Planetary nebula with high oxygen abundance in the galactic bulge

Extensive photoelectric spectra of H1-55, a planetary nebula in the galactic bulge, have been obtained. The temperature and density in the nebula are estimated with a least-squares fit to the diagnostic line ratios, and chi-square tests are used to place confidence limits on the result. The logarithmic oxygen abundance is found to be 9.50, several times the normal abundance in planetary nebulae in the disk. The abundances of other heavy elements are also enhanced, although less dramatically: N = 8.87, S = 7.4:, Ar = 7.4:. The helium, sulfur, and argon abundances are affected by uncertainties in the corrections for unobserved ions. These high abundances are consistent with the nebula's exceptionally low electron temperature of less than 5600 K. They are probably due to high initial abundances in the nebula's progenitor star