2017/09/30 by Naseem Rangwala, Sean W. J. Colgan, Romane Le Gal +8 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Infrared #Line (geometry) #Line-of-sight #Rotational–vibrational spectroscopy #Spectral line #Spectral resolution #Spectrograph #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aaab66
accepted for publication in The Astrophysical Journal
openalex created_date 2017/09/25 · arxiv created 2018/01/25 · openalex publication_date 2018/03/20 · arxiv updated 2018/04/04 · openalex updated_date 2026/08/05
Abstract We present high spectral resolution observations from 12.96 to 13.33 microns toward Orion IRc2 using the mid-infrared spectrograph, Echelon-Cross-Echelle Spectrograph (EXES), at Stratospheric Observatory for Infrared Astronomy (SOFIA). These observations probe the physical and chemical conditions of the Orion hot core, which is sampled by a bright, compact, mid-infrared background continuum source in the region, IRc2. All 10 of the rovibrational C 2 H 2 transitions expected in our spectral coverage are detected with high signal-to-noise ratios (S/Ns), yielding continuous coverage of the R-branch lines from J = 9–8 to J = 18–17, including both ortho and para species. Eight of these rovibrational transitions are newly reported detections. The isotopologue, 13 CCH 2 , is clearly detected with a high S/N. This enabled a direct measurement of the 12 C/ 13 C isotopic ratio for the Orion hot core of 14 ± 1 and an estimated maximum value of 21. We also detected several HCN rovibrational lines. The ortho and para C 2 H 2 ladders are clearly separate, and tracing two different temperatures, 226 K and 164 K, respectively, with a non-equilibrium ortho to para ratio (OPR) of 1.7 ± 0.1. Additionally, the ortho and para V LSR values differ by about 1.8 ± 0.2 km s −1 , while the mean line widths differ by 0.7 ± 0.2 km s −1 , suggesting that these species are not uniformly mixed along the line of sight to IRc2. We propose that the abnormally low C 2 H 2 OPR could be a remnant from an earlier, colder phase, before the density enhancement (now the hot core) was impacted by shocks generated from an explosive event 500 years ago.