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Gaia DR2 provides an unprecedented sample of stars with full 3D position and 3D velocity measurements, creating the need for a self-consistent means of discovering and characterising moving groups or associations which are detectable as phase-space over densities. This is a critical step in piecing together the jigsaw puzzle that is the recent (<200 Myr) star formation history of our solar neighbourhood (<500 pc) which will not only help answer current star formation questions, but also promises to assign a precise age to all nearby, young stars. In this talk I will present Chronostar, a new Bayesian analysis tool that meets this need. Chronostar uses the Expectation-Maximisation algorithm to remove the circular dependency between association membership lists and the fits to their phase-space distributions. I will present on Chronostar’s successful independent (re)discovery of the Beta Pictoris Moving Group, as well as preliminary results on the decomposition of the Scorpius Centaurus OB association. Sco-Cen has a complex formation history (with ages spanning from 3 Myr to 20 Myr) which has resulted in kinematic substructure that, if untangled, would provide insight into how this (and other) association(s) formed. |
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