The sample of 115 B-type stars in Sco OB2 association is examined for existence of visual companions with ADONIS near-infrared adaptive optics system and coronograph in J and K _ { s } bands .
Practically all components in the separation range 0 \aas@@fstack { \prime \prime } 3 – 6 \aas@@fstack { \prime \prime } 4 ( 45 - 900 A.U . )
were detected , with magnitudes down to K = 16 .
The K and J - K photometry of primaries and differential photometry and astrometry of 96 secondaries are presented .
Ten secondaries are new physical components , as inferred from photometric and statistical criteria , while remaining are faint background stars .
After small correction for detection incompleteness and conversion of fluxes into masses , an unbiased distribution of the components mass ratio q is derived .
The power law f ( q ) \propto q ^ { -0.5 } fits well the observations , whereas a q ^ { -1.8 } distribution which corresponds to random pairing of stars is rejected .
The companion star fraction is 0.20 \pm 0.04 per decade of separation , comparable to the highest measured binary fraction among low-mass PMS stars and \sim 1.6 times higher than the binary fraction of low-mass dwarfs in solar neighborhood and open clusters in the same separation range .