The Continuum Emission from Planetary Nebulae

The study of nebular continuum emission is important for several reasons (Pottasch 1984, Planetary Nebulae, Dordrecht: Reidel). First of all, it can provide information about the temperature and the density of the nebula, when the object is large enough, or when the central star is weak enough, so that the nebular continuum is easily observed without interference from the stellar continuum. On the other hand, for small planetary nebulae, both the central star and the nebula contribute to the observed continuum. In this latter case, in order to obtain the stellar continuum the theoretical nebular emission must be used. Thus, studies of the evolution of planetary nebula nuclei through the HR diagram rely on a good calculation of the theoretical nebular continuum.