Extended far-infrared CO emission in the OMC-1 core of Orion

We report on sensitive far-infrared observations of (CO)-C-12 pure rotation al 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 Spa ce Observatory, covering the 43-197 mu m 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 regi on, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-P erot 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 ridg e emission. The fluxes detected in the high-J transitions (J(up) > 34) reve al the presence of a very hot and dense gas component [T = 1500-2500 K; N(C O) = 2 x 10(17) cm(-2)], probably originating from some of the embedded sou rces previously observed in the H-2 near-infrared lines. At all other posit ions in the OMC-1 core, we estimate kinetic temperatures greater than or eq ual to 80 K and as high as 150 K at some positions around IRc2, from a simp le large-velocity gradient model.