Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26as..127..607n&link_type=abstract
Astronomy and Astrophysics Supplement, v.127, p.607-618
Astronomy and Astrophysics
Astrophysics
7
Line: Formation, Line: Profiles, Radiative Transfer, Methods: Numerical, Sun: Flares
Scientific paper
A method of calculating NLTE models of a plan-parallel solar flare atmosphere with stationary plasma flows is presented. To solve the radiative transfer equation, equations of statistical equilibrium (ESE) and the stationary momentum equation, we use the multilevel approximate lambda iteration (MALI) approach. The numerical code is based on the method recently developed by \cite[Rybicky & Hummer (1991, 1992)]{ri91} and allows to take into account macroscopic velocity fields in observer's frame formulation. The preconditioned ESE, constructed by this method, are finally linearized with respect to level populations and electron densities to treat the the hydrogen ionization balance. The numerical code based on this method is used to compute a grid of NLTE flare models with various velocity fields in order to show the influence of the velocity fields on the Hα -line asymmetries. The analysis of the results lead to conclusions that would improve interpretations of flare line asymmetries: 1) The velocities affect the level populations, 2) The type of asymmetry depends on the changes in the optical depth scales and on the run of the source function in the atmosphere. 3) A monotonous velocity affects only one wing of the line profile. 4) To get the velocity field from an observed profile the bisector method should be modified.
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