Physical Processes in Gaseous Nebulae. III. The Balmer Decrement.

This paper contains a numerical solution of the equations derived and formally solved in two earlier papers of the series. Various tables of general interest, including those of functions Xn = hR/n2kT and -[Ei(-X~)], for useful astrophysical ranges of n and Te are given. The Balmer decrement, computed under two alternative hypotheses-A for a nebula transparent to Lyman line radiation, and B for an opaque nebula-is tabulated. The latter hypothesis agrees better with the observed data. The conclusion is reached that the electron temperature, T~, of the nebular gas cannot be effectively determined from observed Balmer decrement data, because the decre- ment is insensitive to temperature. In view of the extreme physical conditions that exist in nebulae, the partition of atoms among the various excited levels approaches surprisingly close to the thermodynamic value