1996A&AS..115..387D

For the purpose of measuring the periods and the spatial extent of OH masing regions in the circumstellar envelopes of OH/IR stars, it has become a common practice to use a piecewise sine function to model the OH flux curves. Although such a function offers a model which accounts for the asymmetry observed, we propose a new and simpler expectation function which reproduces the observed asymmetry naturally. This expectation function is also more reliable and easier to implement in a nonlinear least squares procedure. This model is applied to four cool variable stars which have been monitored for a period of roughly two years in the 1612 and 1667MHz lines of the OH radical.