Water Absorption from Gas Very Near the Massive Protostar AFGL 2136 IRS
  1
  We present ground-based observations of the nu_1 and nu_3 fundamental bands
of H2O toward the massive protostar AFGL 2136 IRS 1, identifying absorption
features due to 47 different ro-vibrational transitions between 2.468 micron
and 2.561 micron. Analysis of these features indicates the absorption arises in
warm (T=506+-25 K), very dense (n(H2)>5*10^9 cm^-3) gas, suggesting an origin
close to the central protostar. The total column density of warm water is
estimated to be N(H2O)=(1.02+-0.02)*10^19 cm^-2, giving a relative abundance of
N(H2O)/N(H2)~10^-4. Our study represents the first extensive use of water vapor
absorption lines in the near infrared, and demonstrates the utility of such
observations in deriving physical parameters.
