On the mass and inclination of the PSR J2019+2425 binary system

We report on 9 years of timing observations of PSR J2019+2425, a millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a significant change over time of the projected semimajor axis of the orbit, (x)over dot/x = (1.3 +/- 0.2) x 10(-15) s(-1), where x = (a(1) sin i)/c. We attribute this to the proper motion of the binary. This constrains the inclination angle to i < 72, with a median likelihood value of 63 degrees. A similar limit on the inclination angle arises from the lack of a detectable Shapiro delay signal. These limits on inclination angle, combined with a model of the evolution of the system, imply that the neutron star mass is at most 1.51 M.; the median likelihood value is 1.33 M.. In addition to these timing results, we present a polarization profile of this source. Fits of the linear polarization position angle to the rotating vector model indicate that the magnetic axis is close to alignment with the rotation axis, alpha < 30.