S R ] 5 O ct 2 01 5 Co-spatial Long-slit UV / Optical Spectra of Ten Galactic Planetary Nebulae with HST / STIS II . Nebular Models , Central Star Properties and He + CNO Synthesis 1

The goal of the present study is twofold. First, we employ new HST/STIS spectra and photoionization modeling techniques to determine the progenitor masses of eight planetary nebulae (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662 and PB6). Second, for the first time we are able to compare each object’s observed nebular abundances of helium, carbon and nitrogen with abundance predictions of these same elements by a stellar model that is consistent with each object’s progenitor mass. Important results include the following: 1) the mass range of our objects’ central stars matches well with the mass distribution of other PN central stars and white dwarfs; 2) He/H is above solar in all of our objects, in most cases likely due to the predicted effects of first dredge up; 3) most of our objects show negligible C enrichment, probably because their low masses preclude 3rd dredge-up; 4) C/O versus O/H for our objects appears to be inversely correlated, perhaps consistent with the conclusion of theorists that the extent of atmospheric carbon enrichment from first dredge-up Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 Department of Astronomy, University of Washington, Seattle, WA 98195 Department of Space Physics and Astronomy, Rice University, Houston, TX 77251 Department of Astronomy, Williams College, Williamstown, MA 01267 National Optical Astronomy Observatory, Tucson, AZ 85719 SUNY College of Technology at Alfred, Alfred, NY 14843 Instituto de Astrof́ısica de Canarias, E-38200 La Laguna, Tenerife, Spain Departamento de Astrof́ısica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain