DISCOVERY OF 3 BINARY MILLISECOND PULSARS

We report the discovery of three binary millisecond pulsars in circula r orbits with low-mass companions from a continuing survey of the sout hern sky with the Parkes radio telescope. The three pulsars, PSR J0034 -0534, PSR J1045-4509, and PSR J2145-0750 have pulse periods of 1.87, 7.47, and 16.05 ms and orbital periods of 1.6, 4.1, and 6.8 days, resp ectively. PSR J2145-0750 has a spin-down age of approximately-greater- than 12 Gyr, which raises interesting questions about its progenitor a nd initial pulse period. The properties of the growing class of radio pulsars with low-mass companions are discussed, and we suggest that th eir velocities, and a tendency for the short-period pulsars to have sm all orbital periods, are consistent with their formation from Type II supernova explosions.