NARROW EMISSION-LINE O-VI PLANETARY-NEBULAE NUCLEI

We present a study of the characteristics of four planetary nebulae (P Ns) with O VI nuclei: NGC 1501, IC 1297, IC 1747, and K 1-16. They hav e high temperature central stars with well-separated narrow O VI lambd a 3811, 34 emission lines. We present intensities of the nebular lines , equivalent widths of the stellar lines, and, where possible, plasma diagnostics and nebular ionic abundance. In order to test the evolutio nary stage of the central stars relative to the nebular properties we calculate Zanstra temperatures and luminosities. We find that the star s have similar physical characteristics and thus represent approximate ly the same phase of post-asymptotic giant branch (P-AGB) evolution. T heir O VI absolute fluxes correlate reasonably well to the central sta rs positions on the HR diagram.