A Non‐LTE Line‐Blanketed Model of a Solar‐Type Star

Abstract

We present LTE and non-LTE (NLTE) atmospheric models of a star with solar parameters and study the effect of treating many thousands of iron-group lines out of LTE on the computed atmospheric structure, the overall absolute flux distribution, and the moderately high resolution spectrum in the visible and near-UV bands. Our NLTE modeling includes the first two or three ionization stages of 20 chemical elements, up to and including much of the Fe group, and includes about 20,000 Fe I and II lines. We investigate separately the effects of treating the light metals and the Fe-group elements in NLTE. Our main conclusions are that (1) NLTE line-blanketed models with direct multilevel NLTE for many actual transitions give results qualitatively similar to those of the more approximate treatment of L. S. Anderson for both the Fe statistical equilibrium and the atmospheric Tkin structure; (2) models with many Fe lines in NLTE have a Tkin structure that agrees more closely with LTE semiempirical models based on center-to-limb variation and a wide variety of spectra lines, whereas LTE models agree more with semiempirical models based only on an LTE calculation of the Fe I excitation equilibrium; and (3) the NLTE effects of Fe-group elements on the model structure and Fλ distribution are much more important than the NLTE effects of all the light metals combined and serve to substantially increase the violet and near-UV F level as a result of NLTE Fe overionization. These results suggest that there may still be important UV opacity missing from the models. However, the choice of the species and multiplet-dependant van der Waals broadening enhancement also plays a significant role in determining whether LTE or NLTE models provide a close fit to the near-UV flux level. We also find that the rms deviation of the shape of the rectified high-resolution synthetic spectrum from that of the observed spectrum is not significantly affected by the inclusion of NLTE effects.