Monte Carlo models of 1612 MHz OH masers in circumstellar shells

Abstract

We present models of the radiative transfer in circumstellar OH masers. In particular we model the 1612 MHz maser line in OH/IR stars. The coupled radiative transfer in expanding circumstellar shells can be simulated by means of a Monte Carlo technique (Spawns & Van Langevelde 1992). We show that such an approach is relatively advantageous for the radiative transport in masers. The combined effects of saturation and beaming can be observed in such models. In the geometry of expanding shells spectra can be obtained that resemble the average spectra in OH/IR stars quite well.