低芯密度球状星团NGC6144和E3的X射线和光学研究
X-ray and Optical Study of Low Core Density Globular Clusters NGC6144 and E3
摘要：
本文报道了钱德拉X射线天文台和哈勃空间望远镜对两个低核密度球状星团NGC 6144和E3的观测结果。通过比较半质量半径内和半质量半径外的X射线源数量，发现NGC 6144半质量半径内有6个X射线源，其中4个预计为背景源; E3半质量半径内也有3个X射线源，其中3个预计为背景源。因此，我们不能排除我们所有的来源都是背景来源。然而，结合X射线和光学观测的结果，我们发现NGC 6144中的1-2个源和E3中的1个源可能是激变变星，而NGC 6144中的1个源可能是活动双星。钱德拉和HST发现的NGC 6144和E3中微弱X射线源的数量高于基于碰撞频率的预测，但更接近基于质量的预测。我们的观测结果强烈地表明，NGC 6144和E3中的致密双星系统是原始起源的。
英文摘要：
We report on the Chandra X-ray Observatory and Hubble Space Telescope observation of two low core density globular clusters, NGC6144 and E3. By comparing the number of X-ray sources inside the half-mass radius to those outside, we found 6 X-ray sources within the half-mass radius of NGC6144, among which 4 are expected to be background sources; 3 X-ray sources are also found within the half-mass radius of E3, of which 3 is expected to be background source. Therefore, we cannot exclude that all our sources are background sources. However, combining the results from X-ray and optical observations, we found that 1-2 sources in NGC6144 and 1 source in E3 are likely to be cataclysmic variables and that 1 source in NGC6144 is an active binary, based on the X-ray and optical properties. The number of faint X-ray sources in NGC6144 and E3 found with Chandra and HST is higher than a prediction based on collision frequency, but is closer to that based on mass. Our observations strongly suggest that the compact binary systems in NGC6144 and E3 are primordial in origin.
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