Sutton, E. C. and Blake, Geoffrey A. and Genzel, R. and Masson, C. R. and Phillips, T. G. (1986) Excitation of methyl cyanide in the hot core of Orion. Astrophysical Journal, 311 (2). pp. 921-929. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120919-141609824
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The excitation of CH_3CN in the hot core of Orion is examined using high-sensitivity observational data at 1.3 mm. Observed line fluxes are analyzed by means of multilevel statistical equilibrium (SE) calculations which incorporate current theoretical values of the collisional excitation rates. The analysis is applied to both optically thin models of the hot core region and models with significant optical depths. Trapping is found to play a critical role in the excitation of CH_3CN. An optically thin analysis yields a kinetic temperature of 275 K and a cloud density of 2 x 10^6 cm^(-3). Unequal column densities are deduced in this case for the two symmetry species: N_A = 1.4 x 10^(14) cm^(-2) and N_E = 2.0 x 10^(14) cm^(-2). The deduced cloud density and temperature are lowered to 1.5 x 10^6 cm^(-3) and 240 K. The model with trapping is favored because of the agreement with measured sizes of the hot core source and the more plausible N_A/N_E ratio. Analysis of radiative excitation in the hot core indicates it is unlikely to significantly affect the ground vibrational state populations of CH_3CN. It most likely is significant for excitation of the V_8 band.
|Additional Information:||© 1986 American Astronomical Society. Received 1986 March 24; accepted 1986 May 21. The authors are grateful to S. Green for his communication of collisional rate data prior to publication. One of us (G. A. B.) acknowledges financial support from the Miller Research Institute.|
|Subject Keywords:||interstellar: molecules; nebulae: Orion Nebula; radiative transfer; acetonitrile; astronomical spectroscopy; mass distribution; molecular clouds; orion nebula; astronomical models; collision rates; optical thickness; radiative transfer; statistical distributions|
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|Deposited By:||Aucoeur Ngo|
|Deposited On:||19 Sep 2012 22:04|
|Last Modified:||26 Dec 2012 16:13|
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