Optical properties of X-ray selected stars in NGC 2244 in the Rosette Nebula

Abstract

We present high spatial resolution optical photometry of NGC 2244 in the Rosette Nebula using the NOAO MOSAIC Imager at Kitt Peak. We obtained BVIR and Hα images of the central cluster and surrounding nebulae, and present results for 138 sources selected from X-ray observations with the ROSAT PSPC and HRI. Color-magnitude diagrams of the cluster show a large number of the stars are still undergoing contraction onto the main sequence. The faintest X-ray selected cluster members have the highest X-ray-to-optical luminosities ( erg s-1; to 10-3) and indicate they are a population of young active late-type stars. Hα emission from the X-ray emitters is also remarkable. We have extended the detections of PMS stars in NGC 2244 well into the range of K spectral types. While most of the cluster stars are located in the color-magnitude diagrams in between the ZAMS and the 3 Myrs isochrone, significantly younger low mass stars exist and confirm earlier reports that star formation is still going on in the Rosette Nebula/NGC 2244 region.