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K. Singer (Duke U. & Maria Mitchell Obs.)
22GHz water vapor masers are thought to arise in the intermediate part of a Mira variable's atmosphere, where bound motions of the gas (radial oscillations and rotation) transform into an unbound outflow. To help quantitatively interpret the spectra and interferometrical maps of these masers, we developed a numerical model, in which maser amplification takes place in a spherically rotating and pulsating shell. The shell can be given any combination of radial and rotational motion, it can be arbitrarily inclined to the line of sight, and it can be arbitrarily filled with active maser regions. The application of the model to a few available VLBI maps of water vapor masers in Miras will be demonstrated. This project was partially supported by the NSF/REU grant AST-9820555.