Oxygen and Neon Abundances of Planetary Nebulae in the Elliptical Galaxy NGC 4697

This paper presents deep spectra of 14 planetary nebulae (PNs) at a varietyof angular distances from the center of the flattened elliptical galaxy NGC4697. Both near the center and among the most outlying PNs we have foundseveral examples of very strong [O III] 5007, about 20 times brighter thanHbeta. This, together with strong [Ne III] lines, implies a lower limit for Oand Ne abundances near solar at the center and also at more than two effectiveradii from the center of NGC 4697. Thus we have found, for the first time fromindividual stars, direct evidence of the existence of a metal-rich populationin elliptical galaxies, confirming metallicities derived from absorption-lineindices and extending the information to angular distances where the stellarsurface brightness is too low for absorption-line studies. A comparison withabundances obtained closer to the center of NGC 4697 from integratedabsorption-line spectra indicates that the metallicity gradient, which is quitesteep within one effective radius, becomes much less pronounced beyond oneeffective radius. The only alternative to this interpretation would be thepresence of a very metal-poor PN population with [Z/H] below -1, which wecannot rule out but would require an extremely bimodal metallicity distributionwith almost no intermediate metallicities.Comment: 43 pages, 14 figures, accepted for publication in Ap