A chemical model for the atmosphere of hot Jupiters

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[1] [1,Venot, O.

[2] 1,Hébrard, E.

[3] 1,Agúndez, M.

[4] 1,Dobrijevic, M.

[5] 1,Selsis, F.

[6] 1,Hersant, F.

[7] 3,Iro, N.

[8] Bounaceur, R.

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Venot, O. (venot@obs.u-bordeaux1.fr) | 1600年 / EDP Sciences卷 / 546期

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Context. The atmosphere of hot Jupiters can be probed by primary transit and secondary eclipse spectroscopy. Owing to the intense UV irradiation; mixing; and circulation; their chemical composition is maintained out of equilibrium and must be modeled with kinetic models. Aims. Our purpose is to release a chemical network and the associated rate coefficients; developed for the temperature and pressure range relevant to hot Jupiters atmospheres. Using this network; we study the vertical atmospheric composition of the two hot Jupiters (HD 209458b and HD 189733b) with a model that includes photolyses and vertical mixing; and we produce synthetic spectra. Methods. The chemical scheme has been derived from applied combustion models that were methodically validated over a range of temperatures and pressures typical of the atmospheric layers influencing the observations of hot Jupiters. We compared the predictions obtained from this scheme with equilibrium calculations; with different schemes available in the literature that contain N-bearing species; and with previously published photochemical models. Results. Compared to other chemical schemes that were not subjected to the same systematic validation; we find significant differences whenever nonequilibrium processes take place (photodissociations or vertical mixing). The deviations from the equilibrium; hence the sensitivity to the network; are larger for HD 189733b; since we assume a cooler atmosphere than for HD 209458b. We found that the abundances of NH3 and HCN can vary by two orders of magnitude depending on the network; demonstrating the importance of comprehensive experimental validation. A spectral feature of NH3 at 10.5 μm is sensitive to these abundance variations and thus to the chemical scheme. Conclusions. Due to the influence of the kinetics; we recommend using a validated scheme to model the chemistry of exoplanet atmospheres. The network we release is robust for temperatures within 300-2500 K and pressures from 10 mbar up to a few hundred bars; for species made of C; H; O; and N. It is validated for species up to 2 carbon atoms and for the main nitrogen species (NH3; HCN; N2; NOx). Although the influence of the kinetic scheme on the hot Jupiters spectra remains within the current observational error bars (with the exception of NH3); it will become more important for atmospheres that are cooler or subjected to higher UV fluxes; because they depart more from equilibrium. ©2012 ESO;

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