The Dependence of Interstellar Reddening on Luminosity Amongst O and B Stars

Abstract

The increase of interstellar reddening of stars with increasing stellar luminosity, found by Blanco & Williams (1959) in the Cepheus IV association, has been found to occur in all clusters and associations containing stars brighter than M v = − 9 (ages < 10 5 year). It is sometimes present in systems with ages in the range 10 5 year to 2 . 10 6 year, never in systems older than 2 . 10 6 year. The effect is found most strongly in the Cygnus II association (Reddish, Lawrence & Pratt 1966). It is concluded that very young early-type stars are surrounded by obscuring clouds having diameters ≼ 1 pc and masses probably ∼ 30 |$M\odot$| . The disappearance of the clouds probably occurs through contraction to disks. The clouds may be remnants of those out of which the stars formed. Wolf–Rayet stars are usually found in star systems which show the effect, rarely in those that do not. Systems showing the effect are absent from the anticentre quadrant which is also devoid of Wolf–Rayet stars. Bok's globules show a similar distribution.