After the completion of the `IAC Morphological Catalog of Northern Galactic PNe' (Manchado et al. 1996), a systematic study on the physical characteristics of PNe, their central stars, and their Populations across morphological types has been started. The IAC sample is the only complete and homogeneous PN survey of morphological character, thus it provides the unique opportunity of determining whether the distribution of morphological types that we see at different Galactic locations, or associated with different nebular chemistry, is due to selection effects, distance indetermination, dust absorption, or other systematical biases.
The main findings (Stanghellini et al. 2002) from this investigation, performed in collaboration with Villaver, Guerrero and Manchado (IAC), can be summarized as follows:
60 of Galactic PNe are elliptical, 26 are round, and 14 are bipolar or quadrupolar. The statistical distance scale is accurate for this study, and we found that the spatial distribution of PNe varies depending on the morphological types: in fact, bipolar PNe are found closer to the Galactic Plane than either elliptical or round PNe. This segregation, noted before as a marginal effect, has been confirmed by us, for the first time, on a complete, homogeneous, and statistically significant PN sample. We also concluded that the PN sample is really complete up to a distance of about 7 kpc.
The distribution of PN nuclei on the logL-logT plane has been analyzed, and the results of Stanghellini et al. (1993) have been confirmed, i.e., that nuclei of bipolar PNe are, on average, more massive than nuclei of elliptical and round PNe. We will also attempt to relate the spectral type of the central stars of PNe with the morphology of the hosts.