Table 5: Candidate and confirmed astrometric binaries in the Hipparcos catalogue. For each subgroup we list the number $N_\star $ of known members, the number of stochastic (X); orbital (O); acceleration (G); component (C); and suspected (S) binaries in the Hipparcos catalogue. For each (S) binary we list between brackets how many of these are also (X)-flagged. The last three columns list the "astrometric binary fraction'' - including the (X), (O), (G) binaries - without the (S) binaries and with the (S) binaries included, and the Hipparcos "visual'' binary fraction, for the (C) binaries only. (V) binaries are not present in Sco OB2.
Subgroup $N_\star $ (X) (O) (G) (C) (S) $\tilde{F}_{M,\rm ~XOG}$ $\tilde{F}_{M,\rm ~XOGS}$ $\tilde{F}_{M,\rm ~C}$
US 120 1 0 4 15 8 (1) $4.2 \pm 1.5\%$ $10.0\pm 2.1\%$ $ 12.5\pm 3.0\%$
UCL 221 0 1 9 36 7 (0) $4.5 \pm 1.5\%$ $\ 7.7\pm 1.9\%$ $ 16.3\pm 3.0\%$
LCC 180 2 0 6 28 11 (2) $4.4 \pm 1.6\%$ $\ 9.4\pm 2.4\%$ $ 15.6\pm 3.0\%$
Sco OB2 521 3 1 19 79 26 (3) $4.4 \pm 1.0\%$ $\ 8.8\pm 1.4\%$ $ 15.2\pm 1.8\%$

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