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The Dynamics, Structure, and Fate of a Young Cluster during Gas Dispersal: Hectoschelle, Chandra, Spitzer, and Gaia Observations of Cep OB3b

The Dynamics, Structure, and Fate of a Young Cluster during Gas Dispersal: Hectoschelle, Chandra, Spitzer, and Gaia Observations of Cep OB3b Thumbnail


Abstract

We present a study of the kinematics and structure of the Cep OB3b cluster based on new spectra obtained with the Hectoschelle spectrograph on the MMT and data from Spitzer, Chandra, and Gaia. At a distance of 819 +/- 16 pc, Cep OB3b is one of the closest examples of a young (similar to 3-5 Myr), large (similar to 3000 total members) cluster at the late stages of gas dispersal. The cluster is broken into two subclusters surrounded by a lower density halo. We fit the empirical density law of King to each subcluster to constrain their sizes and structure. The richer eastern subcluster has circular symmetry, a modest central density, and lacks molecular gas toward its core, suggesting it has undergone expansion due to gas dispersal. In contrast, the western subcluster deviates from circular symmetry, has a smaller core size, and contains significant molecular gas near its core, suggesting that it is in an earlier phase of gas dispersal. We present posterior probability distributions for the velocity dispersions from the Hectoschelle spectra. The east will continue to expand and likely form a bound cluster with similar to 35% of stars remaining. The west is undergoing slower gas dispersal and will potentially form a bound cluster with similar to 75% of stars remaining. If the halo dissipates, this will leave two independent clusters with similar to 300 members; proper motions suggest that the two subcluster are not bound to each other.

Acceptance Date Nov 6, 2019
Publication Date Jan 20, 2019
Publicly Available Date Mar 29, 2024
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
DOI https://doi.org/10.3847/1538-4357/aaf4c1
Keywords open clusters and associations, CEP OB3b, stars, formation, kinematics and dynamics, pre-main sequence, techniques, radial velocities
Publisher URL https://doi.org/10.3847/1538-4357/aaf4c1

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