Non-local thermal equilibrium spectra of atmospheric molecules for exoplanets. Issue 2 (14th March 2022)

• Record Type: Journal Article
• Authors: Wright, Sam O M; Waldmann, Ingo; Yurchenko, Sergei N
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 512:Issue 2(2022)
• Page Start: 2911
• Page End: 2924
• Publication Date: 2022-03-14
• Subjects: infrared: planetary systems -- methods: laboratory: molecular -- molecular data -- techniques: spectroscopic -- planets and satellites: atmospheres; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac654
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Here we present a study of non-local thermodynamic equilibrium (LTE) effects on the exoplanetary spectra of a collection of molecules that 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 (infrared and ultraviolet), molecular types (diatomics and polyatomics), and spectral types (electronic and rovibrational); the importance of different vibrational bands in forming distinct non-LTE spectral features is 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 H2 O the 2.0 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 data base. 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.