2024ApJ...975...99K

Young associations record complete histories of star-forming events through their demographics and dynamics, and Gaia has greatly expanded our knowledge of these associations. We present the first structural and dynamical overview study of the Cep-Her Complex, which has recently emerged as the largest stellar population within 500 pc that still lacks substantial follow-up. We reveal that Cep-Her is not a singular association, but rather an amalgam of four, consisting of the older (τ > 100 Myr) open cluster Roslund 6, in addition to three dynamically coherent and highly substructured young associations that we focus on: Orpheus (25-40 Myr), Cinyras (28-43 Myr), and Cupavo (54-80 Myr). With 9552 ± 960 stars in Orpheus, 3872 ± 455 stars in Cinyras, and 8794 ± 1827 stars in Cupavo, all three are among the largest young associations within 500 pc, rivalling major associations like Sco-Cen. Our novel view of the ages and dynamics of these associations reveals evidence for sequential star formation in Cinyras, in addition to a multiorigin pattern of stellar dispersal in Orpheus that may hint to the presence of multiple clouds at formation. Dynamical simulations indicate that, while some embedded open clusters and central components of these associations are converging, they likely lack the mass necessary to capture one another and undergo hierarchical cluster assembly. Our results provide our first view of the complex star-forming environments that gave rise to the associations of Cep-Her, which will serve as important laboratories for future studies of star and planet formation.