H2 18 O in hot dense molecular cloud cores.

The authors have used the Kitt Peak 12-m telescope to observe the 3₁₃-2₂₀ line (203407 MHz) of para-H₂¹⁸O towards several hot dense sources of molecular line emission. They detect a feature at the correct frequency towards Orion-KL, G34.3+0.2, Sgr B2(N), and W51 e₁/e₂. The problem of blending with emission from other molecular line species is discussed and it is concluded that at least in the case of G34.3+0.2, the identification with H₂¹⁸O is likely to be correct. The rough estimates suggest that in these "hot core" regions, water has an abundance relative to H₂ of order 10^-5 and is thus less abundant than CO. In Orion-KL, the abundance ratio [HDO]/[H₂O] is estimated to be greater than 10^-3.