AI 中文总结
研究疏散星团NGC 3532中蓝色主序星的起源，通过14次NBODY7模拟不同初始条件，发现虽该星团有不少蓝色主序星成员，但因低密度和质量损失，模拟产生合并产物少，恒星合并非主要形成通道，角动量损失机制更有可能。
AI 中文摘要
在年轻和中年恒星团的色-星等图中观测到的主序转折延伸、主序延伸和主序分裂，现在被广泛解释为其中等质量（1.5-1.8M⊙）成员恒星旋转速率分布的结果。然而，占据蓝色主序（bMS）的缓慢旋转恒星群体的起源仍然不确定，恒星合并被认为是一种可能的途径。我们研究恒星合并是否能解释330Myr的银河系疏散星团NGC 3532中观测到的bMS群体。我们进行了14次直接的NBODY7模拟，涵盖不同的初始星团质量、半径、双星比例和双星轨道分布。模拟被选择为在观测不确定性范围内再现NGC 3532的当前属性，从而使我们能够估计其中等质量主序（MS）成员中合并产物的预期数量。该星团在中等质量MS群体中有约37%的bMS成员，它们主要是缓慢旋转者。尽管有如此大的bMS群体，但由于星团的低密度和其演化过程中的大量质量损失，我们的模拟只产生了少数MS-MS合并产物。恒星合并不太可能是NGC 3532和其他疏散星团中观测到的缓慢旋转bMS群体的主要形成通道。我们的结果反而支持在零龄主序之前或之后不久起作用的角动量损失机制，例如主序前恒星-盘相互作用或低质量比双星中的潮汐同步。
英文摘要
Extended main-sequence turnoffs, extended main sequences, and split main sequences observed in the colour-magnitude diagrams of young and intermediate-age star clusters are now widely interpreted as the consequence of a distribution of stellar rotation rates among their intermediate-mass (1.5-1.8~M$_\odot$) members. However, the origin of the slowly rotating population that occupies the blue main sequence (bMS) remains uncertain, and stellar mergers have been proposed as one possible pathway. We investigate whether stellar mergers can account for the observed bMS population in the 330-Myr Galactic open cluster NGC 3532. We perform fourteen direct NBODY7 simulations spanning different initial cluster masses, radii, binary fractions, and binary orbital distributions. The simulations are selected to reproduce the present-day properties of NGC 3532 within the observational uncertainties, allowing us to estimate the expected number of merger products among its intermediate-mass main-sequence (MS) members. The cluster hosts $\approx 37\%$ bMS members among its intermediate-mass MS population, which are predominantly slow rotators. Despite this large bMS population, our simulations produce only a handful of MS-MS merger products, due to the cluster's low density and substantial mass loss during its evolution. Stellar mergers are unlikely to be the dominant formation channel for the observed slowly rotating bMS population in NGC 3532 and other disperse open clusters. Our results instead favour angular-momentum loss mechanisms operating before or shortly after the zero-age main sequence, such as pre-main-sequence star-disk interactions or tidal synchronization in low-mass ratio binaries.
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