SIMBAD references

We present a study of the characteristics of four planetary nebulae (PNs) with OVI nuclei: NGC 1501, IC 1297, IC 1747, and K 1-16. They have high temperature central stars with well-separated narrow OVI λ3811, 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 evolutionary stage of the central stars relative to the nebular properties we calculate Zanstra temperatures and luminosities. We find that the stars have similar physical characteristics and thus represent approximately the same phase of post-asymptotic giant branch (P-AGB) evolution. Their OVI absolute fluxes correlate reasonably well to the central stars positions on the HR diagram.