High-resolution imaging and the H-R diagram of galactic bulge planetary nebulae

Images of six Galactic bulge planetary nebulae in the [O III] 5007 Å line have been obtained at Mauna Kea at the unprecedented resolution of 0″.35 (FWHM), by the technique of real-time photon counting followed by image reconstruction. The results are compared with those obtained at radio wavelengths, and optical spectrophotometry of the nebulae is used to construct a self-consistent photoionization model, to derive chemical abundances and to place the central stars on the H-R diagram. This method is shown to produce similar results to the classical Zanstra technique, but with the advantage that objects with high- or low-temperature central stars can be studied with equal facility. All our objects are observed during their excursion toward high temperatures on the H-R diagram. We find that these objects are optically thick, and lie on the good correlation between mass and nebular diameter found by previous authors. We also find a correlation between luminosity and metallicity, which is equivalent to a correlation between metallicity and mass of the planetary nebula nucleus, or between metallicity and stellar age.