Discovery of Nevii in the Winds of Hot Evolved Stars

We show that a strong P-Cygni feature seen in the far-UV spectra of some very hot ( Te f f & 85 kK) central stars of planetary nebulae (CSPN), which has been previously identified as C III λ977, actually originates from Ne VII λ973. Using stellar atmospheres models, we reproduce this feature seen in the spectra of two [WR]-PG 1159 type CSPN, Abell 78 and NGC 2371, and in one PG 1159 CSPN, K 1-16. In the latter case, our analysis suggests an enhanced neon abundance. Strong neon features in CSPN spectra are important because an overabundance of this element is indicative of processed material that has been dredged up to the surface from the inter-shell region in the “born-again” scenario, an explanation of hydrogen-deficient CSPN. Our modeling indicates the Ne VII λ973 wind feature may be used to discern enhanced neon abundances for stars showing an unsaturated P-Cygni profile, such as some PG 1159 stars. We explore the potential of this strong feature as a wind diagnostic in stellar atmospheres analyses for evolved objects. For the [WR]-PG 1159 objects, the line is present as a P-Cygni line for Te f f & 85 kK, and becomes strong for 100 . Te f f . 155 kK when the neon abundance is solar, and can be significantly strong beyond this range for higher neon abundances. When unsaturated, i.e., for very high Te f f and/or very low mass-loss rates, it is sensitive to Ṁ and very sensitive to the neon abundance. The Ne VII classification is consistent with recent identification of this line seen in absorption in many PG 1159 spectra. Subject headings: stars: atmospheres — stars: Wolf-Rayet — stars: individual (NGC 2371, Abell 78, K 1-16) — planetary nebulae: general — UV: spectroscopy