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Astron. Astrophys. 325, 282-294

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The molecular environment of H2O masers:
VLA ammonia observations

C. Codella1, L. Testi2, and R. Cesaroni3

1Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy
3Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

Received 23 December 1996 / Accepted 6 March 1997


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).

Key words: masers - stars: formation - interstellar medium: molecules - radio lines: interstellar

Send offprint requests to: R. Cesaroni

© European Southern Observatory (ESO) 1997