Post-Newtonian Limits and Gravitational Radiation from the Superstring Effective Action

We consider the gravitational sector of the superstring effective action with axion-matter couplings. The field equations are developed in the post-Newtonian scheme and approximate solutions for a spinning point mass and a cosmic string are presented. Furthermore, assuming vanishing axion mass and vanishing potential for the dilaton, we consider the gravitational radiation in the leading $O(\alpha'^0)$ order. We find that the total luminosity of a radiative source has monopole and dipole components besides the standard quadrupole one. These components may possibly be checked in binary systems.