High-Precision Timing of Millisecond Pulsars. I. Astrometry and Masses of the PSR 1855+09 System

The observing method, data-analysis procedures, and results of a 4.4-year series of timing observations of a binary millisecond pulsar PSR 1855 + 09 are presented. The spin parameters of the pulsar, astrometry of the system, including parallax and proper motion, and orbital parameters including masses of the two components are considered. The parameter values show the orbital inclination to be nearly 90 deg, and they provide mass estimates for the pulsar (1.27 +0.23/-0.15 solar mass) and companion star (0.233 +0.026/-0.017 solar mass). Both masses are found in good agreement with theoretical predictions based on neutron-star physics and evolutionary models of the PSR 1855 + 09 system.