Intrinsic colors of stars in the near-infrared

Intrinsic infrared colors of stars in the Johnson 11 color system are derived. The database is a list of 3946 stars with observations in UBVRIJHKLMN, of all spectral types and luminosity classes, including carbon, T Tauri, and Wolf-Rayet stars. Intrinsic colors were derived from the zero-reddening curve that can be defined in the bluer side of temperature versus observed color diagrams. In a sample of stars of the same spectral type, the bluest stars are considered to have an observed color very near their intrinsic color. The comparison with former derivations from Johnson and Koornneef presents significant differences: new M and N colors, for all spectral types, are bluer than published values, the differences being more important for giants and supergiants; the amplitude of color values in these new results is wider.