  A brief overview of the results of the investigations of the red giant star
Arcturus is given. One-dimensional LTE modeling of the atmospheres of Arcturus
and the Sun as a star is carried out on the basis of synthesis of the extended
wings of the H and K Ca II lines. It is found that the local continuum in this
spectral region is underestimated by an average of 12% in the atlases of
Arcturus. The average deficit in UV absorption amounts to 43% for Arcturus
whereas it is 9% for the Sun. For Arcturus the correction factor to the
continuum opacity at the wavelengths of 390.0, 392.5, 395.0, 398.0, and 400.0
nm equals 2.20, 1.90, 1.70, 1.55, and 1.45. The model atmosphere of Arcturus
obtained from the best-fit of the wings of the H and K Ca II lines corresponds
to the model atmosphere with the fundamental parameters T_eff = 4286 K, log g =
1.66, and [Fe/H]=-0.52 derived by Ramirez and Allende Prieto (2011). The
temperature stratification of Arcturus' atmosphere is presented in tabular
form. To obtain more accurate temperature stratification in the future, we need
a high spectral resolution spectrum calibrated to absolute fluxes with high
accuracy.
