The Progenitors of the Local Pulsar Population

Abstract

After reviewing the space distribution and luminosity function of the local pulsars, we evaluate quantitatively the local evaporation of massive stars (6 solar masses and larger) as a function of time over the past 50 Myr, among which the progenitors of the local supernovae and pulsars are supposed to have occurred. It is shown that the estimated evaporation may well account for the local replenishment of pulsars per decay time (of 4.6 Myr) if these progenitors occur preponderately (about 90%) in the mass range 6 to 10 solar masses. Decreasing percentages are found to have been produced in the intervals of increasing mass, 10 to 20, 20 to 30 solar masses, etc. Regions of active star formation, the OB associations, contribute only a small fraction (15%) of the local replenishment; most of it emerges from the field population of B2-B3 stars. Pulsars therefore are, on galactic scale, a tracer of regions of past spiral structure (20 to 50 Myr ago) rather than of “active” spiral structure.

A few remarks are made on the distribution of the periods of the local pulsar population. The high space velocities of the pulsars cannot be explained as runaway velocities of the progenitors due to binary disintegration following supernova explosion. An alternative explanation of the kick velocities must be sought for.