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L.A. Nelson, E. Dubeau (Bishop's University, Canada)
The dual-line binary millisecond pulsar, PSR J1740-5340, in the globular cluster NGC 6397 provides us with an unprecedented opportunity to test our theoretical understanding of the formation and evolution of binary millisecond pulsars in globular clusters. Extensive photometry and spectroscopy have been carried out on this system and reasonably well constrained values for the mass of the companion (~0.3 Msun), its effective temperature (~5500 K), and radius (~1.6 Rsun) have been inferred. The measurement of the mass ratio (Mns / Mc ~ 5.8) is also the most precise of any non-relativistic binary system containing a neutron star. Taking the metallicity of the cluster to be [Fe/H] = -2 and knowing that the orbital period is 1.35 hours, we calculate evolutionary models of this system on the assumption that a donor star fills its Roche lobe and transfers matter to its neutron star companion. We show that the observed properties of the donor can be accurately reproduced for a wide range of initial donor masses (1 - 2 Msun) and that the donor must be reasonably evolved (e.g., near TAMS) at the onset of mass transfer. Finally we examine scenarios that would lead to a (temporary) cessation of mass transfer allowing for the millisecond pulsar to ‘turn on’.
This research was supported in part by funds from the Natural Sciences and Engineering Research Council (Canada).
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.