Left: separation of the medium-resolution K band spectra HR 5171 A based on their spatial properties resulting from the geometrical models analysis of Sect. 3. The upper orange line is the full spectrum. The yellow line is the spectrum from the uniform disk which its respective normalized flux. The contribution from the Gaussian is characterized by the strong CO emission lines, and the secondary flux is the bottom line at about 12% level in the continuum. Right: the spectrum from the uniform disk is compared to the G8Ib IRTF template in dotted green and the spectrum of Betelgeuse in dashed red. The depth of the CO absoptions is related to the large column of molecular material that is found around the system. Obviously, the CO molecular lines, even those originating in the core of HR 5171 A are affected by the strong veiling from the circumstellar environment and cannot be used for the spectral classification of the primary.