The Hot and Clumpy Molecular Cocoon Surrounding the Ultracompact HII
  Region G5.89-0.39
  We present observations of CH3CN (12-11) emission at a resolution of 2"
toward the shell-like ultracompact HII region G5.89-0.39 with the Submillimeter
Array. The integrated CH3CN emission reveals dense and hot molecular cocoon in
the periphery of the HII 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 to 40 K with the projected distance from Feldt's
star, which is thought to be responsible for powering the HII 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 < 8000 AU, and 2.0 for 8000 AU < r < 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.
