1997A&A...325..282C

We present the results of single dish and interferometric observations of ammonia towards 5 sources selected from a sample of H₂O and OH masers associated with star forming regions. The Medicina telescope was used to observe the NH₃(1,1), (2,2), and (3,3) inversion transitions. High resolution maps in the NH₃(2,2) and (3,3) lines and in the 1.3 cm continuum were then obtained with the Very Large Array. The main result of this research is to confirm the belief that H₂O masers form in hot dense molecular cores which are sites of massive star formation. We also find evidence for the H₂O maser phase to be prior to the appearance of an ultracompact HII region around the embedded high mass star(s).