Nature 325, 416 - 418 (29 January 1987); doi:10.1038/325416a0

A determination of the white-dwarf masses in wide binary radio-pulsar systems

G. J. Savonije

Astronomical Institute Anton Pannekoek, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam, The Netherlands

The recent discovery of two new binary pulsars, PS R1831–00 (ref. 1) and PSR1855 + 09 (ref. 2), brings the total number of these objects to seven. By observations of pulse arrival time one can determine the mass function and a _l sin i, the projected orbital separation of the pulsar from the system's centre of gravity. By adopting a mass for the pulsar the mass of the secondary can be calculated as a function of the unknown orbital inclination angle i. Here I show that one can make use of the fact that four of these binary systems appear to fit neatly into the evolutionary scheme for bright X-ray sources described by Webbink et al.³. This implies that one can apply another constraint to the orbital solution, namely that the (sub)giant progenitor of the present white dwarf secondary should have filled its Roche lobe while spinning up the pulsar companion by mass transfer. With this extra constraint one can determine the mass of the present white dwarf in these systems^4,5,6. It also allows one to set an upper limit of 1.2 M to the mass of the neutron star PSR1855+09.

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