动力学滤波的证据：NGC 6791幸存核心中的高双星比例、硬双星过剩及未分辨三星系统
Evidence for Dynamical Filtering: High Binary Fraction, Hard-binary Excess, and Unresolved Triples in the Surviving Core of NGC 6791
AI总结：
通过对NGC 6791的测光分析，发现其主序星伴星比例高、硬双星过剩且存在未分辨多星系统，支持该星团是经动力学演化的残余星团的结论。
AI中文摘要：
我们利用盖亚数据发布3（Gaia Data Release 3）数据，对年老、富金属疏散星团（OC）NGC 6791的主序星（MS）族进行了深度测光分析。在改正 differential reddening（差分红化）后，我们采用贝叶斯模型比较检验恒星自转是否能解释观测到的主序星展宽，结果强烈反对以自转为主导的解释。因此我们推断，未分辨的多星系统是测光偏移的主要贡献者。我们推导得到质量比q≳0.5的系统的高q伴星比例为54.3%±2.8%，显著高于大多数疏散星团和场星的典型值。推导得到的偏移分布与平坦的质量比分布不一致，反而呈现出高质量比（q~0.8–1.0）的过剩，暗示在动力学演化环境中硬双星的优先存活。我们还识别出一群位于等质量双星极限之上（ΔG>0.75星等）的恒星，仅用普通主序双星难以解释，可合理解释为候选未分辨三星或更高阶多星系统。柯尔莫哥洛夫-斯米尔诺夫检验结合蒙特卡洛标签洗牌实验显示，观测视场内单星与双星/多星族的投影径向分布无统计学显著差异。综合来看，这些结果符合NGC 6791曾是质量更大的星团、经动力学演化后形成当前内部残余的图景。
英文摘要：
We present a deep photometric analysis of the main-sequence (MS) population in the old, metal-rich open cluster (OC) NGC 6791 using Gaia Data Release 3 data. After correcting for differential reddening, we use the Bayesian model comparison to test whether stellar rotation can account for the observed MS broadening and find that a rotation-dominated interpretation is strongly disfavored. We therefore infer that unresolved multiplicity is the primary contributor to the photometric offsets. We derive a high-q companion fraction of $54.3\% \pm 2.8\%$ for systems with $q \gtrsim 0.5$, significantly higher than typical values reported for most OCs and the field. The inferred offset distribution is not consistent with a flat mass-ratio distribution but instead shows an excess toward high mass ratios ($q \sim 0.8$--$1.0$), suggestive of preferential survival of hard binaries in a dynamically evolved environment. We also identify a population of stars lying above the equal-mass binary limit ($ΔG > 0.75$ mag), which is difficult to explain with ordinary MS binaries alone and is plausibly interpreted as candidate unresolved triple or higher-order multiple systems. A Kolmogorov--Smirnov test, together with Monte Carlo label-shuffling experiments, shows no statistically significant difference between the projected radial distributions of the single-star and binary/multiple populations within the observed field. Taken together, these results are consistent with the picture that NGC 6791 is the dynamically processed inner remnant of a once more massive cluster.
