  An asteroid pair consists of two unbound objects with almost identical
heliocentric orbital elements that were formed when a single "rubble pile"
asteroid failed to remain bound against an increasing rotation rate. Models
suggest that the pairs' progenitors gained the fast rotation due to the YORP
effect. Since it was shown that the spin axis vector can be aligned by the YORP
effect, such a behavior should be seen on asteroid pairs, if they were indeed
formed by the described mechanism. Alternatively, if the pairs were formed by a
collision, the spin axes should have a random direction and small or young
bodies might have a tumbling rotation.
  Here I apply the lightcurve inversion method on self-obtained photometric
data, in order to derive the rotation axis vectors and shape models of the
asteroid pairs 2110, 3749, 5026, 6070, 7343 and 44612. Three asteroids resulted
with polar-directed spin axes and three objects with ambiguous results. In
addition, the secondary member 44612 presents the same sense of rotation as its
primary member 2110, and its spin is not tumbling. Finally, I use a rotational
fission model, based on the assumption of an angular momentum conservation, and
match it to the measured spin, shape, and mass ratio parameters in order to
constrain the density of the primary members in the pairs. Using this method,
low density values that are expected from a "rubble pile" are derived. All
these results lead to the conclusion that the disruption of these asteroid
pairs was most likely the outcome of the YORP effect that spun-up "rubble pile"
asteroids.
