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 Title: The Distribution, Excitation, And Abundance Of Ch+ In Orion Kl Author(s): Gupta, Harshal Contributor(s): Pearson, John; Nagy, Zsofia; Morris, Patrick Subject(s): Astronomy Abstract: The CH$^+$ ion was one of the first molecules identified in the interstellar gas more than 75 years ago, but the high observed abundances of CH$^+$ remain a puzzle, because the main reaction proposed for the formation of CH$^+$, {\it viz.}, $\mathrm{C^{+} + H_{2} \rightarrow CH^{+} + H}$, is so endothermic (4640~K), that it is unlikely to proceed at the typical temperatures of molecular clouds. One way in which the high endothermicity may be overcome, is if a significant fraction of the H$_2$ is vibrationally excited, as is the case in dense molecular gas exposed to intense far-ultraviolet radiation fields. Elucidating the formation of CH$^+$ in molecular clouds requires characterization of its spatial distribution, as well as that of the key reactants in the chemical pathways yielding CH$^+$. Here we present high-resolution spectral mACS of the two lowest rotational transitions of CH$^+$ and the fine structure transition of C$^+$ in a $\sim 3^{\prime} \times 3^{\prime}$ region around the Orion Kleinmann-Low (KL) nebula, obtained with the {\em Herschel Space Observatory's} Heterodyne Instrument for the Far-Infrared (HIFI).\footnote{These observations were done as part of the Herschel observations of EXtraordinary sources: the Orion and Sagittarius star-forming regions (HEXOS) Key Programme, led by E. A. Bergin at the University of Michigan, Ann Arbor, MI.} We compare these mACS to those of CH$^+$ and C$^+$ in the Orion Bar photodissociation region (PDR), and discuss the excitation and abundance of CH$^+$ toward Orion KL in the context of chemical and radiative transfer models, which have recently been successfully applied to the Orion Bar PDR.\footnote{Nagy, Z. et al. 2013, A\&A 550, A96} Issue Date: 2014-06-16 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Gupta, H.; Pearson, J.; Nagy, Z.; Morris, P. THE DISTRIBUTION, EXCITATION, AND ABUNDANCE OF CH+ IN ORION KL. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.MF01 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/50956 DOI: https://doi.org/10.15278/isms.2014.MF01 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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