Journal
ASTRONOMY & ASTROPHYSICS
Volume 474, Issue 1, Pages 77-+Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361:20077719
Keywords
galaxy : open clusters and associations : individual : Scorpius OB2; stars : binaries : visual; stars : binaries : general stars :; formation
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We characterize the binary population in the young and nearby OB association Scorpius OB2 (Sco OB2) using available observations of visual, spectroscopic, and astrometric binaries with intermediate-mass primaries. We take into account observational biases by comparing the observations with simulated observations of model associations. The available data indicate a large binary fraction (> 70% with 3 sigma confidence), with a large probability that all intermediate mass stars in Sco OB2 are part of a binary system. The binary systems have a mass ratio distribution of the form f(q)(q) proportional to q(gamma q), with gamma(q) approximate to -0.4. Sco OB2 has a semi-major axis distribution of the form f(a)(a) proportional to a(gamma a) with gamma(a) approximate to -1.0 (Opik's law), in the range 5R(circle dot) less than or similar to a less than or similar to 5 x 10(6) R-circle dot. The log-normal period distribution of Duquennoy & Mayor ( 1991) results in too few spectroscopic binaries, even if the model binary fraction is 100%. Sco OB2 is a young association with a low stellar density; its current population is expected to be very similar to the primordial population. The fact that practically all stars in Sco OB2 are part of a binary ( or multiple) system demonstrates that multiplicity is a fundamental factor in the star formation process, at least for intermediate mass stars.
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