Fine structure in the luminosity function in young stellar populations with <i>Gaia</i> DR2

A pioneering study showed that the fine structure in luminosity function (LF) of young star clusters contains information about evolutionary stage (age) and composition stellar population. The notable features include H-peak, which is result onset hydrogen burning turning pre-main sequence stars into main stars. feature moves toward faint end LF, eventually disappears as population evolves. Another detectable Wielen dip, a dip at M_V ~ 7 mag LF first identified 1974 for solar environment. Later studies also this clusters. caused by increased importance H- opacity certain range low-mass We studied detailed using data from Gaia DR2 PARSEC evolution models with aim to further our understanding populations. analyzed astrometric properties neighborhood (< 20 pc) various relatively nearby 400 50 Myr) open OB associations, compare those generated models. confirmed all populations, including neighborhood, M_G ~7 mag. H-peak present field neighborhood. It likely signals mixed significant number younger than 100 Myr. found its location varies age. Our observations confirm 5 Myr up 47 populations can be used estimate their