Heterodyne spectroscopy of the J = 17-16 CO line in Orion

Extended Far-Infrared CO Emission in the OMC-1 Core of Orion

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 Jup=14 up to Jup=19 have been identified across the whole OMC-1 core, and lines up to Jup=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 (Jup>34) reveal the presence of a very hot and dense gas component [T=1500-2500 K; N&parl0;CO&parr0;=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.