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. |