Young Stellar Populations in the Solar Neighborhood

Young associations provide a record of recent star formation from which the origins of stellar populations can be established and mapped. Using Gaia DR2 astrometric and photometric measurements, combined with a model stellar population, we have identified over 30000 candidate young stars within ~300 pc, tracing an expansive network of nearby associations and clusters. Applying the HDBSCAN clustering algorithm to this data set, we identify 27 groups at the top level, some of which, such as the Sco-Cen, Taurus, Orion, and Perseus associations fragment into identifiable substructure at smaller scales, including extensions that go far beyond the known extent of each of the aforementioned associations, sometimes by up to 100 pc. Isochronal ages computed for the substructures reveal large-scale patterns in the star formation histories for many of the nearby associations we identify, including broad stellar populations in Taurus with ages upwards of 30 Myr, and star formation bursts in Perseus that pre-date the current star-formation activity by about 10 Myr. In Sco-Cen, we find large-scale age gradients that converge on an arc of 20-25 Myr old stars, a feature that appears to mark the earliest source of star formation in the association. In this work, we outline the results from our analysis of this nearby population of young stars, and present some features that merit further investigation.