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Abstract

The Milky Way offers a unique opportunity to study the ‘clumpy-to-smooth’ orbit transition of stars in the Galactic disk: newly born stars are clustered across a wide range of scales, from compact bound objects to ephemeral birth clusterings and loose associations. Subsequently, most groups of stars disperse over time, spreading out in orbit and orbital-phase space and building up the Galactic field population. The age and orbit distribution of such co-natal groups offers the possibility to study on which orbits stars are born, how rapidly these systems disperse, and to what extent the orbit distribution reflects a possible birth from extended molecular gas filaments. Specifically, this thesis shows that with the advent of the powerful Gaia dataset, we can identify stellar groups as small-scale overdensities in orbit and orbital phase space. We explore their distribution and discover that stellar groups are frequently located on similar orbits, aligned at distinct orbital phases. We then develop and apply an isochrone fitting method to derive age estimates of stellar populations, for which we only have a small set of stars initially. We find age-dating ambiguities that exist for groups where neither the lower main-sequence nor the main-sequence turn-off offer age information. Finally, we lay out avenues for exploring age and orbit correlations as a basis to map the dispersal of stellar ensembles in the Milky Way disk.