2000ApJ...539L..87M

We have obtained spectra of the rotational ground-state 1₁₀-1₀₁ 556.936 GHz ortho-H₂¹⁶O and 1₁₀-1₀₁ 547.676 GHz ortho-H₂¹⁸O transitions toward Orion BN/KL using the Submillimeter Wave Astronomy Satellite (SWAS). The ortho-H₂¹⁶O spectrum shows strong evidence for both a broad (Δv≃48 km.s^–1) and a narrow (Δv≃7.5 km.s^–1) component, while the ortho-H₂¹⁸O shows evidence for only a broad (Δv≃24 km.s^–1) component. The broad component emission in both ortho-H₂¹⁶O and ortho-H₂¹⁸O arises primarily from gas heated within the low- and high-velocity outflows and shocked gas surrounding IRc2 in which the ortho-H₂¹⁶O and ortho-H₂¹⁸O fractional abundances are estimated to be 3.5x10^–4 and 7x10^–7, respectively. This finding provides further confirmation that water is efficiently and abundantly produced within warm shock-heated gas. We estimate that the hot core plus the compact ridge contribute ≲10% to the ortho-H₂¹⁶O integrated intensity within the SWAS beam. The narrow component seen in the ortho-H₂¹⁶O spectrum is best fitted by ortho-water emission from the extended ridge (ER) and the higher temperature core of the extended ridge (CER) with a common fractional abundance of 3.3x10^–8. The absence of any discernible narrow component in the ortho-H₂¹⁸O spectrum is used to set 3 σ upper limits on the ortho-water fractional abundance within the ER of 7x10^–8 and within the CER of 5.2x10^–7. This implies that within the dense extended quiescent region, gas-phase water is neither a major repository of oxygen nor a major coolant in Orion BN/KL.