47 Tucanae的JWST测光与天体测量：恒星/褐矮星过渡处恒星序列的不连续性
JWST photometry and astrometry of 47 Tucanae. Discontinuity in the stellar sequence at the star/brown dwarf transition
AI总结：
基于相隔7个月的JWST NIRCam两历元观测，研究47 Tucanae暗端自行成员，在恒星—褐矮星交界发现主序“kink”，并将其归因于贫氧恒星中CH4吸收的快速出现。
摘要：
利用仅相隔7个月、在两个历元拍摄的球状星团47 Tucanae（或称NGC 104）的JWST近红外相机（NIRCam）图像，我们推导了暗至m_F322W2约27等的自行成员资格。我们在主序极低端、约0.08倍太阳质量处，即在m_F322W2约24等和m_F150W2约25等的星等处，识别出一个引人关注的特征。该特征被称为“kink（扭折）”，其特点是主序斜率出现显著不连续。在具有贫氧化学组成的理论等时线中也可见类似不连续，这与CH4吸收的快速出现有关。因此，我们假设，与主序上部和红巨星支相比，该星团在主序底部附近拥有不成比例地更多的贫氧恒星。我们的结果并未显示出褐矮星光度函数在暗星等处上升的强有力或决定性证据，这与可能受到暗弱红色背景星系影响的先前发现相反。在分析中，我们通过使用自行成员资格来处理这种污染。
英文摘要：
Using JWST Near Infrared Camera (NIRCam) images of the globular cluster 47 Tucanae (or NGC 104), taken at two epochs just 7 months apart, we derived proper-motion membership down to $m_{\rm F322W2} \sim 27$. We identified an intriguing feature at the very low-mass end of the main sequence, around $\sim$ 0.08 solar masses, at magnitudes $m_{\rm F322W2} \sim 24$ and $m_{\rm F150W2} \sim 25$. This feature, dubbed "kink", is characterized by a prominent discontinuity in the slope of the main sequence. A similar discontinuity is seen in theoretical isochrones with oxygen-poor chemistries, related to the rapid onset of CH$_4$ absorption. We therefore hypothesize that the cluster hosts disproportionately more oxygen-poor stars near the bottom of the main sequence compared to the upper main sequence and the red giant branch. Our results show no strong or conclusive evidence of a rise in the brown dwarf luminosity function at faint magnitudes, in contrast to previous findings likely affected by faint red background galaxies. In our analysis, we accounted for this contamination by using proper motion membership.
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