OH/IR stars generally have strong 1612 MHz masers, and often masers at 1665 and 1667 MHz as well. These are readily detected from simple ON-source observations, and are thus excellent targets for setting up appropriate velocity and intensity scales. Recently a C-band excited maser was detected from a proto planetary nebula (PPN), the stellar phase that evolves at the cessation of copious mass-loss into the circumstellar shell of an OH/IR star.
This project used the easy to observe 18 cm masers to organize the observing procedure, which included simultaneous observations of the four 18 cm transition. A quasar B1622+23 was used as a calibration source. The search continued for excited-state OH masers at C-band. The observing time allocated allowed for this search to include a strong OH/IR star, an evolved PPN, and a very young PPN. | 