Statistical survey of planetary nebulae: Distances, masses, and distribution in the galaxy

Abstract

On the basis of empirical Σ(D)-dependency at the frequency of 5 GHz constructed using 15 planetary nebulae with the independently measured distances (10⁻¹⁷≥Σ≥1×10⁻²⁰ W m⁻² Hz⁻¹ ster⁻¹), we evaluated distances of 335 objects. Independent evidence of the correctness of the accepted scale are given. Then(D)-dependency is constructed and it is shown that atD<0.08 pc the mean electron density is higher than the one determined by the Seaton method. We showed that the filling factor ɛ diminishes with the increase of the PN diameter (ɛ∼1 atD≤0.08 pc and ɛ∼0.2 atD∼0.4 pc). the ionized mass of 33 PNs is determined. With the diameter increase the ionized mass grows and atD∼0.4 pc reaches the valueM≈0.07M _⊙. We used the new distance scale when investigating the space distribution of PNs. The mean scale height β=130±15 pc and the mean gradient of the change of surface densitym=0.37, which allowed us to estimate the total number of nebulae in the GalaxyN∼4×10⁴. We divided the PNs according to their velocities (withV _LSR>35 km s⁻¹ andV _LSR<35 km s⁻¹) and permitted us to confirm that the PN belong to different sub-systems of the Galaxy. The estimated local formation rate of PNs [ν=(4.6±2.2)×10⁻¹² pc⁻³ yr⁻¹] is a little higher than the one of the white dwarfs. That can be explained by a large number of PNs having binary cores, which used in our sample. The statistical estimation of PN expansion velocity showed thatV _ex increases from 5–7 km s⁻¹ (atD∼0.03 pc) to 40–50 km s⁻¹ (atD∼0.8 pc).