THE HOT AND CLUMPY MOLECULAR COCOON SURROUNDING THE ULTRACOMPACT H II REGION G5.89-0.39

We present observations of CH3CN (12-11) emission at a resolution of similar to 2 '' toward the shell-like ultracompact H II region G5.89-0.39 with the Submillimeter Array. The integrated CH3CN emission reveals a dense and hot-molecular cocoon in the periphery of the H II region G5.89-0.39, with a CH3CN deficient region roughly centered at G5.89-0.39. By analyzing the CH3CN emission using population diagram analysis, we find, for the first time, a decreasing temperature structure from 150 K to 40 K with the projected distance from Feldt's star, which is thought to be responsible for powering the H II region. Our results further indicate that the majority of the heating energy in the observed dense gas is supplied by the Feldt's star. From the derived CH3CN column density profile, we conclude that the dense gas is not uniformly distributed but centrally concentrated, with a power-law exponent of 5.5 for r less than or similar to 8000 AU, and 2.0 for 8000 AU less than or similar to r less than or similar to 20000 AU, where r is the distance to Feldt's star. The estimated large power index of 5.5 can be attributed to an enhancement of CH3CN abundance in the close vicinity of Feldt's star.