Planetary nebulae with multiple shells

It is shown that the central stars of planetary nebulae with giant halos (ratio of outer to inner radius >5) are much cooler than are those of nebulae which consist of double shells with a radius ratio 2. For double shell 4nebulae,thechangeofratioasafunctionofradiusisconsistentwiththeejectionofshellsatdifferenttimes; the inner shell is produced when the outer has a radius of about 0.10 pc. The giant halo and bright double shell nebulae occur for radii at which the inner nebula is becoming opticalty thin, and the central star is near its maximum luminosity. It appears that all of Hromov and Kohoutek's (1968) type 1 nebulae, and perhaps (1/3) of all planetaries, possess double shells. Large halos appear around NOC 7009 and 7662, which make these examples of triple shell planetaries.