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Paper: Simultaneous Determination of the Cosmic Ray Ionization Rate and Fractional Ionization in DR21(OH)
Volume: 449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes
Page: 225
Authors: Hezareh, T.; Houde, M.; Vastel, C.; Peng, R.
Abstract: We present a new method for the simultaneous calculation of the cosmic ray ionization rate, ζH2}, and the ionization fraction, χe, in dense molecular clouds. A simple network of chemical reactions dominant in the creation and destruction of HCNH+ and HCO+ is used in conjunction with observed pairs of rotational transitions of several molecular species in order to determine the electron and H3+ abundances. The cosmic ray ionization rate is then calculated by taking advantage of the fact that, in dark clouds, it governs the rate of creation of H3+. We apply this technique to the case of the star-forming region DR21(OH), where we successfully detected the (J=32) and (J=43) rotational transitions of HCNH+. The significance of our method lies in the ability to determine N(H3+) and χe directly from observations, and estimate ζH2 accordingly. Our results, ζH2=3.1×10–18s–1 and χ=3.2×10–8, are consistent with recent determinations in other objects.
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