Time variations in the OH microwave and infrared emission from late-type stars

The results of a study initiated in the fall of 1969 are reported. The study was concerned with the monthly measurement of the microwave spectra at 1612 MHz and the broadband infrared fluxes at six wavelengths for 10 OH/IR sources. The observations represent the first conclusive evidence for well-defined, periodic variations in the flux from any type of OH microwave emitter. Following the discovery of OH/IR stars that emit mainly at 1665 and/or 1667 MHz the program was expanded to include four of these sources.