The kinematics of molecular clumps surrounding hot cores in G29.96-0.02 and G31.41+0.31

We present high angular resolution interferometric observations of the 3 an d 1.3 mm continuum emission, and HCO + (1-0) and SiO(2-1) v = 0 lines, obta ined with the Owens Valley Radio Observatory millimeter-wave array, toward two hot cores (HCs) associated with two well known ultracompact (UC) H II r egions: G29.96-0.02 and G31.41+0.31. These HCs are believed to host young f orming massive stars which have been suggested to be surrounded by massive rotating accretion disks. The aim of these new observations is to study the structure and kinematics of the molecular clumps surrounding the HCs and n earby UC H II regions at moderately high angular resolution. Our observatio ns reveal that the clumps within which the HCs and UC H II regions are embe dded have a complex kinematical structure. The total mass of the clumps is estimated to be in the range 1000-3000 M-circle dot, consistent with previo us findings. Our observations also show compelling evidence that the clump in G29.96-0.02 is contracting onto the HC position, suggesting that the acc retion process onto the massive young stellar object embedded in the HC is still ongoing. In these objects the kinematical structure that we observe i s also compatible with the presence of a massive rotating disk within the H C, even though we cannot prove this suggestion with our data. The case of G 31.41+0.31 is more complicated, and our data, although consistent with the presence of an inner disk and an infalling envelope around it, do not have the required spatial resolution to resolve the different structures.