Unveiling the dust nucleation zone of IRC+10216 with ALMA
  We report the detection in IRC+10216 of lines of HNC $J$=3-2 pertaining to 9
excited vibrational states with energies up to $\sim$5300 K. The spectrum,
observed with ALMA, also shows a surprising large number of narrow,
unidentified lines that arise in the vicinity of the star. The HNC data are
interpreted through a 1D--spherical non--local radiative transfer model,
coupled to a chemical model that includes chemistry at thermochemical
equilibrium for the innermost regions and reaction kinetics for the external
envelope. Although unresolved by the present early ALMA data, the radius
inferred for the emitting region is $\sim$0.06'' (i.e., $\simeq$ 3 stellar
radii), similar to the size of the dusty clumps reported by IR studies of the
innermost region ($r <$ 0.3''). The derived abundance of HNC relative to H$_2$
is $10^{-8} <$ $\chi$(HNC) $< 10^{-6}$, and drops quickly where the gas density
decreases and the gas chemistry is dominated by reaction kinetics. Merging HNC
data with that of molecular species present throughout the inner envelope, such
as vibrationally excited HCN, SiS, CS, or SiO, should allow us to characterize
the physical and chemical conditions in the dust formation zone.
