Physics
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996oxun.rept.....r&link_type=abstract
Technical Report, Oxford Univ. Oxford United Kingdom
Physics
Emission Spectra, Planetary Nebulae, Stellar Envelopes, Infrared Spectra, Carbon, Oxygen, Stellar Spectra, Spectrum Analysis, Vapor Phases, Nitrogen, Abundance, Infrared Telescopes, Infrared Spectrometers
Scientific paper
Spectra are presented of 21 planetary nebulae spanning the well-known, but still unidentified, narrow emission features at 3.2-3.6 micron. The equivalent width of the 3.29 micron emission band is strongly correlated with the gas-phase carbon to oxygen ratio, as expected for a band origin in carbon-rich grains or molecules. It displays an approximately linear dependence upon the C/O ratio with a threshold near C/O approx. 0.6. The emission band is present in 18 of the 21 nebulae, being absent in 3 of 6 O-rich objects and only weakly present in a fourth. The profile of the 3.29 micron band is closely similar in all of the nebulae and distinct from the band profile seen in some stellar envelopes. Weaker emission features in the 3.4-3.5 micron region are detected in nine objects, and are prominent only in nitrogen-rich type I nebulae. The intensity of the 3.4 micron feature in these objects is correlated with that of the 3.29 micron band, while the ratio of the two bands is strongly correlated with the nitrogen abundance. Possible explanations for this behavior are discussed.
Aitken David K.
Hoare Melvin G.
Lucas Philip W.
Roche Patrick F.
Smith Cotton H.
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