Contents of: VI/111/./abstract/MCOHEN_COOPN.abs

The following document lists the file abstract/MCOHEN_COOPN.abs from catalogue VI/111.
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     Tantalizing relationships have been discovered between the
gas phase C/O abundance ratio in planetaries and the fractions of total
FIR luminosity radiated by the 7.7 and 11.3 micron bands, identified
with C=C stretches and C-H bends, respectively, in polycyclic aromatic
hydrocarbon (PAH) bands.  These relationships point strongly towards a
carbonaceous carrier for the emission features and are believed to be
indicative of the chemical pathway to carbon grain formation in
planetaries.  Indeed, PAHs are likely to be the remnants of the grain
growth process; i.e. the condensation nuclei that failed to grow into
fully-fledged carbon grains.  So far, only small samples of nebulae
have been studied in this context, limited by airborne observations of
the 7.7 micron band, or the existence of adequate IRAS Low Resolution
Spectrometer (LRS) data.  To investigate these trends further, we wish
to supplement the selection of nebulae for which complete SWS01 low-
resolution spectra have already been proposed, by strategically
expanding the sample of planetaries available for study.
     Specifically, we propose to enlarge the sample of planetaries
for which one can compare nebular gas-phase C/O ratio with the ratio
of total luminosity radiated by the various known PAH emission bands
(and by the long wavelength 21 and 30-34 micron features, if present)
to the far-infrared continuum luminosity of the entire nebula.
     The enlarged sample is intended to investigate the range from
C/O = 0.7 to 5.2, with a preference for nebulae that are believed to be
appreciably carbon-rich (C/O>1.4).  In addition, we will carefully
search the spectra for indications of potentially reproducible features
from nebula to nebula that may represent longer wavelength PAH bending
modes than are currently recognized in astronomical environments.
     The objective of this study is to use any relationships between
PAH-related spectral attributes and C/O to try to delineate the
pathways by which carbon dust grains form in planetaries.

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