The parameters of planetary nebulae and their central stars derived from observations

The empirical calibration dependence between the number of Lyman photons emitted by a central star, and a planetary nebula (PN) of a given diameter, is constructed on the basis of UV measurements of PN central star temperatures for the cases of 118 PN central stars. Central star masses are noted to be distributed over the 0.5-1.2 solar mass range. The averaged empirical evolutionary tracks of central stars less and more massive than 0.6 solar masses are found to differ considerably, and it is shown that the majority of central stars may possess hot chromospheres that spread over several tens of radii from the central star. The PN originates in the ionization of matter ejected by a red giant at the superwind stage; the ionization is in turn due to the UV radiation of the central star.