Discovery of five binary radio pulsars

We report on five binary pulsars discovered in the Parkes multibeam Galacti c plane survey. All of the pulsars are old, with characteristic ages (1-11) x 10(9) yr, and have relatively small inferred magnetic fields, (5-90) x 1 0(8) G. The orbital periods range from 1.3 to 15 days. As a group these obj ects differ from the usual low-mass binary pulsars (LMBPs): their spin peri ods of 9-88 ms are relatively long; their companion masses, 0.2-1.1 M., are , in at least some cases, suggestive of CO or more massive white dwarfs; an d some of the orbital eccentricities, 10(-5) less than or similar to e less than or similar to 0.002 are unexpectedly large. We argue that these obser ved characteristics reflect binary evolution that is significantly differen t from that of LMBPs. We also note that intermediate-mass binary pulsars ap parently have a smaller scale height than LMBPs.