Unveiling the Hot Molecular Core in the Ultracompact \hii Region with
  Extended Emission G12.21--0.10
  We present a multiwavelength study of the cometary \hii region G12.21--0.10
using the VLA and OVRO. Both radio continuum (0.3, 0.7, 2 and 3.6~cm) and
spectral lines of H41$\alpha$, $^{13}$CS(2$-$1) \& (1$-$0), and NH$_{\rm
3}$(2,2) \& (4,4) observations are included. We find two 3~mm continuum peaks
toward G12.21--0.10, one of them is spatially coincident with the UC~H~II
region, while the other coincides spatially with a molecular clump. We also
find that the 0.7, 2 and 3.6~cm continuum and H41$\alpha$ line are only
detected toward the UC~H~II region, while the $^{13}$CS, and NH$_{\rm 3}$ is
spatially associated with the molecular clump. Based on the morphology, kinetic
temperature ($\sim$86~K), volumetric density
($\sim$1.5$\times$10$^6$~cm$^{-3}$) and linear size ($\sim$0.22~pc) of the
molecular clump, we suggest this source is consistent with a hot molecular
core.
