TEST OF WHEN FREE PRECESSION OF A PULSAR CANNOT MIMIC AN ORBITING PLANET

Precession can modulate pulsar frequencies in much the same way as the Doppler shift caused by orbital motion with a planetary companion. We derive a relation among observables for situations where a companion is suspected, which if satisfied, would make it difficult to distingui sh planetary modulation of pulsar frequency from that caused by free p recession of an isolated pulsar. Conversely, if the relation cannot be satisfied, precession is ruled out, and a planetary hypothesis thereb y strengthened.