The Distribution, Excitation, And Abundance Of Ch+ In Orion Kl

Gupta, Harshal

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https://hdl.handle.net/2142/50956 Copy

Description

Title

The Distribution, Excitation, And Abundance Of Ch+ In Orion Kl

Author(s)

Gupta, Harshal

Contributor(s)

• Pearson, John
• Nagy, Zsofia
• Morris, Patrick

Issue Date

2014-06-16

Keyword(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}

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/50956

DOI

https://doi.org/10.15278/isms.2014.MF01

Copyright and License Information

Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/

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