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  • SOLAR PHYSICS  (4)
  • ASTROPHYSICS  (2)
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  • 1
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    The laboratory simulation of unmagnetized supernova remnants Absence of a blast wave (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Supernova remnants are experimentally simulated by irradiating spherical targets with eight-beam carbon dioxide laser in a chamber containing finite amounts of neutral gas, the gas being ionized by radiation from the hot target. The expansion velocities of the target plasmas are approximately the same as the expansion velocities of supernova ejecta and the experiment is successfully scaled to the case of a supernova remnant in an unmagnetized, low-density, interstellar medium. No sweep-up of the ambient plasma is detected, indicating that no hydrodynamic shock wave is formed to couple the target ejecta to the ambient gas. The experiment implies that if supernova ejecta couple to the interstellar medium, magnetic-field effects may be crucial to the physical description.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 802-808
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Effects of diffusion and mass flows on C IV and Si IV lines formed in the solar atmosphere (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A model for the transition region is derived from an initial interpretation of EUV observations, assuming ionization equilibrium and constant elemental abundance with height. The effects of diffusion and mass flows are then included in the initial model and the emergent profiles of several C IV and Si IV lines are computed. It is found that diffusion and mass flows have a strong effect on both the emergent intensity and spectral shape of these lines. Diffusion acts to deplete the transition region of heavy ions to an extent which depends on the detailed temperature and density structure. The net effect is a weighting of the coronal emission relative to that in the transition. On the basis of the results, it is suggested that the downflows observed in the network in lines of C IV and Si IV could be due to gravitational settling of the ions following their injection, via diffusion, into the corona from spicules. When flows are superposed on the basic diffusion model, the rapid change in elemental abundance characteristic of the model is virtually eliminated and the coronal contribution to the emission in C IV and Si IV lines becomes negligible relative to that in the transition region. Flows have a strong effect on the computed line intensities and introduce large asymmetries into the line shapes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 250
    Format: text
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  • 3
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    Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. I - Estimate of the electron velocity distribution functions. II - The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 68; Dec. 198
    Format: text
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  • 4
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    Nonequilibrium ionization due to thermal diffusion and mass flows (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Recent calculations of diffusion coefficients are used in the continuity equation to compute ion populations of carbon in the solar transition region. Thermal diffusion causes strong departures from ionization equilibrium in the region where the temperature gradient is steepest. Mass-conserving flows are also included in our calculations. These dominate over thermal diffusion depending on the magnitude of the flows and also lead to departures from ionization equilibrium. These results have important implications for the interpretation of EUV line emission.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 241
    Format: text
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  • 5
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    HRTS II EUV observations of a solar ephemeral region (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: HRTS II has been used to observe the EUV emission of a small bipolar magnetic feature or ephemeral region, where strong EUV line enhancement exhibits contrasts (measured relative to the quiet sun) which range from 10 to 70. The substantiality of the Lyman-alpha and C II-O V emission, and the absence of any measurable emission in coronal forbidden lines, sets a temperature range for the loop's active part of the order of 16,000-300,000 K. The use of the ratios of allowed lines as temperature diagnostics yields temperatures that are very near ionization equilibrium temperatures, and the use of chromospheric lines to form a wavelength standard yields absolute velocities ranging in magnitude from zero to 12 km/sec for C IV, N IV, and O V. This flow is interpreted as a siphon flow.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 428-440
    Format: text
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  • 6
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    On the statistical uncertainties associated with line profile fitting (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The paper considers the statistical uncertainties in the best-fit parameters associated with the fitting of observational data by model line profiles of specific form. The parameters involved are amplitude, center, and width. A general procedure is described for any profile type of parametric form. The case of Gaussian profiles is treated in detail, and numerical solutions are presented for equally spaced data of equal weight. Approximate analytical solutions are derived that give good general agreement with the numerical solutions over the whole range of interest. Approximate solutions are also obtained for the case of Lorentzian profiles. It is shown that the Lorentzian results can be used in conjunction with the Gaussian results to estimate the corresponding parameter uncertainties in the case of the general Voigt profile.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 261
    Format: text
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