X-rays and young clusters: Membership, IMFs and distances
  Sensitive imaging X-ray observations of young stellar clusters (YSCs, ages less than about 10 Myr) are valuable tools for the acquisition of an unbiased census of cluster members needed for Initial Mass Function (IMF) studies. Several dozen YSCs, both nearby and across the Galactic disk, have been observed with the Chandra and XMM-Newton satellites, detecting >10,000 low-mass cluster members. Many of these samples should be nearly complete down to about 1 Mo. An important additional benefit is that the YSC X-ray luminosity function appears to be universal with a lognormal shape, providing a new standard candle for measurement of YSC distances. 
Eric D. Feigelson and Konstantin V. Getman