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The Impact of UV Radiation on Circumstellar Chemistry

Published online by Cambridge University Press:  30 December 2019

Maryam Saberi ,
Wouter Vlemmings ,
Tom Millar  and
Elvire De Beck
Maryam Saberi
Affiliation:
Dep. of Space, Earth and Environment, Chalmers University of Technology & Onsala Space Observatory, 43992 Onsala, Sweden email: maryam.saberi@chalmers.se
Wouter Vlemmings
Affiliation:
Dep. of Space, Earth and Environment, Chalmers University of Technology & Onsala Space Observatory, 43992 Onsala, Sweden email: maryam.saberi@chalmers.se
Tom Millar
Affiliation:
School of Maths and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, Northern Ireland
Elvire De Beck
Affiliation:
Dep. of Space, Earth and Environment, Chalmers University of Technology & Onsala Space Observatory, 43992 Onsala, Sweden email: maryam.saberi@chalmers.se
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Abstract

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UV radiation plays a critical role in the chemistry of circumstellar envelopes (CSEs) around evolved stars on the asymptotic giant branch (AGB). However, the effects of all potential sources of UV radiation have not been included in models. We present preliminary results of adding an internal source of UV to the CSE chemistry and predict large enhancements of atomic and ionic species arising from photo-destruction of parent species. Observations of atomic carbon towards the UV-bright AGB star o Cet are consistent with the modelling. In addition, we calculate the precise depth dependence of the CO photodissociation rate in an expanding CSE. We incorporate this within a chemical network active in the outflows of AGB stars, which includes 933 species and 15182 reactions. Our results show that the CO envelope size is about 30% smaller at half abundance than the most commonly used radius reported by Mamon et al. (1988).

Keywords

astrochemistrystars: abundancesstars: AGB and post-AGBstars: carbonstars: chromospheresstars: circumstellar matterultraviolet: starsbinaries: generalradiative transfer
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S343: Why Galaxies Care About AGB Stars: A Continuing Challenge through Cosmic Time , August 2018 , pp. 191 - 195
Copyright
© International Astronomical Union 2019 

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