High resolution observations of the hot core in G29.96-0.02

We present high angular resolution observations obtained with the Owens Valley and the IRAM Plateau de Bure millimeter-wave interferometers toward the hot core in G29.96-0.02. We observed the ground state CH3CN(6-5), CH3CNII(6-5), vibrationally excited (v8=1) CH3CN(6-5), and the C18O(1-0) rotational transitions, as well as the 2.7 mm continuum emission. Our continuum maps show evidence of a compact source barely resolved whose diameter we estimate to be about 0.06 pc and whose emission mechanism is dominated by thermal emission from warm dust. Both the ground state and the v8 =1 methyl cyanide lines, as well as other serendipituosly detected molecular transitions, arise from a compact source at the same position as the 2.7 mm continuum emission. The C18O observations sample the structure and kinematics of the molecular surroundings of the hot core and from the C18O data we estimate a gas mass of about 1.1 x 103 Msun in a region with a diameter of 0.32 pc, corresponding to an average number density of about 106 cm-3. Our data show evidence of both a temperature and density gradient in the hot core and its molecular surroundings. The density gradient, in particular, is consistent with the infalling scenario suggested by the presence of an East-West oriented velocity gradient, which is however of opposite sign in CH3CN and C18O. We tentatively interpret the C18O velocity gradient as associated with infall, whereas the CH3CN gradient, consistent with that measured in NH3 by Cesaroni et al. (\cite{CHWC98}), is likely to trace a massive rotating disk.