Radio and optical observations of the PSR B1259-63/SS 2883 Be star binary system

We report here on radio timing observations of the 47-ms pulsar PSR B1259–63 (PSR J1302–6350) and optical observations of its binary companion Be star, SS 2883. The two are in a highly eccentric orbit of period 3.4 yr. Radio observations over 1250 days with the Parkes radio telescope now permit a phase-connected solution, which shows that' the next periastron is expected to occur on 1994 January 9.2 ut, and that the pulsar has a period derivative of $$2.3 \times 10^{-15}$$. The pulsar thus has a characteristic age of 0.33 Myr and a surface magnetic field strength of $$3 \times 10^{11} \ {\rm G}$$. Optical photometry of SS 2883 shows that the star is of spectral type of about B2e, indicating its mass to be $$10 \ {\rm M}_{\odot}$$ and its radius $$6 {\rm R}_{\odot}$$. The system can be no further than 1.5 kpc distant, substantially closer than the distance derived from the dispersion measure. High-resolution spectroscopy of the Balmer-series emission lines allows a determination of the underlying stellar rotation velocity, v sin i, of $$180 \ {\rm {km}} \ {\rm s}^{-1}$$. It is likely that the inclination of the plane of the orbit and the inclination of the circumstellar disc are similar, at $$\sim 35^{\circ}$$. The system is a likely progenitor of the high-mass X-ray binaries and double-neutron-star systems such as PSR B 1913+16.