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  • 1
    Publication Date: 2016-06-07
    Description: International Ultraviolet Exploration observations of NGC 3918 and IC 2448 are presented. Combining these observations with data in the optical range and computed model structure, the chemical composition for these objects is derived. For NGC 3918 log C = -3.02, log N = -3.61 and log 0 = -3.22; while for IC 2448 log C = -3.44, log N = -81 and log 0 = 3.54.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 641-647
    Format: application/pdf
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  • 2
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    In:  CASI
    Publication Date: 2017-06-24
    Description: The theoretical calculations of helium triplet line strengths, including collisional enhancement, are compared to astronomical observations. Both are plotted on an I(10830)/I(5876) vs I(5876)/I(4471) plane. It appears that the theory of helium triplet line strengths agrees with present observations, and that the question of an additional depopulation mechanism for the 2 3S population is probably predicted correctly within 30%.
    Keywords: SPACE SCIENCES
    Type: NASA-CR-127064
    Format: application/pdf
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  • 3
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Multi-apertureUBV photometry of NGC 3227 is presented. An interpolation formula based on the galaxy profile allows the reduction of all previous measurements to a ‘standard’ aperture diaphragm.
    Type of Medium: Electronic Resource
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  • 4
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    In:  Other Sources
    Publication Date: 2011-08-16
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: Astronomy and Astrophysics; 20; 3, Se; Sept
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  • 5
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Approximate values for the threshold energies, threshold cross sections, and energy dependence of the cross sections for K-shell photoionization are tabulated for H, He, C, N, O, Ne, Mg, Si, and S in all stages of ionization. The approximation of these data is based on the assumptions that the threshold energy is a simple function of the nuclear charge and the number of electrons present in the atom, and that the threshold values and energy dependence of the cross sections are determined only by the threshold energy.
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: Astrophysical Journal; 177; Nov. 1
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  • 6
    Publication Date: 2011-08-16
    Description: If a collision of two large, massive, fast gas clouds occurs, their kinetic energy is converted to radiation in a pair of shock fronts at their interface. Basic constraints imposed on such a model by observations of QSOs are considered. It is shown that a very large shock area is required if such a collision process is to provide the energy for a QSO. Details regarding the anticipated spectrum are discussed together with the opacity of the neutral clouds.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 173; Apr. 1
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  • 7
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Low density collisionally ionized plasma at equilibrium, calculating permitted, forbidden and semiforbidden radiative cooling coefficients
    Keywords: PHYSICS, PLASMA
    Type: ; ADEMIE DES SCIENCES
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  • 8
    Publication Date: 2011-08-17
    Description: IUE observations indicate that the spectrum of 3C 273 is similar to that of other large-redshift quasars. There is a large excess of flux in the range 2400 A to 5300 A, which encompasses the Balmer jump region but which does not appear to be explainable by Balmer emission. The intensity ratio of Lyman-alpha to H-beta is 5.5, in agreement with other measures and a factor 6 smaller than the recombination value. The only absorption lines in the spectrum are due to our Galaxy. There is marginal evidence for a depression of the continuum shortward of the Lyman-alpha emission line, but the errors are too large to warrant any conclusion that 3C 273 has a rich absorption-line spectrum such as that seen in large-redshift quasars. The absence of emission and absorption lines of Fe II leads to the conclusion that resonance fluorescence probably produces the visual Fe II emission lines.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 230
    Format: text
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  • 9
    Publication Date: 2011-08-17
    Description: A collision between two gas clouds with initial densities of approximately 10 million per cu cm, velocities of about 1000 km/s, and radii of approximately 1 pc is investigated quantitatively by coupling a calculation of the radiation spectrum resulting from the anticipated shock fronts with a computation for the conversion of this high-energy radiation into optical emission in adjacent photoionized regions. The detailed structure of the colliding clouds is discussed, and the effects of an ambient magnetic field are considered. The combined emission-line spectrum is presented along with continuum emission estimates for thermal, synchrotron, and very-high-energy bremsstrahlung mechanisms. It is shown that significant continua can be produced over the range from 300 microns to 3 keV, including a blackbody contribution from a high-density neutral region between the shock fronts, free-free and free-bound radiation from the cooling zones directly behind the shocks, and free-free, free-bound, and two-photon radiation from the photoionized regions immediately ahead of and behind the cooling zones. The theoretical spectrum of the structure resulting from the collision is found to be similar in general and in some details to those observed for typical quasars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 219
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  • 10
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Reduced nebular helium abundances, using capture- cascade and collisional excitation calculations
    Keywords: SPACE SCIENCES
    Type: ; 331-335. (
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