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  • 1
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    Skylab observations of the solar C I multiplets at 1560- and 1657-A (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Skylab spectrograph profile observations of the solar C I multiplets are presented, and the profile variations from center to limb and at various heights above the quiet solar limb are noted. These lines are of interest both because they are formed in the midchromosphere, thereby providing checks and constraints on chromospheric models, and because they are sensitive to the magnitude of the nonthermal microvelocities included in theoretical calculations. The present observations are compared with the C I profiles calculated by Shine et al (1978), discussing the many inconsistencies that emerge, notably between the observed and computed 1560/1657-A ratio and in the center-to-limb and above-the-limb variations of the integrated intensity. The multiplet central cores are discussed in terms of several microturbulent velocity structures.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 892-900
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  • 2
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    The aluminum I autoionization doublet in the quiet solar spectrum (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations are presented of the Al I autoionization doublet 1932 A and 1936 A in the quiet solar spectrum, obtained from the NRL slit spectrograph aboard Skylab and from the University of Hawaii Echelle Rocket Spectrograph. The observed profiles are compared with theoretical spectra computed for the Harvard Smithsonian Reference Atmosphere and the Vernazza, Avrett and Loeser (1976) solar models. It is found that nonlocal thermodynamic equilibrium effects are important in the line-formation problem and the synthetic spectra are in good agreeement with the data.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 248
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  • 3
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    Evidence of redshifts in the average solar line profiles of C IV and Si IV from OSO-8 observations (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Line profiles of C IV and Si V obtained by the Colorado spectrometer on OSO-8 are presented. It is shown that the mean profiles are redshifted with a magnitude varying from 6-20 km/s, and with a mean of 12 km/s. An apparent average downflow of material in the 50,000-100,000 K temperature range is measured. The redshifts are observed in the line center positions of spatially and temporally averaged profiles and are measured either relative to chromospheric Si I lines or from a comparison of sun center and limb profiles. The observations of 6-20 km/s redshifts place constraints on the mechanisms that dominate EUV line emission since it requires a strong weighting of the emission in regions of downward moving material, and since there is little evidence for corresponding upward moving materials in these lines.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 77; Apr. 198
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  • 4
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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
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    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
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  • 5
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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
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    Publication Date: 2019-06-28
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 68; Dec. 198
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  • 6
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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
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  • 7
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    HRTS II EUV observations of a solar ephemeral region (1984)
    In:  Other Sources
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    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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  • 8
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    H I Lyman-alpha in the sun - The effects of partial redistribution in the line wings (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A form for the Lyman-alpha redistribution function that is modified to include the effects of collisional coupling between different energy states is presented. It is noted that this extends the work of Yelnik et al. (1981) and Roussel-Dupre(1982). By separating the source function into its primary components at all heights, the formation of Lyman-alpha radiation is investigated in detail. Frequencies in the line wing can be mapped back in such a way that the heights of formation for a change in lambda of plus or minus 0.5-6 A span the entire solar chromosphere. The usefulness of the Lyman-alpha wing as an atmospheric probe, however, is limited by long thermalization lengths, which result from almost coherent scattering outside of the Doppler core. When the line profiles calculated from the chromospheric models of Vernazza et al. (1981) are compared with the quiet-sun observations of Roussel-Dupre, agreement is found in integrated core intensities and in the line wing shape and normalized center-to-limb behavior. The calculated wing intensities, however, are a factor of four too small.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 272; Sept. 15
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  • 9
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    Preliminary results from the Orbiting Solar Observatory 8 - Observations of optically thin lines (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The University of Colorado spectrometer aboard OSO 8 has measured the high temperature C IV resonance lines (at 1548 and 1551 A) and the Si IV resonance lines (at 1393 and 1402 A) formed in the solar chromosphere-corona transition region. Preliminary results include studies of mean profiles, a comparison of cell and network profiles, and the behavior of the lines at the extreme solar limb.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 210; Dec. 1
    Format: text
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  • 10
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    Skylab observations of the solar O I resonance triplet (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Profile variations from center to limb, as well as at different heights above the quiet solar limb, are illustrated by profile observations of the solar O I resonant triplet at 1302, 1304, and 1306 A that were obtained with the Skylab S082-B spectrograph. Since these lines share a common upper energy level, source function equality should exist for them when the lower states are populated according to their statistical weights. Profile congruency and profile inversion calculations comparisons show, however, that this is not the case, suggesting either errors in the fine structure collision rates, or the H I Ly-beta flux preferentially depopulating the 1302 A lower level, or two-dimensional transfer effects.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 153; 1 De
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