C/O abundance ratios across WCL planetary nebulae with strong PAH and crystalline silicate emission

Details C/O abundance ratios across WCL planetary nebulae with strong PAH and crystalline silicate emission C/O abundance ratios across WCL planetary nebulae with strong PAH and crystalline silicate emission

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8711d&link_type=abstract

HST Proposal ID #8711

Computer Science

Hst Proposal Id #8711 Ism And Circumstellar Matter

Scientific paper

ISO has discovered cool O-rich crystalline silicate and water- ice emission in the far-IR spectra of several planetary nebulae {PNe} which show very strong hot PAH {polycyclic aromatic hydrocarbon, carbon-rich} emission bands in their near- and mid-IR spectra. All of these PNe are young and compact and of low-ionization, and have cool H-deficient Wolf- Rayet central stars. The correlation with carbon-rich WCL Wolf-Rayet central stars suggests that the phenomenon is associated with a recent transition from an O-rich to a C-rich phase by the evolving objects, following the exposure of 3rd dredge-up enriched material. For these nebulae, the gas-phase C/O ratios {two of the nebulae have the largest C/O ratios known} are strongly correlated with the PAH feature strength. The unexpected discovery of cool oxygen-rich particles around them suggests that strong C/O abundance gradients may be present in the nebulae. Long-slit spatially resolved STIS spectra will be acquired of three WCL PNe that simultaneously show PAH and silicate features, in order to test for C/O spatial variations within them that can diagnose the origin of the two contradictory chemistries. Only the HST can provide the required high angular resolution {0arcs1} across these compact { 2"} nebulae for the crucial abundance-diagnostic lines of C ii 2326 Angstrom and O ii 2470 Angstrom .

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