Imaging & Spectroscopy

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy With The Example Of OH In The Atmosphere Of WASP-33b

By Keith Cowing
Status Report
May 19, 2023
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A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy With The Example Of OH In The Atmosphere Of WASP-33b
Individual band contributions of OH in NIR retrieved using the completely populated band cross sections for 0 to 3 with a simulated five secondary eclipses, with the plot highlighting the wavelength region with the strongest lines. — astro-ph.EP

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 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 simple 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 ‘un-peeling’ 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 analysing the individual vibrational state populations behind observed and simulated spectra including reconstructing state population distributions.

Sam O.M. Wright, Stevanus K. Nugroho, Matteo Brogi, Neale P. Gibson, Ernst J. W. de Mooij, Ingo Waldmann, Jonathan Tennyson, Hajime Kawahara, Masayuki Kuzuhara, Teruyuki Hirano, Takayuki Kotani, Yui Kawashima, Kento Masuda, Jayne L. Birkby, Chris A. Watson, Motohide Tamura, Konstanze Zwintz, Hiroki Harakawa, Tomoyuki Kudo, Klaus Hodapp, Shane Jacobson, Mihoko Konishi, Takashi Kurokawa, Jun Nishikawa, Masashi Omiya, Takuma Serizawa, Akitoshi Ueda, SĂ©bastien Vievard, Sergei N. Yurchenko

Comments: Submitted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2305.11071 [astro-ph.EP] (or arXiv:2305.11071v1 [astro-ph.EP] for this version)
Submission history
From: Sam Wright
[v1] Thu, 18 May 2023 15:59:10 UTC (71,615 KB)
Astrobiology, Astrochemistry

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