The rich low-mass population of the massive cluster NGC 6231: X-ray emission, evolutionary status, and IMF

Details The rich low-mass population of the massive cluster NGC 6231: X-ray emission, evolutionary status, and IMF The rich low-mass population of the massive cluster NGC 6231: X-ray emission, evolutionary status, and IMF

Feb 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1094..916d&link_type=abstract

COOL STARS, STELLAR SYSTEMS AND THE SUN: Proceedings of the 15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun.

Computer Science

1

X-Ray, X-Ray Binaries, Stellar Atmospheres, Radiative Transfer, Opacity And Line Formation

Scientific paper

We present a deep Chandra observation of the young, massive cluster NGC 6231 in Sco OB1. We detect more than 1600 point X-ray sources, and we argue that about 90% of them are cluster members, thus enlarging by almost a factor of 3 the known total cluster population. The color-magnitude diagram of almost 1100 optical/NIR counterparts shows that the X-ray selected sample ranges down to 0.3 solar masses, We find a definite age spread (2-10 Myrs) for the low-mass stars. Still lower-mass cluster stars will be probably found among the many hundreds unidentified X-ray sources, which are themselves clustered. Mass segregation is found for the most massive stars. The fraction of circumstellar disk-bearing members is found to be low (<4%), which might be due to either spontaneous evolution or photoevaporation under the action of massive stars. A group of objects shows particularly hard X-ray spectra. The dependence of X-ray properties on mass, stellar structure, disk frequency, and cluster evolutionary status agrees with extrapolations drawn on the basis of the study of younger clusters. We compute the cluster initial mass function over 2.5 orders of magnitudes in mass, and find that it is well modeled by a Salpeter-like power law, over its whole range. A previously claimed deficit of low-mass stars is ruled out with high confidence.

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