  Hipparcos astrometric binaries were observed with the NICI adaptive optics
system at Gemini-S, completing the work of Paper I (Tokovinin et al. 2012).
Among the 65 F, G, K dwarfs within 67pc of the Sun studied here, we resolve 18
new sub-arcsecond companions, re-measure 7 known astrometric pairs, and
establish the physical nature of yet another three wider companions. The 107
astrometric binaries targeted at Gemini so far have 38 resolved companions with
separations under 3". Modeling shows that bright enough companions with
separations on the order of an arcsecond can perturb the Hipparcos astrometry
when they are not accounted for in the data reduction. However, the resulting
bias of parallax and proper motion is generally below formal errors and such
companions cannot produce fake acceleration. This work contributes to the
multiplicity statistics of nearby dwarfs by bridging the gap between
spectroscopic and visual binaries and by providing estimates of periods and
mass ratios for many astrometric binaries.
