The Ionization Structure of Planetary Nebulae: I. Pure Hydrogen Nebulae

Abstract

The problem is formulated in terms of the equations of radiativetransfer, of ionization equilibrium and of the thermal balance. Theintensity of ionizing radiation is I = lyS + 1yd where lyS is theattenuated intensity of stellar radiation and lyd the intensity ofdiffuse radiation produced in the nebula. In Approximation I it isassumed that there is no transfer problem for the diffuse radiation,emission and absorption occurning at the same place. The problemis then solved using a method due to Zanstra and de Jong. Assumingthe star to radiate as a black body, numerical results are obtainedfor a wide range of star temperatures. In Approximation II the transferequation for 1yd is solved using the source function from ApproximationI. For an isothermal plane parallel model it is found that the meanintensities Jy as given by Approximations I and II, never differby more than a few per cent.