The Luminosity Function of Nebulae. I. The Luminosity Function of Resolved Nebulae as Indicated by Their Brightest Stars

The brightest star, arbitrarily defined as the mean of the three or four brightest individual, non-variable stars in a nebula, is calibrated as a criterion of distance (M8 = 6.35, Os =0.41). The luminosity function of resolved nebulae is then derived from the frequency distribution of m8 -inn, which measures the luminosity of a nebula in terms of its bright- est star as the unit. The luminosity function approximates a normal error-curve with Mon=I4.2±,~n=o.85,andMn=-I5.I8. Incomplete data for brightest stars in members of the Virgo cluster suggest a modu- lus, m-M, of 26.6 or slightly larger. Cluster members are roughly comparable with resolved field nebulae, and, within the cluster, different types of nebulae are comparable among themselves