Deuterated water in Orion-KL and NGC 7538.

The first detections of the 3₂₁-4₁₄ and 5₃₂-5₃₃ lines of HDO are reported: both lines are observed in emission toward Orion-KL with velocities typical of the "Hot Core" and the "Compact Ridge", while the 3₂₁-4₁₄ line is seen in absorption toward NGC 7538-IRS1. The presence of highly excited HDO in these two sources suggests that the observed lines form in a hot and dense molecular environment, where the kinetic temperature exceeds 100K. The Orion data are combined with other line results to derive optical depths, excitation temperature, column densities, and relative abundance. An upper limit to the [HDO]/[H₂O] ratio is given which is inconsistent with gas phase ion-molecule or gas phase shock formation schemes. It is suggested that large amounts of HDO are released from grain mantles when the kinetic temperature exceeds 100K. The data from NGC 7538 are used to obtain a direct estimate of the optical depth, which indicates deviations from thermal equilibrium.