Anomalous OH and H2O microwave emission is a common occurrence in circumstellar shells surrounding cool oxygen-rich M supergiants and Mira variables. Infrared spectra have shown that the atmospheric conditions in these stars are such that the concentration of OH molecules is a maximum. For those with H20 microwave emission, strong H20 1.9 μm absorption is present.
There exists a growing number of typical OH/IR sources discovered by radio surveys, for which no associated IR object has yet been found. Preliminary results of TV photography to discover IR counterparts are shown.
Several interesting correlations have been defined between the IR colour, period and amplitude of infrared variability, and the velocity separation of the OH emission peaks. The relationship of these to pulsationally driven mass loss and the observed characteristics of circumstellar dust shells is investigated.
The maser emission from OH/IR and H20 / I R sources is believed to be pumped by IR radiation. Combined studies of the variability of OH and H20 emission and the IR continuum of the Mira sources confirm that IR pumping is probably the dominant mechanism, although the data do not appear to favour any specific pump scheme. The OH masers are at least partially saturated; the degree of saturation of the H20 masers is unclear.