ON THE ORIGIN OF THE ECLIPSING PULSAR PSR-B1718-19 AND ITS WIND

The recent discovery of PSR B 1718 - 19 in NGC 6342, the first globular-cluster pulsar with a high magnetic field and the third eclipsing pulsar (Lyne et al. 1993) may lead to an unambiguous test of pulsar recycling and field decay. The reason for this is that one expects to find rather different companion masses depending on whether the binary was formed via capture of a companion by an old neutron star or whether the neutron star was born in the binary via accretion-induced collapse of a white dwarf. The mass difference leads to almost 2 mag difference in the expected I-magnitude of the companion, which means that one can easily distinguish between the two cases using CCD observations. The mass flow in the system that causes modulation of the radio flux with orbital phase is, in our view, not due to ablation of the companion by radiation from the pulsar. Instead, we propose that the companion is similar to the very active stars found in RS Canum Venaticorum binaries; the cause of mass loss in these binaries is thought to be the combination of convective activity natural to late-type stars and the rapid rotation to which they are forced in close binaries. The analogy with such a well-studied class of binaries offers new perspectives for tackling some of the unsolved problems in the evolution of neutron star binaries.