A MASING [FE-XI] LINE

I draw attention to a maser which occurs within the ground term of Fe10. In many photoionized environments, infrared fine-structure lines a nd the [O I] lambda6300 line become optically thick but maser amplific ation of ionic fine-structure lines is unusual. During the course of d evelopment of a code designed to simulate gas under radiative-collisio nal equilibrium, the radiative transfer of roughly 500 ionic/atomic em ission lines has been treated using escape probabilities. Nearly all f orbidden lines can become optically thick under extreme conditions, bu t the 3Pj = 1, 0 [ Fe XI] 6.08 mum transition is the only line which r outinely mases and can reach optical depths smaller than -5. Maser eff ects can alter the intensity ratio of the infrared line relative to 3P j = 2, 1 lambda7892 by half an order of magnitude under certain condit ions. A model of the coronal line region of Nova Cyg 1975 is presented , which illustrates the effects of this maser.