Reference : An XMM-Newton view of the young open cluster NGC 6231-III. Optically faint X-ray sources
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
http://hdl.handle.net/2268/17659
An XMM-Newton view of the young open cluster NGC 6231-III. Optically faint X-ray sources
English
Sana, H. [> > > >]
Rauw, Grégor mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE) >]
Sung, H. [> > > >]
Gosset, Eric mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE) >]
Vreux, Jean-Marie mailto [Université de Liège - ULg > Département d'astrophysique]
21-May-2007
Monthly Notices of the Royal Astronomical Society
Blackwell Publishing
377
3
945-956
Yes (verified by ORBi)
International
0035-8711
Oxford
[en] stars : pre-main-sequence ; open clusters and associations : individual : NGC 6231 ; X-rays : individual : NGC 6231 ; X-rays : stars
[en] We discuss the properties of the X-ray sources with faint optical counterparts in the very young open cluster NGC 6231. From their positions in the Hertzsprung-Russell diagram, we find that the bulk of these objects probably consists of low-mass pre-main-sequence (PMS) stars with masses in the range 0.3-3.0 M-circle dot. The age distribution of these objects indicates that low-mass star formation in NGC 6231 started more than 10 Myr ago and culminated in a starburst-like event about 1-4 Myr ago when the bulk of the low-mass PMS stars as well as the massive cluster members formed. We find no evidence for a spatial age gradient that could point towards a sequential star formation process. Only a few X-ray sources have counterparts with a reddening exceeding the average value of the cluster or with infrared colours indicating the presence of a moderate near-IR excess. The X-ray spectra of the brightest PMS sources are best fitted by rather hard thermal plasma models and a significant fraction of these sources display flares in their light curve. The X-ray brightest flaring sources have decay times between 2 and 16 ks. The X-ray selected PMS stars in NGC 6231 have log L-X/L-bol values that increase strongly with decreasing bolometric luminosity and can reach a saturation level (log L-X/L-bol similar to -2.4) for non-flaring sources and even more extreme values during flares.
http://hdl.handle.net/2268/17659

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