PSR J2019+2425 and PSR J2322+2057 and the proper motions of millisecond pulsars

Timing observations of millisecond pulsars PSR J2019+2425 and PSR J2322+2057 made over more than 2 years have yielded spin-down, astrometric, and binary parameters. The proper motions of these sources are 23.5 +/- 1.3 and 25 +/- 3 mas/yr, respectively, corresponding to transverse velocities of approximately 100 and 90 km/s. These measurements, combined with other published millisecond pulsar proper motions, indicate that the population has a velocity dispersion of order 60 km/s, comparable to that of low-mass X-ray binaries (from which millisecond pulsars evolve) but much lower than that of normal (non-millisecond) pulsars. The spin-down rates of J2019+2425 and J2322+2057 are extraordinarily low and, when biases induced by motion are removed, formal calculations yield ages of 27 x 10⁹ and 19 x 10⁹ yr, respectively, indicating they have evolved little since becoming millisecond pulsars.