Observations of interstellar sulfur monoxide.

In the reported investigation involving a number of sources, SO emission features were compared with those of other sulfur-containing species including CS, NS, SiS, OCS, SO2, H2S, and H2CS. The sources considered included molecular clouds associated with H II regions, dust clouds, and Ae and Be stars. Six transitions were observed of SO containing S-32 and two transitions of SO containing S-34. It is pointed out that the transitions of SO containing S-34 observed toward the Kleinmann-Low nebula are about as strong as predicted from the terrestrial S-34/S-32 abundance ratio. The velocity, width, and general source distribution of SO, H2S, and CS emission features are closely correlated (except toward the Kleinmann-Low nebula, where no CS is reported). The predictions of the ion-molecule theory agree well with the observed abundances of NS, OCS, and H2S relative to SO.