CN and C/sub 2/H in IRC+10216
We investigate the effects of the production of the radicals CN and C/sub 2/H from the dissociation of HCN and C/sub 2/H/sub 2/ by ambient UV photons in the outer envelope of IRC+10216. We calculate the observable millimeter emission-line characteristics of CN and C/sub 2/H using a model for their excitation by infrared radiation and a simple photochemical model in which these radicals are entirely photoproduced from the progenitor species. For comparison, we also calculate the emission line characteritics for constnt relative abundances, which is the assumption usually made in studies of circumstellar line emission. The available observational data for CN are are well matched by the photoproduction model, but not by the assumption of a constant abundance. For C/sub 2/H, the data are consistent with either a constant abundance or the photoproduction model; in the latter case, the abundance of C/sub 2/H/sub 2/ in the inner envelope needs to be reduced by more than a factor of 10 from that previously assumed, in line with recent laboratory measurements of the infrared line strengths. Our results suggest that the variable abundances induced by photodestgruction of their progenitors do affect the observed emission from these radicals. Higher spatial resolution observations will be important in refining our understanding of the role of photochemistry in the outer envelopes of thick circumstellar envelopes.
- Research Organization:
- Physics Department, New York University
- OSTI ID:
- 6594718
- Journal Information:
- Astrophys. J.; (United States), Vol. 279:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
CARBON STARS
HYDROCARBONS
NITROGEN COMPOUNDS
STAR MODELS
EMISSION SPECTRA
ABUNDANCE
EXCITATION
INFRARED RADIATION
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
RADIATION TRANSPORT
RADICALS
SPATIAL DISTRIBUTION
STELLAR ATMOSPHERES
ATMOSPHERES
CHEMICAL REACTIONS
CHEMISTRY
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ENERGY-LEVEL TRANSITIONS
MAIN SEQUENCE STARS
MATHEMATICAL MODELS
ORGANIC COMPOUNDS
RADIATIONS
SPECTRA
STARS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
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