OH/IR stars without OH masers - Nondetection statistics

Potential OH/IR stars are readily recognized from their far-infrared colors. These are confirmed as OH/IR stars by detecting their 1612 MHz masers. Color selection from the sources listed in the IRAS Point Source Catalog therefore provides an efficient means for identifying new objects. However, this approach is not so efficient with weak sources (S25 < 2 Jy). Color-selected sources with S25 > 2 Jy that are not associated with OH masers have the same color-color range, the same IR flux range, and a similar galactic distribution to the detections. These sources are explicable as normal OH/IR stars in which the OH maser is being suppressed. This would occur when a star with a circumstellar envelope also has a companion star that is able to disrupt the velocity coherence of the normal masing shell. The detection to nondetection ratio then provides a tool for studying the duplicity of these stars over the whole Galaxy.