We performed a survey in up to seven molecular transitions towards a sample of twelve water masers with luminous IRAS counterparts. All sources but one (AFGL5142) were not found to be positionally associated with 3.6 cm continuum emission in the VLA survey of TFTH: this should bias the sample towards embedded high-mass (proto)stars which are too young to develop an UC HII region. Both high and low density tracers have been observed. In all cases, a compact molecular clump is detected at the position of the H2O masers, suggesting that we are looking at the envelopes around young deeply embedded massive stars. Such an idea is confirmed by the broad and - in a few transitions - complex line profiles, which indicate significant turbolence and large velocity fields in the regions. The picture is further supported by the existence of outflows in some sources, arising from embedded young stellar objects. Given the high luminosity and the association with H2O masers, and the embedded nature of the YSOs, we believe that our sample represents an excellent target for future detailed studies of high-mass star formation.
This project was partially supported by ASI grants ARS-96-66 and ARS-98-116 to the Osservatorio Astrofisico di Arcetri.
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