A Southern Survey of OH Masers at 1612 MHz

Abstract

A search for OH at 1612 MHz has been made along the galactic plane from longitude 3400 to the galactic centre, yielding 78 emission sources (mostly new discoveries); a further 5 sources have been found in a less sensitive survey between longitudes 2700 and 3260 Of these 83 sources 55 are masers of the variety showing two intensity peaks spaced in velocity-a characteristic of OH/IR stars. The velocity and spatial distributions of these new OHjIR stars (which are not as yet identified in the optical or infrared) are discussed, with special reference to their kinematic properties and population type; it is still not clear whether they are predominantly late-type giants (Mira variables) or supergiants. The other 28 OH sources detected include 11 of the type lIe variety (extended OH clouds exhibiting 1612 MHz emission with accompanying 1720 MHz absorption) and 4 with accompanying main-line (type 1)OH masers; the remaining 13 sources do not readily fit within existing classification schemes and are discussed individually