  Localized astronomical sources like a double stellar system, rotating neutron
star, or a massive black hole at the center of the Milky Way emit periodic
gravitational waves. For a long time only a far-zone contribution of
gravitational fields of the localized sources (plane-wave-front approximation)
were a matter of theoretical analysis. We demonstrate how this analysis can be
extended to take into account near-zone and intermediate-zone contributions as
well. The formalism is used to calculate gravitational-wave corrections to the
Shapiro time delay in binary pulsars and low-frequency (LF) pulsar timing noise
produced by an ensemble of double stars in our galaxy.
