The Intensity of Forbidden Emission Lines.
Guido Münch · The Astrophysical Journal · 1962
A general formula for the intensity of a forbidden emission line in a two-level atom is derived, taking into consideration induced emissions, saturation effects, and departures from a Boltxmann distribution. The kinetic temperature is supposedly given, but not necessarily is it taken as constant It is shown how this general formula embodies expressions used in the past separately for the optical, infrared, and radio regions of the spectrum As an example of application of the formulae derived, the emission rate in the fine-structure transition of the ground state of C+ is re-evaluated under the conditions prevailing in interstellar H I regions As an illustration of a line arising in a medium with variable temperature, the intensity in the normal direction and flux of the line arising between the lowest two fine-structure levels of the ground state of oxygen is computed, under conditions appropriate to the earth's upper atmosphere. It is found that the outward energy flux in this line compares with the energy input provided by solar X-rays at the time of low solar activity.