  We conducted a deep survey of resolved sub-systems among wide binaries with
solar-type components within 67 pc from the Sun. Images of 61 stars in the K
and H bands were obtained with the NICI adaptive-optics instrument on the 8-m
Gemini-South telescope. Our maximum detectable magnitude difference is about
5mag and 7.8mag at 0.15" and 0.9" separations, respectively. This enables a
complete census of sub-systems with stellar companions in the projected
separation range from 5 to 100 AU. Out of 7 such companions found in our
sample, only one was known previously. We determine that the fraction of
sub-systems with projected separations above 5 AU is 0.12 +- 0.04 and that the
distribution of their mass ratio is flat, with a power-law index 0.2 +- 0.5.
Comparing this with the properties of closer spectroscopic sub-systems
(separations below 1 AU), it appears that the mass-ratio distribution does not
depend on the separation. The frequency of sub-systems in the separation ranges
below 1 AU and between 5 and 100 AU is similar, about 0.15. Unbiased statistics
of multiplicity higher than two, advanced by this work, provide constraints on
star-formation theory.
