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.
Instrument
SWS01
Temporal Coverage
1996-03-30T07:23:24Z/1996-04-06T08:46:56Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, COHEN et al., 1999, '\d_commaPAH\d_comma EMISSION BANDS IN SELECTED PLANETARY NEBULAE A STUDY OF THE BEHAVIOUR WITH GAS PHASE C\/O RATIO', 1.0, European Space Agency, https://doi.org/10.5270/esa-dwk321m
