We simulated encounters between a neutron star and primordial and tida
l-capture binaries. Using a three-body code, we simulated 31,000 encou
nters, then reran a small number of cases with a three-dimensional smo
othed particle hydrodynamics (SPH) code to determine the importance of
hydrodynamical effects. In the case of encounters involving a tidal-c
apture binary, comprising of a white dwarf and a main-sequence star, w
e find that most exchange encounters will produce a single merged obje
ct with the white dwarf and neutron star engulfed in a common envelope
of gas donated by the main-sequence primary of the original binary. A
small fraction of exchanges induce a merger of the white dwarf and ma
in-sequence star, with this object being unbound to the neutron star,
and the two objects having a large (approximately 100 km s-1) relative
speed at infinity. For encounters involving a primordial binary, fewe
r encounters require the inclusion of hydrodynamical effects. Those in
volving collisions or close encounters tend to produce a binary compri
sed of the two merged stars (now forming one star) and the third star.
The binaries produced typically have large enough separations to prev
ent the formation of a single merged object until subsequent stellar e
volution of one of the components causes it to fill its Roche lobe. Cl
ean exchanges produce binaries with large eccentricities; they are typ
ically sufficiently wide to avoid circularization.