EDP Sciences
Free access
Issue
A&A
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)

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 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

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