TIMING MEASUREMENTS AND THEIR IMPLICATIONS FOR 4 BINARY MILLISECOND PULSARS

We present timing observations of four millisecond pulsars, using data obtained over three years at the Australia Telescope National Facilit y (ATNF) Parkes and Nuffield Radio Astronomy Laboratory (NRAL) Jodrell Bank radio telescopes, Astrometric, spin and binary parameters are up dated, and substantially improved for three pulsars, PSRs J0613-0200, J1045-4509 and J1643-1224, We have measured the time variation of the projected semimajor axis of the PSR J0437-4715 orbit due to its proper motion, and use it to constrain the inclination of the orbit and the mass of the companion, Some evidence is found for changes in the dispe rsion measures of PSRs J1045-4509 and J1643-1224, Limits are placed on the existence of planetary mass companions, ruling out companions wit h masses and orbits similar to the terrestrial planets of the Solar sy stem for eight pulsars.