2 00 5 Is the emerging massive cluster NGC 2244 a twin cluster ?

We present in this paper the first near infrared study of the young open cluster NGC 2244, which is well known for its partially embedded nature in the Rosette Nebula. Based on the spatially complete 2 Micron All Sky Survey, the young OB cluster indicates apparent substructures. It is surprisingly resolved into a compact core that matches well the congregation of massive OB stars in the optical, a satellite cluster at a distance of 6.6 pc in its west and probably a major stellar aggregate resembling an arc in structure right below the core. This infrared study provides various new updates on its nature of the young open cluster, including its central position, physical scale and stellar population. A disk fraction of ∼ 20.5± 2.8% is achieved for its members with masses above 0.8 M⊙. NGC 2244 is hence a unique example for the study of embedded clusters. Subject headings: HII regions — infrared: stars — stars: formation — stars: pre-main sequence — open clusters and associations: individual (NGC 2244)