THE MOLECULAR ENVIRONMENT OF H2O MASERS - VLA AMMONIA OBSERVATIONS

We present the results of single dish and interferometric observations of ammonia towards 5 sources selected from a sample of H2O and OH mas ers associated with star forming regions. The Medicina telescope was u sed to observe the NH3(1,1), (2,2), and (3,3) inversion transitions. H igh 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 resul t of this research is to confirm the belief that H2O masers form in ho t dense molecular cores which are sites of massive star formation. We also find evidence for the H2O maser phase to be prior to the appearan ce of an ultracompact HII region around the embedded high mass star(s) .