Pumping of main line OH masers in the circumstellar envelopes of Type I Mira variables

Abstract

We have investigated the pumping of OH masers in the circumstellar envelopes of Mira variables. The location of the masing OH and the physical conditions within the circumstellar shell are approximated from a simple, spherically symmetric model of the mass loss. Parameters for the models are chosen to reproduce the conditions within Mira variables which show Type I (main line dominant) maser emission. The level populations of OH are calculated using the escape probability formalism and a modified Sobolev approximation. Pumping effects from direct stellar radiation, collisions, dust FIR emission, and FIR line overlaps are included