An X-ray census of young stars in the massive southern star-forming complex NGC 6357

Junfeng Wang, Leisa K. Townsley, Eric D. Feigelson, Konstantin V. Getman, Patrick S. Broos, Gordon P. Garmire, Masahiro Tsujimoto

Research output: Contribution to journalArticle

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Abstract

We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H H region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs s-1; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (log Lh[2-8 keV] ≥ 30.3 ergs s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX - 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a BO-B2 protostar.

Original languageEnglish (US)
Pages (from-to)100-127
Number of pages28
JournalAstrophysical Journal, Supplement Series
Volume168
Issue number1
DOIs
StatePublished - Jan 1 2007

Fingerprint

census
stars
erg
x rays
O stars
pillar
luminosity
power law
spatial resolution
Orion nebula
probe
blue stars
infrared photometry
Wolf-Rayet stars
globules
protostars
open clusters
extremely high frequencies
young
substructures

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

@article{7088e07b1bd041ac8130e9351542ecfb,
title = "An X-ray census of young stars in the massive southern star-forming complex NGC 6357",
abstract = "We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H H region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs s-1; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (log Lh[2-8 keV] ≥ 30.3 ergs s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX - 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a BO-B2 protostar.",
author = "Junfeng Wang and Townsley, {Leisa K.} and Feigelson, {Eric D.} and Getman, {Konstantin V.} and Broos, {Patrick S.} and Garmire, {Gordon P.} and Masahiro Tsujimoto",
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An X-ray census of young stars in the massive southern star-forming complex NGC 6357. / Wang, Junfeng; Townsley, Leisa K.; Feigelson, Eric D.; Getman, Konstantin V.; Broos, Patrick S.; Garmire, Gordon P.; Tsujimoto, Masahiro.

In: Astrophysical Journal, Supplement Series, Vol. 168, No. 1, 01.01.2007, p. 100-127.

Research output: Contribution to journalArticle

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T1 - An X-ray census of young stars in the massive southern star-forming complex NGC 6357

AU - Wang, Junfeng

AU - Townsley, Leisa K.

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AU - Garmire, Gordon P.

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N2 - We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H H region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs s-1; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (log Lh[2-8 keV] ≥ 30.3 ergs s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX - 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a BO-B2 protostar.

AB - We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H H region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs s-1; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (log Lh[2-8 keV] ≥ 30.3 ergs s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX - 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a BO-B2 protostar.

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