English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present deep high-resolution (R~15,000) and high-quality UVES opticalspectrophotometry of nine planetary nebulae with dual-dust chemistry. Wecompute physical conditions from several diagnostics. Ionic abundances for alarge number of ions of N, O, Ne, S, Cl, Ar, K, Fe and Kr are derived fromcollisionally excited lines. Elemental abundances are computed usingstate-of-the-art ionization correction factors. We derive accurate C/O ratiosfrom optical recombination lines. We have re-analyzed additional high-qualityspectra of 14 PNe from the literature following the same methodology.Comparison with asymptotic giant branch models reveals that about half of thetotal sample objects are consistent with being descendants of low-massprogenitor stars (M < 1.5 Msun). Given the observed N/O, C/O, and He/H ratios,we cannot discard that some of the objects come from more massive progenitorstars (M > 3--4 Msun) that have suffered a mild HBB. None of the objects seemto be a descendant of very massive progenitors. We propose that in most of theplanetary nebulae studied here, the PAHs have been formed through thedissociation of the CO molecule. The hypothesis of a last thermal pulse thatturns O-rich PNe into C-rich PNe is discarded, except in three objects, thatshow C/O > 1. We also discuss the possibility of a He pre-enrichment to explainthe most He-enriched objects. We cannot discard other scenarios like extramixing, stellar rotation or binary interactions to explain the chemicalabundances behaviour observed in our sample.

C/O ratios in planetary nebulae with dual-dust chemistry from faint optical recombination lines