CO and H2O vibrational emission toward Orion Peak 1 and Peak 2

ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the ro-vibrational lines of CO v = 1 0 at 4.45-4.95 mum and of H2O nu(2) = 1-0 at 6.3-7.0 mum. Toward Peak 1 the total flux in both bands is, assuming isotropic emission, approximate to2.4 and approximate to0.53 L., respectively. This corresponds to approximate to14 and approximate to3% of the total H-2 luminosity in the same beam. Two temperature components are found to contribute to the CO emission from Peak 1/2: a warm component, with T-k = 200-400 K, and a hot component with T-k similar to 3 x 10(3) K. At Peak 2 the CO flux from the warm component is similar to that observed at Peak 1, but the hot component is a factor of approximate to2 weaker. The H2O band is approximate to25% stronger toward Peak 2, and seems to arise only in the warm component. The P-branch emission of both bands from the warm component is significantly stronger than the R-branch, indicating that the line emission is optically thick. Neither thermal collisions with H-2 nor with H I seem capable of explaining the strong emission from the warm component. Although the emission arises in the postshock gas, radiation from the most prominent mid-infrared sources in Orion BN/KL is most likely pumping the excited vibrational states of CO and H2O. CO column densities along the line of sight of N(CO) = 5-10 x 10(18) cm(-2) are required to explain the band shape, the flux, and the P-R-asymmetry, and beam-filling is invoked to reconcile this high N(CO) with the upper limit inferred from the H-2 emission. CO is more abundant than H2O by a factor of at least 2. The density of the warm component is estimated from the H2O emission to be similar to2 x 10(7) cm(-3). The CO emission from the hot component is neither satisfactorily explained in terms of non-thermal (streaming) collisions, nor by resonant scattering. Vibrational excitation through collisions with H-2 for densities of similar to 3 x 10(8) cm(-3) or, alternatively, with atomic hydrogen, with a density of at least 10(7) cm(-3), are invoked to explain simultaneously the emission from the hot component and that from the high excitation H-2 lines in the same beam. A jump shock is most probably responsible for this emission. The emission from the warm component could in principle be explained in terms of a C-shock. The underabundance of H2O relative to CO could be the consequence of H2O photodissociation, but may also indicate some contribution from a jump shock to the CO warm emission.