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The effect of intermediate-scale motions on line formationThe 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.
Document ID
19760033063
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Shine, R. A.
(Joint Institute for Laboratory Astrophysics Boulder, Colo., United States)
Date Acquired
August 8, 2013
Publication Date
December 1, 1975
Publication Information
Publication: Astrophysical Journal
Volume: 202
Subject Category
Solar Physics
Accession Number
76A16029
Funding Number(s)
CONTRACT_GRANT: NGL-06-003-057
Distribution Limits
Public
Copyright
Other

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