SOFIA Probes the Heart of Hot Core Chemistry
Columbia, MD--June 22, 2021. High-resolution molecular line surveys provide a chemical inventory for star forming regions — essential for establishing the relative importance of potential chemical networks, understanding organic chemistry associated with star formation, and providing constraints on the supply pathways of key organic molecules in Earth-like planet formation.
The image shows the Orion region taken by the Gemini South Telescope. The cross marks the approximate position of the Orion hot core located at the center of an explosion generated by a multibody dynamical encounter about 500 years ago. The red and blue nebulosity trace finger-like tendrils resulting from the blast. The SOFIA EXES spectrum across the bottom of the image shows the signature of the HNC molecule – the series of intensity dips near 21.6µm.
Previous high spectral resolution line surveys have been limited to radio, sub-mm, and far-infrared wavelengths, but mid-infrared (MIR) observations are the only way to study symmetric molecules like CH₄, C₂H₂, and C₂H₆ that have no dipole moment and thus cannot be observed through rotational transitions. The MIR astronomical missions such as the Infrared Space Observatory (ISO) and Spitzer had low to moderate resolving power. Therefore, they were only able to identify molecular bands and could not resolve their individual ro-vibrational transitions needed to identify specific molecules with certainty. Due to the lack of high spectral resolution data in the MIR, the model chemical networks require testing and refinement in this regime.
But SOFIA was able to detect HNC, HCN, and H13CN in an Orion hot core. These results probe a key stage in stellar evolution as young protostars heat their natal, icy mantles to unlock reservoirs of molecules. This work is part of a wider mid-infrared survey that has detected a forest of molecular transitions. Researchers are not only building an inventory of molecules and creating a legacy archive, but also constructing a valuable reference database for future James Webb Space Telescope observations. The findings were published in a paper entitled The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core, Nickerson, et al., 2021/01, in ApJ, 907, 51.
Contributed by Sarah Nickleson, Naseem Rangwalla, and Joan Schmelz