(Abridged) The dynamical ejection of stars from star clusters affects the shape of the stellar mass function (MF) in these clusters, because the escape probability of a star depends on its mass. The objective of this paper is to provide and to apply a simple physical model for the evolution of the MF in star clusters for a large range of the parameter space. The model is derived from the basic principles of two-body encounters and energy considerations. It is independent of the adopted mass loss rate or initial mass function (IMF), and contains stellar evolution, stellar remnant retention, dynamical dissolution in a tidal field, and mass segregation. It is found that the MF evolution in star clusters depends on the disruption time, remnant retention fraction, initial-final stellar mass relation, and IMF. Low-mass stars are preferentially ejected after t~400 Myr. Before that time, masses around 15-20% of the maximum stellar mass are lost. The degree of low-mass star depletion grows for increasing disruption times, but can be quenched when the retained fraction of massive remnants is large. The highly depleted MFs of certain Galactic globular clusters are explained by the enhanced low-mass star depletion that occurs for low remnant retention fractions. Unless the retention fraction is exceptionally large, dynamical evolution always decreases the mass-to-light ratio. The modeled evolution of the MF is consistent with N-body simulations when adopting identical boundary conditions. However, it is found that the results from N-body simulations only hold for their specific boundary conditions and should not be generalised to all clusters. It is concluded that the model provides an efficient method do understand the evolution of the stellar MF in star clusters under widely varying conditions.
The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters
迄今为止，基于恒星演化模型，讨论了球状星团（GC）中多恒星星族（MSP）形成的多种可能性，包括渐近巨星分支星、快速旋转主序星、超大质量主序星和质量转移的大质量双星。但是，自洽的，非常年轻的GC的动力学模拟通常不被考虑。在这项工作中，我们执行直接$N$体模拟这样的系统总质量高达$3.2\times10^5$ M $_\odot$，考虑到观测约束的原始双星性质，并讨论恒星合并驱动的双星恒星演化和动力学演化的GC。在富含双星的星团中，恒星合并的发生率显著提高，因此由合并驱动的喷射/风污染的气体形成的恒星将出现MSPs。因此，我们强调恒星合并可能是将MSP形成与星团动力学联系起来的重要过程，并且多个MSP形成通道可以自然地协同工作。这里研究的情况下，也考虑到可能的头重脚轻的国际货币基金组织，可能是特别相关的解释高质量分数的MSP（质量预算问题）和没有MSP的年轻和低质量的星团。
The impact of stellar rotation on the morphology of star cluster colour-magnitude diagrams is widely acknowledged. However, the physics driving the distribution of the equatorial rotation velocities of main-sequence turn-off (MSTO) stars is as yet poorly understood. Using Gaia Data Release 2 photometry and new Southern African Large Telescope medium-resolution spectroscopy, we analyse the intermediate-age ($\sim1\,$Gyr-old) Galactic open clusters NGC 3960, NGC 6134 and IC 4756 and develop a novel method to derive their stellar rotation distributions based on SYCLIST stellar rotation models. Co…
Measuring the distribution of stellar spin axis orientations in a coeval group of stars probes the physical processes underlying the stars' formation. In this paper, we use spectro-photometric observations of the open cluster NGC 2516 to determine the degree of spin alignment among its stars. We combine TESS light curves, ground-based spectroscopy from the Gaia-ESO and GALAH surveys, broad-band stellar magnitudes from several surveys, and Gaia astrometry to measure 33 stellar inclinations and quantify overall cluster rotation. Our measurements suggest that stellar spins in this cluster are iso…
We present a large suite of MHD simulations of turbulent, star-forming giant molecular clouds(GMCs) with stellar feedback, extending previous work by simulating 10 different random realizations for each point in the parameter space of cloud mass and size. It is found that oncethe clouds disperse due to stellar feedback, both self-gravitating star clusters and unbound stars generally remain, which arise from the same underlying continuum of substructured stellar density, ie. the hierarchical cluster formation scenario. The fraction of stars that are born within gravitationally-bound star cluste…
No evidence for multiple stellar populations in the low-mass Galactic globular cluster E 3
多重恒星星族是银河系球状星团中普遍存在的现象。尽管产生新一代恒星的浓缩物质的来源仍然不清楚，但自我浓缩很可能只在质量足以保留这种浓缩物质的星团中才是可行的。利用SOAR/Goodman多目标光谱技术，分析了低质量（M~1.4 x 10^4 M_sun）球状星团E3中23颗红巨星支星的蓝CN吸收特征，寻找了该星团中的多星族.我们发现，CN丰度并不呈现典型的双峰行为中看到的集群托管多恒星星族，而是一个单峰分布，表明存在一个真正的单一恒星星族，或丰富的水平远远低于集群，从高分辨率光谱显示两个人口的证据。E3将是第一个真正的银河系古老的球状星团，没有发现自我富集的迹象。
