SIRIUS项目：恒星形成过程中原初双星的动力学演化
SIRIUS Project: Dynamical Evolution of Primordial Binaries during Star Cluster Formation
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中文总结 AI 辅助
SIRIUS项目通过自洽N体/光滑粒子流体动力学模拟对比三种恒星形成模型，发现原初双星显著影响最终双星属性但对星团结构影响有限，密近双星需在恒星形成阶段形成以匹配观测结果。
中文摘要 AI 辅助
双星族群与恒星形成过程密切相关，但其原初属性会被其诞生星团内后续的动力学相互作用改变。本研究旨在阐明不同的原初双星族群如何影响正在形成的恒星星团的多重性和全局结构的演化。我们采用自洽N体/光滑粒子流体动力学模拟研究恒星形成过程中原初双星的动力学演化，该模拟追踪分子云坍缩为恒星星团的过程。我们系统对比三种恒星形成模型：密近双星（CB）、宽双星（WB）和单星（SS）形成模型。在CB和WB模型中，多重性分数因动力学相互作用随时间降低，其中WB模型的分数降至与SS模型相当的水平；所有模型中大质量恒星的多重性分数均较高，而仅CB模型显示低质量恒星有相对较高的分数。由于假设形成等质量双星，CB和WB模型的质量比分布在q=1处出现过剩，而SS模型无明显趋势。频繁的少体相互作用在星团内外产生不同的恒星族群：星团内部的多重性分数系统性更高，外部的质量函数斜率更浅；最终所有模型的恒星密度轮廓大致相似。原初双星族群显著影响最终双星属性，但对其宿主星团结构的影响有限。我们的结果表明，密近双星需要在恒星形成阶段形成，才能重现观测到的低质量恒星多重性分数和等质量双星的过剩现象。
英文摘要
Binary populations are closely linked to the star formation process; however, their primordial properties can be changed by subsequent dynamical interactions within their natal clusters. The aim of this study is to clarify how different primordial binary populations affect the evolution of multiplicity and the global structure of forming star clusters. We investigate the dynamical evolution of primordial binaries during star cluster formation using self-consistent Nbody/smoothed particle hydrodynamics simulations that follow the collapse of a molecular cloud to a star cluster. We systematically compare three star formation models: close binary (CB), wide binary (WB), and single star (SS) formation model. In CB and WB models, the multiplicity fraction decreases with time due to dynamical interactions. In particular, the fraction in the WB model drops to a level comparable to that in the SS model. The multiplicity fraction of high-mass stars is similarly high in all models, whereas only the CB model shows a relatively high fraction for low-mass stars. Due to the assumption of equal-mass binary formation, the CB and WB models exhibit an excess at q= 1 in the mass-ratio distribution, while the SS model has no clear trend. Frequent few-body interactions generate distinct stellar populations inside and outside the cluster: the multiplicity fraction within the cluster is systematically higher, while mass functions in the outside have a shallower slope. Finally, stellar density profiles in the clusters are broadly similar among all models. The primordial binary population significantly affects the final binary properties, while having only a limited impact on their host cluster structures. Our results suggest that close binaries need to form at the star formation stage to reproduce the observed multiplicity fraction of low-mass stars and the excess of equal-mass binaries.
