Astron. J., 154, 87-87 (2017/September-0)
The structure of the young star cluster NGC 6231. I. Stellar population.
KUHN M.A., MEDINA N., GETMAN K.V., FEIGELSON E.D., GROMADZKI M., BORISSOVA J. and KURTEV R.
Abstract (from CDS):
NGC 6231 is a young cluster (age ∼2-7 Myr) dominating the Sco OB1 association (distance ∼1.59 kpc) with ∼100 O and B stars and a large pre-main-sequence stellar population. We combine a reanalysis of archival Chandra X-ray data with multiepoch near-infrared (NIR) photometry from the VISTA Variables in the Via Lactea (VVV) survey and published optical catalogs to obtain a catalog of 2148 probable cluster members. This catalog is 70% larger than previous censuses of probable cluster members in NGC 6231. It includes many low-mass stars detected in the NIR but not in the optical and some B stars without previously noted X-ray counterparts. In addition, we identify 295 NIR variables, about half of which are expected to be pre-main-sequence stars. With the more complete sample, we estimate a total population in the Chandra field of 5700-7500 cluster members down to 0.08 M☉ (assuming a universal initial mass function) with a completeness limit at 0.5 M☉. A decrease in stellar X-ray luminosities is noted relative to other younger clusters. However, within the cluster, there is little variation in the distribution of X-ray luminosities for ages less than 5 Myr. The X-ray spectral hardness for B stars may be useful for distinguishing between early-B stars with X-rays generated in stellar winds and B-star systems with X-rays from a pre-main-sequence companion (>35% of B stars). A small fraction of catalog members have unusually high X-ray median energies or reddened NIR colors, which might be explained by absorption from thick or edge-on disks or being background field stars.
© 2017. The American Astronomical Society. All rights reserved.
open clusters and associations: individual: NGC 6231 - stars: formation - stars: massive - stars: pre-main sequence - stars: variables: T Tauri, Herbig Ae/Be - X-rays: stars - X-rays: stars
VizieR on-line data:
<Available at CDS (J/AJ/154/87): table1.dat table3.dat table4.dat table5.dat>
Table 3: CXOVVV JHHMMSS.ss+DDMMSS.s N=2148.
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