Discovery of five binary radio pulsars

We report on five binary pulsars discovered in the Parkes multibeam Galactic 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 10(8) G. The orbital periods range from 1.3 to 15 days. As a group these objects differ from the usual low-mass binary pulsars (LMBPs): their spin periods 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; and 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 observed characteristics reflect binary evolution that is significantly different from that of LMBPs. We also note that intermediate-mass binary pulsars apparently have a smaller scale height than LMBPs.