2003A&A...407..225O

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), CH₃¹³CN(6-5), vibrationally excited (v₈=1) CH₃CN(6-5), and the C¹⁸O(1-0) rotational transitions, as well as the 2.7mm continuum emission. Our continuum maps show evidence of a compact source barely resolved whose diameter we estimate to be about 0.06pc 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 2.7mm 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 1.1x10³M_☉ in a region with a diameter of 0.32pc, corresponding to an average number density of about 10⁶cm^–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. (1998A&A...331..709C), is likely to trace a massive rotating disk.