Far-infrared excited hydroxyl lines from Orion KL outflows

As part of the first far-IR line survey toward Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at similar to 48, similar to 65, similar to 71, similar to 79, similar to 98, and similar to 115 mu m). Observations were performed with the Long Wavelength Spectrometer Fabry-Perot on board the Infrared Space Observatory. In total, more than 20 resolved OH rotational lines, with upper energy levels up to similar to 620 K, have been detected at angular and velocity resolutions of similar to 80 '' and similar to 33 km s(-1), respectively. The OH line profiles show a complex behavior evolving from pure absorption, P Cygni type, to pure emission. We also present a large-scale, 6' declination raster in the OH (2)Pi(3/2) J = 5/2(+) -3/2(-) and (2)Pi(3/2) J = 7/2(-) -5/2(-) lines (at 119.441 and 84.597 mu m) revealing a decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths, and velocity offsets between emission and absorption line peaks, we conclude that most of the excited OH arises from Orion outflow(s), that is, the plateau spectral component. We determine an averaged OH abundance relative to H-2 of x(OH) = (0.5-1.0) x 10(-6), a kinetic temperature of >= 100 K, and a density of n(H-2) similar or equal to 5 x 10(5) cm(-3). Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner hot core regions and from the expanding flow itself.