2020/06/27 by Beomdu Lim, Jongsuk Hong, Hyeong-Sik Yun +7
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Computer science #Context (archaeology) #Galaxy #Geology #Milky Way #Physics #Population #Star cluster #Star formation #Stars #Stellar kinematics #Stellar population #Stellar, planetary, and galactic studies #Velocity dispersion #Virial theorem #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/aba0a3
12 pages, 4 figures, 2 tables, accepted for publication in the Astrophysical Journal
arxiv created 2020/06/27 · openalex publication_date 2020/08/01 · arxiv updated 2020/08/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Abstract Stellar kinematics provides the key to understanding the formation process and dynamical evolution of stellar systems. Here, we present a kinematic study of the massive star-forming region (SFR) W4 in the Cassiopeia OB6 association using the Gaia Data Release 2 and high-resolution optical spectra. This SFR is composed of a core cluster (IC 1805) and a stellar population distributed over 20 pc, which is a typical structural feature found in many OB associations. According to a classical model, this structural feature can be understood in the context of the dynamical evolution of a star cluster. The core-extended structure exhibits internally different kinematic properties. Stars in the core have an almost isotropic motion, and they appear to reach virial equilibrium given their velocity dispersion (0.9 ± 0.3 km s −1 ) comparable to that in a virial state (∼0.8 km s −1 ). On the other hand, the distributed population shows a clear pattern of radial expansion. From the N -body simulation for the dynamical evolution of a model cluster in subvirial state, we reproduce the observed structure and kinematics of stars. This model cluster experiences collapse for the first 2 Myr. Some members begin to radially escape from the cluster after the initial collapse, eventually forming a distributed population. The internal structure and kinematics of the model cluster appear similar to those of W4. Our results support the idea that the stellar population distributed over 20 pc in W4 originate from the dynamical evolution of IC 1805.