Improved parameters for four binary pulsars

Timing observations of four of the seven known binary pulsars, PSRs 0655 + 64, 0820 + 02, 1831 - 00, and 2303 + 46, have yielded much improved measurements of their celestial coordinates, periods, period derivatives, and orbital parameters. New upper limits for the orbital eccentricity and rate of change of orbital period of 2 x 10 to the -5th and 1.4 x 10 to the -11th s/s, respectively, are obtained for PSR 0655 + 64. For PSR 0820 + 02, a tight limit of 0.016 deg/yr is placed on the rate of advance of the longitude of periastron. A reliable period derivative of (1.43 + or - 0.18) x 10 to the -17th s/s is obtained for PSR 1831 - 00, and a measurement of the general relativistic advance of periastron is measured at 0.0092 + or - 0.0018/yr for PSR 2303 + 46. The latter value implies a total system mass of 2.3 + or - 0.6 solar masses, probably divided about equally between the pulsar and a neutron star companion. 25 references.