Comments on the cluster main-sequence fitting method. III. Empirical UBV reddening lines for early-type stars

Abstract

Reddening line parameters in the UBV system have been derived for early-type stars in six restricted (2[degrees symbol]-3[degrees symbol] radius) Milky Way fields associated with open clusters and/or associations. The curvature terms are very similar from one field to another, with mean [angled bracket]Y[angled bracket] = 0.021 [plus or minus] 0.006, and indicate that there is very little (almost negligible) curvature in the reddening lines for OB stars. The slope terms differ quite significantly from one field to another over a range of at least X = 0.62 to 0.80, implying that mean galactic reddening relations should not be used for dereddening UBV data for individual stars. No significant spectral type dependence of X is found for O-, B-, and A-type stars, contrary to published results. A correlation of [lambda][subscript max] with X for extinction by nearby dust clouds indicates that galactic variations in reddening line slope are likely to be due to variations in dust grain size distributions along different galactic lines of sight.