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OH/IR source

(OH/IR star)
(AGB star with strong OH maser)

An OH/IR source is a source of infrared and OH maser electromagnetic radiation. They are assumed to be asymptotic giant branch stars surrounded by dust (which re-emits the star's light as infrared) and OH (which mases).

Of interest is the maser EMR from varying distances from us given the size of the cloud, which is growing, so its position in the cloud can be discerned by the Doppler shift. Any variability in the star allows the relative position of the masers to be worked out, yielding the size of the surrounding OH cloud.