Grey extinction in the solar neighbourhood?

Abstract

Some of the close O and B dwarfs appear to be fainter than indicated by thei Hipparcos distances, intrinsic absolute magnitudes attributed to their spectral types, and estimated selective interstellar extinction. This discrepancy is explained in the paper by the grey (neutral) interstellar extinction in the visual range of spectrum. The measure of such an effect is related to discrete features of the interstellar matter.