Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH<sub>2</sub>)

Clark, Victoria; Yurchenko, Sergei N.

doi:10.1039/d1cp00839k

Cited by 9 publications

(5 citation statements)

References 111 publications

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“…Additionally, when generating molecular cross sections, ExoCross can handle the values 𝐹 𝑣 as external parameters (Clark & Yurchenko 2021). Expanding this to include both vibrational and rotational temperatures, in this work we use a simplified bi-temperature Treanor approximation model and investigate spectral signatures of different vibrational bands contributing to a generic non-LTE spectrum.…”

Section: Methodsmentioning

confidence: 99%

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

Wright,

Waldmann,

Yurchenko

2022

Preprint

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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 CH 4 the 3.15 𝜇m band region; for H 2 O the 2.0 𝜇m and 2.7 𝜇m band regions; for TiO, a strong variation in intensity in the bands between 0.5 and 0.75 𝜇m; and a sole CO signature between 5 and 6 𝜇m. 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 H 2 O in the atmosphere of WASP-12b using the TauREx 3 atmospheric modelling code.

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Section: Methodsmentioning

confidence: 99%

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

Wright,

Waldmann,

Yurchenko

2022

Preprint

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“…Individual vibrational populations can be provided in the EXOCROSS program in order to isolate each desired band; in each case, the vibrational population N v was set to 1 for the desired state and 0 for the remaining states, and a partition function is inferred. Using this method, we produced seven sets of cross sections for each of the lower states ( v″ = 0, 1, 2, 3, 4, 5, and 6 For this case, we see that the strengths of the Δv = 2 bands increase with v quadratically, using an extension of the double harmonic approximation to the overtone bands (Clark & Yurchenko 2021), while the intensity increase of the Δv = 3 band is approximately cubic (Pastorek et al 2022). Due to the relative line strengths, the Δv = 3 sequence will be far less significant than the Δv = 2 band features, until the v5 (v″ = 5) and v6 (v″ = 6) systems.…”

Section: Nir Spectrum Of Oh and Cross-section Generationmentioning

confidence: 99%

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy with the Example of OH in the Atmosphere of WASP-33b

Wright

Nugroho

Brogi

et al. 2023

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Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail, by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-33b as an example. We simulate low-resolution spectroscopic data for observations with the JWST's NIRSpec instrument and use high-resolution observational data obtained from the Subaru InfraRed Doppler instrument (IRD). Vibrational band–specific OH cross-section sets are constructed and used in retrievals on the (simulated) low- and (real) high-resolution data. Low-resolution observations are simulated for two WASP-33b emission scenarios: under the assumption of local thermal equilibrium (LTE) and with a toy non-LTE model for vibrational excitation of selected bands. We show that mixing ratios for individual bands can be retrieved with sufficient precision to allow the vibrational population distributions of the forward models to be reconstructed. A fit for the Boltzmann distribution in the LTE case shows that the vibrational temperature is recoverable in this manner. For high-resolution, cross-correlation applications, we apply the individual vibrational band analysis to an IRD spectrum of WASP-33b, applying an “unpeeling” technique. Individual detection significances for the two strongest bands are shown to be in line with Boltzmann-distributed vibrational state populations, consistent with the effective temperature of the WASP-33b atmosphere reported previously. We show the viability of this approach for analyzing the individual vibrational state populations behind observed and simulated spectra, including reconstructing state population distributions.

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“…With modern technological advances in astrophysical exploration allowing studies of increasingly complex phenomena in atmospheres of exoplanets, it is becoming possible to study non-local thermodynamic equilibrium (non-LTE) effects (Fisher and Heng, 2019) which are already wellknown elsewhere, such as in the spectra of stars, planets, comets and interstellar medium (ISM) (López-Puertas and Taylor, 2001). Non-LTE spectroscopy is based on modeling of rotational, vibrational and electronic populations and therefore introduces special requirements both on the molecular data and spectral simulation software, such as, for example, provision of rovibronic assignment or non-Boltzmann populations, with non-LTE methods of different levels of complexity ranging from simplified bi-temperature models (Pannier and Laux, 2019;Clark and Yurchenko, 2021) to sophisticated non-LTE radiative transfer calculations (Funke et al, 2012). This line of research is been actively explored by ExoMol (Wright et al, 2021).…”

Section: Frontiers Inmentioning

confidence: 99%

High Accuracy Molecular Line Lists for Studies of Exoplanets and Other Hot Atmospheres

Tennyson

Yurchenko

2022

Front. Astron. Space Sci.

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The desire to characterize and model the atmospheres of the many extrasolar planets that have been discovered over the last three decades is a major driver of current astronomy. However, this goal is impacted by the lack of spectroscopic data on the molecules in question. As most atmospheres that can be studied are hot, some surprisingly so, this activity requires spectroscopic information not readily available from laboratory studies. This article will review the current status of available molecular spectroscopic data, usually presented as line lists, for studies of exoplanet atmospheres and, indeed, the atmospheres of other astronomical objects hotter than the Earth such as brown dwarfs, cool stars and even sunspots. Analysis of exoplanet transit spectra and the calculation of the relevant opacities often require huge datasets comprising billions of individual spectroscopic transitions. Conversely, the newly-developed high-resolution Doppler-shift spectroscopy technique has proved to be a powerful tool for detecting molecular species in exoplanet atmospheres, but relies on the use of smaller, highly accurate line lists. Methods of resolving issues arising from the competing demands of completeness versus accuracy for line lists are discussed.

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Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH₂)

Abstract: This paper sets out a robust methodology for modelling spectra of polyatomic molecules produced in reactive or dissociative environments, with vibrational populations outside local thermal equilibrium (LTE). The methodology is...

Cited by 9 publications

References 111 publications

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy with the Example of OH in the Atmosphere of WASP-33b

High Accuracy Molecular Line Lists for Studies of Exoplanets and Other Hot Atmospheres

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Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH2)

Abstract: This paper sets out a robust methodology for modelling spectra of polyatomic molecules produced in reactive or dissociative environments, with vibrational populations outside local thermal equilibrium (LTE). The methodology is...

Cited by 9 publications

References 111 publications

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy with the Example of OH in the Atmosphere of WASP-33b

High Accuracy Molecular Line Lists for Studies of Exoplanets and Other Hot Atmospheres

Contact Info

Product

Resources

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Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH₂)