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Title:
Interstellar absorption lines toward NGC 2264 and AFGL 2591 - Abundances of H2, H3(+), and CO
Authors:
Black, John H.; van Dishoeck, Ewine F.; Willner, Steven P.; Woods, R. Claude
Affiliation:
AA(Steward Observatory, Tucson, AZ), AB(California Institute of Technology, Pasadena), AC(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA), AD(Wisconsin, University, Madison)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 358, Aug. 1, 1990, p. 459-467. Research supported by NSF. (ApJ Homepage)
Publication Date:
08/1990
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Absorption Spectra, Abundance, Galactic Cosmic Rays, Interstellar Gas, Line Spectra, Carbon Monoxide, Hydrogen, Infrared Spectra, Infrared Spectrophotometers, Interstellar Matter, Stellar Spectrophotometry
DOI:
10.1086/168999
Bibliographic Code:
1990ApJ...358..459B

Abstract

Interstellar absorption-line spectroscopy of NGC 2264 is reported which shows that the CO molecule has a column density of 5 x 10 to the 18th/sq cm and a rotational excitation temperature of 28 K. A direct upper limit on the H2 column density implies that at least 6 percent of a solar carbon abundance is in the form of CO. The upper limit on the H3(+) abundance implies that the cosmic-ray ionization rate is of the order of 10 to the -16th/s or less. The H3(+) upper limit, together with a previous radio detection of H2D(+) emission, implies either an enormous overabundance of the deuterated molecule or else that most of the radio emission comes from clouds not located directly between use and the infrared source. Observations of the sources AFGL 2591 and NGC 2024 IRS2 indicate that upper limits on H3(+) imply cosmic ray ionization rates of less than 3 and 60 x 10 to the -17th/s, respectively.

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