The local space density and formation rate of planetary nebulae

Astronomy and Astrophysics – Astronomy

Scientific paper

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Planetary Nebulae, Space Density, Star Distribution, Stellar Evolution, White Dwarf Stars, Black Holes (Astronomy), Least Squares Method, Neutron Stars

Scientific paper

Previously compiled distance and distribution data on planetary nebulae are reanalyzed, taking account of observational selection effects, to improve estimates of the local density of such nebulae. Selection effects of small angular diameters and surface-brightness limitations are modeled, and a correction is applied to allow for incompleteness in the fourth quadrant of galactic longitude. A density of about 150 planetaries per cu kpc is determined for nebula radii of 0.15 to 0.60 pc, which is approximately double the previous estimate of Cahn and Kaler (1971). The revised density and an expansion velocity of 30 km/s are used to estimate a planetary-nebula production rate of approximately 0.11/cu kpc per year, which is three times larger than both the previous estimate and the estimated formation rate of white dwarfs. It is concluded that either a large fraction of planetary-nebula central stars become neutron stars or black holes rather than white dwarfs or the white-dwarf formation rate has been severely underestimated.

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