NEW LOOK AT CARBON ABUNDANCES IN PLANETARY-NEBULAE .1. PB-6, HU-2-1, K648, AND H4-1

We introduce and describe a new long-term project whose goal is to emp loy final archived IUE spectra to study carbon abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity. In this paper we report on initial results for PB 6, Hu 2-1, K648, and H4-1. Our UV line strengths for H4-1 are the first such data to be published for this object. By combining our measured UV li ne strengths with optical line strengths found in the literature for e ach object, we have determined values for the abundance ratios He/H, O /H, C/O, N/O, and Ne/O using a combined atomic level-balancing-photoio nization model approach. Eventually, the abundances from this and subs equent studies will be analyzed using a newly improved stellar evoluti on code for intermediate-mass stars with the goal of determining carbo n yields for stars of this mass range.