INTERPRETATION OF HYDROGEN RADIO RECOMBINATION LINES

Computations of the high level populations of hydrogen in gaseous nebulae are used to compare observations of radio recombination lines with theoretical predictions based on possible line enhancement. Attempts to confirm the existence of maser action from electron temperatures derived on the assumption of thermodynamic equilibrium are inconclusive. There is evidence that most of the low (≲5000 K) derived temperatures can be increased by at most a few percent by allowing for line enhancement. Measured ratios of the peak temperatures of lines of the same frequencies originating from different upper quantum levels, indicate maser action if Stark broadening is not taken into account. The inclusion of Stark broadening allows confirmation of maser action only in the central regions of the Orion Nebula in the case of the 137 β/109 α ratio, and in Orion, and, possibly, IC 1795 and M17, in the case of the 197 β/156 α ratio. © 1969 D. Reidel Publishing Company.