Proper Motion of Binary Pulsars as a Source of Secular Variations of Orbital Parameters

The proper motion of a binary pulsar gradually changes the apparent geometrical orientation of its orbital plane. Consequently, the derived values of the projected semimajor axis of the orbit and the longitude of orbital periastron have systematic errors that limit the precision of fundamental tests of relativistic gravity in the strong gravity field regime unless this effect is taken into account. On the other hand, possible observation of this effect with relativistic contributions calculated using general relativity may provide a tool for determining the orbital inclination and the longitude of the ascending node of the binary. This same technique may also be used in optical spectral observations of binary stars that possess a sufficiently high-quality determination of their radial velocity curve.