High-n Balmer transitions in gaseous nebulae

The intensities of the Balmer lines arising from levels with principal quantum number n > 15, and the intensity of the apparent continuum formed by the overlapping of the Balmer lines, have been measured in the Orion Nebula (NGC 1976) and the planetary nebula NGC 7027. These observed intensities have been compared with the predictions of Brocklehurot's recombination theory in order to deduce the electron temperature and density of the nebulae. We find that % = 8600 + 1500 K and logjo N, = 4.1 + 0.3 for NGC 1976 and that T, = 69000 + 15000 K and logio AT, = 5.6 + 0.3 for NGC 7027.