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  • 1
    Publication Date: 2011-08-24
    Description: We present observations of the molecular component of the Orion Bar, a prototypical Photodissociation Region (PDR) illuminated by the Trapezium cluster. The high angular resolution (6 sec-10 sec) that we have achieved by combining single-dish and interferometric observations has allowed us to examine in detail the spatial and kinematic morphology of this region and to estimate the physical characteristics of the molecular gas it contains. Our observations indicate that this PDR can be essentially described as a homogeneously distributed slab of moderately dense material (approximately 5 x 10(exp 4)/cu cm), in which are embedded a small number of dense (greater than 10(exp 6)/cu cm) clumps. The latter play little or no role in determining the thickness and kinetic temperature structure of this PDR. This observational picture is largely supported by PDR model calculations for this region, which we describe in detail in this work. We also find our model predictions of the intensities of a variety of atomic and molecular lines to be in good general agreement with a number of previous observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 422; 1; p. 136-152
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  • 2
    Publication Date: 2013-08-29
    Description: We present preliminary millimeter-wavelength images of the photodissociation region (PDR) in the Orion Bar, observed with the Berkeley- Illinois-Maryland array (BIMA). These new BIMA observations have attained 5 arc sec resolution in the J=l-O emission lines of HCO+ (formyl ion) and HCN (hydrogen cyanide). The results are compared with previous observations of the J=1-0 transition lines of (13)CO. We find that the HCO+ and HCN have different spatial distributions. HCN appears to lie primarily inside dense clumps of gas, which are defined by areas of intense (13)CO emission. However, the HCO+ emission appears to be only loosely associated with the surfaces of the gas clumps. We suggest that HCO+ abundance is enhanced by the presence of vibrationally excited H2 on the surfaces of dense clumps, and that the HCN abundance is attenuated by photo destruction outside the cores of dense clumps of gas.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 87-90
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