Abstract:
Triple and higher-order stellar systems are common products of star formation, and their frequency depends strongly on the mass. About 10 0000 hierarchies are expected within 100 pc, but only a quarter of those are presently catalogued. The diversity of their architectures is related to several processes responsible for formation and early evolution: pure N-body dynamics, dynamics with tides, fragmentation of disks and cores, and dissipative capture. Each mechanism leaves its characteristic imprints, illustrated by real systems matching the predicted features. Tentative classification of hierarchies into families assiciated with particular formation scenarios is a new emerging field. Large surveys play an increasing role in improving the multiplicity statistics and in finding rare systems. As an example, relative alignment of eclipsing binaries in triples with known inclinations of outer orbits is discussed, suggesting that only a quarter of such systems are aligned.
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