The Structure of the Young Star Cluster NGC 6231. I. Stellar Population

Michael A. Kuhn, Nicolás Medina, Konstantin V. Getman, Eric D. Feigelson, Mariusz Gromadzki, Jordanka Borissova, Radostin Kurtev

Research output: Contribution to journalArticle

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Abstract

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 Lactéa (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 (assuming a universal initial mass function) with a completeness limit at 0.5 . 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.

Original languageEnglish (US)
Article number87
JournalAstronomical Journal
Volume154
Issue number3
DOIs
StatePublished - Sep 2017

Fingerprint

star clusters
B stars
catalogs
near infrared
x rays
luminosity
early stars
census
pre-main sequence stars
infrared photometry
O stars
star distribution
young
stellar winds
completeness
hardness
color
stars
estimates
energy

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kuhn, Michael A. ; Medina, Nicolás ; Getman, Konstantin V. ; Feigelson, Eric D. ; Gromadzki, Mariusz ; Borissova, Jordanka ; Kurtev, Radostin. / The Structure of the Young Star Cluster NGC 6231. I. Stellar Population. In: Astronomical Journal. 2017 ; Vol. 154, No. 3.
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abstract = "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 Lact{\'e}a (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 (assuming a universal initial mass function) with a completeness limit at 0.5 . 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.",
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The Structure of the Young Star Cluster NGC 6231. I. Stellar Population. / Kuhn, Michael A.; Medina, Nicolás; Getman, Konstantin V.; Feigelson, Eric D.; Gromadzki, Mariusz; Borissova, Jordanka; Kurtev, Radostin.

In: Astronomical Journal, Vol. 154, No. 3, 87, 09.2017.

Research output: Contribution to journalArticle

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