We have studied the star formation history and the initial mass function ( IMF ) using the age and mass derived from spectral energy distribution ( SED ) fitting and from color-magnitude diagrams .
We also examined the physical and structural parameters of more than 1,000 pre-main sequence stars in NGC 2264 using the on-line SED fitting tool ( SED fitter ) of Robitaille et al .

We have compared the physical parameters of central stars from SED fitter and other methods .
The temperature of the central star is , in many cases , much higher than that expected from its spectral type .
The mass and age from SED fitter are not well matched with those from color-magnitude diagrams .
We have made some suggestions to improve the accuracy of temperature estimates in SED fitter .

In most cases these parameters of individual stars from SED fitter in a star forming region ( SFR ) or in the whole cluster showed nearly no systematic variation with age or with any other relevant parameter .
On the other hand , the median properties of stars in NGC 2264 SFRs showed an evident evolutionary effect and were interrelated to each other .
Such differences are caused by a larger age spread within an SFR than between them .

The cumulative distribution of stellar ages showed a distinct difference among SFRs .
A Kolmogorov-Smirnov test gave a very low probability of them being from the same population .
The results indicate that star formation in NGC 2264 started at the surface region ( Halo and Field regions ) about 6 – 7 Myr ago , propagated into the molecular cloud and finally triggered the recent star formation in the Spokes cluster .
The kind of sequential star formation that started in the low-density surface region ( Halo and Field regions ) implies that star formation in NGC 2264 was triggered by an external source .

The IMF of NGC 2264 was determined in two different ways .
One method used the stellar mass from the SED fitting tool , the other used the stellar mass from color-magnitude diagrams .
The first IMF showed a distinct peak at m \approx 2M _ { \odot } , but the second did not .
We attribute the peak as an artifact of the SED fitting tool because there is no such IMF with a peak at m \approx 2M _ { \odot } .
The slope of the IMF of NGC 2264 for massive stars ( \log m \geq 0.5 ) is -1.7 \pm 0.1 , which is somewhat steeper than the so-called standard “ Salpeter-Kroupa ” IMF .
We also present data for 79 young brown dwarf candidates .