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  • 1
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    A non-LTE model for the Jovian methane infrared emissions at high spectral resolution (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: High resolution spectra of Jupiter in the 3.3 micrometer region have so far failed to reveal either the continuum or the line emissions that can be unambiguously attributed to the nu(sub 3) band of methane (Drossart et al. 1993; Kim et al. 1991). Nu(sub 3) line intensities predicted with the help of two simple non-Local Thermodynamic Equilibrium (LTE) models -- a two-level model and a three-level model, using experimentally determined relaxation coefficients, are shown to be one to three orders of magnitude respectively below the 3-sigma noise level of these observations. Predicted nu(sub 4) emission intensities are consistent with observed values. If the methane mixing ratio below the homopause is assumed as 2 x 10(exp -3), a value of about 300 K is derived as an upper limit to the temperature of the high stratosphere at microbar levels.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 424; 1; p. L61-L64
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    CO formation in the metal-rich ejecta of SN 1987A (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model for the formation of CO in the expanding ejecta of SN 1987A suggests that the 4.6-micron and 2.3 micron emissions noted in the SN spectrum may originate from the inner metal-rich regions of the ejecta. Also reported are the assignment of a 2.26-micron excess feature in the high-resolution IR spectra to the v = 2 to 0 overtone of CO(+) and the possible identification of a 2.95-micron feature with the v = 2 to 0 transition of electronically excited CO. The results suggest that the regions in which CO formation takes place must be ionized to a substantially lower degree than regions which dominate the line emission of heavier metals.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 342; 406-415
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  • 3
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    On PAHs as interstellar grains - Infrared absorption coefficients (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Consideration is given to the proposal that PAHs are the source of IR continuum and emission features and the visible diffuse bands. Absolute IR cross-sections have been obtained for eight PAHs. The results show that a thermal continuum is not consistent with the spectra obtained, and that an array of normal molecules shows a spectrum that is more complex than the observed spectrum. The cross-sections of the UV spectra are 2-3 orders of magnitude larger than those of the IR spectra. It is suggested that, to account for these observations, structure must be produced in the UV extinction curve.
    Keywords: ASTROPHYSICS
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  • 4
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    Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Simplification of astrophysical calculations can be achieved by invoking the condition of local thermodynamic equilibrium; however, recent investigations suggest that this assumption may not be valid for certain astrophysical regions. To examine the effects of multiquantum translation to vibration transitions in expanding circumstellar envelopes, vibrational populations of the lowest 20 levels of CO have been calculated as a function of pressure and radiation density for H atom-CO collisions. Significant departure from local thermodynamic equilibrium is indicated, which implies lower dissociation rates for molecular components and a subsequent enhancement in the rate of grain formation by many orders of magnitude. Stabilization of intermediate species before they can dissociate may facilitate the formation of refractory grain cores in very hot, dilute outflows. As the present calculations indicate, laboratory measurements of state-to-state translation to vibration rates are needed for a more complete understanding of circumstellar chemistry.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 463-469
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