Comparing Radiative Transfer Codes and Opacity Samplings for Solar Irradiance Reconstructions

Abstract

Some techniques developed to reproduce solar irradiance variations make use of synthetic radiative fluxes of quiet and magnetic features. The synthesis of radiative fluxes of astronomical objects is likely to be affected by uncertainties resulting from approximations and specific input employed for the synthesis. In this work we compare spectra obtained with three radiative transfer codes with the purpose of investigating differences in reproducing solar irradiance variations. Specifically, we compare spectral synthesis produced in non-local thermodynamic equilibrium obtained with COSI and RH using 1-D atmosphere models. We also compare local thermodynamic equilibrium syntheses emerging from 3-D MURaM simulations of the solar atmosphere obtained with two sets of opacity tables generated with the ATLAS9 package and with the RH code, and test the effects of opacity sampling on the emergent spectra. We find that, although the different codes and methodologies employed to synthesize the spectrum reproduce overall the observed solar spectrum with a similar degree of accuracy, subtle differences in quiet Sun spectra may translate into larger differences in the computation of the contrasts of magnetic features, which, in turn, critically affect the estimates of solar variability.