1998A&A...331..709C

We present high angular resolution (∼0.4", corresponding roughly to 0.015pc) VLA observations in the ammonia (4,4) inversion transition of 3 hot cores associated with UC HII regions (G10.47+0.03, G29.96-0.02, G31.41+0.31), We have for the first time resolved the emission from these structures and present maps of the integrated intensity and optical depth. The main findings of this work are the existence of velocity and temperature gradients in the cores, suggesting that they are rotating disk-like structures with temperature decreasing with increasing distance R from the centre as R^–3/4. In G10.47+0.03, the blue-shifted absorption seen towards three embedded UC HII regions is used to derive their position along the line of sight. Finally, the evolutionary status and the star formation efficiency of the three cores is discussed, and we conclude that at least in the case of G10.47+0.03 the Miller & Scalo (1979ApJS...41..513M) Initial Mass Function is inappropriate to describe the stellar content of the core. Also, we suggest that early type stars tend to form from filaments of dense molecular gas which fragment along their axis.