(sub)stellar members of NGC 2244 spectra

We evaluated cluster membership using three gravity-sensitive spectral indices based on the shape of the H-band. Furthermore, we evaluated the infrared excess from Spitzer of all the candidate members of the cluster. Finally, we estimated the mass of all the candidate members of the cluster and derived the initial mass function, star-to-BD number ratio and disk fraction.

The initial mass function is well represented by a power law (dN/dM {prop.to} M^-alpha^) below 0.4M_{sun}_, with a slope alpha=0.7-1.1 depending on the fitted mass range. We calculated a star-to-BD number ratio of 2.2-2.8. We find the low-mass population of NGC 2244 to be consistent with nearby star- forming regions, although it is at the high end of BD production.

We find BDs in NGC 2244 to be, on average, closer to OB stars than to low-mass stars, which could potentially be the first piece evidence that OB stars affect the formation of BDs. We find a disk fraction of all the members with a spectral type later than K0 of 39+/-9% which is lower than typical values found in nearby star-forming regions of similar ages.