An XMM-Newton view of the young open cluster NGC 6231 III. Optically faint X-ray sources

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dc.creatorSana, H.
dc.creatorRauw, G.
dc.creatorSung, H.
dc.creatorGosset, E.
dc.creatorVreux, J. -M.
dc.date2007-03-06
dc.date.accessioned2026-07-07T11:00:58Z
dc.date.available2026-07-07T11:00:58Z
dc.descriptionWe 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 H-R diagram, we find that the bulk of these objects probably consists of low-mass pre-main sequence stars with masses in the range 0.3 to 3.0 M$_{\odot}$. 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 to 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 $\log{L_{\rm X}/L_{\rm bol}}$ values that increase strongly with decreasing bolometric luminosity and can reach a saturation level ($\log{L_{\rm X}/L_{\rm bol}} \sim -2.4$) for non-flaring sources and even more extreme values during flares.
dc.descriptionAccepted by MNRAS, 14pages, 19 figures
dc.identifierhttps://arxiv.org/abs/astro-ph/0703104
dc.identifierhttp://arxiv.org/abs/astro-ph/0703104
dc.identifierMon.Not.Roy.Astron.Soc.377:945-956,2007
dc.identifierdoi:10.1111/j.1365-2966.2007.11672.x
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/187823
dc.subjectAstrophysics
dc.titleAn XMM-Newton view of the young open cluster NGC 6231 III. Optically faint X-ray sources
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