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  • ASTROPHYSICS  (9)
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  • 1
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    HCN production from Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations of the HCN J=1-0 rotational transition at 3.4 mm wavelength in comet P/Halley with a 14m antenna were obtained during 56 individual observing sessions between Nov. 1985 and May 1986. The HCN production rate is well correlated with the total visual magnitude of the comet, indicating that HCN follows the overall gas and dust production. However, comparison of HCN production to the total gas production of the comet indicates that it is a relatively minor consitiuent with 0.1% of the abundance of H2O. Spectra obtained by binning the HCN data with heliocentric distance show that the HCN line width, and thus the parent outflow velocity, increases with decreasing heliocentric distance, and that there is a tendency for the lines to be blue shifted as expected from the observed anisotropic outgassing from the nucleus. There is evidence of day-to-day time variability in the total HCN emission and variations in the HCN hyperfine ratios from their LTE values.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 577-581
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  • 2
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    Search for molecules in Comet Halley at millimeter wavelengths (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Data collected with the Five College Radio Astronomy Observatory 13.7-m radio telescope are used to search for the possible CN parent molecules HNC, HC3N, and CH3CN in Comet Halley at millimeter wavelengths. Maximum relative abundances for HNC/HCN of 0.3, for HC3N/HCN of 0.4, and for CH3CN/HCN of 0.8 are obtained, showing that these three molecules are not a major source of the CN radical observed in optical and UV spectroscopy. Upper limits to the beam averaged column densities and production rates of these molecules are determined (in addition to an upper limit for the beam averaged column density for the formyl ion of less than 10 to the 11th/sq cm), providing important constraints for chemical models of the coma.
    Keywords: ASTROPHYSICS
    Type: Cometary radio astronomy; Sept. 24-26, 1986; Green Bank, WV; United States
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  • 3
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    Observations of HCN in Comet Halley (1987)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Observations of the HCN J = 1-0 rotational transition at 3.4 mm wavelength in comet P/Halley are discussed. The data were obtained during a total of 56 individual observing sessions between Nov. 18, 1985 and May 11, 1986, and represent the first time that a cometary parent molecule has been so extensively monitored. The HCN production rate is well correlated with the total visual magnitude of the comet, indicating that HCN follows the overall gas production. There is also evidence of time variability and variations in the HCN hyperfine ratios from their LTE values. Spectra obtained by binning the HCN data with heliocentric distance show that the HCN line width, and thus the parent outflow velocity, increases with decreasing heliocentric distance.
    Keywords: ASTROPHYSICS
    Type: Cometary radio astronomy; Sept. 24-26, 1986; Green Bank, WV; United States
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  • 4
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    Chemical abundances in cold, dark interstellar clouds (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Current tabulations are presented of the entire range of known interstellar molecules, giving attention to that subset which has been identified in the cold, dark interstellar clouds out of which the sun has been suggested to have formed. The molecular abundances of two such clouds, Taurus Molecular Cloud 1 and Lynd's 134N, exhibit prepossessing chemical differences despite considerable physical similarities. This discrepancy may be accounted for by the two clouds' differing evolutionary stages. Two novel classes of interstellar molecules are noted: sulfur-terminated carbon chains and silicon-terminated ones.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 91; 2-6
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  • 5
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    Detection of a new carbon-chain molecule, CCO (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A new carbon-chain molecule, CCO 3Sigma(-), has been detected in the cold dark molecular cloud TMC-1. The excitation temperature and the column density of CCO are, respectively, about 6 K and about 6 x 10 to the 11th/sq cm. This column density corresponds to a fractional abundance relative to H2 of about 6 x 10 to the -11th. This value is two orders of magnitude less than the abundance of the related carbon-chain molecule CCS, and about half that of C3O. The formation mechanism for CCO is discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 380; L39-L42
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  • 6
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    Detections of C-13-substituted C3H2 in astronomical sources (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The more abundant C-13-substituted variant of the new interstellar ring molecule, C3H2, has been detected in TMC-1 and Sgr B2, and a tentative detection has been made in IRC + 10216. The fractional abundance relative to H2 is 1-2 x 10 to the -8th in TMC-1, a value similar to that of HCN. In Sgr B2, the C-12 species shows a self-absorbed profile and the relative abundance of C3H2 is about an order of magnitude less than in TMC-1. In IRC + 10216, the fractional abundance of C3H2 is an order of magnitude greater than that in TMC-1.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 311; L27-L31
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  • 7
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    Newly detected molecules in dense interstellar clouds (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The last year or so has seen the identification of several new interstellar molecules, including C2S, C3S, C5H, C6H, and (probably) HC2CHO in the cold, dark cloud TMC-1, and the discovery of the first interstellar phosphorus-containing molecule, PN, in the Orion 'plateau' source. Further interesting results include the observations of (C-13))3H2 and C3HD, and the first detection of HCOOH (formic acid) in a (C-13)3H2 cold cloud.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 3-5
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  • 8
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    HCN production from comet Halley (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The HCN J = 1-0 rotational transition at 3.4 mm wavelength has been detected and has been monitored in comet P/Halley during a total of 56 individual observing sessions between November 18, 1985 and May 11, 1986. The HCN spectra show significant daily variations in total intensity, but the average HCN production rate is well correlated with the visual magnitude of the comet over the range of heliocentric distance observed (between 0.59 and 1.8). Observations of the ratios of the F = 2-1 and F = 1-1 hyperfine components also exhibit significant daily variations but are, in the mean, consistent with the 5:3 ratio expected from the statistical weights of the hyperfine levels. The outflow velocity of the coma, deduced from the HCN linewidths, is 0.87 + or - 0.12 km/s, which is consistent with recent theoretical estimates as well as the measurements of the Giotto spacecraft.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 310; L55-L60
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  • 9
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    Variations in the HCN/HNC abundance ratio in the Orion molecular cloud (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Observations of the rare isotopes of HCN and HNC have been used to determine the relative abundance of these two chemical isomers along the central ridge of the Orion molecular cloud. The abundance ratio HCN/HNC decreases by more than an order of magnitude from the relatively warm plateau and hot core sources toward the KL nebula to the colder, more quiescent clouds to the north and south. Even in the cooler regions, however, the ratio is an order of magnitude larger than that found in previous investigations of cold dark clouds. The kinetic temperature in the regions studied is determined from new observations of methylacetylene (CH3CCH), together with other recent estimates of the gas temperature near KL. The results suggest that the warmer portions of the cloud are dominated by different chemical pathways that those in the general instellar cloud material.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 310; 383-391
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