Birthrate of planetary nebulae

We reexamine the planetary nebulae in the greater solar neighborhood and find the local number density to be about 80 kpc-3 and a local birth (and death) rate of some 4--6 x 10-3 kpc-3 yr-1. For the corresponding whole-galaxy figures we adopt tentatively a total planetary population of about 38,000 +- 12,000 and a production rate of 2 or 3 per year. A simplified model of galactic star formation predicts that the local death rate of stars with main-sequence masses between 1 and 5 M/sub sun/ is 2--3 x 10-3 kpc-3 yr-1; and Weidemann's statistics and cooling times for white dwarfs yield a comparable production rate for those objects of 2--5 x 10-3 kpc-3 yr-1. These several local rates, derived from entirely different sets of data, are all comparable and therefore reinforce the widely held idea that planetary nebulae are cosmically evanescent episodes between the main-sequence and white-dwarf stages in the evolution of all or most modestly massive stars.The model of star formation also predicts that the local death rate of stars with main-sequence masses greater than 5 M/sub sun/ is a few times 10-4 kpc-3 yr-1, in rough agreement with current estimates of the local production rate of supernovae and of pulsars. We suggest that neutron stars of all ages up to the age of the Galaxy may account for a modest fraction of the local mass density required by the Oort limit.We also explore the planetary nebulae far from the galactic plane and suggest that there are no more than about 100 such systems in the halo of the Galaxy. With the unproved assumption that halo planetaries are physically comparable to those in the disk, we are able to calculate an approximate upper limit to the mass of the halo of 2--5 x 109 M/sub sun/, or 1--3 percent of the conventionally accepted mass of the Galaxy