High Spectral Resolution SOFIA/EXES Observations of C2H2 towards Orion-IRc2

Abstract

We present high-spectral resolution observations from 12.96 - 13.33 microns towards Orion IRc2 using the mid-infrared spectrograph, EXES, on 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 ten of the rovibrational C2H2 transitions expected in our spectral coverage, are detected with high S/N, 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, 13CCH2, is clearly detected with high signal-to-noise. This enabled a direct measurement of the 12C/13C 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 C2H2 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, while, the mean line widths differ by 0.7 +/- 0.2 km/s, suggesting that these species are not uniformly mixed along the line of sight to IRc2. We propose that the abnormally low C2H2 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 yrs ago.

arXiv commentaccepted for publication in The Astrophysical Journal

References in corpus (28)

• Complex Chemistry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model
• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Molecular Hydrogen Formation on Astrophysically Relevant Surfaces
• On the Formation of CO2 and Other Interstellar Ices
• TEXES: A Sensitive High-Resolution Grating Spectrograph for the Mid-Infrared
• A line confusion limited millimeter survey of Orion KL (I): sulfur carbon chains
• Spitzer observations of HH54 and HH7-11: mapping the H2 ortho-to-para ratio in shocked molecular gas
• Herschel observations of EXtra-Ordinary Sources: Analysis of the HIFI 1.2 THz Wide Spectral Survey Toward Orion KL I. Methods
• Interstellar chemistry of nitrogen hydrides in dark clouds
• Explosive Outflows Powered by the Decay of Non-Hierarchical Multiple Systems of Massive Stars: Orion BN/KL
• Submm line imaging of Orion-KL with the Submillimeter Array
• Explosive Disintegration of a Massive Young Stellar System in Orion
• The ALMA View of the OMC1 Explosion in Orion
• Tracing the Bipolar Outflow from Orion Source I
• Binding Energy of Molecules on Water Ice: Laboratory Measurements and Modeling
• Unveiling Sources of Heating in the Vicinity of the Orion BN/KL Hot Core as Traced by Highly Excited Inversion Transitions of Ammonia
• Sticking of molecules on non-porous amorphous water ice
• ISO observations toward the reflection nebula NGC 7023: A nonequilibrium ortho- to para-H2 ratio
• High Resolution Mid-Infrared Spectroscopy of NGC 7538 IRS 1: Probing Chemistry in a Massive Young Stellar Object
• The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive Protostellar Outflow
• The chemistry of C3 & Carbon Chain Molecules in DR21(OH)
• Ortho-para transition in molecular hydrogen
• Discovery of an expanding molecular bubble in Orion BN/KL
• ALMA Images of the Orion Hot Core at 349 GHz
• SOFIA/EXES Observations of Water Absorption in the Protostar AFGL 2591 at High Spectral Resolution
• Physical Relation of Source I to IRc2 in the Orion KL Region
• H${}_2$ ortho-to-para conversion on grains: A route to fast deuterium fractionation in dense cloud cores?
• Resolving the chemical substructure of Orion-KL

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• High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5
• The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk
• Precision Analysis of ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}$ Ratios in Orion IRc2 Acetylene Isotopologues via ${\chi }^2$ Fitting