Formation, evolution, and survival of massive star clusters Proceedings IAU Symposium No. 316, 2015 C. Charbonnel & A. Nota, eds. c  International Astronomical Union 2017 doi:10.1017/S174392131501056X The Orion Nebula in the Far-Infrared: High-J CO and fine-structure lines mapped by FIFI-LS/SOFIA Randolf Klein 1 , Leslie W. Looney 2 , Erin Cox 2 , Christian Fischer 3 , Christof Iserlohe 3 , Alfred Krabbe 3 1 SOFIA-USRA, NASA Ames Research Center, MS 232-12, PO box 1, Moffet Field, CA 94035 email: rklein@sofia.usra.edu 2 University of Illinois, Dept. of Astronomy, MC-221, 1002 W. Green St., Urbana, IL 61801 Deutsches SOFIA Institut, Pfaffenwaldring 29, D-70569 Stuttgart Abstract. The Orion Nebula is the closest massive star forming region allowing us to study the physical conditions in such a region with high spatial resolution. We used the far infrared integral-field spectrometer, FIFI-LS, on-board the airborne observatory SOFIA to study the atomic and molecular gas in the Orion Nebula at medium spectral resolution. The large maps obtained with FIFI-LS cover the nebula from the BN/KL-object to the bar in several fine structure lines. They allow us to study the conditions of the photon-dominated region and the interface to the molecular cloud with unprecedented detail. Another investigation targeted the molecular gas in the BN/KL region of the Orion Nebula, which is stirred up by a violent explosion about 500 years ago. The explosion drives a wide angled molecular outflow. We present maps of several high-J CO observations, allowing us to analyze the heated molecular gas. Keywords. stars: formation, infrared: ISM, ISM: Orion Nebula 1. Preliminary Results The observations were taken during the commissioning of FIFI-LS (Klein et al. 2014) on board of NASA’s airborne observatory SOFIA (Young et al. 2012) last year and as recent as March 2015. The data reduction and calibration is still under development. Mainly, the atmospheric absorption correction and flux calibration is still in works. The results of the fine structure line observations of [CII] and [OI] are shown in Fig. 1. Next to the line emission, a FIFI-LS observation also yields the underlying continuum. The continuum emission is peaking in the BN/KL object, where deeply embedded proto- stars heat the dust (De Buizer et al. 2012). The dust east of the Trapezium is the second peak. The Bar is not very prominent in the dust continuum. However, the [CII] emission clearly traces the Orion Bar, and the north-eastern wall of the cavity, which is cleared out by the trapezium stars. The emission comes from the Photon-Dominated-Region (PDR), where the UV-radiation from the Trapezium Cluster irradiates the surrounding molecular gas. Figure 1 also shows the [OI] lines, which trace the Bar like the [CII] lines, as these fine- structure lines are the main cooling lines in a PDR. When the flux calibration is done, we can start interpreting the line ratios in term of density, temperature, and excitation conditions. Since the Bar is a nearly edge-on PDR, the width and position of the line emission can indicate how far the UV can penetrate. 153 https://doi.org/10.1017/S174392131501056X Published online by Cambridge University Press