Photochemistry and molecular ions in carbon-rich circumstellar envelopes

An earlier theory of ionization of C-rich circumstellar envelopes based on the photochemical model is extended to include the temperature dependence of ion-molecule reactions with polar molecules, particularly HCN, and line self-shielding of CO dissociating radiation. The results are applied to the...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 1987-06, Vol.180 (1-2), p.183-190
Main Authors: Glassgold, A. E., Mamon, G. A., Omont, A., Lucas, R.
Format: Article
Language:English
Subjects:
Astronomy
Astrophysics
Circumstellar shells, clouds, and expanding envelopes. Circumstellar masers
Earth, ocean, space
Exact sciences and technology
Stars
Stellar characteristics and properties
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Summary:An earlier theory of ionization of C-rich circumstellar envelopes based on the photochemical model is extended to include the temperature dependence of ion-molecule reactions with polar molecules, particularly HCN, and line self-shielding of CO dissociating radiation. The results are applied to the abundances of HCO(+) and HNC in C-rich circumstellar envelopes. With standard parameters for IRC + 10216, the model is found to be consistent with the new upper limit to the antenna temperature of the J = 1-0 line of HCO(+) obtained with the IRAM 30-m telescope. The photochemical model provides a natural explanation of the relatively large ratio of HCN to HNC observed for C-rich circumstellar envelopes, and good agreement is obtained for the H(C-13)N/HNC antenna temperature ratio measured for IRC + 10216.
ISSN:0004-6361
1432-0746