$H$ vs. $J-K$ color-magnitude diagram, and b) fall between an unreddened and unreddened 3 Myr pre-main sequence isochrone, properly shifted to the estimated distance to DR15. The extinction-limited samples assure a minimum contamination from extragalactic sources (which mostly will fall in the area below the extinction vector and the sensitivity limit) and will minimize a bias due to the decrease in the number of detected sources as a function of extinction.

In their study, @Muench:2000aa showed that the observed shape of the KLF (mostly defined by the peak value) of a pre-main sequence population is particularly sensitive to three intrinsic parameters: the underlying Initial Mass Function (IMF), the mean age of the population, and to a lesser extent, the age spread or period of formation. Our analysis consists of constructing a grid of artificial KLF for each of our samples, and compare them with our observed function. We constructed this grid by assuming a fixed IMF and let the time parameters, mean age and age spread, to run free.

For each population (DR15-C,DR15-W, DR15-SW and DR15-SE) we the used code of @Muench:2000aa to simulate artificial KLFs for clusters with the same number of sources and the same distributions for extinction 