Simple relativistic model for theb1structure function of theρmeson

Motivated by the recent discussion of the $b_1$ structure function in spin-1 systems in QCD, we discuss a simple, constituent-quark, light-cone wave-function model for the $\rho$ meson. When the constraints following from the calculation of $\rho$ distribution amplitude moments, as found by QCD sum rules, are incorporated into the model, helicity-zero and -one wave functions have quite different shapes. As a consequence, we obtain $b_1\sim F_1$.