A masing [Fe XI] line

I draw attention to a maser which occurs within the ground term of Fe⁺¹⁰. In many photoionized environments, infrared fine-structure lines and the [O I] λ6300 line become optically thick but maser amplification of ionic fine-structure lines is unusual. During the course of development of a code designed to simulate gas under radiative-collisional equilibrium, the radiative transfer of roughly 500 ionic/atomic emission lines has been treated using escape probabilities. Nearly all forbidden lines can become optically thick under extreme conditions, but the ³Pj = 1, 0 [Fe xi] 6.08 μm transition is the only line which routinely mases and can reach optical depths smaller than -5. Maser effects can alter the intensity ratio of the infrared line relative to ³Pj = 2, l λ7892 by half an order of magnitude under certain conditions. A model of the coronal line region of Nova Cyg 1975 is presented, which illustrates the effects of this maser.