EDP Sciences
Free access
Volume 384, Number 3, March IV 2002
Page(s) 890 - 898
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20020094

A&A 384, 890-898 (2002)
DOI: 10.1051/0004-6361:20020094

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

T. W. Berghöfer1 and D. J. Christian2

1  Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
2  Computer Sciences Corporation, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

(Received 29 June 2001 / Accepted 17 January 2002)

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 H $\alpha$ 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 ( ${L_{\rm x}} \sog 7\times10^{30}$ erg s -1; ${L_{\rm x}/L_{\rm bol}} \approx 10^{-2}$ to 10-3) and indicate they are a population of young active late-type stars. H $\alpha$ 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.

Key words: galaxy -- open clusters and associations: individual: NGC 2244 -- stars: early-type -- stars: late-type -- stars: activity -- stars: pre-main sequence -- X-ray: stars

Offprint request: T. Berghöfer, thomas.berghoefer@desy.de

SIMBAD Objects
Tables at the CDS

© ESO 2002