Spatial variations of the equivalent widths of neutral iron lines in the solar granulation

Details Spatial variations of the equivalent widths of neutral iron lines in the solar granulation Spatial variations of the equivalent widths of neutral iron lines in the solar granulation

Feb 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001kfnt...17...24s&link_type=abstract

Kinematika i Fizika Nebesnykh Tel, vol. 17, no. 1, p. 24-36

Physics

1

Scientific paper

Using accelerated Lambda-iteration method, we solved 2D nonequilibrium radiation transfer problem for quasi-stationary and fully nonstationary solar granulation models. Neutral iron lines were calculated for a 21-level atom model. We took into account the Doppler shifts of the absorption coefficient profiles (due to convective motions) along the ray path. We studied the spatial variations of the equivalent widths (W) for four lines: lambdalambda 388.625, 525.021, 670.357, and 671.032 nm - strong, moderate, and two weak ones, correspondingly, which are formed in different layers of the solar atmosphere. The spatial variations of the equivalent widths over granular-intergranular regions are sensitive to non-LTE effects due to photoionization processes: the non-LTE modelling produces a small negative slope in the equivalent width - continuum intensity dependence, while the LTE calculation produces a positive slope. It is shown that the interaction of descending flows is overestimated, which leads to a stronger negative correlation between the equivalent width and intensity in the non-LTE modelling. The non-LTE effects make weaker the equivalent widths of spectral lines in granules and filter their fluctuations. The depletion of Fe I levels by the UV radiation leads to a smaller height interval where the line is formed, and that is why the non-LTE line profiles for forbidden transitions are more sensitive to local conditions and reflect the conditions in deeper atmosphere layers.

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