As part of the first far-IR line survey towards Orion KL , we present the detection of seven new rotationally excited OH \Lambda –doublets ( at \sim 48 , \sim 65 , \sim 71 , \sim 79 , \sim 98 and \sim 115 \mu m ) .
Observations were performed with the Long Wavelength Spectrometer ( LWS ) Fabry–Perots on board the Infrared Space Observatory ( ISO ) .
In total , more than 20 resolved OH rotational lines , with upper energy levels up to \sim 620 K , have been detected at an angular and velocity resolutions of \sim 80 ^ { \prime \prime } and \sim 33 km s ^ { -1 } respectively .
OH line profiles show a complex behavior evolving from pure absorption , P–Cygni type to pure emission .
We also present a large scale 6 ^ { \prime } 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 the 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 ) , i.e .
the “ plateau ” spectral component .
We determine an averaged OH abundance relative to H _ { 2 } of \chi ( OH ) = ( 0.5–1.0 ) \times 10 ^ { -6 } , a kinetic temperature of \gtrsim 100 K and a density of n ( H _ { 2 } ) \simeq 5 \times 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 .