Friday 4 June at 2:30pm

Tatsuhiko Hasegawa - Univ. of Calgary

"A Chemical Model of the Molecular Envelope of the Planetary Nebula NGC 7027"

ABSTRACT: "A chemical model is presented of the molecular envelope surrounding the carbon-rich planetary nebula NGC 7027. The chemical model predicts high abundances of HCO+, CO+, and other molecular ions in the molecular envelope of NGC 7027. The model helps us explain a recent observational finding (by Bachiller et al. 1997, AA, 324, 1123) that the HCO+ emission increases with the evolutionary sequence, IRC+10216 -> CRL2688 -> CRL618 -> NGC7027; i.e., from a carbon-rich circumstellar envelope to a proto-planetary nebula and further to a young planetary nebula. The model also suggests that OH, H2O, and H3O+ can be abundantly formed in a carbon-rich environment via efficient photodissociation of CO and subsequent gas reactions at high temperatures (800K). The result is consistent with ISO observations (OH detection and debated H2O detection in NGC 7027) and useful for planning future JCMT and ODIN observations."