Discovery of NeVII in the Winds of Hot Evolved Stars

Details Discovery of NeVII in the Winds of Hot Evolved Stars Discovery of NeVII in the Winds of Hot Evolved Stars

2005-02-03

arxiv.org/abs/astro-ph/0502074v1

Astrophys.J. 627 (2005) 424-431

Astronomy and Astrophysics

Astrophysics

9 pages, 6 figures (3 color). Accepted for publication in the Astrophysical Journal

Scientific paper

10.1086/429484

We show that a strong P-Cygni feature seen in the far-UV spectra of some very hot (Teff >~ 85 kK) central stars of planetary nebulae (CSPN), which has been previously identified as CIII lambda 977, actually originates from NeVII lambda 973. 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 NeVII lambda 973 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 Teff >~ 85 kK, and becomes strong for 100 <~ Teff <~ 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 Teff and/or very low mass-loss rates, it is sensitive to Mdot and very sensitive to the neon abundance. The NeVII classification is consistent with recent identification of this line seen in absorption in many PG 1159 spectra.

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