The Pre–Main-Sequence Stars and Initial Mass Function of NGC 2264

UBVRI and Hα CCD photometry has been performed in the southern region of NGC 2264 around the Cone Nebula. A nearly complete list of pre–main-sequence (PMS) members in the cluster has been made from the compilation of Hα emission stars identified in this study plus those selected in previous investigations, together with stars with X-ray emission. Using the H-R diagram, we tested a set of four PMS evolution models based on the PMS age and age spread estimate for the cluster and the mass-age relationship among individual stars. The resultant initial mass function (IMF) is in good agreement with the field star IMF of the solar neighborhood, with an IMF slope Γ = -1.7 in the mass range 0.3 ≤ log m ≤ 0.8.