For spectroscopic binaries the orbital velocity curve shows the radial component of the star's velocity as a function of time. The analogous plot for pulsars is the apparent pulse period against time. Two examples are given in Fig. 22 .
Constraints on the mass of the orbiting companion can be placed by combining the projected semi-major axis and the orbital period to obtain the mass function:
where G is the universal gravitational constant. Assuming a pulsar mass of (see below), the mass of the orbiting companion can be estimated as a function of the (initially unknown) angle i between the orbital plane and the plane of the sky. The minimum companion mass occurs when the orbit is assumed edge-on (). For a random distribution of orbital inclination angles, the probability of observing a binary system at an angle less than some value is . This implies that the chances of observing a binary system inclined at an angle is only 10%; evaluating the companion mass for this inclination angle constrains the mass range between and at the 90% confidence level.
|Binary and Millisecond Pulsars at the New Millennium
Duncan R. Lorimer
© Max-Planck-Gesellschaft. ISSN 1433-8351
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