Show pageOld revisionsBacklinksBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ===== The Detection of Argonium, ArH+, in the Interstellar Medium ===== The //J// = 1 – 0 and 2 – 1 transitions of <sup>36</sup>ArH<sup>+</sup> were detected in emission with the SPIRE instrument on the //Herschel// satellite toward the Crab Nebula supernova remnant, also known as M 1, by:\\ M. J. Barlow, B. M. Swinyard, P. J. Owen, J. Cernicharo, H. L. Gomez, R. J. Ivison, O. Krause, T. L. Lim, M. Matsuura, S. Miller, G. Olofsson, and E. T. Polehampton,\\ **[[https://doi.org/10.1126/science.1243582|Detection of a Noble Gas Molecular Ion, <sup>36</sup>ArH<sup>+</sup>, in the Crab Nebula]]**\\ //Science// **342**, (2013) 1343.\\ <sup>40</sup>Ar is the most abundant isotope on Earth, but it is almost exclusively formed in the radioactive decay of <sup>40</sup>K. Interestingly, the only other feature seen clearly in the entire spectrum was the strongest fine structure component of OH<sup>+</sup>, there is also a hint of the next weaker FS component. More recently,\\ P. Schilke, D. A. Neufeld, H. S. P. Müller, C. Comito, E. A. Bergin, D. C. Lis, M. Gerin, J. H. Black, M. Wolfire, N. Indriolo, J. C. Pearson, K. M. Menten, B. Winkel, Á. Sánchez-Monge, T. Möller, B. Godard, and E. Falgarone,\\ reported on\\ **[[https://doi.org/10.1051/0004-6361/201423727|Ubiquitous argonium (ArH<sup>+</sup>) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas]]**\\ //Astron. Astrophys.// **566** (2014), Art. No. A29.\\ The 1 – 0 transition was observed in absorprtion with HIFI on board of the //Herschel// satellite toward numerous prominent continuum sources, first, and most notably, toward Sagittarius B2(M), then Sgr B2(N), and later also toward W51e, W49N, W31C, and G34.26+0.15. Interestingly, the molecule displays absorption at velocities associated with diffuse molecular clouds on the line of sight toward the contiunuum sources, but is conspicuously absent (at least in most cases) at the velocity of the corresponding continuum source itself. Model calculations indicate that ArH<sup>+</sup> resides mostly in very atomic diffuse molecular clouds with a molecular fraction of around 0.001 to 0.0001 or less. It is thus a very good tracer of such interstellar material. Moreover, it is also a good indicator of the cosmic ray ionization rate in addition to or instead of OH<sup>+</sup>, H<sub>2</sub>O<sup>+</sup>, or H<sub>3</sub><sup>+</sup>.\\ \\ The authors also detected the 1 – 0 transition of <sup>38</sup>ArH<sup>+</sup> toward Sgr B2(M). The <sup>36</sup>Ar/<sup>38</sup>Ar is compatible within error bars with the the local ISM value of about 5.5. ---- Contributor(s): H. S. P. Müller; 12, 2013; 06, 2014 ---- molecules/ism/arh-plus.txt Last modified: 2019/10/18 13:20by mueller