NEW OH MAIN-LINE DETECTIONS OF OH IR STARS

High-sensitivity observations have been made of main-line emission from the hydroxyl molecule in OH/IR stars. Forty-one new main-line emission sources were detected. Eighteen of these showed masers in both main lines. Eight additional stars previously seen in one line have now been detected in the second line. The emission velocities generally show double-peaked "shell structure" which tends to overlap that of the 1612 MHz velocities, suggesting that they may be at the same radius in the stellar atmosphere. In some cases the range of the 1667 MHz emission velocity is slightly, but clearly, greater than the 1612 MHz spread. The 1665 MHz emission showed no such breadth, being within or coterminous with the 1612 MHz velocity. A total of 55 stars was detected; most show the classic double-peaked profile centered on the stellar velocity (as indicated by the 1612 MHz emission). Nine of the 55 have stronger emission at 1665 MHz than at 1667 MHz. The velocity correlation among the 1612, 1665, and 1667 MHz lines show a good qualitative (semi-quantitative) support for the idea of competitive gain (amplification of one maser hf transition at the expense of another) under saturated maser conditions. Color-color plots of 60-mu/25-mu versus 25-mu/12-mu show no significant difference between detections and nondetections of the main lines, a conclusion also reached for 1612 MHz masers by Lewis, Eder, and Terzian.