Journal Article

A timing formula for main-sequence star binary pulsars

Norbert Wex

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 298, issue 1, pages 67-77
Published in print July 1998 | ISSN: 0035-8711
Published online July 1998 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1998.01570.x
A timing formula for main-sequence star binary pulsars

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Abstract

In binary radio pulsars with a main-sequence star companion, the spin-induced quadrupole moment of the companion gives rise to a precession of the binary orbit. As a first approximation one can model the secular evolution caused by this classical spin-orbit coupling by linear-in-time changes of the longitude of periastron and the projected semi-major axis of the pulsar orbit. This simple representation of the precession of the orbit neglects two important aspects of the orbital dynamics of a binary pulsar with an oblate companion. First, the quasiperiodic effects along the orbit, owing to the anisotropic 1/r3 nature of the quadrupole potential. Secondly, the long-term secular evolution of the binary orbit, which leads to an evolution of the longitude of periastron and the projected semi-major axis, which is non-linear in time.

In this paper a simple timing formula for binary radio pulsars with a main-sequence star companion is presented which models the short-term secular and most of the short-term periodic effects caused by the classical spin-orbit coupling. I also give extensions of the timing formula that account for long-term secular changes in the binary pulsar motion. It is shown that the short-term periodic effects are important for the timing observations of the binary pulsar PSR B1259-63. The long-term secular effects are likely to become important in the next few years of timing observations of the binary pulsar PSR J0045-7319. They could help to restrict or even determine the moments of inertia of the companion star and thus probe its internal structure.

Finally, I reinvestigate the spin-orbit precession of the binary pulsar PSR J0045-7319 since the analysis given in the literature is based on an incorrect expression for the precession of the longitude of periastron. A lower limit of 20° for the inclination of the B star with respect to the orbital plane is derived.

Keywords: binaries: general; pulsars: general; pulsars: individual: PSR J0045-7319; pulsars: individual: PSR B1259-63

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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