Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

Abstract

Here we present a study of non-LTE effects on the exoplanetary spectra of a collection of molecules which are key in the investigation of exoplanet atmospheres: water, methane, carbon monoxide and titanium oxide. These molecules are chosen as examples of different spectral ranges (IR and UV), molecular types (diatomics and polyatomics) and spectral types (electronic and ro-vibrational); the importance of different vibrational bands in forming distinct non-LTE spectral features are investigated. Most notably, such key spectral signatures for distinguishing between the LTE and non-LTE cases include: for CH4 the 3.15 $\mu$m band region; for H2O the 2.0 $\mu$m and 2.7 $\mu$m band regions; for TiO, a strong variation in intensity in the bands between 0.5 and 0.75 $\mu$m; and a sole CO signature between 5 and 6 $\mu$m. The analysis is based on the ExoMol cross sections and takes advantage of the extensive vibrational assignment of these molecular line lists in the ExoMol database. We examine LTE and non-LTE cross sections under conditions consistent with those on WASP-12b and WASP-76b using the empirically motivated bi-temperature Treanor model. In addition, we make a simplistic forward model simulation of transmission spectra for H2O in the atmosphere of WASP-12b using the TauREx 3 atmospheric modelling code.

Accepted for publication in MNRAS

References in corpus (9)

• Array Programming with NumPy
• The 2020 release of the ExoMol database: molecular line lists for exoplanet and other hot atmospheres
• The Orbit of WASP-12b is Decaying
• Wind of Change: retrieving exoplanet atmospheric winds from high-resolution spectroscopy
• ARES I: WASP-76 b, A Tale of Two HST Spectra
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines
• A new approach to spectroscopic phase curves: The emission spectrum of WASP-12b observed in quadrature with HST/WFC3
• Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH2)

Cited by in corpus (4)

• Data availability and requirements relevant for the Ariel space mission and other exoplanet atmosphere applications
• Dual-comb Spectroscopy of Ammonia Formation in Non-thermal Plasmas
• Computing excited states of molecules using normalizing flows
• Collisional Excitation in Space: Recent Advances and Future Challenges in the JWST Era