2001A&A...366..662N


C.D.S. - SIMBAD4 rel 1.7 - 2020.10.28CET07:26:53

2001A&A...366..662N - Astronomy and Astrophysics, volume 366, 662-667 (2001/2-1)

Polyatomic species in diffuse cloud and clump interfaces.

NGUYEN T.K., HARTQUIST T.W. and WILLIAMS D.A.

Abstract (from CDS):

Diffuse clouds embedded in a flowing intercloud medium will develop warm interface layers in which the thermal pressures should significantly exceed those within the cloud. We have investigated the gas-phase formation of polyatomic molecules within such warm interfaces. If an interface occupies a few percent of the total molecular column density along that line-of-sight, then many polyatomic species in that interface should have detectable abundances. We have compared the results of interface models with observational data on polyatomic species obtained by Liszt and Lucas. Some models give results that are in harmony with measured ratios of several species including C2H, HCO+ and OH; these models have background radiation fields intensities that are lower than the standard by an order of magnitude. The number densities of molecular hydrogen are of the order of 102cm–3 in regions with temperatures of several thousand degrees. Such conditions in an interface do not conflict with the lower pressures inferred from CO data, as most of the CO is expected to be in the cold bulk of the material rather than in interfaces. The constancy of the sum of MHD wave ``pressure" and thermal pressure implies higher thermal pressures in interfaces than in the cold cloud and cold clump material. The radiation and thermal pressure conditions required to explain the observed abundance ratios may be more likely in interfaces around diffuse clumps within Giant Molecular Clouds than those around the isolated ``field" diffuse clouds observed in ultraviolet absorption. Some measured abundance ratios, the most notable of which is that of the abundances of H2CO and HCO+, are not well matched by model results, though on the basis of the models the relevant species would be expected to be observable in some cases. It is possible that the adopted chemical network is incomplete.

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Journal keyword(s): ISM: abundances - clouds - molecules

Simbad objects: 1

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Number of rows : 1

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME dze Oph Cloud Cld 16 37 09 -10 34.0           ~ 106 0

    Equat.    Gal    SGal    Ecl

C.D.S. - SIMBAD4 rel 1.7 - 2020.10.28CET07:26:53

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NAME dze Oph Cloud -- Cloud
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Cld (Ref)
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    • B : 0.01-0.1" + 2MASS, Tyc
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ICRS coord. (ep=J2000) :
16 37 09.0 -10 34 00 [ ] E ~
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
FK4 coord. (ep=B1950 eq=1950) :
16 34 23.6 -10 28 00 [ ]
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
Gal coord. (ep=J2000) :
006.2802 +23.5898 [ ]
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References (106 between 1850 and 2020) (Total 106)
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2020.10.28-07:26:53

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