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F. Camilo (Columbia University), A. G. Lyne, I. H. Stairs, N. P. F. McKay, D. J. Morris, M. Kramer, G. Hobbs (Jodrell Bank Observatory, UK), R. N. Manchester, J. F. Bell (ATNF, Australia), V. M. Kaspi (McGill University, Canada), N. D'Amico, A. Possenti (Osservatorio Astronomico di Bologna, Italy), F. Crawford (MIT)
The Parkes Multibeam Pulsar Survey has discovered over 500 radio pulsars to date. Of these, at least eight have been identified as members of binary systems. Three are reported on elsewhere: PSR J1811-1736 is a double-neutron star system with a 104-ms pulsar in an eccentric 19-day orbit (Lyne et al 2000, MNRAS, 698, 702); PSR J1141-6545 is a young 394-ms pulsar in a relativistic, eccentric, 5-hr orbit with a 1 M\odot white-dwarf companion (Kaspi et al 2000, ApJ, in press); and PSR J1740-3052 is a 570-ms pulsar in a 231-day eccentric orbit with a companion of mass at least 11 M\odot, possibly a late-type star (Stairs et al, this meeting). This paper concerns itself with the remaining 5 systems.
Pulsars J1232-6501, J1435-6100, J1454-5846, J1810-2005, and J1904+0412 are all old, ``recycled'' pulsars, with characteristic ages greater than about 1 Gyr. As a group they differ from the usual millisecond pulsar-Helium white dwarf systems in that: (i) their spin periods, 9-88 ms, are larger than those typical for standard millisecond pulsars; (ii) the pulsar companions' masses, 0.2-1.1 M\odot, are in at least some cases suggestive of CO or more massive white dwarfs; and (iii) some of the systems have relatively large eccentricities (as much as 0.002). Such observed characteristics suggest that the evolution of these systems differs from that of the standard millisecond pulsars (thought to undergo a long-lived phase of stable mass-transfer in a low-mass X-ray binary phase).
We discuss these systems and proposed scenarios for their evolution, and comment on the sudden flurry of discoveries of what, until recently, were rare objects.