  As a part of our ongoing Volume-limited A-Star (VAST) adaptive optics survey,
we have obtained observations of 26 binary systems with projected separations
<100 AU, 13 of which have sufficient historical measurements to allow for
refinement of their orbital elements. For each system with an estimated orbit,
the dynamical system mass obtained was compared with the system mass estimated
from mass-magnitude relations. Discrepancies between the dynamical and
theoretical system mass can be explained by the presence of a previously
unresolved spectroscopic component, or by a non-solar metallicity of the
system. Using this approach to infer the presence of additional companions, a
lower limit to the fraction of binaries, triples, and quadruples can be
estimated as 39, 46, and 15 per cent, for systems with at least one companion
within 100 AU. The fraction of multiple systems with three or more components
shows a relative increase compared to the fraction for Solar-type primaries
resolved in previous volume-limited surveys. The observations have also
revealed a pair of potentially young ($<$100 Myr) M-dwarf companions, which
would make an ideal benchmark for the theoretical models during the pre-Main
Sequence contraction phase for M-dwarfs. In addition to those systems with
orbit fits, we report 13 systems for which further orbital monitoring
observations are required, 11 of which are newly resolved as a part of the VAST
survey.
