The solar neutral iron spectrum

Abstract

The profiles of eighteen neutral iron lines of varying strengths were synthesized from disk center to the limb using source functions from detailed statistical equilibrium calculations. Emphasis is placed upon the analysis of the strong Fe i lines between 3500 A and 4500 A which are formed at and below the region of the initial temperature rise in the chromosphere. The major results are as follows: (1) We find an iron abundance of 1.5 × 1−5 relative to hydrogen (7.2 on a logarithmic scale with hydrogen equal to 12) that is independent of the assumed microturbulence model since it is based upon the far wing profiles of the strong lines. The far wings are formed in the photosphere where both the ionization and excitation equilibria are in detailed balance, so this abundance is directly comparable to other LTE abundances. (2) The strong line cores indicate that the chromospheric electron densities in the region of the initial temperature rise are similar to those derived by Henze (1969) from eclipse observations; i.e. higher than the HSRA model (Gingerich et al., 1971) by factors of two to five. We present (3) an anisotropic (angle-dependent) microturbulent velocity model, and (4) a mean macroturbulent velocity that aids in fitting the line cores. The formation of the two Fe i lines λ5232.95 and λ5250.21 is also discussed.