Issue |
A&A
Volume 641, September 2020
|
|
---|---|---|
Article Number | A47 | |
Number of page(s) | 14 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202037672 | |
Published online | 07 September 2020 |
Non-local thermodynamic equilibrium transmission spectrum modelling of HD 209458b
1
Space Research Institute (IWF), Austrian Academy of Science,
Schmiedlstraße 6,
8042
Graz,
Austria
e-mail: mitchelleric.young@oeaw.ac.at
2
Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd.,
85721
Tuscon,
USA
3
Hamburg Observatory, University of Hamburg,
Gojenbergsweg 112,
21029
Hamburg,
Germany
4
Laboratory for Atmospheric and Space Physics, University of Colorado Boulder,
80309
Boulder,
USA
Received:
5
February
2020
Accepted:
23
June
2020
Context. Exoplanetary upper atmospheres are low density environments where radiative processes can compete with collisional ones and introduce non-local thermodynamic equilibrium (NLTE) effects into transmission spectra.
Aims. We develop a NLTE radiative transfer framework capable of modelling exoplanetary transmission spectra over a wide range of planetary properties.
Methods. We adapted the NLTE spectral synthesis code Cloudy to produce an atmospheric structure and atomic transmission spectrum in both NLTE and local thermodynamic equilibrium (LTE) for the hot Jupiter HD 209458b, given a published T–P profile and assuming solar metallicity. Selected spectral features, including Hα, NaI D, HeI λ10 830, FeI and II ultra-violet (UV) bands, and C, O, and Si UV lines, are compared with literature observations and models where available. The strength of NLTE effects are measured for individual spectral lines to identify which features are most strongly affected.
Results. The developed modelling framework that computes NLTE synthetic spectra reproduces literature results for the HeI λ10 830 triplet, the NaI D lines, and the forest of FeI lines in the optical. Individual spectral lines in the NLTE spectrum exhibit up to 40% stronger absorption relative to the LTE spectrum.
Key words: planets and satellites: general / planets and satellites: individual: HD 209458b / planets and satellites: atmospheres / radiative transfer / techniques: spectroscopic
© ESO 2020
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