Context: The shape of the stellar initial mass function (IMF) of a star cluster near its upper mass limit is a focal topic of investigation as it determines the high mass stellar content and hence the dynamics of the cluster at its embedded phase as well as during its young gas-free phase. The massive stellar content of a young cluster, however, can be substantially modified due to the dynamical ejections of the massive stars so that the present-day high-mass stellar mass function (hereafter MF) can be different than that with which the cluster is born. Aims: In the present study, we provide a preliminary estimate of this evolution of the high-mass IMF of a young cluster due to early ejections of massive stars, using the Large Magellanic Cloud massive, young cluster R136 as an example. Methods: To that end, we utilize the results of the state-of-the-art calculations by Banerjee, Kroupa & Oh (2012) comprising direct N-body computations of realistic, binary-rich, mass-segregated models of R136. In particular, these calculations provide the ejection fraction of stars as a function of stellar mass. Results: We find that if the measured IMF of R136 is granted to be canonical, as observations indicate, then the "true" high-mass IMF of R136 at its birth must be at least moderately top-heavy when corrected for the dynamical escape of massive stars. Conclusions: The top-heaviness of the true high-mass IMF over the observationally determined one is a general feature of massive, young clusters where the dynamical ejection of massive stars is efficient. We discuss its implications and possible improvements over our current estimate.
Older Ages for 23 Pre-Main Sequence Stars in Upper Scorpius Using Dynamical Mass-Constrained Stellar Evolutionary Models
University of Arizona（亚利桑那大学）；National Radio Astronomy Observatory（国家射电天文台）；California Institute of Technology（加州理工学院）；National Taiwan Normal University（台湾师范大学）
Orbit-based structural decomposition and stellar population recovery for edge-on barred galaxies
Westlake University（西湖大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Villanova University（维拉诺瓦大学）；University of Michigan（密歇根大学）；University of Vienna（维也纳大学）；Cardiff University（卡迪夫大学）
The most massive stars dominate the chemical enrichment, mechanical and radiative feedback, and energy budget of their host environments. Yet how massive stars initially form and how they evolve throughout their lives is ambiguous. The mass loss of the most massive stars remains a key unknown in stellar physics, with consequences for stellar feedback and populations. In this work, we compare grids of very massive star (VMS) models with masses ranging from 80-1000Msun, for a range of input physics. We include enhanced winds close to the Eddington limit as a comparison to standard O-star winds, …
Line-driven ablation of circumstellar discs: IV. The role of disc ablation in massive star formation and its contribution to the stellar upper mass limit
Strong gravitational lensing can provide accurate measurements of the stellar mass-to-light ratio $Υ$ in low-redshift ($z$ $\lesssim$ 0.05) early-type galaxies, and hence probe for possible variations in the stellar initial mass function (IMF). However, true multiple imaging lens systems are rare, hindering the construction of large nearby lens samples. Here, we present a method to derive upper limits on $Υ$ in galaxies with single close-projected background sources, where no counter-image is detected, down to some relative flux limit. We present a proof-of-principle application to three galax…
A method to deconvolve stellar rotational velocities III. The probability distribution function via Maximum Likelihood utilizing Finite Distribution Mixtures
We aim to study spatial and kinematic substructures of the region encompassed by Upper Scorpius and Ophiuchus star-forming regions, determining dynamical traceback ages and studying the star formation history of the complex. We identified seven different groups in this region. Four groups (nu Sco, beta Sco, sigma Sco and delta Sco) are part of Upper Scorpius, two groups (rho Oph and alpha Sco) are in Ophiuchus, and another group (pi Sco) is a nearby young population. We found an age gradient from the rho Oph group (the youngest) to the delta Sco group (<~5 Myr), showing that star formation was…
Dust masses of disks around 8 Brown Dwarfs and Very Low-Mass Stars in Upper Sco OB1 and Ophiuchus
本文介绍了ALMA波段7对天蝎座OB 1上的7个天体和蛇夫座的1颗M3星的尘埃和CO气体的观测结果，这些天体的光谱类型在M5.5和M7.5之间。我们检测到未解决的连续发射，但一个源，和$^{12}$ CO J=3-2线在两个源。我们约束这些系统的尘埃和气体的含量使用网格的模型计算的辐射转移代码MCFOST，并找到磁盘尘埃质量之间的0.1和1 M $_\oplus$，这表明恒星质量/磁盘质量的相关性可以外推的质量低至0.05 M $_\odot$的褐矮星。我们在上斯科探测到CO排放的一个圆盘，2 MASS J15555600，也是具有最温暖的内部圆盘的圆盘，如其H - [4.5]光度颜色所示。使用我们的辐射转移网格，我们扩展恒星光度和质量平均磁盘尘埃温度之间的相关性最初来自恒星质量的物体到棕矮星制度的$\langle T_{dust} \rangle \approx 22 (L_{*} /L_{\odot})^{0.16} K$，适用于光谱类型的M5和以后。这比早期光谱型天体的关系略浅，产生较温暖的低质量盘。两种处方在0.27 L $_\odot$交叉，对应于0.1和0.2 M $_\odot$之间的质量，取决于年龄。
On the derivation of dynamical masses of the stellar clusters in the circumnuclear region of NGC2903
（摘要）利用高分辨光谱学方法，在蓝波段和远红波段，计算了四个环核恒星形成区（CNSFR）和螺旋星系NGC 2903的核心的气体和恒星速度色散。恒星的速度分散已获得从CaII三重态（CaT）线在8494，8542，8662 A，使用互相关技术，而气体的速度分散已被测量高斯拟合的Hbeta线。CNSFR的直径约为100至150 pc，在哈勃太空望远镜的分辨率下显示出复杂的结构，有大量的子团，线性直径在3至8 pc之间。它们的恒星速度色散范围从39到67公里/秒。这些数值，再加上在档案HST图像上测量的大小，得出单个星团的动力学质量上限在1.8 x 10 $^6$ M $_\odot$和8.7 x 10 $^6$ M之间，整个CNSFR的质量上限在4.9 x 10 $^6$ M和4.3 x 10 $^7$ M $_\odot$之间。...
