Large high-excitation planetary nebulae

Absolute total and relative emission-line fluxes are given for: (1) the two planetary nebulae, Abell 30 and 78, that exhibit zones of nearly pure helium near their cores, and (2) a list of other large, high-excitation nebulae that are outwardly similar to A30 and A78, and which are prime candidates for further investigation. All the nebulae are optically thin in the hydrogen Lyman continuum and have luminous central stars. They are morphologically similar, most being spherical shells