  Two hundred and forty-two members of the Praesepe and alpha Persei clusters
ranging from B (~5Msun) to early-M (~0.5 Msun) have been surveyed with high
angular resolution imaging. The 39 binary and 1 quadruple systems detected
encompass separations from 0".053 to 7".28; 28 of the systems are new
detections and there are 9 candidate substellar companions. The main results
from the survey are: * Over the projected separation range of 26-581 AU and
magnitude differences of DeltaK < 4.0 mag, the companion star fraction (CSF)
for alpha Persei is 0.09 +/- 0.03 and for Praesepe is 0.10 +/- 0.03. This
fraction is consistent with the field G-dwarf value, implying that there is not
a systematic decline in multiplicity with age on timescales of at 4 +1/-1.5 AU,
significantly smaller value than both the field G-dwarf and the nearby T Tauri
distributions. A simple population synthesis model suggests that the G-dwarf
binary population is a combination of ~30% dark cloud and ~70% giant molecular
cloud systems. * An exploration of the binary star properties reveals a cluster
CSF that increases with decreasing target mass and a cluster mass ratio
distribution that rises more sharply for higher mass stars, but is independent
of binary separation. These observational trends are consistent with several
models of capture in small clusters and simulations of accretion following
fragmentation in a cluster environment. * Among the cluster A stars, there is a
higher fraction of binaries in the subset with X-ray detections, consistent
with the hypothesis that lower mass companions are the true source of X-ray
emission. * In alpha Persei, the rotational velocities for solar-type binaries
with separations less that 60 AU the rotational evolution of young stars.
