K_s-band magnitudes as a function of the spectral sub-types for luminosity classes V-IV (left panel), III (middle panel) and II-I (right panel). Different symbols identify the single stars, the low-amplitude RV variables and the binaries. Symbols for single and binaries of a given spectral-types have been shifted, compared to one another, by a small amount amount along the x-axis to improve the clarity of the plots.