The Mid-Infrared Molecular Inventory Towards Orion IRc2 and Hot Molecular Cores
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Sarah Nickerson
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Hot molecular cores associated with high mass protostars are a rich source of chemistry in the ISM, connecting star formation to planetary systems such as our own. They represent a key stage in stellar evolution as a young protostar heats its natal, icy mantle to unlock reservoirs of molecules. The mid-infrared (MIR), provides the only access to rovibrational transitions and molecules with no permanent dipole moment, and probes hot core material closest to embedded protostars. We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2 to 28.3 micron. With SOFIA/EXES we target the enigmatic source Orion IRc2 that probes the edge of the hot core. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The MIR observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. While these components have similar temperatures and line widths, molecular species in one have higher column densities. They are both likely linked to pure rotational H2 emission also covered by this survey. This work provides evidence for the scenario that they are distinct components unrelated to the classic components in the Orion BN/KL region. We have established over 350 unique features and have identified nine species with two isotopes: H2O, HNC, SO2, H2, C2H2, 13CCH2, HCN, H13CN, CS, SiO, and CH4. Further observations were completed this spring with SOFIA/EXES towards five more conventional hot cores. We are analyzing these new spectra in order to build a broader understanding of the unique chemistry revealed by the MIR in star forming regions and to compare the hot cores to one another.

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