Architecture of Hierarchical Stellar Systems and Their Formation

Accumulation of new data on stellar hierarchical systems and the progress in numerical simulations their formation open door to genetic classification these systems, where properties a certain group (family) objects are tentatively related mechanisms early evolution. A short review structure statistical trends known hierarchies is given. Like binaries, they can be formed by disk core fragmentation events happening sequentially or simultaneously followed evolution masses orbits driven continuing accretion gas dynamical interactions between stars. Several basic scenarios proposed associated qualitatively with architecture real although quantitative predictions for still pending. The general trend increasing orbit alignment decreasing system size points critical role accretion-driven migration, which also explains typically comparable stars belonging same system. some bears imprints chaotic interactions. Characteristic features each family illustrated several systems.