主讲人简介：

庞晓莹

Biography:
1. 2019-11 until the present, Xi'an Jiaotong Liverpool University, School of Science, Physics department, assistant professor
2. 2013-10 to 2019-11, Shanghai Institute of Technology, School of Science, Lecturer.
3. 2012-9 to 2013-9, National Astronomical Observatory of China, postdoc research, working with Prof. Rainer Spurzem on NBODY simulations of star clusters.

Education:
1. 2008-9 to 2012-5, Heidelberg University, Astronomy, P.h.D: star cluster evolution based on HST data.
2. 2005-9 to 2018-6, Shanghai Normal University, Master.

讲座内容简介：

疏散星团形成于银盘，瓦解之后成为场星的贡献者，是银盘的形成与演化的有效探针。疏散星团的瓦解是内部动力学过程和外部潮汐力共同作用的结果，最终导致星团的三维形态发生巨大改变。以太阳近邻区500pc内的疏散星团为研究对象，结合Gaia EDR3和高精度视向速度观测数据(空间位置、自行、视向速度)，使用自适应神经网络机器学习方法在五维参数(三维空间位置+二维自行)空间中判定星团成员。该方法在寻找低密度、空间延展的潮汐臂时更高效。此算法同时也认证了恒星聚群的分层结构。通过成员星的空间分布，构建疏散星团的三维形态，并用椭球体模型对形态进行量化。在我们十几疏散星团样本中，大银盘的潮汐作用已经影响星团形态，部分星团的拉伸方向与银道面平行。通过恒星的三维速度分析疏散星团的动力学状态，发现大部分星团（其中包括了双星团和拥有分层结构的恒星结构）都在膨胀，处于过维里状态。年轻星团NGC2232也处于气体耗散后的膨胀状态，正在经历重新维里化过程。同时运行NBODY多体数值模拟星团的演化，加入气体耗散，与观测星团性质进行比较。发现质量较大的星团（>250太阳质量）符合瞬时耗散模型，质量小的星团（<250太阳质量）更接近绝对耗散模型。其中，年纪最轻的恒星聚群的膨胀率最高。一个可能的机制是超新星把气体吹散，抑制了恒星形成。NBODY数值模拟预言该聚群的分层结构在未来100Myr内持续膨胀，直到完全瓦解。

Abstract:

Open clusters are formed in the Galactic disk and will contribute to field stars after the disruption. They are good probes for the formation and evolution of the disk. The disruption of open clusters is a consequence of internal and external dynamical processes, which will lead to a dramatic change in the 3D morphology of open clusters. We study a dozen open clusters, plus a cluster pair and a stellar complex within 500 pc in the solar neighborhood based on the data from Gaia EDR3, we determine members of open clusters in 5D parameter space (3D spatial positions + 2D proper motions) via the self-adapted unsupervised learning algorithms based on an artificial neural network, which is advantageous at identifying low density and extended tidal structures. The hierarchical structures of the stellar complex are also disentangled via the same algorithm. Through the spatial positions of member stars, we will establish the 3D morphology of open clusters, and do statistical quantification and analysis of the morphology by parametrization of an ellipsoid model. The dynamical state of open clusters is investigated with 3D velocities and velocity dispersions. Most clusters in our samples are supervirial and expanding after gas expulsion (including the cluster pair and the hierarchical stellar complex), except for one cluster NGC 2232 that is probably undergoing revirialization. N-body models of rapid gas expulsion with an SFE of ≈ 1/3 are consistent with clusters more massive than 250 M⊙, while clusters less massive than 250 M⊙ tend to agree with adiabatic gas expulsion models. The expansion rate in the youngest stellar complex is the most significant. We propose that supernova plays a role of quenching star formation in its hierarchical structures, which will keep expanding for the future 100 Myr and become unbound according to our simulation results.