility that radiation pressure might trigger
planetary nebula (PN) ejection during helium-shell flashes in asymptotic-
giant-branch (AGB) stars. We find that the outward flux at the base of the
hydrogen envelope during a flash will reach the Eddington limit when the
envelope mass falls below a critical value that depends on the core mass and
composition. These results may help to explain the helium-burning PN nuclei
found in the Magellanic Clouds.

Astrophysics