Abstract
New UBVI and Hα photometry has been performed for the young open cluster NGC 2244. We classified 30 OB stars as being members of the cluster using proper-motion data and spectral types from previous investigators, along with photometric diagrams obtained in this study. We measured Hα emission strength of the stars by Hα photometry and set up a selection criterion to select pre–main-sequence (PMS) stars with Hα emission. Fourteen PMS stars and seven PMS candidates were found using the criterion. In addition, six stars found near the positions of ROSAT HRI X-ray sources were assumed to be PMS stars and the optical counterparts of these X-ray sources. We determined a reddening of E(B-V) = 0.47 ± 0.04 for the cluster and a total-to-selective extinction ratio of RV = 3.1 ± 0.2. The distance modulus derived was V0 - MV = 11.1. By comparing our photometric results with theoretical evolution models, we derived a main-sequence turnoff age of 1.9 Myr and a PMS age spread of about 6 Myr. The slope of the initial mass function, Γ, calculated in the mass range 0.5 ≤ log m ≤ 2.0 could be flat (Γ = -0.7 ± 0.1).
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