  We present plane-parallel and spherical LTE and NLTE atmospheric models of a
variety of stellar parameters of the red giant star Arcturus (alpha Boo,
HD124897, HR5340) and study their ability to fit the measured absolute flux
distribution. Our NLTE models include tens of thousands of the strongest lines
in NLTE, and we investigate separately the effects of treating the light metals
and the Fe group elements Fe and Ti in NLTE. We find that the NLTE effects of
Fe group elements on the model structure and flux distribution are much more
important than the NLTE effects of all the light metals combined, and serve to
substantially increases the violet and near UV flux level as a result of NLTE
Fe over-ionization. Both the LTE and NLTE models predict significantly more
flux in the blue and UV bands than is observed. We find that within the
moderately metal-poor metallicity range, the effect of NLTE on the overall UV
flux level decreases with decreasing metallicity. These results suggest that
there may still be important UV opacity missing from the models. We find that
models of solar metallicity giants of similar spectral type to Arcturus fit
well the observed flux distributions of those stars from the red to the near UV
band. This suggests that the blue and near UV flux discrepancy is metallicity
dependent, increasing with decreasing metallicity.
