SIMBAD references

We calculate filling factors (ε) and ionized masses (M_i) for a total of 84 galactic and extragalactic planetary nebulae (PNe) at known distances. To do these calculations, from the equation of energy propagation within a gaseous nebula, we have chosen forbidden line electron densities, observed angular diameters, and Hβ fluxes, from the most recent measurements available in the literature. Statistical analysis on the distributions of ε and M_i show that (1) the range of values of these parameters is wider than what was previously found; (2) the mean value of the filling factor is between 0.3 and 0.4, for the different sets; (3) the mean value of the ionized mass is between 0.1 and 0.25 M_☉, 0.2 M_☉ representing an upper limit to the ionized mass for galactic disk PNe, and a typical value for galactic bulge and extragalactic PNe; (4) a clear correlation between ε and the dimensions of the PNe was not found when distance-independent sets of PNe were used; (5) for extragalactic PNe, where distance errors are not a factor, the filling factors and the ionized masses anticorrelate tightly with the electron densities. The results indicate that the modified Shklowsky distance method is correct.