A SYSTEMATIC STUDY OF IRAS SELECTED PROTOPLANETARY NEBULA CANDIDATES .2. OH AND CO OBSERVATIONS

We present OH maser observations of a sample of 62 IRAS-selected proto -planetary nebula (PPN) candidates, and CO observations of the 29 sour ces in this sample which are brighter than 25 Jy in the IRAS 25 mu m b and. Sixteen sources have been detected in (J = 1 - 0) or (J = 2 - 1). We observed and detected two sources in (J = 3 - 2). We have detected sixteen sources (four of which are CO sources) in the 1612 MHz transi tion of OH. Half of these are also detected at 1667 and/or 1665 MHz. T he CO and OH spectra are characteristic of emission from an expanding circumstellar shell, with an average expansion velocity of similar to 15 kms. The OH maser sources are not variable over a period of one to five years, with only a few exceptions. Several OH sources show multip le components in their spectra, sometimes strongly circularly polarize d. One double-peak OH maser source, IRAS 20406+2953, shows an enigmati c variability in circular polarization.