  We investigate the propagation of gravitational waves in the context of
fourth order gravity nonminimally coupled to a massive scalar field. Using the
damping of the orbital period of coalescing stellar binary systems, we impose
constraints on the free parameters of extended gravity models. In particular,
we find that the variation of the orbital period is a function of three mass
scales which depend on the free parameters of the model under consideration; we
can constrain these mass scales from current observational data.
