A MASSIVE YOUNG EMBEDDED OBJECT ASSOCIATED WITH THE UC-H-II-REGION G31.41+0.31

We have used the IRAM Plateau de Bure Interferometer to make high angu lar resolution observations of the star-forming region surrounding the ultracompact H II region G31.41+0.31. We have produced maps in the gr ound state CH3CN(6-5), (CH3CN)-C-13(6-5) and vibrationally excited CH3 CN(6-5) transitions, and in the 3 mm continuum emission. From these, w e derive estimates of the size and mass of the hot molecular core know n from earlier ammonia observations. The core angular diameter as meas ured in both methyl cyanide and the 3 mm continuum is similar to 1'' c orresponding to similar to 0.04 pc. If the continuum emission is due t o heated dust, we derive a mass of similar to 1000 M., but with large uncertainties. A remarkable velocity gradient (similar to 400 km s(-1) pc(-1)) in the SW-NE direction is observed in CH3CN implying an equil ibrium mass similar to 1000 M., consistent with the value quoted above . We discuss two possible scenarios (disk or outflow) for explaining t his gradient and conclude that the molecular core must be dynamically unstable.