A SEARCH FOR OH MASER EMISSION FROM POSTASYMPTOTIC GIANT BRANCH STARS

We present a survey for OH maser emission at 18 cm in the direction of 196 IRAS point sources. The primary aim of the survey was to detect O H maser emission from post-asymptotic giant branch (post-AGE) stars. O H emission and/or absorption was detected in the direction of 77 sourc es of which 57 OH detections were previously unknown, giving an overal l detection rate of 39 per cent. Fourteen maser sources associated wit h evolved stars or planetary nebulae were found, corresponding to 7 pe r cent of the total observed. These included three planetary nebulae ( two new OH detections), nine post-AGE stars (three new OH detections) and two cold OH/IR stars (both previously known). Two sources were of uncertain identification (both new OH detections). The remainder of th e OH sources were identified with young stellar objects and with HII r egions. The survey included the detection of OH maser emission from HD 101584, an early-type supergiant at high Galactic latitude. For sever al of the post-AGE stars, changes have occurred in the OH spectral pro files over a period of several years. This is interpreted as evidence for rapid changes in the stellar winds, due either to interactions wit h stellar companions, novae-like events or rapid stellar evolution.