2000ApJ...530L.123S

We report on sensitive far-infrared observations of ¹²CO pure rotational transitions in the OMC-1 core of Orion. The lines were observed with the long-wavelength spectrometer in the grating mode on board the Infrared Space Observatory, covering the 43-197 µm wavelength range. The transitions from J_up=14 up to J_up=19 have been identified across the whole OMC-1 core, and lines up to J_up=43 have been detected toward the central region, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-Perot mode of some of the CO lines. In KL/IRc2, the lines are satisfactorily accounted for by a three-temperature model describing the plateau and ridge emission. The fluxes detected in the high-J transitions (J_up>34) reveal the presence of a very hot and dense gas component [T=1500-2500 K; N(CO)=2x10¹⁷ cm^–2], probably originating from some of the embedded sources previously observed in the H₂ near-infrared lines. At all other positions in the OMC-1 core, we estimate kinetic temperatures ≥80 K and as high as 150 K at some positions around IRc2, from a simple large-velocity gradient model.