Reflections on the photodissociation of CO in circumstellar envelopes

Abstract

Carbon monoxide (CO) is the most abundant molecule after molecular hydrogen and is important for the chemistry in circumstellar envelopes around evolved stars. When modelling the strength and shape of molecular lines, the size of the CO envelope is an input parameter and influences the derived mass-loss rates. In particular the low-J transition CO lines are sensitive to the CO photodissociation radius. Recently, new CO photodissociation radii have been published using different formalisms that differ considerably. One set of calculations is based on an escape-probability formalisms that uses numerical approximations derived in the early-eighties. The accuracy of these approximations is investigated and it is shown that they are less accurate than claimed. Improved formalism are derived. Nevertheless, the changes in CO envelope size are small to moderate, less than 2\% for models with $10^{-7}<\dot{M}<10^{-4}$ \msolyr\ and at most 7\% for model with $\dot{M}=10^{-8}$ \msolyr.

A&A, accepted for publication

References in corpus (5)

• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
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Cited by in corpus (3)

• ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1 -- Determination of a new mass-loss rate prescription for red supergiants
• Multi-line study of the radial extent of SiO, CS, and SiS in AGB envelopes
• Exploring circumstellar chemistry in X-ray emitting AGB stars