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Description
A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound "moving groups", which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V~<6mag), with spectral types earlier than ~B5. The Hipparcos measurements allow a major improvement in this situation. Moving groups are identified in the Hipparcos Catalog by combining de Bruijne's (1999MNRAS.306..394H) refurbished convergent point method with the "Spaghetti method" of Hoogerwerf & Aguilar (1999, MNRAS, in press). Astrometric members are listed for 12 young stellar groups, out to a distance of ~650pc. These are the three subgroups Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2, {alpha} Persei (Per OB3), Cas-Tau, Lac OB1, Cep OB2, and a new group in Cepheus, designated as Cep OB6.
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