A quantitative study of the O stars in NGC 2244

Abstract. NGC2244 located in the Rosette Nebula is a young open cluster composed of
seven O-type stars. A first paper focused on the multiplicity of these stars, revealed only one
binary system out of the seven studied stars. The minimum binary fraction of this cluster
(~ 14%) diff ers to the average fraction measured on the nearby clusters (~ 44%). In order to
better constrain this discrepancy, an analysis based on the determination of the stellar and wind
parameters of these stars with the CMFGEN atmosphere code was performed. The main results
con rfim that all the stars have an age between 0 and 5 Myr, and that the N surface abundance
appears to be consistent with the evolutionary models for a population of stars of the same age.
Moreover, this investigation exhibits the existence of dynamical interactions inside this young
open cluster sufficiently strong to eject the hottest component from its centre.