Other
Scientific paper
Dec 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975apj...202..543s&link_type=abstract
Astrophysical Journal, vol. 202, Dec. 1, 1975, pt. 1, p. 543-550.
Other
28
Line Spectra, Sawtooth Waveforms, Sine Waves, Solar Atmosphere, Solar Spectra, Absorption Spectra, Astronomical Models, Atmospheric Attenuation, Electron Density (Concentration), Velocity Distribution
Scientific paper
The problem of LTE and non-LTE line formation in the presence of nonthermal velocity fields with geometric scales between the microscopic and macroscopic limits is investigated in the cases of periodic sinusoidal and sawtooth waves. For a fixed source function (the LTE case), it is shown that time-averaged line profiles progress smoothly from the microscopic to the macroscopic limits as the geometric scale of the motions increases, that the sinusoidal motions produce symmetric time-averaged profiles, and that the sawtooth motions cause a redshift. In several idealized non-LTE cases, it is found that intermediate-scale velocity fields can significantly increase the surface source functions and line-core intensities. Calculations are made for a two-level atom in an isothermal atmosphere for a range of velocity scales and non-LTE coupling parameters and also for a two-level atom and a four-level representation of Na I line formation in the Harvard-Smithsonian Reference Atmosphere (1971) solar model. It is found that intermediate-scale velocity fields in the solar atmosphere could explain the central intensities of the Na I D lines and other strong absorption lines without invoking previously suggested high electron densities.
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