SIMBAD references

2007MNRAS.377..945S - Mon. Not. R. Astron. Soc., 377, 945-956 (2007/May-3)

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


Abstract (from CDS):

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. The age distribution of these objects indicates that low-mass star formation in NGC 6231 started more than 10Myr ago and culminated in a starburst-like event about 1-4Myr 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 16ks. The X-ray selected PMS stars in NGC 6231 have logLX/Lbol values that increase strongly with decreasing bolometric luminosity and can reach a saturation level (logLX/Lbol∼ -2.4) for non-flaring sources and even more extreme values during flares.

Abstract Copyright: 2007 The Authors. Journal compilation © 2007 RAS

Journal keyword(s): stars: pre-main-sequence - Open clusters and associations: individual: NGC 6231 - X-rays: individual: NGC 6231 - X-rays: stars

Simbad objects: 38

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