Understanding the formation of stellar clusters requires following the interplay between gas and newly formed stars accurately. We therefore couple the magnetohydrodynamics code FLASH to the N-body code ph4 and the stellar evolution code SeBa using the Astrophysical Multipurpose Software Environment (AMUSE) to model stellar dynamics, evolution, and collisional N-body dynamics and the formation of binary and higher-order multiple systems, while implementing stellar feedback in the form of radiation, stellar winds and supernovae in FLASH. We here describe the algorithms used for each of these pr…
We highlight the importance of eclipsing double-line binaries in our understanding on star formation and evolution. We review the recent discoveries of low-mass and sub-stellar eclipsing binaries belonging to star-forming regions, open clusters, and globular clusters identified by ground-based surveys and space missions with high-resolution spectroscopic follow-up. These discoveries provide benchmark systems with known distances, metallicities, and ages to calibrate masses and radii predicted by state-of-the-art evolutionary models to a few percent. We report their density and discuss current …
The emergence of the galactic stellar mass function from a non-universal IMF in clusters
研究了单代星系质量函数（SGMF）如何依赖于星团初始恒星质量函数（IMF）的变化。我们表明，集群到集群的IMF的变化导致多组分SGMF在一个给定的质量范围内的每个组件可以描述一个不同的幂律函数。我们还表明，分散的$\approx 0.3$ M $_{\odot}$在IMF的特征质量，观察到年轻的银河系星团，导致低质量斜率的SGMF匹配所观察到的银河系恒星质量函数，即使当IMF在低质量端的个别集群是陡峭得多。
Numerous protoplanetary discs show distinct spiral arms features. While possibly caused by a range of processes, detailed pattern analysis points at close stellar flybys as cause for some of them. Surprisingly, these discs reside in young low-mass clusters, where close stellar flybys are expected to be rare. This fact motivated us to take a fresh look at the frequency of close flybys in low-mass clusters. In the solar neighbourhood, low-mass clusters have smaller half-mass radii than their more massive counterparts. We show that this observational fact results in the mean and central stellar d…
A recent study suggests that the observed multiplicity of super-Earth (SE) systems is correlated with stellar overdensities: field stars in high phase-space density environments have an excess of single-planet systems compared to stars in low density fields. This correlation is puzzling as stellar clustering is expected to influence mostly the outer part of planetary systems. Here we examine the possibility that stellar flybys indirectly excite the mutual inclinations of initially coplanar SEs, breaking their co-transiting geometry. We propose that flybys excite the inclinations of exterior su…
Massive stars reveal variations of the stellar initial mass function in the Milky Way stellar clusters
我们调查恒星初始质量函数（IMF）是否是普遍的，或者它是否在银河系中的年轻星团之间有显着差异。我们提出了一种方法来揭示的变化范围的参数，描述的年轻星系团的人口的IMF的形状。这些参数分别是低恒星质量区和高恒星质量区的斜率$γ$和$Γ$，以及特征质量$M_{ch}$。该方法完全依赖于高质量的内容的集群，但能够产生的信息的分布参数，描述IMF在整个恒星质量范围内。这是通过将最近的银河系星系团目录中单个和孤独的大质量O星的分数与用IMF参数的各种分布函数构建的模拟星系团库进行比较来实现的。的合成集群校正的影响的二进制人口，恒星演化，样本不完整，和弹出的O型星。我们的研究结果表明，广泛的分布的IMF参数，以再现银河系星团中的单个和孤独的O星的分数。它们也不支持星团质量与最大恒星质量关系的存在。我们提出了一个概率公式的IMF，其中的IMF的参数被描述为高斯分布函数围绕$γ=0.91$，$Γ=1.37$，和$M_{ch}=0.41$ M $_{\odot}$，并与分散的$σ_γ=0.25$，$σ_Γ=0.60$，和$σ_{M_{ch}}=0.27$ M $_{\odot}$在这些值。
First results on the cluster galaxy population from the Subaru Hyper Suprime-Cam survey. III. Brightest cluster galaxies, stellar mass distribution, and active galaxies
According to the classical view of globular clusters, stars inside globular clusters are evolved from the same giant molecular cloud. Then their stars' chemical compositions must be the same. But recent photometric and spectroscopic studies of globular clusters reveal the presence of more-than-one stellar populations inside globular clusters. This finding challenges our classical view of globular clusters. In this work, we investigated the possibility of solving multiple stellar populations problem in globular clusters using dark matter assumptions. We showed that the presence of dark matter i…
Observations of an ancient stellar stream provide the first evidence of a vanished population of extremely metal-poor stellar clusters. Their remnants might reveal how the early assembly of the Milky Way proceeded.
Stellar cluster formation in a Milky Way-sized galaxy at z>4 -- II. A hybrid formation scenario for the nuclear star cluster and its connection to the nuclear stellar ring
