  We show that for Drell-Yan events by unpolarized hadronic projectiles and
nuclear targets, azimuthal asymmetries can arise from the nuclear distortion of
the hadronic projectile wave function, typically a spin-orbit effect occurring
on the nuclear surface. The asymmetry depends on quantities that enter also the
spin asymmetry in the corresponding Drell-Yan event on polarized free nucleonic
targets. Hence, this study can be of help in exploring the spin structure of
the nucleon, in particular the transverse spin distribution of partons inside
the proton. All arguments can be extended also to antinucleon projectiles and,
consequently, apply to possible future measurements involving nuclear targets
at the foreseen HESR ring at GSI.
