3-D non-LTE radiative transfer effects in Fe I lines: II. Line formation in 3-D radiation hydrodynamic simulations

摘要

We investigate the effects of horizontal radiative transfer (RT) a NLTE onimportant diagnostic iron lines in a realistic 3-D HD simulation. Using amulti-level atom we compute and compare widely used Fe I line profiles at 3different levels of approximation (3-D NLTE, 1-D NLTE, LTE). We find that theinfluence of horizontal RT is of the same order of magnitude as that of NLTE,although spatially more localized. Also, depending on the temperature of thesurroundings, horizontal RT is found to weaken or strengthen spectral lines.Line depths and equivalent width may differ by up to 20% against thecorresponding LTE value if 3-D RT is applied. Residual intensity contrasts inLTE are found to be larger than those in 3-D NLTE by up to a factor of two.When compared to 1-D NLTE, we find that horizontal RT weakens the contrast byup to 30% almost independently of the angle of line of sight. While the CLV ofthe 1-D and 3-D NLTE contrasts are of similar form, the LTE contrast CLV showsa different run. The determination of temperatures by 1-D NLTE inversions ofspatially resolved observations may produce errors of up to 200 K if oneneglects 3-D RT. We find a linear correlation between the intensity differenceof 1-D and 3-D NLTE and a simple estimate of the temperature in the horizontalenvironment of the line formation region. This correlation could be used tocoarsely correct for the effects of horizontal RT in inversions done in 1-DNLTE. Horizontal RT is less important if one considers spatially averaged lineprofiles because local line strengthening and weakening occur with similarfrequency in our HD atmosphere. Thus, the iron abundance is underestimated by0.012 dex if calculated using 1-D NLTE RT. Since effects of horizontal RT arelargest for spatially resolved quantities, the use of 3-D RT is particularlyimportant for the interpretation of high spatial resolution observations.