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Detection of absorption by H2 in molecular clouds: A direct measurement of the H2:CO ratio
Lacy, J. H.; Knacke, R.; Geballe, T. R.; Tokunaga, A. T.
AA(University of Texas, Austin, TX, US), AB(University of Texas, Austin, TX, US), AC(Joint Astronomy Centre, Hilo, HI, US), AD(Joint Astronomy Centre, Hilo, HI, US)
The Astrophysical Journal, vol. 428, no. 2, pt. 2, p. L69-L72 (ApJL Homepage)
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NASA/STI Keywords:
Abundance, Astronomical Models, Carbon Monoxide, Hydrogen, Infrared Absorption, Infrared Astronomy, Molecular Clouds, Arrays, Data Reduction, Infrared Detectors, Spectrographs
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Vibrational absorption by H2 and CO has been searched for toward infrared sources embedded in molecular clouds. H2 was detected toward NGC 2024 IRS 2 and possibly toward NGC 2264 (GL 989). CO was detected toward both sources. The results are consistent with the H2 ortho:para ratio being equilibrated at the cloud temperature. Toward NGC 2024, H2:CO = (3700-2600+3100) (2 sigma limits), and toward NGC 2264, H2:CO less than 6000. Approximately one-third of all carbon is in gas-phase CO.

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