The very young open cluster ( OC ) NGC 2244 in the Rosette Nebula was studied with field-star-decontaminated 2MASS photometry , which shows the main-sequence ( MS ) stars and an abundant pre-MS ( PMS ) population .
Fundamental and structural parameters were derived with colour-magnitude diagrams ( CMDs ) , stellar radial density profiles ( RDPs ) and mass functions ( MFs ) .
Most previous studies centred NGC 2244 close to the bright K0V star 12 Monocerotis , which is not a cluster member .
Instead , the near-IR RDP indicates a pronounced core near the O5 star HD 46150 .
We derive an age within 1—6 Myr , an absorption \mbox { $ A _ { V } $ } = 1.7 \pm 0.2 , a distance from the Sun \mbox { $d _ { \odot } $ } = 1.6 \pm 0.2 kpc ( \approx 1.5 kpc outside the Solar circle ) , an MF slope \chi = 0.91 \pm 0.13 and a total ( MS + PMS ) stellar mass of \sim 625 \mbox { $M _ { \odot } $ } .
Its RDP is characterised by the core and cluster radii \mbox { $R _ { c } $ } \approx 5.6 \arcmin ( \approx 2.6 pc ) and \mbox { $R _ { RDP } $ } \approx 10 \arcmin ( \approx 4.7 pc ) , respectively .
Departure from dynamical equilibrium is suggested by the abnormally large core radius and the marked central stellar excess .
We also investigate the elusive neighbouring OC NGC 2239 , which is low-mass ( m _ { MS + PMS } \approx 301 \mbox { $M _ { \odot } $ } ) , young ( 5 \pm 4 Myr ) rather absorbed ( \mbox { $ A _ { V } $ } = 3.4 \pm 0.2 ) , and located in the background of NGC 2244 at \mbox { $d _ { \odot } $ } = 3.9 \pm 0.4 kpc .
Its RDP follows a King-like function of \mbox { $R _ { c } $ } \approx 0.5 \arcmin \approx 0.5 pc and \mbox { $R _ { RDP } $ } \approx 5.0 \arcmin \approx 5.6 pc .
The MF slope , \chi = 1.24 \pm 0.06 , is essentially Salpeter ’ s IMF .
NGC 2244 is probably doomed to dissolution in a few 10 ^ { 7 } yr. Wide-field extractions and field-star decontamination increase the stellar statistics and enhance both CMDs and RDPs , which is essential for faint and bright star clusters .