An X-Ray Census of Young Stars in the Massive Southern Star-forming Complex NGC 6357
An X-Ray Census of Young Stars in the Massive Southern Star-forming Complex NGC 6357
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DOI：
10.1086/509147
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发表时间：
2006-09
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通讯作者：
Junfeng Wang;L. Townsley;E. Feigelson;K. Getman;P. Broos;G. Garmire;M. Tsujimoto
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文献类型：
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作者：
Junfeng Wang;L. Townsley;E. Feigelson;K. Getman;P. Broos;G. Garmire;M. Tsujimoto
我们提出了第一个高空间分辨率的X射线研究的大质量恒星形成区NGC 6357，在38 KS钱德拉/ACIS观测。在这个巨大的H II区复合体中最明亮的组成部分是大质量的疏散星团Pismis 24。它包含两颗已知最明亮和最蓝的恒星，但研究仍然很少;只有少数光学明亮的恒星成员被识别。我们调查了集群的范围和初始质量函数，并检测到~800 X射线源的极限灵敏度为~1030尔格·秒-1;这提供了第一个可靠的探测丰富的中等质量和低质量的人口这个大规模的集群，增加了已知成员的数量从光学研究的一个因素~50。在NGC 6357中观测到的X射线光度函数的高光度端（log Lh[2-8 keV] ≥ 30.3 ergs s-1）与猎户座星云和仙王座B中观察到的幂律关系明显一致，产生了NGC 6357总星团数量的第一个估计值，是已知猎户座数量的几倍。我们调查的结构的集群，发现小规模的子结构叠加在一个球形集群与6 pc的程度，并讨论其关系的星云形态。确认了长期存在的LX - 10- 7 Lbol O星关联。24颗候选O星和一颗可能的新的被遮蔽的大质量YSO或Wolf-Rayet星星。根据现有的红外测光法（假设年龄约为100万年），许多星团成员被估计为中等质量恒星，但只有少数显示出K波段的过剩。我们报告的第一次检测到的X射线发射从蒸发的气体小球在一个分子柱的尖端，这个源可能是一个B 0-B2原恒星。
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 II 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 - 10-7Lbol 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 B0-B2 protostar.