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  • Other Sources  (8)
  • 2020-2024  (1)
  • 1990-1994  (7)
  • 1955-1959
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  • 1
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    Lithium and Sr isotopic composition of salar deposits in the Central Andes across space and time: the Salar de Pozuelos, Argentina (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-22
    Description: The Central Andes of South America host the largest known lithium resources in a confined area, but the primary lithium sources of the salar deposits and the mobilisation process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate near-surface chemical weathering in a cold and dry climate as the dominant mobilisation process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favoured source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by chemical weathering with only minor hydrothermal mobilisation of Li.
    Description: Universität Bremen (1013)
    Keywords: ddc:553.6 ; Central Andes ; Salar deposits ; Lithium isotopes ; Lithium deposits
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Anatomy of a Photodissociation Region: High angular resolution images of molecular emission in the Orion Bar (1994)
    In:  Other Sources
    Details
    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
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    High resolution CO images of Seyfert Galaxies (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The CO (J = 1-0) emission of three Seyfert galaxies, NGC 3227, NGC 7469, and NGC 5033 was imaged. The CO emission in NGC 3227 and NGC 7469 appears as compact structures centered on the active nuclei, containing substantial fractions of the single-dish flux. In NGC 3227, 10 percent of the CO flux detected by the interferometer is contained within the ionized narrow-line region. The unresolved molecular gas concentrations in the nucleus of NGC 3227 imply a CO mass of 65 million solar masses concentrated within a diameter less than 50 pc. The CO emission in NGC 5033 is not detected at this resolution, implying a CO structure size of 20 to 60 arcsec. Continuum emission at 2.7 mm is not detected in any of the three galaxies. In the center of NGC 7469, the H2 mass is comparable to the dynamical mass. Kinematic studies of the detected gas reveal a rotational motion of the gas in NGC 3227 and NGC 7469, allowing identification of the gas in NGC 7469 with a nuclear starburst. These data are consistent with the idea that interactions between galaxies cause gas to concentrate in their nuclei thereby feeding starburst and Seyfert activity.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 59-61
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Anatomy of the Photodissociation Region in the Orion Bar (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photo-dissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(l) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.
    Keywords: Astronomy
    Type: NASA-TM-112723 , NAS 1.15:112723 , Science; 262; 86-89
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    NASA TECHNICAL REPORTS
  • 5
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    10 micron imaging of UZ Tauri: Evidence for circumstellar disk clearing due to a close companion star (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present 10 micrometer images of the multiple T Tauri star system UZ Tau taken with the Berkeley mid-infrared array camera at the United Kingdom Infrared Telescope (UKIRT) and evidence that UZ Tau E and W are a common proper pair. The mid-infrared emission is resolved for the first time into the two components UZ Tau E and UZ Tau W. The mid-infrared excess deduced for UZ Tau W appears to be much lower than that observed for UZ Tau E. This excess emission is consistent with an optically thin circumstellar disk in the case of UZ Tau W, whereas UZ Tau E's excess is consistent with an optically thick disk. We suggest that the close binary star pair in UZ Tau W is responsible for the observed difference between UZ Tau E and W's mid-infrared excess. In the proposed model, the binary star interacts with the local circumstellar disk environment and clears out much of the material inside its orbital radius (approximately 50 AU). As a result, the hot dust, observed at mid-infrared wavelengths, in UZ Tau W is suppressed compared to its 'wider' companion UZ Tau E. This scenario can also plausibly account for differences observed in UZ Tau E's and UZ Tau W's optical line strengths and profiles.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 434; 2; p. 707-712
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Mid-infrared imaging of Markarian 231 and Arp 220 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: High angular resolution observations of Arp 220 and Mrk 231 provide images of the nuclei and show that the source of the strong mid-IR emission is confined to regions less than about 0.5 arcsec or 400 pc in diameter in Mrk 231 and less than 1.5 arcsec x 0.9 arcsec or 320 x 530 pc in Arp 220. If much of the far-IR emission also derives from such a small region, the implied radiation densities are quite high, equivalent to one O star per cu pc. Although in normal galaxies the near-IR traces an older population of evolved, cool stars, such high radiation densities in the IR bright galaxies suggest the possibility that the spatial correlation observed between the near-IR, mid-IR, and radio may hold because emission in all three bands is associated with hot interstellar gas and dust.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 387; L17-L19
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Models of clumpy photodissociation regions (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: FIR fine structure line and submillimeter line emissions important in the cooling of photodissociation regions (PDRs) as they would arise in clumpy regions are investigated with a simple two-component model for clumpy PDRs consisting of high-density clumps embedded in a lower density interclump medium. The effects of varying the densities of the clump and interclump material in a self-consistent manner are studied. It is found that, while the clump filling factor moderately affects the penetration of the UV field, the density of the interclump material is the most important factor in determining the penetration of the UV field. Observational evidence for the effects of clumpiness in PDRs is found in the spatially extended C II and C I forbidden line emissions which reveal the extent of the UV penetration, and in the observed high intensities of the high CO transitions which indicate the presence of high-density clumps.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 1; p. 216-228.
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Far-infrared observations of M17SW - The clumpy structure of the photodissociation region (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Forbidden O I 63-micron and forbidden Si II 35-micron fine-structure line emission in M17SW was mapped, and the intensities of the forbidden O I 63 and 146 microns, forbidden Si II 35 microns, and forbidden C II 158 microns were measured at four positions. New 50- and 100-micron continuum maps of the M17SW cloud at comparable resolution to the FIR line observations are presented. Analysis in terms of a homogeneous model yields an incident UV field of 56,000 habings, a density of 30,000 cu cm, and a temperature of about 300 K for the atomic gas. It is concluded that the M17SW photodissociation region is clumpy in nature. The observed forbidden Si II and high-J CO imply the presence of high-density clumps. The clumps dominate the emission in the forbidden O I, Si II, and high-level CO lines, while the forbidden C II, C I, and low-level CO arise mostly in the interclump gas. The extended (about 15 pc) forbidden C II and forbidden C I emission is attributed to the halo gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 390; 2 Ma; 499-513
    Format: text
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    NASA TECHNICAL REPORTS
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