AbstractAbout 40% of potential OH / IR stars, color selected from the IRAS Point Source Catalog, have no 1612 MHz masers. While these objects are rarely carbon rich, they are usually associated with circumstellar shells. The natural explanation for these "OH / IR star color mimics" is that they are systems with a degenerate companion collecting an accretion disk from a red giant wind. This provides them with an extra source of UV for dissociating their molecules. The persistent absence of the

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... ual complement of masers from an O-rich shell is then a pointer to the presence of a degenerate companion. These occur in association with ~45% of old giant stars.