Interstellar reddening and IR-excesses of O and B stars.

A mean law of interstellar reddening is established using two-color diagrams based on B, V, R, I, J, K and L magnitudes of 350 O and B stars. The law is valid for all directions of our Galaxy covered by the selected stars. The stars were selected from the work of Johnson (1965) and Lamla (1965) according to the following criteria: stars must have normal spectra; no stars with anomalous continua; no close visual binaries with small magnitude differences; no Be stars or stars with peculiar spectra. The reddening constant R is derived to be 3.14 plus or minus 0.10. Only 20 of the stars studied were found above the determined upper scattering limit, indicating an apparent infrared excess. These deviations are explained as additive emission in the vicinity of the stars or as variations and anomalies of the intrinsic colors of the stars.