On the Classification of Emission-Line Spectra of Planetary Nuclei

Emission-line spectra of nuclei of planetary nebulae are ordered into five classes according to whether they closely resemble spectra of Population I Of and WoJf-Rayet ~tar6 or show marked differences from the latter. Spectra that are closely similar to those of Population I ~tar~ are in the minority. One of the classes-which we call the 0 VI sequence-includes spectra which corre6pond to extremely high excita~ tion; the nucleus of NGC 5189, which has been tentatively identified as an X-ray source, has a spectrum that falls in this class