Building the Mid-Infrared Inventory for the Orion Hot Core
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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. With SOFIA/EXES, we conducted a high resolution (R~60,000) spectral survey from 7.2 to 28 um of the hot core Orion IRc2. We have so far established over 350 unique features and have identified nine species with two isotopes. For the first time, we have identified HNC and H13CN in the MIR. Together with HCN, these three species provide key insights into the hot core. We utilize a gas-grain chemical network to model the HCN/HNC evolution, which reaches our derived HCN/HNC=72 after 10^6 years. This is much older than the region’s explosive event 500 years ago, suggesting that the hot core’s origins predate this. Our derived 12C/13C=13 is lower than measurements at longer wavelengths. Several other recent observations towards star-forming regions also show similarly unexpectedly low isotope ratios. This points to the possibility that the isotope chemistry in these regions is not yet fully understood.

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