We present high spectral resolution observations around 13 micron of Orion IRc2 taken with the EXES instrument onboard the SOFIA airborne observatory. Rovibrational transitions of C2H2 were detected in both the Ortho and Para states. Additionally, transitions from its 13CCH2 isotopologue and HCN were also detected. We find that the Ortho and Para clearly trace different temperatures with the Ortho to Para ratio (OPR) of 0.6, which is far from its equilibrium value of 3. This result could not be measured from previous, more limited observations of C2H2. Preliminary analysis indicates that the low Ortho to Para ratio is most likely the result of an interaction with a low-velocity shock. We will discuss constraints provided by these new observations on the physical conditions and astrochemistry of Orion’s hot molecular core in this complex star forming region, including comparison of these observations with the current models of hot core chemistry. This project began as a search for c-C3H3+, the most important precursor in the formation of c-C3H2 - an interstellar organic ring molecule widespread in the ISM. There has been interest in detecting c-C3H3+ in astrophysical environments for more than 25 years. Using these EXES observations along with ab initio calculations from the Ames quantum chemistry group, we report for the first time an observed 3σ upper limit on the column density of c-C3H3+. This will help with the future searches for this molecule using ALMA and JWST. We will also present preliminary results from an on-going SOFIA Cycle-5 impact program to use EXES to conduct an unbiased molecular line survey towards Orion IRc2 from 12.5 - 28.3 microns with a S/N of 100. This survey (due to its higher resolving power; R = 50,000) is expected to do 5 - 50 times better than ISO in detecting isolated, narrow lines. This will allow us to (a) resolve the ro-vibrational structure of the gas phase molecules in order to identify them, (b) resolve their kinematics, (c) detect new gas phase molecules that were missed by ISO, and (d) provide useful constraints on Orion's hot core chemistry as sampled by IRc2. The proposed observations will provide the best infrared measurements (to date) of molecular column densities and physical conditions - providing strong constraints on the current chemical network models for star forming regions.

SOFIA/EXES high spectral resolution observations of Orion IRc2

254th National Meeting (2017)

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